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Cancer

Cancer

Definition

Cancer is not just one disease, but a large group of almost 100 diseases. It is a genetic disease, with two main characteristics of uncontrolled growth of the cells in the human body and the ability of those cells to migrate from the original site and spread to distant sites.

Description

One out of every four deaths in the United States is from cancer. It is second only to heart disease as a cause of death in the United States. About 1.2 million Americans are expected to be diagnosed with cancer each year, of which more than 500,000 are diagnosed as terminally ill. Cancer can attack anyone. Since the occurrence of cancer increases as people age, most cases are seen in adults, middle-aged or older. The most common cancers are skin cancer, lung cancer , colon cancer, breast cancer (in women), and prostate cancer (in men). In addition, cancer of the kidneys, ovaries, uterus, pancreas, bladder, rectum, blood (leukemia ), and lymph nodes (lymphoma) are also included among the 12 major cancers that affect most Americans.

Cancer, by definition, is a disease of the genes. A gene is a small part of DNA, which is the master molecule of the cell. Genes make proteins, which are the ultimate workhorses of the cells. It is these proteins, along with other substances, that allow our bodies to carry out the many processes that permit people to breathe, think, move, etc. Many genes produce proteins that are involved in controlling the processes of cell growth and division. An alteration, or mutation, to the DNA molecule can disrupt the genes and produce faulty proteins. This causes the cell to become abnormal and lose its restraints on growth. The abnormal cell begins to divide uncontrollably and eventually forms a new growth known as a tumor or neoplasm (medical term for cancer meaning "new growth"). In a healthy individual, the immune system can recognize the neoplastic cells and destroy them before they get a chance to divide. However, some mutant cells may escape immune detection and survive to become tumors or cancers.

Tumors are of two types, benign or malignant. A benign tumor is slow growing, does not spread or invade surrounding tissue, and once removed, it does not usually recur. A malignant tumor, on the other hand, invades surrounding tissue and has the capacity to spread to other parts of the body. If the cancer cells have spread to the surrounding tissues, then, even after the primary malignant tumor is removed, it generally recurs either locally or to a distant site. A majority of cancers are caused by changes in the cell's DNA because of damage due to the cell's environment. Environmental factors that are responsible for causing the initial mutation in the DNA are called carcinogens, and there are many types. Some cancers also have a genetic basis. In other words, an individual could inherit faulty DNA from a patient's parents, which could predispose the patient to getting cancer. There is also the two "hit" theory, where there is a combination of a genetic mutation and a stimulation of cell division and/or replication, due to environmental circumstances. While this scientific evidence points to both factors (environmental and genetic) playing a role, less than 10% of all cancers are purely hereditary. Cancers that are known to have a hereditary link are breast cancer, colon cancer, ovarian cancer , and uterine cancer . In late 2001, scientists took one step closer to identifying genetic markers that indicate cancer susceptibility. Called "low penetrance genes," these markers are believed to combine to increase risk for cancer.

There are several different types of cancers. Carcinomas are cancers that arise in the epithelium (the layer of cells covering the body's surface and lining the internal organs and various glands). Ninety percent of human cancers fall into this category. Melanomas are cancers that originate in the skin, usually in the pigment cells

(melanocytes). Sarcomas are cancers of the supporting tissues of the body, such as bone, muscle, and blood vessels. Cancers of the blood and lymph glands are called leukemias and lymphomas respectively. Gliomas are cancers of the nerve tissue.

Causes & symptoms

Causes & risk factors

The major risk factors for cancer are: tobacco, alcohol, diet, sexual and reproductive behavior, infectious agents, family history, occupation, environment, and pollution. According to the estimates of the American Cancer Society (ACS), approximately 40% of the cancer deaths in 2003 were due to tobacco and excessive alcohol use. An additional one-third of the deaths were related to diet and nutrition . Many of the one million skin cancer cases were due to overexposure to ultraviolet light from the sun's rays. It should be noted that medical science has not been able to pinpoint many of the exact causes of cancer, but has been able to estimate risk factors and occurrence associated with various agents.

Tobacco. Eighty to ninety percent of lung cancer cases occur in smokers. Smoking has also been shown to be a contributory factor in cancers of the upper respiratory tract, esophagus, larynx, bladder, pancreas, and probably liver, stomach, breast, and kidney, as well. Recently, scientists have also shown that second-hand smoke (or passive smoking) can increase one's risk of developing cancer.

Alcohol. Excessive consumption of alcohol is a risk factor in certain cancers, such as liver cancer. Alcohol, in combination with tobacco, significantly increases the chances that an individual will develop mouth, pharynx, larynx, and esophageal cancers.

Diet. Thirty five percent of all cancers are estimated to be due to dietary causes. Excessive intake of fat leading to obesity has been associated with cancers of the breast, colon, rectum, pancreas, prostate, gall bladder, ovaries, and uterus.

Sexual and reproductive behavior. The human papillomavirus, which is sexually transmitted, has been implicated to cause cancer of the cervix. In addition, it has also been shown that women who have not had children or have children late in life have an increased risk for both ovarian and breast cancer.

Infectious agents. In the last 20 years, scientists have obtained evidence to estimate that 15% of the world's cancer deaths may be traced to viruses, bacteria, or parasites.

Family history. Certain cancers like breast, colon, ovarian, and uterine cancer, recur generation after generation in some families. A few cancers, such as the eye cancer "retinoblastoma," a type of colon cancer, and a type of breast cancer known as "early-onset breast cancer," have been shown to be linked to certain genes that can be tracked within a family. It is therefore possible that inheriting particular genes makes a person susceptible to certain cancers.

Occupational hazards. There is evidence to estimate that certain occupational hazards account for 4% of all cancer deaths. For example, asbestos workers have an increased incidence of lung cancer. Similarly, a higher likelihood of getting bladder cancer is associated with dye, rubber, and gas workers; skin and lung cancer with smelters, gold miners, and arsenic workers; leukemia with glue and varnish workers; liver cancer with PVC manufacturers; and lung, bone, and bone marrow cancer with radiologists and uranium miners.

Environmental radiation. Exposure is believed to cause 12% of all cancer deaths. Ultra-violet radiation from the sun accounts for a majority of melanoma deaths. Other sources of radiation are x rays, radon gas, and ionizing radiation from nuclear material.

Pollution. Several studies have shown that there is a well established link between asbestos and cancer. Chlorination of water may account for a small rise in cancer risk. Studies released in 2003 showed that cadmium, a natural metal found in food, water, and cigarette smoke, disturbs a system in our cells essential to preventing cancer. The main danger from pollution occurs when dangerous chemicals from the industries escape into the surrounding environment. It has been estimated that 1% of cancer deaths are due to air, land, and water pollution.

Alternative medicine tends to disagree with conventional medicine about the causes of cancer, claiming that environmental pollution and emotional and psychological factors are major influences upon the disease. Samuel S. Epstein, a professor of Occupational and Environmental Medicine at the University of Illinois and the chairman of the Cancer Prevention Coalition, is one of the strongest critics of the National Cancer Institute and the American Cancer Society (ACS). Epstein tends to echo many of the beliefs of alternative practitioners. He claims that mainstream medicine, driven by politics, profits, and pharmaceutical sales, is not discussing or sufficiently researching some major factors behind cancer, or researching ways of preventing those causes. Epstein asserts that a primary cause of cancer is the massive pollution of the air, water, food, and workplace. For instance, since the 1940s over 100,000 new chemicals have been added to the environment, and each year in the United States alone, over 10 lb (4.5 kg) of pesticides and herbicides per person are used on the food supply, chemicals that are proven to be carcinogenic. Epstein believes that the human immune system simply cannot handle all the new carcinogens and stresses in the environment, and cancer represents this breakdown of the immune system. He is also a critic of some conventional cancer therapies like radiation and chemotherapy, claiming that the therapies themselves are highly carcinogenic and are often responsible for recurrent cancer. Epstein points out that despite the "war on cancer" by mainstream medicine, mortality rates have not been significantly improved by its methods, and more research needs to be dedicated to preventative and alternative measures instead of pharmaceuticals and invasive treatments.

Symptoms

Cancer is a progressive disease, and goes through several stages with varying symptoms. Some symptoms are produced early and may occur due to a tumor that is growing within an organ or a gland. As the tumor grows, it may press on the nearby nerves, organs, and blood vessels.

This causes pain and some pressure that may be the earliest warning signs of cancer. Despite the fact that there are several hundred different types of cancers, producing very different symptoms, the ACS has established the following seven symptoms as possible warning signals of cancer:

  • changes in the size, color, or shape of a wart or a mole
  • a sore that does not heal
  • persistent cough , hoarseness, or sore throat
  • a lump or thickening in the breast or elsewhere
  • unusual bleeding or discharge
  • chronic indigestion or difficulty in swallowing
  • any change in bowel or bladder habits

Many other diseases besides cancer, could produce the same symptoms. However, it is important to have these symptoms checked as soon as possible, especially if they linger. The earlier a cancer is diagnosed and treated, the better the chance of it being cured. Many cancers, such as breast cancer, may not have any early symptoms. Therefore, it is important to undergo routine screening tests, such as breast self-exams and mammograms.

Diagnosis

Diagnosis begins with a thorough physical examination and a complete medical history. The doctor will ob serve, feel, and palpate (apply pressure by touch) different parts of the body in order to identify any variations from the normal size, feel, and texture of the organ or tissue. As part of the physical exam, the doctor will inspect the oral cavity, or the mouth. By focusing a light into the mouth, he or she will look for abnormalities in color, moisture, surface texture, or presence of any thickening or soreness in the lips, tongue, gums, the hard palate on the roof of the mouth, and the throat.

To detect thyroid cancer, the doctor will observe the front of the neck for swelling. He may gently manipulate the neck and palpate the front and side surfaces of the thyroid gland (located at the base of the neck) to detect any nodules or tenderness. As part of the physical examination, the doctor will also palpate the lymph nodes in the neck, under the arms, and in the groin. Many illnesses and cancers cause a swelling of the lymph nodes.

The doctor may conduct a thorough examination of the skin to look for sores that have been present for more than three weeks and that bleed, ooze, or crust; irritated patches that may itch or hurt, and any change in the size of a wart or a mole. Examination of the female pelvis is used to detect cancers of the ovaries, uterus, cervix, and vagina. In the visual examination, the doctor looks for abnormal discharges or the presence of sores. Then, using gloved hands the physician palpates the internal pelvic organs such as the uterus and ovaries to detect any abnormal masses. Breast examination includes visual observation where the doctor looks for any discharge, unevenness, discoloration, or scaling. The doctor palpates both breasts to feel for masses or lumps. For males, inspection of the rectum and the prostate is also included in the physical examination. The doctor inserts a gloved finger into the rectum and rotates it slowly to feel for any growths, tumors, or other abnormalities. The doctor also conducts an examination of the testes, where the doctor observes the genital area and looks for swelling or other abnormalities. The testicles are palpated to identify any lumps, thickening, or differences in the size, weight, and firmness.

If the doctor detects an abnormality on physical examination, or the patient has some symptom that could be indicative of cancer, the doctor may order diagnostic tests. Laboratory studies of sputum (sputum cytology), blood, urine, and stool can detect abnormalities that may indicate cancer. Sputum cytology is a test where the phlegm that is coughed up from the lungs is microscopically examined. It is often used to detect lung cancer.

A blood test for cancer is easy to perform, usually inexpensive and risk-free. Blood tests can be either specific or nonspecific. Often times, in certain cancers, the cancer cells release particular proteins (called tumor markers) and blood tests can be used to detect the presence of these tumor markers. However, with a few exceptions, tumor markers are not used for routine screening of cancers, because several noncancerous conditions also produce positive results. Blood tests are generally more useful in monitoring the effectiveness of the treatment, or in following the course of the disease and detecting recurrent disease.

Imaging tests such as computed tomography scans (CT scans), magnetic resonance imaging (MRI), ultra-sound, and fiberoptic scope examinations help doctors determine the location of the tumor even if it is deep within the body. Conventional x rays are often used for initial evaluation, because they are relatively cheap, painless, and easily accessible. In order to increase the information obtained from a conventional x ray, air or a dye (such as barium or iodine ) may be used as a contrast medium to outline or highlight parts of the body.

The most definitive diagnostic test is the biopsy, wherein a piece of tissue is surgically removed for microscope examination. Besides confirming a cancer, the biopsy also provides information about the type of cancer, the stage it has reached, the aggressiveness of the cancer, and the extent of its spread. Since a biopsy provides the most accurate analysis, it is considered the gold standard of diagnostic tests. Screening examinations, conducted regularly by healthcare professionals, can result in the detection of cancers of the breast, colon, rectum, cervix, prostate, testes, tongue, mouth, and skin at early stages, when treatment is more likely to be successful. Some of the routine screening tests recommended by the ACS are sigmoidoscopy (for colorectal cancer ), mammography (for breast cancer), pap smear (for cervical cancer), and the PSA test (for prostate cancer). Self-examinations for cancers of the breast, testes, mouth, and skin can also help in detecting the tumors before the symptoms become serious.

Diagnosis in alternative treatment often relies on conventional diagnostic tools for determining the type and stage of cancer, but will supplement those tools with diagnostic techniques that strive to evaluate the overall health of a person, in order to treat a person holistically. For instance, Ayurvedic medicine and traditional Chinese medicine place high priorities during diagnosis on the patient's emotional and psychological history, as well as considerations like lifestyle, relationships, and the degree of social and spiritual support, in order to have insight into the cause and proper treatment of a particular cancer. These alternative practices also have highly developed diagnostic techniques for the body, including pulse diagnosis ; methods of analyzing the tongue, eyes, skin, hair, and fingernails; palpating and finding problems in the organs and abdomen; and listening to the breath for clues to the internal environment.

Treatment

Choosing an alternative cancer treatment

There are a multitude of alternative treatments available to help a person with cancer. They are usually integrated with allopathic treatments like surgery, chemotherapy, and radiation therapy, where only an estimated 4% exclusively use alternative medicine. Chemotherapy and radiation treatments are some of the most painful and toxic of conventional treatments, and often have unpredictable results. As a rule, alternative treatments are less invasive, nontoxic, and have minimal side effects. When used as adjuncts to conventional treatment, some alternative treatments have been shown to decrease pain and side effects, aid in the recovery process, and improve the quality of life of cancer patients.

Alternative treatment of cancer is a complicated arena and choosing one from the many can seem a difficult task, as can choosing an alternative practitioner. Patients should consult as many trained health practitioners as feasible when choosing alternative therapies. If patients are willing to ask questions and thoroughly re-search their options, they can increase their chances of getting the best possible alternative support for the difficult task of treating cancer.

When choosing alternative treatment, individuals should evaluate practitioners, therapies, and services delivered by clinics or practitioners, as well as the extent of documentation and published literature regarding these concerns. When looking for practitioners, patients should evaluate their training and credentials and their reputations in the healing community. Referrals from other patients should be requested. Furthermore, they should seek practitioners who are knowledgeable and familiar with a broad spectrum of options of treating cancer, including those used by conventional medicine, and who are willing to work in conjunction with conventional doctors if the patient and treatment requires it. Conversely, if patients choose a physician who employs and recommends conventional, allopathic methods, that physician should be willing to communicate with patients, as well as communicate with an alternate provider. Another major consideration when choosing a practitioner is whether he or she seems trustworthy, ethical, and compassionate.

Patients should also evaluate the particular therapy offered by a practitioner or clinic. They should find out exactly how the therapy works and the principles behind it; whether it is harmless or potentially damaging, and the positive benefits it offers; what literature and scientific studies exist for the therapy; and what other patients say about the treatment.

Finally, patients should evaluate the quality of service that the practitioner or clinic offers. Cost, reputation, quality of support personnel, and attention to individual needs are important considerations when evaluating the service dimension of a treatment.

Types of alternative treatment

Alternative medicine generally views cancer as a holistic problem. That is, cancer represents a problem with the body's overall health and immunity. As such, treatment is holistic as well, striving to strengthen and heal the physical, mental, and spiritual aspects of patients. Alternative cancer treatments may emphasize different basic approaches, which include traditional medicines, psychological approaches, nutritional and dietary approaches, physical approaches, integrated approaches, and experimental programs.

TRADITIONAL MEDICINES. Traditional Chinese medicine uses acupuncture, acupressure massage, herbal remedies, and movement therapies like t'ai chi and qigong to treat cancer. Traditional Chinese herbal remedies have already contributed a significant number of anticancer drugs, as studies have shown their anti-cancer properties and immune stimulants. A 2001 report noted that the ancient compound artemisinin (worm-wood ) appears surprisingly effective in targeting certain cancer cells and helping to destroy them. The therapy is much less expensive than many traditional options, but further study was underway. Acupuncture has been shown to reduce some tumors and significantly reduce pain and improve immune system activity.

Ayurvedic medicine utilizes detoxification , herbal remedies, massage, exercise, yoga , breathing techniques, and meditation as part of its cancer treatment. Panchakarma is an extensive detoxification and strengthening program that is recommended for cancer sufferers and those undergoing chemotherapy and radiation. Panchakarma uses fasting , special vegetarian diets , enemas, massage, herbal medicines, and other techniques to rid the body of excess toxins that are believed to contribute to chronic diseases like cancer, and to strengthen the immune system. Ayurvedic herbs are also being demonstrated to have significant anticancer properties.

Naturopathy and homeopathy are traditional Western healing systems using herbal medicines and other techniques to strengthen the immune system and reduce the pain of cancer treatment. Western herbalism is also beginning to compile studies of many herbs that have anticancer and immune strengthening properties.

PSYCHOLOGICAL APPROACHES. Alternative treatments that seek to help patients with the mental and spiritual challenges that cancer poses include psychotherapy , support groups, guided imagery , meditation, biofeedback , and hypnosis.

Psychological approaches work with the idea that the mind and emotions can profoundly influence the health of the body and diseases like cancer. Many studies have acknowledged that mind and emotions play a key role in cancer and immune functioning, and psychological approaches are being used by many conventional programs, including Harvard Medical School. A new field of academic medicine called psychoneuroimmunology has begun that studies the interactions between mental states and immune response.

Studies have shown that patients who approach their cancer with positive attitudes and peaceful acceptance have higher survival rates than those patients who react with negative emotions, like depression , cynicism, or helplessness. Alternative treatments use psychological approaches to help patients overcome the mental and emotional barriers to healing.

PHYSICAL APPROACHES. Physical approaches to cancer include exercise; massage therapies; movement therapies like yoga, t'ai chi and qigong; breathing techniques; and relaxation techniques. These therapies strive to increase immune system response, promote relaxation and stress reduction, and reduce side effects of conventional treatments such as pain, nausea , weakness, and physical immobility.

NUTRITIONAL AND DIETARY APPROACHES. Diet is now recognized by scientists to play a major role in reducing the risk of some cancers. A 1992 report in Oncology claimed that nutritional factors may account for up to 70% of avoidable cancer mortality in this country. Many nutritionists also state that cancer patients have heightened needs for diets free of toxic chemicals and full of cancer-fighting nutrients. Diet and nutrition can improve both a cancer patient's chances for recovery and quality of life during treatment. In laboratory studies, vitamins such as A, C, and E, as well as compounds such as isothiocyanates and dithiolthiones found in broccoli, cauliflower, and cabbage, and the antioxidant beta-carotene found in carrots, have been shown to protect against cancer. Additionally, bioflavonoids and lycophene found in green tea help in the prevention of cancer.

Dietary approaches for cancer include vegetarianism , raw food diets, macrobiotics, the Gerson diet, and the Livingston-Wheeler nutritional program, discussed below. Cancer diets generally emphasize fresh fruits, vegetables, whole grains, and legumes, and restrict intake of fat, meat, dairy products, sugar, processed foods, and other foods believed to tax cancer patients. Nutritional approaches to cancer include antioxidant and vitamin supplementation and the use of numerous herbal extracts. There are many herbs that have been shown to have anticancer, immune enhancing, and symptom reducing properties, and patients are recommended to consult competent herbalists for herbal support.

INTEGRATED APPROACHES. Keith Block is a conventional physician and oncologist who is integrating many alternative practices into his cancer treatment center affiliated with the Chicago Medical School in Illinois. His program seeks to provide individualized cancer treatment using conventional therapies while integrating alternative healing techniques. Block advocates a special diet (based on vegetarianism and macrobiotics), exercise, psychological support, and herbal and nutritional supplements. Block's program has received acclaim for both treatment success and satisfaction of patients.

EXPERIMENTAL PROGRAMS. Antineoplaston therapy was developed by Stanislaw Burzynski, a Polish physician who began practicing in Houston, Texas. Burzynski has isolated a chemical, deficient in those with cancer, which he believes stops cancer growth, and his treatment has shown some promise.

Dr. Joseph Gold, the director of the Syracuse Cancer Research Institute, discovered that the chemical hydrazine sulfate has many positive effects in cancer patients, including stopping weight loss, shrinking tumors, and increasing survival rates.

The Livingston therapy was developed by the late Dr. Virginia Livingston, an American physician. She asserted that cancer is caused by certain bacteria that she claimed are present in all tumors. She advocated a detoxification program and special diet that emphasized raw or lightly cooked and primarily vegetarian foods, with special vitamin and nutritional supplements.

The Gerson therapy was for years the best known nutritional therapy for cancer. It is available in two clinics in California and Mexico. It consists of a basic vegetarian diet low in salt and fat, with high doses of particular nutrients using raw fruit and vegetable juices. The Gerson therapy also requires patients to drink raw calf's liver juice, believed to aid the liver, and advocates frequent coffee enemas, which are claimed to help the body evacuate toxins.

Allopathic treatment

The aim of allopathic (conventional) cancer treatment is to remove all or as much of the tumor as possible and to prevent the recurrence or spread of the primary tumor. While devising a conventional treatment plan for cancer, the likelihood of curing the cancer has to be weighed against the side effects of the treatment. If the cancer is very aggressive and a cure is not possible, then the treatment should be aimed at relieving symptoms and controlling the cancer for as long as possible. Cancer treatment can take many different forms, and it is always tailored to the individual patient. The decision on which type of treatment is the most appropriate depends on the type and location of cancer, the extent to which it has already spread, the patient's age, sex, general health status, and personal treatment preferences. The major types of treatment are: surgery, radiation, chemotherapy, immunotherapy, hormone therapy, and bone marrow transplantation.

Surgery

Surgery is the removal of a visible tumor and is the most frequently used cancer treatment. It is most effective when a cancer is small and confined to one area of the body. Surgery can be used for many purposes. Treatment of cancer by surgery involves removal of the tumor to cure the disease. Along with the cancer, some part of the normal surrounding tissue may also be removed to ensure that no cancer cells remain in the area. Since cancer usually spreads via the lymphatic system, adjoining lymph nodes may be examined and sometimes removed, as well. Preventive or prophylactic surgery involves removal of an abnormal looking area that is likely to become malignant over time. The most definitive tool for diagnosing cancer is a biopsy. Sometimes a biopsy can be performed by inserting a needle through the skin. However, at other times, the only way to obtain tissue sample for biopsy is by performing a surgical operation.

Radiation

Radiation kills tumor cells. Radiation is used alone in cases where a tumor is unsuitable for surgery. More often, it is used in conjunction with surgery and chemotherapy. Radiation can be either external or internal. In the external form, the radiation is aimed at the tumor from outside the body. In internal radiation (also known as brachytherapy), a radioactive substance in the form of pellets or liquid is placed at the cancerous site by means of a pill, injection, or insertion in a sealed container.

Chemotherapy

Chemotherapy is the use of drugs to kill cancer cells. It destroys the hard-to-detect cancer cells that have spread and are circulating in the body. Chemotherapeutic drugs can be taken either orally or intravenously, and may be given alone or in conjunction with surgery, radiation, or both. The toxic effects of chemotherapy are severe. In 2003, a new technique was developed to streamline identification of drug compounds that are toxic to cancerous cells but not to healthy cells. The technique identified nine drugs, one of which had never before been identified for use in cancer treatment. Researchers began looking into developing the new drug for possible use. In addition, it may make the body less tolerant to the side effects of other treatments that follow, such as radiation therapy. The more common use of chemotherapy is adjuvant therapy, which is given to enhance the effectiveness of other treatments. For example, after surgery, adjuvant chemotherapy is given to destroy any cancerous cells that still remain in the body.

Immunotherapy

Immunotherapy uses the body's own immune system to destroy cancer cells. This form of treatment is being intensively studied in clinical trials and is not yet widely available to most cancer patients. The various immunological agents being tested include substances produced by the body (such as the interferons, interleukins, and growth factors), monoclonal antibodies, and vaccines. Unlike traditional vaccines, cancer vaccines do not prevent cancer. Instead, they are designed to treat people who already have the disease. Cancer vaccines work by boosting the body's immune system and training the immune cells to specifically destroy cancer cells.

Hormone therapy

Hormone therapy is standard treatment for some types of cancers that are hormone-dependent and grow faster in the presence of particular hormones. These include cancer of the prostate, breast, and uterus. Hormone therapy involves blocking the production or action of these hormones. As a result, the growth of the tumor slows down and survival may be extended for several months or years. However, in 2003, the Women's Health Initiative found that even relatively short-term use of estrogen plus progestin is associated with increased risk of breast cancer, diagnosis at a more advanced stage of the disease, and a higher number of abnormal mammograms. The longer a woman used HRT, the more her risk increased. This contradicted earlier beliefs that HRT could prevent breast cancer. So checking with a physician for the latest information is advised.

Bone marrow transplantation

The bone marrow is the tissue within the bone cavities that contains blood-forming cells. Healthy bone marrow tissue constantly replenishes the blood supply and is essential to life. Sometimes, the amount of drugs or radiation needed to destroy cancer cells also unfortunately destroys bone marrow. Replacing the bone marrow with healthy cells counteracts this adverse effect. A bone marrow transplant is the removal of marrow from one person and the transplant of the blood-forming cells either to the same person or to someone else. Bone marrow transplantation, while not a therapy in itself, is often used to rescue a patient, by allowing those with cancer to undergo very aggressive therapy.

In 2001, interest grew in adding hyperthermia to conventional therapy such as radiation. By raising tumors to high fever temperatures, the performance of certain cancer drugs was noted. Hyperthermia is thought to destroy cancer cells much the same way that the body uses fever to naturally combat other forms of disease.

Many different specialists generally work together as a team to treat cancer patients. An oncologist is a physician who specializes in cancer care. The oncologist provides chemotherapy, hormone therapy, and any other non-surgical treatment that does not involve radiation. The oncologist often serves as the primary physician and coordinates the patient's treatment plan. There are many other specialists involved in cancer treatment, and virtually any type of medical or surgical specialist may become involved with care of the cancer patient, should it become necessary.

Expected results

Lifetime risk is the term that cancer researchers use to refer to the probability that an individual, over the course of a lifetime, will develop cancer or die from it. In the United States, men have a one in two lifetime risk of developing cancer, and for women the risk is one in three. Overall, African Americans are more likely to develop cancer than Caucasians. African Americans are also 30% more likely to die of cancer than Caucasians. Many cancers are curable if detected and treated at their early stages. A cancer patient's prognosis is affected by many factors, particularly the type of cancer the patient has, the stage of the cancer, the extent to which it has metastasized, and the aggressiveness of the cancer. In addition, the patient's age, general health status, and the effectiveness of the treatment being pursued are also important factors. To help predict the future course and outcome of the disease and the likelihood of recovery from the disease, doctors often use statistics. The five-year survival rates are the most common measures used. The number refers to the proportion of people with cancer who are expected to be alive five years after initial diagnosis, compared with a similar population that is free of cancer. It is important to note that while statistics can give some information about the average survival experience of cancer patients in a given population, they cannot be used to indicate individual prognosis, because no two patients or cancers are exactly alike. The unpredictability of cancer can be seen as positive, as well as negativesome patients have experienced recoveries in cases that were deemed incurable.

Alternative medicine rarely claims to be able to cure cancer on a regular basis, but many treatments seem to help with controlling symptoms, controlling the pain and side effects of conventional treatments, and increasing the quality of life for cancer sufferers. Alternative therapies have also shown unexpected results and cures. Alternative therapies may be strongest as preventative measures, before major problems like cancer occur in the body.

Prevention

Most practitioners agree that the best treatment for cancer is prevention. Having sound physical and mental health can significantly reduce the chances of getting cancer. The following guidelines are generally recommended by doctors, nutritionists, and alternative practitioners for cancer prevention and recovery:

  • Refraining from smoking.
  • Not drinking alcohol excessively.
  • Exercising regularly, at least 20 minutes per day, preferably outdoors in the fresh air.
  • Avoiding exposure to radiation. This includes avoiding unnecessary x rays, not residing near sources of natural or human-made radiation, and avoiding occupational exposure to radiation.
  • Avoiding exposure to harmful chemicals in food, the home, and workplace.
  • Maintaining proper body weight, particularly avoiding obesity.
  • Practicing safe sex.
  • Protecting the skin from overexposure to sunlight. Avoiding the midday sun between 11 a.m. and 3 p.m. and never allowing the skin to become sunburned help with prevention.
  • Eating a healthy diet. Becoming educated on and practicing dietary principles reduces the risk of cancer. These principles include eating plenty of fresh fruits, vegetables, beans, and whole grains and consuming organically grown foods when possible. Minimizing overeating and reducing intake of meat and dairy products while increasing fiber are recommended. Avoiding processed and canned foods, including soft drinks, and avoiding sugar and refined starch products like white flour also helps. Reducing the intake of fat, avoiding hydrogenated vegetable oils like margarine and shortening, and drinking filtered or spring water have been recommended.
  • Striving to maintain sound mental and emotional health is believed to help prevent cancer. Learning a technique like yoga, t'ai chi, meditation, or others can reduce stress and promote relaxation. Maintaining healthy relationships and social support systems also relieves stress.

Resources

BOOKS

Galland, Leo, m.d. The Four Pillars of Healing. New York: Random House, 1997.

Lerner, Michael. Choices in Healing: Integrating the Best of the Conventional and Complementary Approaches to Cancer. Cambridge, Massachusetts: MIT Press, 1994.

Walters, Richard. Options: The Alternative Cancer Therapy Book. New York: Avery Publishing Group, 1993.

Weil, Andrew, m.d. Natural Health, Natural Medicine. New York: Houghton Mifflin, 1995.

Yance, Donald R. Herbal Medicine, Healing and Cancer. Chicago: Keats Publishing, 1999.

PERIODICALS

Alternative Therapies Magazine. PO Box 17969, Durham, NC 27715. (919) 668-8825. http://www.alternative-therapies.com.

"Cadmium Studies Suggest New Pathway to Human Cancer." Drug Week (July 4, 2003): 77.

"HRT Linked to Higher Breast Cancer Risk, Later Diagnosis, Abnormal Mammograms." Women's Health Weekly (July 17, 2003):2.

"Hyperthermia and Hypoxia Spell Cancer Destruction." Cancer Weekly, November 27, 2001: 20.

"Ancient Chinese Folk Remedy may hold Key to Nontoxic Cancer Treatment." Cancer Weekly, December 18, 2001: 12.

"Genetic Identification Techniques Yield Clues to Cancer Susceptibility." Cancer Weekly November 13, 2001: 19.

"Technique Streamlines Search for Anticancer Drugs." Cancer Weekly (April 15, 2003): 62.

ORGANIZATIONS

The Alliance for Alternative Medicine. PO Box 59, Liberty Lake, WA 99019.

American Cancer Society, National Headquarters.1599 Clifton Road, N.E. Atlanta, Georgia 30329 (800) 227-2345. <http://www.cancer.org>.

Cancer Prevention Coalition, c/o University of Illinois School of Public Health, 2121 West Taylor Street Chicago, IL 60612. (312) 996-2297 [email protected] <http://www.preventcancer.com>.

The Health Resource. 209 Katherine Drive, Conway, AR 72032. (501) 329-5272.

National Cancer Institute. 9000 Rockville Pike, Building 31, room 10A16, Bethesda, MD 20892. (800) 4226237. <http://www.cancer.gov>.

OTHER

Cancer Nutrition Center. [cited October 2002]. <http://www.cancernutrition.com>.

Douglas Dupler

Teresa G. Odle

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Cancer

Cancer

Definition

Cancer is not just one disease, but a large group of almost 100 diseases. Its two main characteristics are uncontrolled growth of the cells in the human body and the ability of these cells to migrate from the original site and spread to distant sites. If the spread is not controlled, cancer can result in death.

Description

One out of every four deaths in the United States is from cancer. It is second only to heart disease as a cause of death in the states. About 1.2 million Americans are diagnosed with cancer annually; more than 500,000 die of cancer annually.

Cancer can attack anyone. Since the occurrence of cancer increases as individuals age, most of the cases are seen in adults, middle-aged or older. Sixty percent of all cancers are diagnosed in people who are older than 65 years of age. The most common cancers are skin cancer, lung cancer, colon cancer, breast cancer (in women), and prostate cancer (in men). In addition, cancer of the kidneys, ovaries, uterus, pancreas, bladder, rectum, and blood and lymph node cancer (leukemias and lymphomas) are also included among the 12 major cancers that affect most Americans.

Cancer, by definition, is a disease of the genes. A gene is a small part of DNA, which is the master molecule of the cell. Genes make "proteins," which are the ultimate workhorses of the cells. It is these proteins that allow our bodies to carry out all the many processes that permit us to breathe, think, move, etc.

Throughout people's lives, the cells in their bodies are growing, dividing, and replacing themselves. Many genes produce proteins that are involved in controlling the processes of cell growth and division. An alteration (mutation) to the DNA molecule can disrupt the genes and produce faulty proteins. This causes the cell to become abnormal and lose its restraints on growth. The abnormal cell begins to divide uncontrollably and eventually forms a new growth known as a "tumor" or neoplasm (medical term for cancer meaning "new growth").

In a healthy individual, the immune system can recognize the neoplastic cells and destroy them before they get a chance to divide. However, some mutant cells may escape immune detection and survive to become tumors or cancers.

Tumors are of two types, benign or malignant. A benign tumor is not considered cancer. It is slow growing, does not spread or invade surrounding tissue, and once it is removed, doesn't usually recur. A malignant tumor, on the other hand, is cancer. It invades surrounding tissue and spreads to other parts of the body. If the cancer cells have spread to the surrounding tissues, even after the malignant tumor is removed, it generally recurs.

A majority of cancers are caused by changes in the cell's DNA because of damage due to the environment. Environmental factors that are responsible for causing the initial mutation in the DNA are called carcinogens, and there are many types.

There are some cancers that have a genetic basis. In other words, an individual could inherit faulty DNA from his parents, which could predispose him to getting cancer. While there is scientific evidence that both factors (environmental and genetic) play a role, less than 10% of all cancers are purely hereditary. Cancers that are known to have a hereditary link are breast cancer, colon cancer, ovarian cancer, and uterine cancer. Besides genes, certain physiological traits could be inherited and could contribute to cancers. For example, inheriting fair skin makes a person more likely to develop skin cancer, but only if he or she also has prolonged exposure to intensive sunlight.

There are several different types of cancers:

  • Carcinomas are cancers that arise in the epithelium (the layer of cells covering the body's surface and lining the internal organs and various glands). Ninety percent of human cancers fall into this category. Carcinomas can be subdivided into two types: adenocarcinomas and squamous cell carcinomas. Adenocarcinomas are cancers that develop in an organ or a gland, while squamous cell carcinomas refer to cancers that originate in the skin.
  • Melanomas also originate in the skin, usually in the pigment cells (melanocytes).
  • Sarcomas are cancers of the supporting tissues of the body, such as bone, muscle and blood vessels.
  • Cancers of the blood and lymph glands are called leukemias and lymphomas respectively.
  • Gliomas are cancers of the nerve tissue.

Causes and symptoms

The major risk factors for cancer are: tobacco, alcohol, diet, sexual and reproductive behavior, infectious agents, family history, occupation, environment and pollution.

JANETD. ROWLEY (1925)

Janet Davison Rowley was born in New York City on April 5, 1925, to Ethel Mary (Ballantyne) and Hurford Henry Davison. Rowley attended the University of Chicago, earning her B.S. degree in 1946 and her M.D. degree in 1948. She also married Donald A. Rowley in 1948, and the couple ultimately had four sons. Rowley completed both her internship and residency at Chicago hospitals before returning to the University of Chicago Medical School where she conducted research from 19621969. She became an associate professor, and finally, in 1977, earned her position as a full professor.

Rowley's research has focused on understanding cancer, with special emphasis on its cytogenetic causes. Her development and use of Giemsa and quinacrine stains enabled Rowley to discover oncogenes and to ultimately show a consistent shifting or translocation of genetic material in chronic myeloid leukemia cells. Rowley's discoveries and continued research have shown that malignant cells in humans undergo this translocation and deletion of genes that cause tumors to grow. Her research has given oncologists new pathways to explore concerning gene therapies for the treatment of cancer.

Co-editor and co-founder of the journal, Genes, Chromosomes and Cancer, Rowley has published an abundance of materials including Chromosome Changes in Leukemia (1978), Genes and Cancer (1984), and Advances in Understanding Genetic Changes in Cancer (1992). Rowley has also received many awards and honors for her work and research.

According to estimates of the American Cancer Society (ACS), approximately 40% of cancer deaths in 1998 were due to tobacco and excessive alcohol use. An additional one-third of the deaths were related to diet and nutrition. Many of the one million skin cancers diagnosed in 1998 were due to over-exposure to ultraviolet light from the sun's rays.

Frequency Of Cancer-Related Death
Cancer Site Number of Deaths Per Year
Lung 160,100
Colon and rectum 56,500
Breast 43,900
Prostate 39,200
Pancreas 28,900
Lymphoma 26,300
Leukemia 21,600
Brain 17,400
Stomach 13,700
Liver 13,000
Esophagus 11,900
Bladder 12,500
Kidney 11,600
Multiple myeloma 11,300

Tobacco

Eighty to 90% of lung cancer cases occur in smokers. Smoking has also been shown to be a contributory factor in cancers of upper respiratory tract, esophagus, larynx, bladder, pancreas, and probably liver, stomach, breast, and kidney as well. Recently, scientists have also shown that second-hand smoke (or passive smoking) can increase one's risk of developing cancer.

Alcohol

Excessive consumption of alcohol is a risk factor in certain cancers, such as liver cancer. Alcohol, in combination with tobacco, significantly increases the chances that an individual will develop mouth, pharynx, larynx, and esophageal cancers.

Diet

Thirty-five percent of all cancers are due to dietary causes. Excessive intake of fat leading to obesity has been associated with cancers of the breast, colon, rectum, pancreas, prostate, gall bladder, ovaries, and uterus.

Sexual and reproductive behavior

The human papillomavirus, which is sexually transmitted, has been shown to cause cancer of the cervix. Having too many sex partners and becoming sexually active early has been shown to increase one's chances of contracting this disease. In addition, it has also been shown that women who don't have children or have children late in life have an increased risk for both ovarian and breast cancer.

Infectious agents

In the last 20 years, scientists have obtained evidence to show that approximately 15% of the world's cancer deaths can be traced to viruses, bacteria, or parasites. The most common cancer-causing pathogens and the cancers associated with them are shown in table form.

Family history

Certain cancers like breast, colon, ovarian, and uterine cancer recur generation after generation in some families. A few cancers, such as the eye cancer "retinoblastoma," a type of colon cancer, and a type of breast cancer known as "early-onset breast cancer," have been shown to be linked to certain genes that can be tracked within a family. It is therefore possible that inheriting particular genes makes a person susceptible to certain cancers.

Occupational hazards

There is evidence to prove that certain occupational hazards account for 4% of all cancer deaths. For example, asbestos workers have an increased incidence of lung cancer. Similarly, a higher likelihood of getting bladder cancer is associated with dye, rubber and gas workers; skin and lung cancer with smelters, gold miners and arsenic workers; leukemia with glue and varnish workers; liver cancer with PVC manufacturers; and lung, bone and bone marrow cancer with radiologists and uranium miners.

Environment

Radiation is believed to cause 1-2% of all cancer deaths. Ultra-violet radiation from the sun accounts for a majority of melanoma deaths. Other sources of radiation are x rays, radon gas, and ionizing radiation from nuclear material.

Pollution

Several studies have shown that there is a well-established link between asbestos and cancer. Chlorination of water may account for a small rise in cancer risk. However, the main danger from pollution occurs when dangerous chemicals from the industries escape into the surrounding environment. It has been estimated that 1% of cancer deaths are due to air, land, and water pollution.

COMMON PATHOGENS AND THE CANCERS ASSOCIATED WITH THEM
Causative Agent Type of Cancer
Viruses
Papillomaviruses Cancer of the cervix
Hepatitis B virus Liver cancer
Hepatitis C virus Liver cancer
Epstein-Barr virus Burkitt's lymphoma
Cancers of the upper
pharynx
Hodgkin's lymphoma, Non-Hodgkin's
lymphoma, Gastric cancers
Human
immunodeficiency
virus (HIV)
Kaposi's sarcoma Lymphoma
Bacteria
Helicobacter pylori Stomach cancer Lymphomas

Cancer is a progressive disease, and goes through several stages. Each stage may produce a number of symptoms. Some symptoms are produced early and may occur due to a tumor that is growing within an organ or a gland. As the tumor grows, it may press on the nearby nerves, organs, and blood vessels. This causes pain and some pressure which may be the earliest warning signs of cancer.

Despite the fact that there are several hundred different types of cancers, producing very different symptoms, the ACS has established the following seven symptoms as possible warning signals of cancer:

  • changes in the size, color, or shape of a wart or a mole
  • a sore that does not heal
  • persistent cough, hoarseness, or sore throat
  • a lump or thickening in the breast or elsewhere
  • unusual bleeding or discharge
  • chronic indigestion or difficulty in swallowing
  • any change in bowel or bladder habits

Many other diseases, besides cancer, could produce the same symptoms. However, it is important to have these symptoms checked, as soon as possible, especially if they linger. The earlier a cancer is diagnosed and treated, the better the chance of it being cured. Many cancers such as breast cancer may not have any early symptoms. Therefore, it is important to undergo routine screening tests such as breast self-exams and mammograms.

Diagnosis

Diagnosis begins with a thorough physical examination and a complete medical history. The doctor will observe, feel and palpate (apply pressure by touch) different parts of the body in order to identify any variations from the normal size, feel, and texture of the organ or tissue.

As part of the physical exam, the doctor will inspect the oral cavity, or the mouth. By focusing a light into the mouth, he will look for abnormalities in color, moisture, surface texture, or presence of any thickening or sore in the lips, tongue, gums, the hard palate on the roof of the mouth, and the throat. To detect thyroid cancer, the doctor will observe the front of the neck for swelling. He may gently manipulate the neck and palpate the front and side surfaces of the thyroid gland (located at the base of the neck) to detect any nodules or tenderness. As part of the physical examination, the doctor will also palpate the lymph nodes in the neck, under the arms and in the groin. Many illnesses and cancers cause a swelling of the lymph nodes.

The doctor may conduct a thorough examination of the skin to look for sores that have been present for more than three weeks and that bleed, ooze, or crust; irritated patches that may itch or hurt, and any change in the size of a wart or a mole.

Examination of the female pelvis is used to detect cancers of the ovaries, uterus, cervix, and vagina. In the visual examination, the doctor looks for abnormal discharges or the presence of sores. Then, using gloved hands the physician palpates the internal pelvic organs such as the uterus and ovaries to detect any abnormal masses. Breast examination includes visual observation where the doctor looks for any discharge, unevenness, discoloration, or scaling. The doctor palpates both breasts to feel for masses or lumps.

For males, inspection of the rectum and the prostate is also included in the physical examination. The doctor inserts a gloved finger into the rectum and rotates it slowly to feel for any growths, tumors, or other abnormalities. The doctor also conducts an examination of the testes, where the doctor observes the genital area and looks for swelling or other abnormalities. The testicles are palpated to identify any lumps, thickening or differences in the size, weight and firmness.

If the doctor detects an abnormality on physical examination, or the patient has some symptom that could be indicative of cancer, the doctor may order diagnostic tests.

Laboratory studies of sputum (sputum cytology), blood, urine, and stool can detect abnormalities that may indicate cancer. Sputum cytology is a test where the phlegm that is coughed up from the lungs is microscopically examined. It is often used to detect lung cancer. A blood test for cancer is easy to perform, usually inexpensive and risk-free. The blood sample is obtained by a lab technician or a doctor by inserting a needle into a vein and is relatively painless. Blood tests can be either specific or non-specific. Often, in certain cancers, the cancer cells release particular proteins (called tumor markers ) and blood tests can be used to detect the presence of these tumor markers. However, with a few exceptions, tumor markers are not used for routine screening of cancers, because several non-cancerous conditions also produce positive results. Blood tests are generally more useful in monitoring the effectiveness of the treatment, or in following the course of the disease and detecting recurrent disease.

Imaging tests such as computed tomography scans (CT scans), magnetic resonance imaging (MRI), ultrasound and fiberoptic scope examinations help the doctors determine the location of the tumor even if it is deep within the body. Conventional x rays are often used for initial evaluation, because they are relatively cheap, painless and easily accessible. In order to increase the information obtained from a conventional x ray, air or a dye (such as barium or iodine) may be used as a contrast medium to outline or highlight parts of the body.

The most definitive diagnostic test is the biopsy, wherein a piece of tissue is surgically removed for microscope examination. Besides confirming a cancer, the biopsy also provides information about the type of cancer, the stage it has reached, the aggressiveness of the cancer and the extent of its spread. Since a biopsy provides the most accurate analysis, it is considered the gold standard of diagnostic tests.

Screening examinations conducted regularly by healthcare professionals can result in the detection of cancers of the breast, colon, rectum, cervix, prostate, testis, tongue, mouth, and skin at early stages, when treatment is more likely to be successful. Some of the routine screening tests recommended by the ACS are sigmoidoscopy (for colorectal cancer), mammography (for breast cancer), pap smear (for cervical cancer ), and the PSA test (for prostate cancer). Self-examinations for cancers of the breast, testes, mouth, and skin can also help in detecting the tumors before the symptoms become serious.

A recent revolution in molecular biology and cancer genetics has contributed a great deal to the development of several tests designed to assess one's risk of getting cancers. These new techniques include genetic testing, where molecular probes are used to identify mutations in certain genes that have been linked to particular cancers. At present, however, there are a lot of limitations to genetic testing and its utility appears ambiguous, emphasizing the need to develop better strategies for early detection.

Treatment

Treatment and prevention of cancers continue to be the focus of a great deal of research. In 2003, research into new cancer therapies included cancertargeting gene therapy, virus therapy, and a drug that stimulated apoptosis, or self-destruction of cancer cells, but not healthy cells. However, all of these new therapies take years of clinical testing and research.

The aim of cancer treatment is to remove all or as much of the tumor as possible and to prevent the recurrence or spread of the primary tumor. While devising a treatment plan for cancer, the likelihood of curing the cancer has to be weighed against the side effects of the treatment. If the cancer is very aggressive and a cure is not possible, then the treatment should be aimed at relieving the symptoms and controlling the cancer for as long as possible.

Cancer treatment can take many different forms, and it is always tailored to the individual patient. The decision on which type of treatment is the most appropriate depends on the type and location of cancer, the extent to which it has already spread, the patient's age, sex, general health status and personal treatment preferences. The major types of treatment are: surgery, radiation, chemotherapy, immunotherapy, hormone therapy, and bone-marrow transplantation.

Surgery

Surgery is the removal of a visible tumor and is the most frequently used cancer treatment. It is most effective when a cancer is small and confined to one area of the body.

Surgery can be used for many purposes.

  • Treatment. Treatment of cancer by surgery involves removal of the tumor to cure the disease. This is typically done when the cancer is localized to a discrete area. Along with the cancer, some part of the normal surrounding tissue is also removed to ensure that no cancer cells remain in the area. Since cancer usually spreads via the lymphatic system, adjoining lymph nodes may be examined and sometimes are removed as well.
  • Preventive surgery. Preventive or prophylactic surgery involves removal of an abnormal looking area that is likely to become malignant over time. For example, 40% of people with a colon disease known as ulcerative colitis, ultimately die of colon cancer. Rather than live with the fear of developing colon cancer, these people may choose to have their colons removed and reduce the risk significantly.
  • Diagnostic purposes. The most definitive tool for diagnosing cancer is a biopsy. Sometimes, a biopsy can be performed by inserting a needle through the skin. However, at other times, the only way to obtain a tissue sample for biopsy is by performing a surgical operation.
  • Cytoreductive surgery is a procedure where the doctor removes as much of the cancer as possible, and then treats the remaining area with radiation therapy or chemotherapy or both.
  • Palliative surgery is aimed at curing the symptoms, not the cancer. Usually, in such cases, the tumor is so large or has spread so much that removing the entire tumor is not an option. For example, a tumor in the abdomen may be so large that it may press on and block a portion of the intestine, interfering with digestion and causing pain and vomiting. "Debulking surgery" may remove a part of the blockage and relieve the symptoms. In tumors that are dependent on hormones, removal of the organs that secrete the hormones is an option. For example, in prostate cancer, the release of testosterone by the testicles stimulates the growth of cancerous cells. Hence, a man may undergo an "orchiectomy" (removal of testicles) to slow the progress of the disease. Similarly, in a type of aggressive breast cancer, removal of the ovaries (oophorectomy ) will stop the synthesis of hormones from the ovaries and slow the progression of the cancer.

Radiation therapy

Radiation kills tumor cells. Radiation is used alone in cases where a tumor is unsuitable for surgery. More often, it is used in conjunction with surgery and chemotherapy. Radiation can be either external or internal. In the external form, the radiation is aimed at the tumor from outside the body. In internal radiation (also known as brachytherapy), a radioactive substance in the form of pellets or liquid is placed at the cancerous site by means of a pill, injection or insertion in a sealed container.

Chemotherapy

Chemotherapy is the use of drugs to kill cancer cells. It destroys the hard-to-detect cancer cells that have spread and are circulating in the body. Chemotherapeutic drugs can be taken either orally (by mouth) or intravenously, and may be given alone or in conjunction with surgery, radiation or both.

When chemotherapy is used before surgery or radiation, it is known as primary chemotherapy or "neoadjuvant chemotherapy." An advantage of neoadjuvant chemotherapy is that since the cancer cells have not been exposed to anti-cancer drugs, they are especially vulnerable. It can therefore be used effectively to reduce the size of the tumor for surgery or target it for radiation. However, the toxic effects of neoadjuvant chemotherapy are severe. In addition, it may make the body less tolerant to the side effects of other treatments that follow such as radiation therapy. The more common use of chemotherapy is adjuvant therapy, which is given to enhance the effectiveness of other treatments. For example, after surgery, adjuvant chemotherapy is given to destroy any cancerous cells that still remain in the body. In 2003, a new technique was developed to streamline identification of drug compounds that are toxic to cancerous cells but not to healthy cells. The technique identified nine dugs, one of which had never before been identified for use in cancer treatment. Researchers began looking into developing the new drug for possible use.

Immunotherapy

Immunotherapy uses the body's own immune system to destroy cancer cells. This form of treatment is being intensively studied in clinical trials and is not yet widely available to most cancer patients. The various immunological agents being tested include substances produced by the body (such as the interferons, interleukins, and growth factors), monoclonal antibodies, and vaccines. Unlike traditional vaccines, cancer vaccines do not prevent cancer. Instead, they are designed to treat people who already have the disease. Cancer vaccines work by boosting the body's immune system and training the immune cells to specifically destroy cancer cells.

Hormone therapy

Hormone therapy is standard treatment for some types of cancers that are hormone-dependent and grow faster in the presence of particular hormones. These include cancer of the prostate, breast, and uterus. Hormone therapy involves blocking the production or action of these hormones. As a result the growth of the tumor slows down and survival may be extended for several months or years.

Bone marrow transplantation

The bone marrow is the tissue within the bone cavities that contains blood-forming cells. Healthy bone marrow tissue constantly replenishes the blood supply and is essential to life. Sometimes, the amount of drugs or radiation needed to destroy cancer cells also destroys bone marrow. Replacing the bone marrow with healthy cells counteracts this adverse effect. A bone marrow transplant is the removal of marrow from one person and the transplant of the blood-forming cells either to the same person or to someone else. Bone-marrow transplantation, while not a therapy in itself, is often used to "rescue" patients, by allowing those with cancer to undergo aggressive therapy.

Many different specialists generally work together as a team to treat cancer patients. An oncologist is a physician who specializes in cancer care. The oncologist provides chemotherapy, hormone therapy, and any other non-surgical treatment that does not involve radiation. The oncologist often serves as the primary physician and coordinates the patient's treatment plan.

The radiation oncologist specializes in using radiation to treat cancer, while the surgical oncologist performs the operations needed to diagnose or treat cancer. Gynecologist-oncologists and pediatric-oncologists, as their titles suggest, are physicians involved with treating women's and children's cancers respectively. Many other specialists also may be involved in the care of a cancer patient. For example, radiologists specialize in the use of x rays, ultrasounds, CT scans, MRI imaging and other techniques that are used to diagnose cancer. Hematologists specialize in disorders of the blood and are consulted in case of blood cancers and bone marrow cancers. The samples that are removed for biopsy are sent to a laboratory, where a pathologist examines them to determine the type of cancer and extent of the disease. Only some of the specialists who are involved with cancer care have been mentioned above. There are many other specialties, and virtually any type of medical or surgical specialist may become involved with care of the cancer patient should it become necessary.

Alternative treatment

There are a multitude of alternative treatments available to help the person with cancer. They can be used in conjunction with, or separate from, surgery, chemotherapy, and radiation therapy. Alternative treatment of cancer is a complicated arena and a trained health practitioner should be consulted.

Although the effectiveness of complementary therapies such as acupuncture in alleviating cancer pain has not been clinically proven, many cancer patients find it safe and beneficial. Bodywork therapies such as massage and reflexology ease muscle tension and may alleviate side effects such as nausea and vomiting. Homeopathy and herbal remedies used in Chinese traditional herbal medicine also have been shown to alleviate some of the side effects of radiation and chemotherapy and are being recommended by many doctors.

Certain foods including many vegetables, fruits, and grains are believed to offer protection against various cancers. However, isolation of the individual constituent of vegetables and fruits that are anti-cancer agents has proven difficult. In laboratory studies, vitamins such as A, C and E, as well as compounds such as isothiocyanates and dithiolthiones found in broccoli, cauliflower, and cabbage, and beta-carotene found in carrots have been shown to protect against cancer. Studies have shown that eating a diet rich in fiber as found in fruits and vegetables reduces the risk of colon cancer. Exercise and a low fat diet help control weight and reduce the risk of endometrial, breast, and colon cancer.

Certain drugs, which are currently being used for treatment, could also be suitable for prevention. For example, the drug tamoxifen (Nolvadex), which has been very effective against breast cancer, is currently being tested by the National Cancer Institute for its ability to prevent cancer. Similarly, retinoids derived from vitamin A are being tested for their ability to slow the progression or prevent head and neck cancers. Certain studies have suggested that cancer incidence is lower in areas where soil and foods are rich in the mineral selenium. More trials are needed to explain these intriguing connections.

Prognosis

"Lifetime risk" is the term that cancer researchers use to refer to the probability that an individual over the course of a lifetime will develop cancer or die from it. In the United States, men have a one in two lifetime risk of developing cancer, and for women the risk is one in three. Overall, African Americans are more likely to develop cancer than whites. African Americans are also 30% more likely to die of cancer than whites.

Most cancers are curable if detected and treated at their early stages. A cancer patient's prognosis is affected by many factors, particularly the type of cancer the patient has, the stage of the cancer, the extent to which it has metastasized and the aggressiveness of the cancer. In addition, the patient's age, general health status and the effectiveness of the treatment being pursued also are important factors.

To help predict the future course and outcome of the disease and the likelihood of recovery from the disease, doctors often use statistics. The five-year survival rates are the most common measures used. The number refers to the proportion of people with cancer who are expected to be alive, five years after initial diagnosis, compared with a similar population that is free of cancer. It is important to note that while statistics can give some information about the average survival experience of cancer patients in a given population, it cannot be used to indicate individual prognosis, because no two patients are exactly alike.

Prevention

According to nutritionists and epidemiologists from leading universities in the United States, a person can reduce the chances of getting cancer by following some simple guidelines:

  • eating plenty of vegetables and fruits
  • exercising vigorously for at least 20 minutes every day
  • avoiding excessive weight gain
  • avoiding tobacco (even second hand smoke)
  • decreasing or avoiding consumption of animal fats and red meats
  • avoiding excessive amounts of alcohol
  • avoiding the midday sun (between 11 A.M. and 3 P.M.) when the sun's rays are the strongest
  • avoiding risky sexual practices
  • avoiding known carcinogens in the environment or work place

KEY TERMS

Benign Mild, nonmalignant. Recovery is favorable with treatment.

Biopsy The surgical removal and microscopic examination of living tissue for diagnostic purposes.

Bone marrow Spongy material that fills the inner cavities of the bones. The progenitors of all the blood cells are produced in this bone marrow.

Carcinogen Any substance capable of causing cancer by mutating the cell's DNA.

Chemotherapy Treatment with certain anticancer drugs.

Epithelium The layer of cells covering the body's surface and lining the internal organs and various glands.

Hormone therapy Treatment of cancer by inhibiting the production of hormones such as testosterone and estrogen.

Immunotherapy Treatment of cancer by stimulating the body's immune defense system.

Malignant A general term for cells and the tumors they form that can invade and destroy other tissues and organs.

Metastasis The spread of cancer from one part of the body to another.

Radiation therapy Treatment using high-energy radiation from x-ray machines, cobalt, radium, or other sources.

Sore An open wound, bruise or lesion on the skin.

Tumor An abnormal growth resulting from a cell that lost its normal growth control restraints and started multiplying uncontrollably.

X rays High-energy radiation used in high doses, either to diagnose or treat disease.

In addition, following the advice of physicians in refraining from certain activities or drugs that are proven as risk factors for certain cancers can help lower one's risk. For instance, while physicians have long known a small increased risk for breast cancer was linked to use of HRT, a landmark study released in 2003 proved the risk was greater than thought. The Women's Health Initiative found that even relatively short-term use of estrogen plus progestin is associated with increased risk of breast cancer, diagnosis at a more advanced stage of the disease, and a higher number of abnormal mammograms. The longer a woman used HRT, the more her risk increased.

Resources

BOOKS

Simone, Joseph V. "Oncology: Introduction." In Cecil Textbook of Medicine, edited by Russel L. Cecil, et al. Philadelphia: W.B. Saunders Company, 2000.

PERIODICALS

"HRT Linked to Higher Breast Cancer Risk, Later Diagnosis, Abnormal Mammograms." Women's Health Weekly July 17, 2003: 2.

"New Way to Stop Cancer Cell Growth Described." Gene Therapy Weekly December 12, 2002: 9.

"Researchers Find New Way to Trigger Self-Destruction of Certain Cancer Cells." Biotech Week July 16, 2003: 285.

"Technique Streamlines Search for Anticancer Drugs." Cancer Weekly April 15, 2003: 62.

"Virus Therapy Attacks Cancer Cells." Cancer Weekly July 29, 2003: 50.

ORGANIZATIONS

American Cancer Society. 1599 Clifton Road, N.E. Atlanta, GA 30329 (800) 227-2345. http://www.cancer.org.

Cancer Research Institute (National Headquarters). 681, Fifth Avenue, New York, NY 10022 (800) 992-2623. http://www.cancerresearch.org.

National Cancer Institute. 9000 Rockville Pike, Building 31, room 10A16, Bethesda, Maryland, 20892 (800) 422-6237. http://wwwicic.nci.nih.gov.

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Cancer

Cancer

Definition

Cancer is a group of diseases characterized by uncontrolled growth of tissue cells in the body and the invasion by these cells into nearby tissue and migration to distant sites.

Description

Cancer results from alterations (mutations) in genes that make up DNA, the master molecule of the cell. Genes make proteins, which are the ultimate workhorses of the cells, responsible for the many processes that permit humans to breathe, think, and move, among other functions. Some of these proteins control the orderly growth, division, and reproduction of normal tissue cells. Gene mutations can produce faulty proteins, which in turn produce abnormal cells that no longer divide and reproduce in an orderly manner. These abnormal cells divide uncontrollably and eventually form a new growth known as a tumor or neoplasm. A healthy immune system can usually recognize neoplastic cells and destroy them before they divide. However, mutant cells may escape immune detection and become tumors or cancers.

Studies of the origins of cancer have shown that a combination of genetic influences and environmental causes over time triggers gene mutations, which may explain why most cancers are seen in adults of middle age or older (60%) and cancer is rare children. Many cancers have been shown to result from exposure to environmental toxins (carcinogens) and related alterations in DNA. Faulty DNA can also be inherited, predisposing an individual to develop cancer, although fewer than 10 percent of cancers are purely hereditary. Hereditary links have been shown in cancers of the breast, colon, ovaries, and uterus. Inherited physiological traits can also contribute to cancer, such as inheriting fair skin increasing the risk of skin cancer, but only if accompanied by prolonged exposure to intensive sunlight.

Tumors can be benign or malignant. A benign tumor is not cancer. It is slow growing, does not invade surrounding tissue, and once removed, does not usually recur. A malignant tumor is cancerous. It invades surrounding tissue and spreads to nearby or distant organs (metastasis). If the cancer cells have spread to surrounding tissue, even after the malignant tumor is removed, it will typically recur.

Cancer falls into several general categories:

  • Carcinoma (90% of all cancer) are solid tumors arising in the layer of cells (epithelium) covering the body's surface and lining internal organs and glands. Adenocarcinomas develop in an organ or gland and squamous cell carcinomas originate in the skin.
  • Melanoma originates in the skin, usually in pigment cells (melanocytes).
  • Sarcoma is cancer of supporting tissue such as bone, muscle, and blood vessels.
  • Leukemias and lymphomas are cancers of the blood and lymph glands.
  • Gliomas are cancers of the nerve tissue.

The most common cancers affecting adults are cancer of the skin, lung, colon, breast, and prostate. Cancer of the kidneys, ovaries, uterus, pancreas, bladder, rectum, and the leukemias and lymphomas are among the 12 major cancers affecting Americans of all ages. Although children and adolescents do develop solid tumors, the most common high-risk cancers among children are:

  • acute myeloid leukemia
  • acute lymphoblastic leukemia
  • neuroblastoma
  • glioma
  • sarcoma of bone (osteosarcoma) and soft tissue

Demographics

Childhood cancer is rare, occurring in about 14 in 100,000 children in the United States each year. However, in the entire U.S. population, one of every four deaths is from cancer, second only to deaths from heart disease. About 1.2 million cancer cases are diagnosed annually and more than 500,000 die, of whom 2,700 are children or adolescents.

Causes and symptoms

Genetic predisposition, environmental causes, and individual developmental problems are responsible for most childhood cancer. The presence of other disorders, such as Down syndrome , has also been shown to be associated with cancer in children. The major risk factors that apply to adult cancer are tobacco, alcohol, sexual and reproductive behavior, and occupation, none of which increases risk in children. Other well-known risk factors, such as family history, infectious agents, diet, environmental toxins, and pollution, can apply equally to children.

Tobacco

Approximately 80 to 90 percent of lung cancer cases occur in smokers. Smoking is also the leading cause of bladder cancer and has been shown to contribute to cancers of the upper respiratory tract, esophagus, larynx, kidney, pancreas, stomach, and possibly breast as well. Second-hand smoke (passive smoking) has been shown to increase cancer risk in children and adults who live with smokers.

Infectious agents

Cancer deaths worldwide can be traced to viruses, bacteria, or parasites. Epstein-Barr virus (EBV), for example, is associated with lymphoma, the hepatitis viruses are associated with liver cancer, HIV is associated with Kaposi's sarcoma, and the bacteria Helicobacter pylori is associated with stomach cancer.

Genetic predisposition

Certain cancers such as breast, colon, ovarian, and uterine cancer recur generation after generation in some families. Eye cancer (retinoblastoma ), a type of colon cancer, and early-onset breast cancer have been shown to be linked to the inheritance of specific genes.

Environmental sources

Radiation is believed to cause 1 to 2 percent of all cancer deaths. Ultraviolet radiation from the sun accounts for a majority of melanoma deaths. Other sources of radiation are x-rays, radon gas, and ionizing radiation from nuclear material.

Pollution

Studies have established links between environmental toxins, such as asbestos, and cancer. Chlorination of water may account for a small rise in cancer risk. However, the main danger from pollutants occurs when toxic industrial chemicals are released into the surrounding environment. As of 2004 an estimated 1 percent of cancer deaths are believed to be due to air, land, and water pollution.

Cancer is a progressive disease that goes through several stages, each producing a number of symptoms. Early symptoms can be produced by the growth of a solid tumor in an organ or gland. A growing tumor may press on nearby nerves, organs, and blood vessels, causing pain and pressure that may be the first warning signs of cancer. Other symptoms can include sores that do not heal, growths on the skin or below the skin, unusual bleeding, difficulty digesting food or swallowing, and changes in bowel or bladder function. Fever can be present as well as fatigue and weakness.

When to call the doctor

Despite the fact that there are hundreds of different types of cancer, each producing different symptoms, the American Cancer Society has established the following seven symptoms as possible warning signals of cancer:

  • changes in the size, color, or shape of a wart or a mole
  • a sore that does not heal
  • persistent cough , hoarseness, or sore throat
  • a lump or thickening in the breast or elsewhere
  • unusual bleeding or discharge
  • chronic indigestion or difficulty swallowing
  • any change in bowel or bladder habits

Parents should report any such symptoms to the pediatrician along with unexplained fever or frequent infections. Vision problems, weight loss, lack of appetite, depression, swollen glands, paleness, or general weakness are other reasons for parents to consult the pediatrician. Generally, the earlier cancer is diagnosed and treated, the better the chance of a cure, although not all cancers have early symptoms.

Diagnosis

Diagnosis begins with a complete medical history, including family history of cancer, and a thorough physical examination. The doctor observes and palpates (applies pressure by touch) different parts of the body in order to identify any variations from normal size, feel, and texture of an organ or tissue. The doctor looks inside the mouth for abnormalities in color, moisture, surface texture, or the presence of any thickening or sores in the lips, tongue, gums, the roof of the mouth, or the throat. The doctor observes the front of the neck for swelling and may gently manipulate the neck and palpate the front and side surfaces of the thyroid gland at the base of the neck, looking for nodules or tenderness. The doctor also palpates the lymph nodes in the neck, under the arms, and in the groin, looking for enlargement. The skin is examined for sores that are slow to heal, especially those that bleed, ooze, or crust; irritated patches that may itch or hurt; and any change in the size of a wart or a mole.

In adolescent females, a pelvic exam may be conducted to detect cancers of the ovaries, uterus, cervix, and vagina. The doctor first looks for abnormal discharges or the presence of sores. Then the internal pelvic organs such as the uterus and ovaries are palpated (touched while applying gentle pressure) to detect abnormal masses. Breast examination evaluates unevenness, discoloration, or scaling; both breasts are palpated to feel for masses or lumps.

In adolescent males, inspection of the rectum and prostate may be included in the physical examination. The doctor inserts a gloved finger into the rectum and rotates it slowly to feel for growths, tumors, or other abnormalities. The testes are examined visually, looking for unevenness, swelling, or other abnormalities. The testicles are palpated to identify lumps, thickening or differences in size, weight, or firmness.

If an abnormality is detected on physical examination, or symptoms suggestive of cancer are noted, diagnostic tests will be performed. Laboratory studies of sputum, blood, urine, and stool can detect abnormalities that may confirm cancer. Sputum cytology involves the microscopic examination of phlegm that is coughed up from the lungs. Tumor markers, specific proteins released by certain types of cancer cells, can be detected by performing a test on venous blood. If leukemia or lymphoma is suspected, a complete blood count (CBC) with peripheral smear (differential) is done to evaluate the number, appearance, and maturity of red blood cells (RBCs) and white blood cells (WBCs) and to measure hemoglobin, hematocrit, and platelet count . A bone marrow biopsy may be done to determine what type of cells is present in the bone marrow. Blood chemistries will be done to help determine if liver or kidney problems are present. Blood chemistries are also useful in monitoring the effectiveness of treatment for all types of cancer and in following the course of the disease and detecting recurrences.

Diagnostic imaging techniques such as computed tomography (CT scans), magnetic resonance imaging (MRI), ultrasound, and fiberoptic scope examinations (such as colonoscopy or sigmoidoscopy) can help determine the location, size, and characteristics of a tumor even if it is deep within the body. Conventional x rays are often used for initial evaluation, because they are relatively cheap, painless, and easily accessible. In order to increase the information obtained from a conventional x ray, air or contrast media (such as barium or iodine) may be used to enhance the images.

The most definitive diagnostic test for cancer is a biopsy, which is the surgical removal of a piece of suspect tissue for staining and microscope examination (cytochemistry). By examining certain cell characteristics, abnormalities can be identified and the presence of specific types of cells can be diagnostic for certain cancers. The biopsy provides information about the type of cancer, its stage, the aggressiveness of the cancer in invading nearby tissue or organs, and the extent of metastases at diagnosis. The pathologist who evaluates cancer cells in biopsied tissue designates the cancer as being stage I, II, III, or IV, in terms of the degree of metastasis.

Newer molecular and cellular diagnostic testing, such as polymerase chain reaction (PCR), allows the molecular genetic analysis of tumors. Cytogenetic analysis of tumor chromosomes, for example, can identify structural abnormalities that may explain the unique origins of cancer in an individual child. Spectral karyotyping (SKY), an advanced method of screening chromosomes for numeric and structural abnormalities, is used to evaluate pediatric tumors. Gene sequences can also be evaluated in a method (comparative genomic hybridization) that compares samples from a tumor and normal tissue after both have been exposed to the same radioactive material. This method can determine gains and losses in DNA in the region of the tumor, detecting alterations that have caused the cancer. The developing science of proteomics studies specific proteins in cells and may someday be able to provide detailed assessment of cancer cells.

Treatment

The aim of cancer treatment is to remove or destroy all or as much of the primary tumor as possible and to prevent its recurrence or metastases. While devising a treatment plan for cancer, the likelihood of curing the cancer has to be weighed against the side effects of the treatment. If the cancer is highly aggressive and cure is not likely, treatment will be aimed at relieving symptoms and controlling the cancer for as long as possible.

Cancer treatment is always tailored to the individual. The treatment choice depends on the type and location of cancer, the extent to which it has already spread, and the age, sex, and general health status of the individual. The major types of treatment are: surgery, radiation, chemotherapy , immunotherapy, hormone therapy, and bone-marrow transplantation.

Advances in molecular biology and cancer genetics have contributed greatly to the development of therapies that provide cell-targeted treatment. Genetic testing uses molecular probes to identify gene mutations that have been linked to specific cancers. In the early 2000s ongoing research is focused on new treatment and prevention methods, including molecular-targeted therapies, virus therapy, immunotherapy, and drug therapy that stimulates the self-destruction of cancer cells (apoptosis).

Targeted molecular therapy, although as of 2004 still the subject of concentrated research, was being used effectively in pediatric study subjects where it has been shown to reduce the toxicity seen with conventional chemotherapy. Unlike chemotherapy, which treats all cells uniformly, targeted molecular therapy can focus on selected cells without affecting normal cells and tissues. This refinement frees children from some of the long-term toxic effects and complications that can negatively affect quality of life and survival even if the cancer is cured.

Surgery

Surgical removal of a solid tumor is most effective with small tumors confined to one area of the body. Surgery removes the tumor (tumor resection) and usually part of the surrounding tissue to ensure that no cancer cells remain in the area. Since cancer usually spreads via the lymphatic system, adjoining lymph nodes are sometimes removed as well. Surgery may also be preventive or prophylactic, removing an abnormal looking area of tissue that is likely to become malignant over time. During surgery biopsies may also be performed on tissue that may be affected by metastases. Surgery is not a typical treatment for leukemia or lymphoma, which arise in the circulatory system and lymphatic systems that extend throughout the body. Children with osteosarcoma (bone cancer) and other solid tumors are candidates for surgery, however.

Surgery may be performed in conjunction with radiation (cytoreductive surgery) or chemotherapy. The surgeon removes as much of the cancer as possible and the remaining area is treated with radiotherapy or chemotherapy or both. In advanced metastatic cancer when cure is unlikely, palliative surgery aims at reducing symptoms. Debulking surgery, for example, removes part of a tumor that is pressing on other organs and causing pain. In tumors that are dependent on hormones, one option is to remove organs that secrete the hormones.

Radiation therapy

Radiation kills tumor cells and is used alone when a tumor is in a poor location for surgery. More often, it is used in conjunction with surgery and chemotherapy. Radiation can be either external or internal. External radiation is aimed at the tumor from outside the body. In internal radiation (brachytherapy), radioactive liquid or pellets are delivered to the cancerous site via a pill, injection, or insertion in a sealed container.

Chemotherapy

Chemotherapy is the administration of drugs that kill cancer cells (cytotoxic drugs). It destroys hard-to-detect cancer cells that have spread (metastasized) through the circulation or lymph system. Chemotherapeutic drugs are given orally or intravenously, either alone or in conjunction with surgery, radiation, or both. When chemotherapy is used before surgery or radiation, it is known as primary chemotherapy or neoadjuvant chemotherapy. Because the cancer cells have not yet been exposed to anti-cancer drugs, they are especially vulnerable, allowing neoadjuvant therapy to effectively reduce tumor size. However, the toxic effects of neoadjuvant chemotherapy may be severe, because normal cells are also destroyed. Chemotherapy may also make the body less tolerant of the side effects of other treatments such as radiation therapy. Adjuvant therapy is the more common type of chemotherapy, used to enhance the effectiveness of other treatments.

Immunotherapy

Immunotherapy uses the body's own immune system, specifically a type of disease-fighting white cell called T-cells, to destroy cancer cells. Tumor-specific proteins that are part of unique genetic mutations in pediatric cancer, for example, are believed to be ideal targets for anti-tumor immune processes. Various immunological agents are as of 2004 still in clinical trials and are not as of that year widely available, though initial results are promising. Monoclonal antibodies are used to

Common childhood cancers
Percentage of total childhood cancers Type of cancer
source: Margo Hoover-Regan. http://www.csupomona.edu/~cancerbio/pediatric%20cancer%20-%20Dr.%20Hoover-Regan.htm. Updated May 15, 2000.
39% Leukemia (white blood cell cancer) and lymphoma (lymph system cancer)
20.7% Brain cancers (brain and spinal cord tumors)
7.3% Neuroblastoma (nerve cell cancer, most commonly in the adrenal gland)
6.1% Wilms' tumor (kidney cancer that can metastasize to lung)
4.7% Osteosarcoma (bone cancer) and Ewing's sarcoma (cancer in the bone shaft)
3.4% Rhabdomyosarcoma (muscle tissue cancer, most often in head and neck)
2.9% Retinoblastoma (malignant eye tumor)
16.4% Germ cell cancer (ovarian or testicular cancers) and others

fight cancer cells in much the same way as antibodies that are produced by the body's own immune system work to fight infection. Other substances are also being used experimentally. They include substances such as interferons, interleukins, growth factors, monoclonal antibodies, and vaccines. Unlike traditional vaccines, cancer vaccines do not prevent cancer but are designed to treat existing disease. They work by boosting the immune system and training immunized cells to destroy cancer cells.

Hormone therapy

Hormone therapy is standard treatment for cancers that are hormone-dependent and grow faster in the presence of specific hormones, such as cancer of the prostate, breast, and uterus. Hormone therapy blocks the production or action of these hormones, slowing growth of the tumor and extending survival for months or years.

Bone marrow transplantation

Bone marrow is the tissue within bone cavities that produces blood cells. Healthy bone marrow tissue constantly replenishes the blood supply and is essential to life. Sometimes drugs or radiation needed to destroy cancer cells also destroys bone marrow and only replacement with healthy cells counteracts this adverse effect. A bone marrow transplant involves removing marrow from a donor and transplanting blood-forming cells to a recipient. While not a therapy in itself, bone marrow transplantation may allow a cancer patient to undergo aggressive therapy.

Many specialists work together to treat cancer patients. The oncologist is a physician who specializes in cancer care and usually coordinates the treatment plan, directing chemotherapy, hormone therapy, and any treatment that does not involve radiation or surgery. The radiation oncologist uses radiation to treat cancer, while the surgical oncologist performs surgery to diagnose or treat cancer. Gynecologist-oncologists and pediatric-oncologists, as their titles suggest, are physicians who treat women's and children's cancers. Radiologists read the x rays, ultrasound images, CT scans, and MRI images to help diagnose cancer. Hematologists specialize in disorders of the blood and bone marrow and are consulted in the evaluation of leukemia, lymphoma, and bone cancer.

Alternative treatment

A range of alternative treatments are available to help treat cancer that can be used in conjunction with, or separate from, surgery, chemotherapy, and radiation. Alternative treatment of cancer is a complicated arena and a trained complementary health practitioner should be consulted.

Although the effectiveness of complementary therapies such as acupuncture in alleviating cancer pain have not as of 2004 been clinically proven, many cancer patients find it safe and beneficial. Bodywork therapies such as massage and reflexology ease muscle tension and may alleviate side effects such as nausea and vomiting . Homeopathy and herbal remedies used in Chinese traditional herbal medicine also have been shown to alleviate some of the side effects of radiation and chemotherapy and are being recommended by many doctors.

Prognosis

Most cancers show good cure rates if detected and treated at early stages. The prognosis involves the type of cancer, its degree of invasiveness, and the extent of metastases at diagnosis. In addition, age, general health status, and response to treatment are important factors. Cancer deaths in children have shown consistent declines, decreasing between 1975 and 2000 from 50 in 1 million diagnosed to 25 in 1 million. However, cancer is the leading cause of death among children and adolescents, responsible for 2,700 deaths each year in the United States.

Prevention

Prevention of cancer means being aware of causes and risks, which involve a combination of genetic and environmental factors. Except for family history, specific genetic causes or an inherited predisposition are generally unknown in individuals until revealed in the diagnostic process. Known environmental causes can be avoided, however. A list of guidelines offered by nutritionists and epidemiologists from leading U.S. universities to reduce the risk of cancer includes some that may apply to children and adolescents:

  • Eat plenty of vegetables and fruits, especially cruciferous vegetables such as broccoli, cauliflower, and cabbage.
  • Decrease or avoid eating animal fats and red meats.
  • Exercise vigorously for at least 20 minutes every day.
  • Avoid excessive weight gain.
  • Avoid tobacco (including second hand smoke).
  • Avoid excessive amounts of alcohol.
  • Avoid midday sun (between 11 a.m. and 3 p.m.) when rays are the strongest.
  • Avoid risky sexual practices and multiple partners.
  • Avoid known carcinogens in the environment or work place.

Certain drugs being used as of 2004 for treatment could also be suitable for prevention, at least prevention of recurrences. For example, the drug tamoxifen has been very effective against breast cancer and is in 2004 being used to prevent recurrence in breast cancer survivors. Similarly, retinoids derived from vitamin A are being tested for their ability to slow the progression of or to prevent head and neck cancers. Certain studies suggest that cancer incidence is lower in areas where soil and foods are rich in the mineral selenium.

Nutritional concerns

Certain foods, including many vegetables, fruits, and grains, are believed to offer protection against various cancers. In laboratory studies, vitamins such as A, C, and E, as well as beta-carotene found in carrots and isothiocyanate and dithiolthione compounds found in cruciferous vegetables, such as broccoli, cauliflower, and cabbage, have been shown to provide protection against certain types of cancer. Studies have shown that eating a diet rich in fiber as found in fruits, vegetables, and whole grains can reduce the risk of colon cancer.

KEY TERMS

Benign In medical usage, benign is the opposite of malignant. It describes an abnormal growth that is stable, treatable, and generally not life-threatening.

Biopsy The surgical removal and microscopic examination of living tissue for diagnostic purposes or to follow the course of a disease. Most commonly the term refers to the collection and analysis of tissue from a suspected tumor to establish malignancy.

Bone marrow The spongy tissue inside the large bones in the body that is responsible for making the red blood cells, most white blood cells, and platelets.

Carcinogenic A substance that can cause cancer to develop.

Chemotherapy Any treatment of an illness with chemical agents. The term is usually used to describe the treatment of cancer with drugs that inhibit cancer growth or destroy cancer cells.

Epithelium The layer of cells that covers body surfaces, lines body cavities, and forms glands.

Hormone therapy Treating cancers by changing the hormone balance of the body, instead of by using cell-killing drugs.

Immunotherapy A mode of cancer treatment in which the immune system is stimulated to fight the cancer.

Malignant Cells that have been altered such that they have lost normal control mechanisms and are capable of local invasion and spread to other areas of the body. Often used to describe a cancer.

Metastasis A secondary tumor resulting from the spread of cancerous cells from the primary tumor to other parts of the body.

Radiation therapy A cancer treatment that uses high-energy rays or particles to kill or weaken cancer cells. Radiation may be delivered externally or internally via surgically implanted pellets. Also called radiotherapy.

Sore A wound, lesion, or ulcer on the skin.

Tumor A growth of tissue resulting from the uncontrolled proliferation of cells.

Parental concerns

A diagnosis of childhood cancer raises many uncertainties and concerns for parents, including how to acquire the most effective therapy. Advances in molecular and cellular technologies have improved both the diagnosis and treatment of pediatric cancer and also carry with them the possibility of someday curing and preventing cancer in children. While cancer was at one time nearly always fatal in children, as of 2004 more than 75 percent of children diagnosed with cancer enjoyed disease-free survival. Targeted molecular therapy and immunotherapies are the ongoing focus of concentrated research, and studies using these cell-selective technologies in treating children have shown encouraging results, both in earlier responses and reduced toxicity and complications longer term. Parents can be assured of access to the current knowledge base in molecular biology and advanced treatment technologies that promise better outcomes.

See also Leukemias, acute; Leukemias, chronic.

Resources

BOOKS

Janes-Hodder, Honna, et al. Childhood Cancer: A Parent's Guide to Solid Tumor Cancers, 2nd ed. Cambridge, MA: O'Reilly Media Inc., 2002.

Woznick, Leigh A., and Carol D. Goodheart. Living with Childhood Cancer: A Practical Guide to Help Families Cope. Washington, DC: American Psychological Association (APA), 2002.

ORGANIZATIONS

American Cancer Society. 1599 Clifton Road, NE, Atlanta, GA 30329. Web site: <www.cancer.org>.

Cancer Research Institute (National Headquarters). 681 Fifth Avenue, New York, NY 10022. Web site: <www.cancerresearch.org>.

National Cancer Institute. 9000 Rockville Pike, Building 31, room 10A16, Bethesda, MD 20892. Web site: <wwwicic.nci.nih.gov>.

National Children's Cancer Society. 1015 Locust Suite 600, St. Louis, MO 63101. Web site: <www.nationalchildrenscancersociety.com>.

WEB SITES

"Childhood Cancer." Kid's Health, 2004. Available online at <www.kidshealth.org/parent/medical/cancer/cancer.html> (accessed December 8, 2004).

L. Lee Culvert Rosalyn Carson-DeWitt, MD Teresa G. Odle

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Cancer

Cancer

To many people, the word cancer is synonymous with death; however, that is not the reality. In industrialized countries cancer mortality rates have slowly and progressively declined between 1950 and 2000. In 2000 overall cure rates reached approximately 50 percent. Nevertheless, cancer remains the second leading cause of death in industrialized countries and a rapidly increasing cause of death in developing countries.

The scope of the problem in the United States is large. Some 1.2 million people were diagnosed with potentially fatal cancer in the year 2000. Of these, 59 percent were expected to live for at least five years (in some, the cancer may be continuously present for more than five years) with or without evidence of cancer. People of all ages, from birth to advanced age, can manifest cancer, making it the second-leading cause of death in the United States. In children cancer is unusual, but it has consistently been the leading cause of death from disease. As mortality rates from cardiovascular disease decline, the proportion of cancer deaths increases. It is anticipated that the mortality rate from cancer will surpass that from heart disease by the year 2050. Direct and indirect financial costs of cancer in the United States for the year 2000 were $178 billion.

Developing countries represented 80 percent of the world's approximately 6 billion people in the year 2000. In these countries, cancer has grown from a minor public health issue in the early 1990s to a rapidly expanding problem by the beginning of the twenty-first century. The emergence of a middle class, with attendant changes in lifestyle, increased longevity and exposure to potential carcinogens, and expectations of improved medical delivery systems have fueled the growing impact of cancer in the third world. The financial resources and socio-medical infrastructure needed to diagnose and treat, much less screen and prevent these cancers, are lacking in the developing world.

A controversial issue in the United States is whether there has been progress in the "War on Cancer" declared by Congress in 1971. Since then a large flow of tax dollars has been directed to basic and clinical research with the goal of eliminating cancer. Mortality rates from all forms of cancer have declined slightly from 1990 through 2000, but with large variations among different types of cancer. Optimistic explanations include significant improvements in treatment and prevention. More pessimistic analyses suggest that some of the more common cancers can be diagnosed earlier so that benchmark five-year mortality rates have diminished, but that the actual course of the disease is unaffected because treatments are not really more effective.

Biology

Cancer is a disease whereby the genes regulating individual cell behavior and interactions with other cells malfunction. It is therefore a "genetic" disease, although not necessarily "inherited." Cancers clearly traced to inherited susceptibility are unusual, accounting for fewer than 10 percent of cases. Rather, the majority of cancers seem to result from complicated interactions between the environment and "normal" cells.

The routine operations of cell growth, division, cell-to-cell communication, and programmed cell death (apoptosis) are complex and must be tightly controlled to preserve the integrity of the organism. Chromosomes, which contain DNA molecules organized into genes, control these regulatory processes. Similar mechanisms are present in all animals and plants, are highly conserved through evolution, and so must provide significant survival benefit. The phenomenon of cancer is infrequent in wild animals and has only come to prominence in human beings since 1900. These statistics suggest that interactions of environmental agents with the genes result in fixed alterations that eventually manifest themselves as cancer. Public health measures have increased longevity so that the progressive, possibly inherent deterioration of regulatory functions accompanying aging allows less effective repair of chronic genetic damage.

Although no single cause has been or is likely to explain all of cancer, research has demonstrated that environmental factors predominate in the development of most cancer. Proven causes of DNA damage leading to malignant change include viruses, radiation, and chemicals. Viruses such as Epstein-Barr, HIV, and papilloma can contribute to cancer development (carcinogenesis). Both therapeutic and normal environmental exposure to radiation increase the risk of cancer. Multiple chemicals have been linked to cancer, of which the best examples are the constituents of tobacco. How these and other unknown environmental factors, particularly dietary and airborne, interact with human genes to cause irreversible, malignant transformation is the subject of intensive research.

Malignant cells can multiply and divide in the tissue of origin and can travel through the circulatory system and create secondary deposits (metastases) in vital organs. These capabilities underlie the phenomena of invasive lumps (tumors) and the potential for the dissemination of cancer. Most cancer cells, whether at the primary or secondary site, divide at about the same rate as their cells of origin. Malignant cells, however, do not typically undergo normal programmed cell death (apoptosis) and consequently accumulate. Most often, the cause of death in cancer is a poorly understood wasting process (cachexia).

Prevention and Screening

Prevention of cancer, or the reduction of risk for a person who has never experienced the disease, is a desirable goal. For those cancers resulting from known environmental exposures, such an approach has been most successful. Avoidance of tobacco products is no doubt the best proven means of preventing cancer. In industrialized countries, regulatory agencies monitor chemical and radiation exposure. Dietary habits are felt to influence the risk of developing certain cancers, but there is very little evidence that dietary manipulations lead to significant risk reduction.

Screening is the attempt to diagnose an established cancer as early as possible, usually before the onset of symptoms, in order to optimize the outcome. A screening technique is designed to simply, safely, and cheaply identify those patients who may have a certain type of cancer. If screening-test result is positive, further testing is always necessary to rule the diagnosis in or out. There is considerable controversy in this field. It cannot be assumed that early detection is always in the patient's best interest, and the overall financial costs in screening a population must be weighed against the actual benefits. Screening may be counterproductive under the following conditions:

  1. Treatment is not more effective with early detection.
  2. The patient will die of an unrelated condition before the diagnosed cancer could be troublesome or fatal.
  3. The screening examination can be harmful.
  4. The screening examination is falsely "negative" and thus falsely reassuring.
  5. The treatment causes complications or death in a patient in whom the cancer itself would not have led to problems.

In spite of these limitations, there have been successes. Good evidence exists that not only early detection but also improved survival can be achieved in breast, cervical, and colorectal cancers. With minimal danger and cost, appropriate populations screened for these diseases benefit from reduced mortality. Prostate cancer, however, is more problematic. Measurement of prostate-specific antigen (PSA), a substance made by both normal prostate as well as malignant prostate cells, can identify a patient with prostate cancer before any other manifestations. But because of the relatively elderly population (often with unrelated potentially serious conditions) at risk, it has been difficult to prove that treatment confers a quantitative or qualitative benefit. Continued efforts will be made to create screening techniques that truly allow more effective treatment for cancers detected earlier.

Diagnosis and Treatment

Once a malignancy is suspected, tests (usually imaging techniques, such as X rays, ultrasounds, nuclear medicine scans, CAT scans, and MRIs) are performed for confirmation. Ultimately a biopsy, or removal of a piece of tissue for microscopic examination, is necessary for determination of the presence and type of cancer. Staging tests reveal whether the disease has spread beyond its site of origin. Because of the inability of current techniques to detect microscopic deposits of cancer, a cancer may frequently appear to be localized but nevertheless exist elsewhere in the body below the threshold of clinical detection.

The diagnostic and staging process should permit the optimal clarification of the goals of treatment. Curative treatment intends permanent elimination of cancer, whereas palliative treatment intends to relieve symptoms and possibly prolong life. In every cancer situation there are known probabilities of cure. For example, a specific patient with "localized" breast cancer may have a 5060 percent chance of cure based on predictive factors present at the time of diagnosis. Follow-up "negative" tests, however, do not yield the certainty that there is no cancer, whereas the documented presence of recurrent cancer has clear significance. Cancer, indeed, is the most curable of all chronic diseases, but only the uneventful passage of time allows a patient to become more confident of his or her status.

Surgery is the oldest and overall most effective cancer treatment, particularly when tumors appear to be localized and cure is the goal. It is a preferred modality for breast, prostate, skin, lung, colon, testicular, uterine, brain, stomach, pancreas, and thyroid tumors. The aims of cancer surgery include elimination of as much cancer as possible, preservation of organ function, and minimal risk and suffering for the patient. Occasionally surgery is intentionally palliative, particularly when other treatment modalities are added in an effort to improve symptoms.

Radiation therapy has been a mainstay of cancer treatment since the 1940s, when doctors first began to understand its potential benefits and short and long-term risks. Therapeutic ionizing radiation is generated by a linear accelerator and delivered externally to a well-defined area. It thus shares with surgery an advantage for localized tumors. The inherent differences in radiation sensitivity between malignant tissues and the surrounding normal tissues permits the exploitation of radiation for therapeutic benefit. When the cancerous tissue is less sensitive to radiation than the normal tissues, radiation can cause more harm than good. Radiation has been a useful primary treatment modality in tumors of the head and neck, lung, cervix, brain, pancreas, and prostate. For tumors that have metastasized to tissues such as bone and brain, radiation has been very useful for palliative purposes.

Systemic treatments, either by themselves or in concert with surgery and/or radiation, offer the most rational options for a disease, which so often has spread before diagnosis. The ideal treatment would be a substance that travels throughout the body, neutralizes every cancer cell, but causes no harm to any normal cell. Research has not yet yielded such a completely specific and non-toxic substance.

The 1950s saw the advent of anticancer drugs that came to be known as "chemotherapy." By the year 2001 approximately sixty chemotherapy drugs became commercially available. In general these drugs cause irreversible cell damage and death. They tend to be more destructive to rapidly dividing cells and so take their heaviest toll on relatively few malignancies as well as predictability on normal tissues (mucous membranes, hair follicles, and bone marrow). For some very sensitive disseminated cancers such as testicular, lymphomas, and leukemias, chemotherapy can be curative. For many others, such as advanced breast, ovarian, lung, colon cancers, chemotherapy may offer palliative benefits. Since the 1980s chemotherapy has played an important role in the multimodality treatment of localized breast, colon, lung, and bladder tumors. Except for curable and highly chemosensitive malignancies, chemotherapy kills at most 99.99999 percent of cells, but with a burden of trillions of cancer cells, millions of resistant cells remain. Even using high-dose chemotherapy, it appears that by the year 2001 chemotherapy may have reached a plateau of effectiveness.

Insights into the basic genetic, molecular, and regulatory abnormalities of malignant cells have opened up entirely new systemic approaches. "Natural" substances such as interferons and inter-leukins have therapeutically modulated cell proliferation and led to regression of some tumors. Antiangiogenesis agents interfere with the malignant cell's need for accessing new blood vessels. Chemicals designed to inhibit the inappropriate production of growth factors by malignant cells have been synthesized and show promise. Monoclonal antibodies aimed at proteins concentrated on the malignant cell's surface have achieved tumor shrinkage. By the year 2000 the thrust in basic cancer research had focused on manipulation of the fundamental processes that allow malignancies to grow and spread.

The Internet has allowed patients, families, and medical providers rapid access to information previously obtainable only through libraries or physicians. Such information, however, may be unfiltered, unsubstantiated, and misleading. Even when the information is correct, consumers may be unable to process it properly because of fears concerning their condition. All observers agree, however, that this form of communication will rapidly affect cancer research and treatment.

"Complementary" or "alternative" modalities have existed for many years and represent nonscientific means of attempting to cure or palliate cancer. The multitude of available products and techniques is enormous: herbal extracts, vitamins, magnetic therapies, acupuncture, synthetic chemicals, modified diets, and enemas. The vast majority of these have never been evaluated in a rigorously controlled scientific way that would allow more definitive and precise evaluation of their benefits and risks. Nevertheless, evidence has shown that as many as 50 percent of all cancer patients, irrespective of treatability by conventional methods, try at least one form of complementary medicine. Some proponents feel that these treatments should serve as adjuncts to conventional ones, while others feel that all conventional treatments are toxic and should be replaced by alternative ones. To investigate the potential of these approaches, the National Institutes of Health established the Institute of Alternative Medicine in 1996.

End-of-Life Care

Because approximately 50 percent of cancer patients will die from their cancer, management of their dying takes on great importance. In the 1980s and 1990s multiple studies demonstrated that such basic concerns as pain and symptom control, respect for the right of the individual to forego life-prolonging measures, and spiritual distress have been mismanaged or ignored by many health care providers. In spite of the emergence of the modern hospice movement and improvements in techniques of symptom alleviation, most cancer patients die in hospitals or in nursing homes while receiving inadequate palliative care. The American Society of Clinical Oncology (ASCO) in 1998 mandated that part of fellowship training for oncologists include the basics of palliative care in order to rectify these problems.

See also: Causes of Death; Pain and Pain Management; Symptoms and Symptom Management

Bibliography

Ambinder, Edward P. "Oncology Informatics 2000." Cancer Investigation 19, supp. 1 (2001):3033.

Burns, Edith A., and Elaine A. Leventhal. "Aging, Immunity, and Cancer," Cancer Control 7, no. 6 (2000):513521.

Chu, Edward, and Vincent T. DeVita Jr. "Principles of Cancer Management: Chemotherapy." In Vincent DeVita, Jr., Samuel Hellman, and Steven A. Rosenberg eds., Cancer: Principles and Practice of Oncology, 6th edition. Philadelphia: Lippincott, Williams & Wilkins, 2001.

DeVita Jr., Vincent T. and Ghassan K. Abou-Alfa. "Therapeutic Implications of the New Biology." The Cancer Journal 6, supp. 2 (2000):S113S121.

Groopman, Jerome. "The Thirty-Years War." The New Yorker, 4 June 2001, 5263.

Hong, Waun Ki, Margaret R. Spitz, and Scott M. Lippman. "Cancer Chemoprevention in the 21st Century: Genetics, Risk Modeling, and Molecular Targets." Journal of Clinical Oncology 18, Nov. 1 supp. (2000):9s18s.

Ishibe, Naoko, and Andrew Freedman. "Understanding the Interaction between Environmental Exposures and Molecular Events in Colorectal Carcinogenesis." Cancer Investigation 19, no. 5 (2000):524539.

Lichter, Allen S. and Theodore S. Lawrence. "Recent Advances in Radiation Oncology." New England Journal of Medicine 332, no 6 (1995):371379.

Plesnicar, Stojan, and Andrej Plesnicar. "Cancer: A Reality in the Emerging World." Seminars in Oncology 28, no. 2 (2000):210216.

Rosenberg, Steven A. "Principles of Cancer Management: Surgical Oncology." In Vincent DeVita, Jr., Samuel Hellman, and Steven A. Rosenberg eds., Cancer: Principles and Practice of Oncology, 6th edition. Philadelphia: Lippincott, Williams & Wilkins, 2001.

Task Force on Cancer Care at the End of Life. "Cancer Care during the Last Phase of Life." Journal of Clinical Oncology 16, no. 5 (1998):19861996.

Walter, Louise C., and Kenneth E. Covinsky. "Cancer Screening in Elderly Patients." Journal of the American Medical Association 285, no. 21 (2001):27502778.

Wein, Simon. "Cancer, Unproven Therapies, and Magic," Oncology 14, no. 9 (2000):13451359.

Internet Resources

American Cancer Society. "Statistics." Available from www.cancer.org.

JAMES BRANDMAN

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Cancer

CANCER

Cancer is the end product of a multistep process (carcinogenesis) that occurs over many years. The term "cancer" actually refers to numerous distinct diseases characterized by abnormal cell growth and differentiation. Cancers are categorized by the organ and/or cell of origin. For example, squamous cell carcinoma of the lung arises from pulmonary epithelial tissue, whereas adenocarcinoma of the breast arises from mammary duct epithelium. The natural history of a cancer is highly dependent on the organ and cell type from which it is derived. In addition, prognosis is influenced by the stage and histologic grade of the cancer. Staging is generally designated by the TNM (tumor, nodes, metastasis) staging system, which takes into account the size of the primary tumor(T), the extent to which local lymph nodes (glands) are involved (N), and whether or not distant metastases are present (M). The histologic grade, determined by microscopic examination of the biopsy specimen, provides an objective assessment of the degree of cellular differentiation.

INCIDENCE, PREVALENCE, AND MORTALITY

The worldwide burden of cancer is a major health problem, with more than 8 million new cases and 5 million deaths per year. The burden from cancer may be described in terms of incidence (number of new cases per 100,000 each year), prevalence (number of people at a given point in time with a cancer diagnosis), and mortality (number of cancer deaths). With few exceptions, cancer incidence, prevalence, and mortality rates are higher in industrialized countries (e.g., United States, European nations) than in developing countries (e.g., African nations, China). Incidence rates for specific cancers can be dramatically affected by the use of screening procedures to identify asymptomatic disease. This is illustrated by the dramatic increase in the incidence of prostate cancer that accompanied the introduction of prostate-specific antigen (PSA) screening in the late 1980s. Similarly, prevalence rates may be a poor index for comparing cancers, because they are dependent upon incidence, natural history, and treatment efficacy. For example, due to the relatively short life expectancy of individuals with pulmonary neoplasms, the prevalence of lung cancer is much lower than that of prostate cancer, despite the higher mortality rates associated with lung cancer. In addition to the impact of screening and natural history, prevalence rates increase as treatment improves, because therapeutic advances enable individuals to live longer following a cancer diagnosis.

Worldwide, lung cancer is the leading cause of cancer mortality, followed by stomach cancer. Smoking remains the leading preventable cause of cancer, and mortality and incidence rates of lung cancer rise and fall with smoking rates. The current trend shows a leveling off of smoking-related cancers in developed countries, possibly because of health-promotion and disease-prevention efforts. Geographical variations occur in cancer incidence and mortality, with Africa and Asia generally having lower rates than North America and Europe. However, it has been noted that differences in data collection and diagnostic practices make worldwide cancer comparisons somewhat difficult. Overall, worldwide incidence rates of breast, colon and rectum, and prostate cancers are highest in developed countries, while cancers of the cervix, mouth and pharynx, esophagus, and liver are higher in developing countries. Migration studies generally report that migrants from developing countries to developed countries adopt cancer incidence rates equivalent to those of their new country. For example, studies of Japanese and Chinese immigrants living in the United States show that their risks for prostate and breast cancers increase dramatically the longer they reside in the United States. Similar trends for increased risk are seen among African immigrants in European countries. Geographical variations in cancer incidence and mortality also exist in the United States. Each cancer site shows some variation, such as higher prostate cancer mortality rates in the South Central and southern Atlantic states, and higher breast cancer mortality rates in the northeastern states. The Atlas of United States Mortality, published by the Centers for Disease Control and Prevention, provides detailed geographic information on cancer mortality rates in the United States, and is available online at http://www.cdc.gov/nchs/data/atlasmet.pdf.

In the United States, cancer is the second leading cause of death; although there has been a slight decline in the number of people dying from cancer since 1990, with more than one-half of those who develop cancer being cured or surviving for over five years. Because cancer is many diseases, some cancers are more common and/or more curable than others. For example, although nonmelanoma skin cancer, mainly caused by overexposure to ultraviolet (UV) radiation from the sun, is responsible for the largest number of new cancer cases each year, mortality rates associated with it are low.

Incidence, prevalence, and mortality in the United States vary by cancer site, between whites and blacks, and between men and women. By order of incidence, the three most common cancers in men are prostate, lung, and colorectal; in women the three most common cancers are breast, lung, and colorectal. These cancer sites represent more than one-half of both new cases of cancer and deaths from cancer each year. Lung cancer is the leading cause of death from cancer for men and women, accounting for almost one-third of cancer deaths.

Although cancer risk increases with age, malignant diseases are an important cause of morbidity and mortality in the pediatric population. The most frequent cancers in children are leukemias, tumors of the nervous systems, lymphomas, soft-tissue sarcomas, and kidney tumors. Other than lung cancer, which increases dramatically after age forty, three out of every four deaths from cancer occur in individuals older than sixty years of age.

CAUSES OF CANCER

Environmental and lifestyle factors such as tobacco use, diet, alcohol consumption, and exposure to sunlight play a primary role in the development of the majority of cancers. In addition, exposure to occupational factors and to specific pathogens (e.g., viruses, bacteria), hormones, and radiation also contributes to cancer at particular sites. However, the question still remains as to why one person exposed to a given environmental or lifestyle risk factor develops cancer and another person does not. The importance of hereditary factors (gene-environment interactions) cannot be overemphasized in this regard. True "hereditary cancers," those attributable to specific genes that are passed from one generation to another, account for only a small proportion of cancer cases, however.

Exposure to carcinogens in tobacco smoke accounts for almost one-third of cancer cases, especially cancers of the lung, respiratory tract, esophagus, bladder, pancreas, and, most likely, cancers of the stomach, liver, and kidneys. Carcinogens found in the environment and the workplace (e.g., asbestos, benzene, vinyl chloride compounds, dyes, arsenic, petroleum products) and cancers associated with exposure to these chemicals (e.g., lung and bladder) are higher in urban areas than in rural areas. Diet also influences the risk of cancer, although researchers are unsure of the mechanisms involved. In general, evidence supports an increased risk of various cancers (e.g., colon, rectum) with a high intake of red meats, and a decreased risk of various cancers (e.g., lung, colon, stomach) with a high intake of vegetables and fruits. Other food constituents, such as vitamins and minerals, are also being investigated for their ability to prevent cancer.

Other possible causes of cancer include pathogens, such as hepatitis B and C viruses in liver cancer, and the Helicobacter pylori bacterium in stomach cancer. Hormonal factors contributing to cancer have focused on estrogen, progesterone, and testosterone, and their role in reproductive organ cancers. These steroid hormones are being investigated because they influence the growth of cells, particularly those of the prostate, ovary and cervix, and breast. Radiation exposure, especially UV radiation from the sun, is a significant contributor to cancer of the skin, and using sunscreens has been shown to reduce skin cancer risk.

Interactions between genes and environmental exposures are of great importance in determining one's risk of developing cancer. For instance, genes and nutrients can interact to increase or decrease the risk of cancer depending on genetic variations known as polymorphismsdifferent forms of the same gene that may either increase or decrease the risk of cancer. For example, different polymorphisms in the gene that determines how vitamin D is metabolized can influence the risk of prostate cancer; one polymorphism is associated with increased risk of prostate cancer and another is associated with decreased risk. Polymorphisms in the genes that are responsible for repairing radiation damage to skin cells also play a role in increasing or decreasing cancer risk.

CANCER PREVENTION AND TREATMENT

Many cancer risk factors are avoidable. Preventing cancer by attention to diet and by quitting or never starting smoking are the most significant strategies to reduce cancer risk. Prevention of cancer is being investigated in clinical trials on dietary patterns (high intake of vegetables and fruits; low intake of saturated fats) and dietary constituents such as vitamins, minerals, and soy. Future progress may depend partly on strategies such as chemopreventionthe use of natural or synthetic substances to prevent cancer cells from forming, progressing, or recurring. For example, the antiestrogen hormone tamoxifen has been shown to reduce the risk of developing breast cancer by 50 percent among women at high risk for this disease. It also has been shown to reduce the risk of developing a new primary breast cancer in the opposite breast among women with a history of breast cancer. Chemopreventive agents also are being investigated for prevention of colon, rectum, prostate, and lung cancers.

SCREENING AND EARLY DETECTION

Mammography has been shown to reduce breast cancer mortality among women over the age of fifty, and Pap smear screening has dramatically reduced mortality from cervical cancer. In addition, there is growing evidence that fecal occult blood testing and endoscopic screening significantly reduce mortality from colorectal cancer. Identification of mutations is becoming an important tool for identifying individuals at high risk of various cancers. For instance, DNA repair-gene mutations (e.g., MSH2, PMS1) have been associated with a higher risk of colon cancer, as have mutations in the tumor suppressor genes BRCA1 and BRCA2 in breast cancer. Although it is believed that inherited risk for cancer accounts for a small proportion of total cancer cases each year, identifying this risk may help researchers determine how cancer develops and progresses, and may provide a tool for targeting prevention or treatment strategies.

Prognosis is dependent on the type of cancer diagnosed, the stage of the disease at the time of diagnosis, and the effectiveness of currently available therapy. Surgery, radiation, chemotherapy, hormonal therapy, and immunologic therapy form the basis of modern cancer treatment. Surgery is generally the treatment of choice for localized tumors, although radiation often is an appropriate alternative. Lasers are being used for small noninvasive tumors of the skin, cervix, and throat. Radiation therapy is often recommended as primary therapy (e.g., for Hodgkin's disease and early stage tumors of the head and neck), and is an important adjunct to lumpectomy for the treatment of breast cancer. Radiation therapy also plays an important role in the symptomatic management of patients with advanced cancer (e.g., bone or brain metastases). In contrast to surgery and radiation, chemotherapy is a systemic, rather than local, therapy, because the drugs are distributed throughout the body. Chemotherapy generally is required to treat advanced cancers that are not amenable to surgical removal or radiation therapy. Chemotherapy is often used after surgery (adjuvant therapy) to reduce the risk of relapse. The most common indication for adjuvant chemotherapy is following surgery for localized breast or colorectal cancer.

Hormone therapy represents a very important category of cancer treatment for breast cancer (tamoxifen and raloxifene) and prostate (androgen blockers) cancer. In addition, immunotherapy (also called biologic therapy) is being used to boost the immune system to fight cancer cells. Monoclonal antibodies are one type of immunotherapy that can be used to fight specific cancer cells or to carry chemotherapeutic agents to a tumor. Interferon is another immunotherapy that has shown promise in slowing the growth of tumors. Each of these treatments has advantages and disadvantages, and should be discussed with a physician.

CANCER IN DEVELOPING COUNTRIES

Cancer trends are of great concern to the public health community. As developing countries become more industrialized, incidence and mortality rates for cancers of the breast, colon, rectum, and prostate begin to rise. Also, smoking is increasing worldwidealong with lung cancer incidence and mortality rates. Liver cancer shows the same trends as lung cancer, but for a different reason. Infection with the hepatitis B or C viruses is a major risk factor for liver cancer. In some countries, where a vaccine for hepatitis B is widely used to vaccinate infants, liver cancer incidence in later life has declined; however, incidence rates in developing countries, where vaccination is not widely available, appear to be increasing. Another virus, the human papillomavirus (HPV), is an important risk factor for cervical cancer. Cervical cancer and HPV are more common in equatorial countries (e.g., in Latin America, sub-Saharan Africa, and Southeast Asia) and less common in countries in northern latitudes. Screening and treatment for early stages of cervical cancer have made significant inroads for reducing the incidence and mortality of this disease.

Howard L. Parnes

Darrell Anderson

(see also: Breast Cancer; Carcinogen; Cervical Cancer; Colorectal Cancer; Environmental Determinants of Health; Environmental Tobacco Smoke; Genetics and Health; Geography of Disease; Geriatrics; Incidence and Prevalence; Lung Cancer; Melanoma; Mortality Rates; Nutrition; Occupational Safety and Health; Oral Cancer; Ovarian Cancer; Prevention; Preventive Health Behavior; Prostate Cancer; Screening; Skin Cancer )

Bibliography

Doll, R., and Peto, R. (1981). "The Causes of Cancer: Quantitative Estimates of Avoidable Risks of Cancer in the United States Today." Journal of the National Cancer Institute 66:11911308.

Fleming, I. D.; Cooper, J. S.; Henson, D. E.; Hutter, >R. V. P.; Kennedy, B. J.; Murphy, G. P.; Sullivan, B. O.; Sobin, L. H.; and Yarbro, J. W. (1997). AJCC Cancer Staging Manual, 5th edition. New York: Lippincott Williams & Wilkins.

Greenlee, R. T. (2000). "Cancer Statistics, 2000." CA: A Cancer Journal for Clinicians 50:733.

Greenwald, P.; Kramer, B. S.; and Weed, D., eds. (1995). Cancer Prevention and Control. New York: Marcel Dekker.

Lichtenstein, P.; Holm, N. V.; Verkasalo, P. K.; Iliadou, A.; Kaprio, J.; Koskenvuo, M.; Pukkala, E.; Skytthe, A.; and Hemminki, K. (2000). "Environmental and Heritable Factors in the Causation of Cancer Analyses of Cohorts of Twins from Sweden, Denmark, and Finland." New England Journal of Medicine 343(2):7885.

Parkin, D. M.; Pisani, P.; and Ferlay, J. (1999). "Global Cancer Statistics." CA Cancer J Clin 49(1):3364.

(1999). "Estimates of the Worldwide Incidence of 25 Major Cancers in 1990." International Journal of Cancer 80(6):827841.

Pickle, L. W.; Mugiole, M.; Jones, G. K.; and White, A. A. (1996). Atlas of United States Mortality. Hyattsville, MD: U.S. Department of Health and Human Services (DHHS Publication No. [PHS] 971015).

Pisani, P.; Parkin, D. M.; Bray, F.; and Ferlay, J. (1999). "Estimates of the Worldwide Mortality from 25 Cancers in 1990." International Journal of Cancer 83(1):1829.

Schottenfeld, D., and Fraumeni, J. F., Jr., eds. (1996). >Cancer Epidemiology and Prevention, 2nd edition. New York: Oxford University Press.

"What You Need to Know About Cancer." Scientific American 275(Spec. Issue, September 1996).

World Cancer Research Fund (1997). Food, Nutrition and the Prevention of Cancer: A Global Perspective. Washington, DC: American Institute for Cancer Research.

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Cancer

Cancer

Cancer is a disease characterized by the uncontrolled growth and spread of abnormal cells. Around the world, over 10 million cancer cases occur annually. Half of all men and one-third of all women in the United States will develop some form of cancer during their lifetime. It is one of the most feared diseases, primarily because half of those diagnosed with cancer in the United States will die from it. Cancer is a leading cause of death around the world, causing over 6 million deaths a year. The exact causes of most types of cancer are still not known, and there is not yet a cure for cancer. However, it is now known that the risk of developing many types of cancer can be reduced by adopting certain lifestyle changes, such as quitting smoking and eating a better diet .

Prevalence

Cancer is, in general, more common in industrialized nations, but there has been a growth in cancer rates in developing countries, particularly as these nations adopt the diet and lifestyle habits of industrialized countries. Over one million people in the United States get cancer each year. Anyone can get cancer at any age; however, about 80 percent of all cancers occur in people over the age of fifty-five.

Cancer can affect any site in the body. About one hundred human cancers are recognized. The four most common cancers in the United States are: lung, colon/rectum, breast, and prostate . Together, these cancers account for over 50 percent of total cancer cases in the United States each year.

There is a marked variation among countries in incidence of different cancers. Most of the variation in cancer risk among populations, and among individuals, is due to environmental factors, such as cigarette smoking and certain dietary patterns, that can affect one's risk of developing cancer. For example, individuals living in Australia have the highest worldwide lifetime risk of skin cancer, at over 20 percent, due to the high level of exposure to the sun of people in Australia. People in India have twenty-five times the average risk of developing oral cancer sometime during their lives due to the popularity of chewing tobacco in that country. In fact, India has the world's highest incidence of oral cancer, with 75,000 to 80,000 new cases a year. The population of Japan has the highest rates of stomach cancer in the world due to the high consumption of raw fish by the Japanese.

Types of Cancer

Cancers are classified according to the types of cells in which they develop. Most human cancers are carcinomas, which arise from the epithelial cells that form the superficial layer of the skin and some internal organs. Leukemias affect the blood and blood-forming organs such as bone marrow , the lymphatic system , and the spleen. Lymphomas affect the immune system . Sarcoma is a general term for any cancer arising from muscle cells or connective tissues.

Growth and Spread of Cancer

Cancer develops when cells in a particular part of the body begin to grow out of control. Normal body cells grow, divide, and die in an orderly way. Cancer cells, however, continue to grow and divide without dying. Instead, they outlive normal cells and continue to form new abnormal cancer cells. As most cancer cells continue to grow, they lump together and form an extra mass of tissue. This mass is called a malignant tumor.

As a malignant tumor grows, it damages nearby tissue. Some cancers, like leukemia, do not form tumors. Instead, these cancer cells involve the blood and blood-forming organs and circulate through other tissues, where they grow.

Cancer can begin in one part of the body and spread to others. The spread of a tumor to a new site is called metastasis. This process occurs as cancer cells break away from a tumor and travel through the bloodstream or the lymph system to other areas of the body. Once in a new location, cancer cells continue to grow out of control and form a new malignant tumor.

Causes of Cancer

The exact cause of cancer is not known. Most cancers result from permanent damage to genes or from mutations, which occur either due to internal factors, such as hormones , immune conditions, metabolism , and the digestion of nutrients within cells, or by exposure to environmental or external factors. A chemical or other environmental agent that produces cancer is called a carcinogen.

Overall, environmental factors, defined broadly to include tobacco use, diet, infectious diseases , chemicals, and radiation, are believed to cause between 75 and 80 percent of all cancer cases in the United States. Tobacco use, including cigarettes, cigars, chewing tobacco, and snuff, can cause cancers of the lung, mouth, throat, larynx, bladder, kidney, esophagus, and pancreas. Smoking alone causes one-third of all cancer deaths in the United States. Heavy consumption of alcohol has also been shown to increase the risk of developing cancer of the mouth, pharynx, larynx, esophagus, liver, and breast.

Overweight and obesity are associated with increased risk of cancers of the breast, colon, endometrium, esophagus, kidney, and gallbladder. The following chemicals have been found to cause cancer: coal tars and their derivatives, such as benzene; some hydrocarbons; aniline, a substance used to make dyes; and asbestos. Radiation from a variety of sources, including the ultraviolet light from the sun, is known to lead to skin cancer.

Several infectious agents have also been implicated in cancer. Evidence suggests that chronic viral infections are associated with up to one-fifth of all cancers. These include hepatitis B virus (HBV), which can lead to cancer of the liver; the Epstein-Barr virus, a type of herpes virus that causes infectious mononucleosis and has been associated with Hodgkin's disease, non-Hodgkin's lymphomas, and nasopharyngeal cancer; the human immunodeficiency virus (HIV), which is associated with an increased risk of developing several cancers, especially Kaposi's sarcoma and non-Hodgkin's lymphoma; and human papilloma viruses (HPV), which have been proven to cause cervical cancer and have also been associated with cancers of the vagina, vulva, penis, and colon. The bacterium Helicobacter pylori has been linked to stomach cancer.

About 5 to 10 percent of cancers are hereditary, in that a faulty gene or damaged DNA that has been inherited predisposes a person to be at a very high risk of developing a particular cancer. Two genes, BRCA1 and BRCA2, have been found to cause some breast cancers. Other genes have been discovered that are associated with some cancers that run in families, such as cancers of the colon, rectum, kidney, ovary, esophagus, lymph nodes , skin melanoma, and pancreas.

Carcinogenesis Process

All cancers involve the malfunction of genes that control cell growth and division. The process by which cancers develop is called carcinogenesis. This process usually starts when chemicals or radiation damage DNA, the genetic structure inside cells. Viruses induce carcinogenesis by introducing new DNA sequences. Most of the time, when DNA becomes damaged the body is able to repair it. In cancer cells, however, the damaged DNA is not repaired. While normal cells with damaged DNA die, cancer cells with damaged DNA continue to multiply.

There is a long time lag between exposure to a carcinogen and the occurrence of cancer. While cellular mutations cause cancer to develop, it is not exactly clear how this happens. Carcinogenesis is a multistep process, in which as many as ten distinct mutations may have to accumulate in a cell before it becomes cancerous. The fact that so many mutations are needed for a cancer to develop indicates that cell growth is normally controlled through many sets of checks and balances.

When cells in some area of the body divide without control, these cells accumulate and form lumps. A tumor, or neoplasm, is an abnormal lump or mass of tissue that may compress, invade, and destroy normal tissue. Tumors may be benign or malignant. Cancer is a malignant neoplasm, though not all tumors are malignant. A noncancerous growth is called a benign tumor. Benign tumors do not metastasize and, with very rare exceptions, are not life threatening.

The cell cycle is regulated by a large number of cellular genes that are expressed, or exhibited, at different stages of the cycle. The genes code for, or determine, growth factors , growth-factor receptors, and proteins that control gene functions and cell survival. Damaged DNA can lead to cancer because the cell cycle is distorted by the alteration and activation of oncogenes, genes that stimulate cell growth, or by the inactivation of tumor suppressor genes, which ordinarily suppress cell growth. Activated oncogenes drive abnormal, unregulated cell proliferation and lead to tumor formation. Mutations of the tumor suppressor gene p53 are found in about 50 percent of human cancers.

In experimental animals, three stages of chemical carcinogenesis have been identified. These are: (1) initiation, where DNA is irreversibly altered; (2) promotion, which is the multiplication of altered cells; and (3) progression, which involves chromosomal changes, high growth rate, invasiveness, and potential to metastasize.

Prevention

All cancers caused by cigarette smoking and heavy use of alcohol could be prevented completely. Approximately 30 percent of all cancers worldwide are due to tobacco use. Many of the skin cancers could be prevented by protection from sunlight. Certain cancers that are related to infectious exposures, such as HBV, HPV, HIV, and Helicobacter could be prevented through behavioral changes, vaccines , or antibiotics . Research shows that about 30 to 40 percent of all cancers worldwide are due to dietary factors and lack of physical activity, including obesity, and could therefore have been prevented. By making changes in regard to diet, exercise, healthy weight maintenance, and tobacco use, the incidence of cancer around the world could be reduced by 60 to 70 percent.

The Relationship between Diet, Physical Activity, and Cancer

While the exact mechanisms by which diet is related to cancer have not been completely understood, research has shown that food plays a role in cancer prevention. For example, populations whose diet includes at least five servings of fruits and vegetables a day have lower rates of some of the most common cancers. Fruits and vegetables contain many antioxidants and phytochemicals , such as vitamins A, C, and E, and beta-carotene, which have been shown to prevent cancer. It is not completely clear, however, whether it is individual phytochemicals, or a combination of them, or the fiber in fruits and vegetables that result in reduced risk of cancer.

Studies have shown the risk of prostate cancer drops for men who eat tomato products, possibly because of the phytochemical lycopene. In addition, it has been shown that colon cancer declines among those who drink green tea, which contains antioxidants and phytochemicals, and who regularly eat soy products and foods rich in selenium, an antioxidant.

Those who eat a diet low in fat , especially animal fat, also have lower cancer rates, but again it is not clear whether it is the calories , the amount and distribution of body fat, or the likelihood that a low-fat diet is high in fiber, fruits, and vegetables that is protective against cancer. High-fiber diets are thought to reduce the risk of colon cancer because the fiber helps move food through the lower digestive tract, possibly reducing the contact of any carcinogens with the bowel lining.

Scientific evidence indicates that physical activity may reduce the risk of certain cancers. This effect may be due to the fact that physical activity is associated with the maintenance of a healthy body weight. Other mechanisms by which physical activity may help to prevent certain cancers may involve both direct and indirect effects. For colon cancer, physical activity accelerates the movement of food through the intestine, thereby reducing the length of time that the bowel lining is exposed to potential carcinogens. For breast cancer, vigorous physical activity may decrease the exposure of breast tissue to circulating estrogen , a hormone that has been implicated in breast cancer. Physical activity may also affect cancers of the colon, breast, and other sites by improving energy metabolism and reducing circulating concentrations of insulin and related growth factors.

Because of these factors, recommendations of the American Cancer Society to reduce the risk of cancer include: consumption of a mostly plant-based diet, including five or more servings of fruits and vegetables each day; consumption of whole grains in preference to processed or refined grains and sugar; limited consumption of high-fat foods, particularly from animal sources; physical activity; and limited consumption of alcohol.

Nutrition for People with Cancer

People with cancer often have increased nutritional needs. As such, it is important for them to consume a variety of foods that provide the nutrients needed to maintain health while fighting cancer. These nutrients include: protein, carbohydrates , fat, water, vitamins, and minerals . Nutrition suggestions for people with cancer often emphasize eating high-calorie, high-protein foods. Protein helps to ensure growth, repair body tissue, and maintain a healthy immune system. Therefore, people with cancer often need more protein than usual.

Great progress has been made in the fight against cancer, and cancer detection and treatments have improved significantly. However, there is a disparity in cancer death rates between developed and developing countries. Between 80 and 90 percent of cancer patients in developing countries have late-stage and often incurable cancer at the time of diagnosis.

A growing body of evidence shows that simple changes in diet and lifestyle can help prevent many cancers. Further research into the exact mechanisms by which certain diets may help prevent cancer is ongoing.

see also Antioxidants; Functional Foods; Phytochemicals.

Gita C. Gidwani

Bibliography

American Institute for Cancer Research (1997). Food, Nutrition, and the Prevention of Cancer: A Global Perspective. Washington, DC: Author.

Cooper, Geoffrey M. (1992). Elements of Human Cancer. Boston: Jones and Bartlett.

Tortora, Gerald J., and Grabowski, Sandra Reynolds (2003). Principles of Anatomy and Physiology, 10th edition. New York: Wiley.

Internet Resources

American Cancer Society. "Cancer Facts and Figures, 2002." Available from <http://www.cancer.org/downloads>

National Cancer Institute (2000). "Cancer Facts: Questions and Answers About Cancer." Available from <http://www.nci.nih.gov>

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Cancer

Cancer


Cancer develops when cells in the body begin to grow out of control. Normal cells grow, divide, and die. But cancer cells, instead of dying, continue to

LIFETIME RISK OF CANCER FROM KNOWN CAUSES
risk factor risk
source: u.s. environmental protection agency
excessive sun exposure 1 in 3
cigarette smoking (one pack or more per day) 8 in 100
natural radon in indoor air at home 1 in 100
outside radiation 1 in 1,000
environmental tobacco smoke (in room with a smoker) 7 in 10,000
human-made chemicals in indoor air at home 2 in 10,000
outdoor air in industrialized areas 1 in 10,000
human-made chemicals in drinking water 1 in 100,000
human-made chemicals in most foods (including pesticides) 1 in 100,000 or less
chemical exposure at uncontrolled hazardous waste sites 1 in 10,000 to 1 in 1,000



grow and form new abnormal cells. Cancer cells often travel to other body parts where they grow and replace normal tissue. This process, called metastasis, occurs as the cancer cells are transported by the bloodstream or lymph vessels. Cancer cells develop because of damage to DNA. DNA carries the genetic information of every cell and directs all its activities. When DNA becomes damaged, the body is able to repair it. But in cancer cells, the damage is not repaired.

Some anomalies that increase the risk of cancer are present at birth in the genes of all cells in the body, including reproductive cells. These can be passed from parent to child. This is known as inherited susceptibility and is an uncommon cause of cancer. Most cancers result from genetic changes that occur over decades within the cells of a particular organ. These changes can usually be traced to an interaction of genetics and the environment, including behavior and lifestyle. Other factors that influence cancer risk are age, race, gender, preexisting disease, and nutritional impairment.


Environmental Factors

The term "environment" includes air, water, and soil, as well as substances and conditions in the home and workplace. It also includes:

  • Diet
  • Use of tobacco, alcohol, or drugs
  • Exposure to chemicals
  • Exposure to ultraviolet (UV) light from the sun and in tanning parlors and other forms of radiation

Only recently have scientists proved the existence of an interaction between environmental toxins and one's genetic makeup. Researchers hope that when people are knowledgeable about inherited susceptibility, they will be motivated to avoid carcinogens that increase their risk. For example, scientists at the State University of New York at Buffalo report evidence that a genetic variation (mutation) in a gene which helps detoxify carcinogens may put smokers with this mutation at increased risk for breast cancer.

Overexposure to UV radiation from the sun and cigarette smoking pose the greatest known risks of developing cancer. Other factors contribute much less significantly to cancer development. The approximate lifetime risk of developing cancer from known causes is listed in descending order of risk in the bar graph. Note that the risk from exposure to chemicals at hazardous waste sites can vary widely, depending on the chemical, and the length and type of exposure. For comparison, consider the fact that the lifetime risk of death from a fall is 1 in 270, according to the National Safety Council. The lifetime risk of any given American dying as an automobile passenger or a motorcycle rider are 1 in 244 and 1 in 1,536 respectively.


Categories of Carcinogenicity

Substances or agents that cause cancer are called carcinogens . The more likely something is to cause cancer, the more carcinogenic it is. Cigarette smoke is more carcinogenic than chlorinated community drinking water.

The U.S. Environmental Protection Agency (EPA) classifies carcinogenicity into five categories. A category A substance is known to cause cancer in humans, generally based on epidemiological (large population) data showing sufficient evidence to support a causal association between exposure to the substance and cancer. Category A carcinogens include asbestos, benzene, radon, and coal gasification. Category B includes "probable" human carcinogens known to cause cancer in animals but not yet definitively shown to cause cancer in humans. Category B carcinogens include chloroform, carbon tetrachloride, gasoline, and progestins. Category C includes "possible" human carcinogens for which the data show "limited evidence" of carcinogenicity in the absence of human data. Chemicals for which the data are incomplete, inadequate, or ambiguous are "not classifiable" and reside in category D. Those in category E are "probably not carcinogenic."

Determining carcinogenicity can be a harrowing and lengthy process. For example, the debate over possible risks posed by electromagnetic fields (EMF) has been raging for decades. Magnetic fields originate from everything with an electrical current. Elevated field levels can occur in homes close to power lines, or occasionally from improper household wiring. A form of EMF called "extremely low frequency (ELF) electric and magnetic fields" recently was classified as "possibly carcinogenic" by the International Agency for Research on Cancer (IARC).

Concerns about EMF from power lines began to mount in the 1970s, when epidemiological studies first showed a possible link to childhood cancer. But the research has produced inconsistent and conflicting findings, leading the World Health Organization (WHO) in 2002 to launch a more complete series of follow-up studies.

Military personnel in proximity to radio frequency (RF) emitted by radar equipment may have an increased risk of brain cancer, according to a small published Israeli study. But when it comes to RF, cellular phones have been receiving the bulk of attention from the media and in lawsuits claiming that cell phone use resulted in plaintiffs' brain tumors. While researchers have shown that the use of these handheld devices increases a driver's risk of experiencing a traffic accident, the brain tumor connection remains unproved.

When a person develops a malignancy, it can be very difficult to attribute a particular cause or source. Though smoking underlies the bulk of environment-induced lung disease, there are other contributors or possible contributors in human surroundings. Some evidence suggests that air pollutants produced by the burning of fossil fuels play a role in causing lung cancer among city dwellers. A high level of radon in the homesuch as exists in parts of the Midwest and northeastis a cancer risk factor, especially for smokers. Radon is a heavy, radioactive gaseous element formed by the natural decay or disintegration of radium in the earth's crust. Other environmental pollutants that may play roles in cancer include airborne arsenic and microscopic asbestos fibers inhaled into the lungs.

Radon is not alone in adding to the lethality of cigarette smoking. Asbestos exposure and smoking also multiply each other's lethality (a "synergistic" effect). On an individual basis, both smoking and asbestos exposure can cause lung cancer, but taken together, they multiply the risk of lung cancer significantly. Studies in the science of epidemiology confirm that the combination of smoking and asbestos exposure creates a risk of cancer much higher than just adding together their separate risks. Evidence suggests that asbestos-exposed workers who quit smoking can reduce their risk of developing lung cancer by as much as 50 percent within five years of quitting.


Cancer Clusters

The study of disease clusters is one method scientists use to study the public health implications of carcinogens. A cancer cluster is defined as a greater-than-expected number of cancer cases that occurs within a group of people in a geographic area over a specific period of time. Studies of suspected cancer clusters usually focus on heredity and environment. Such clusters may be suspected when people report that several family members, friends, neighbors, or coworkers have been diagnosed with the same or related cancer(s).

In the early 1980s a leukemia cluster was identified in the Massachusetts town of Woburn. In a case that was the subject of A Civil Action, later made into a major motion picture, three companies were accused of contaminating drinking water and causing illnesses. The case went to trial in Anne Anderson, et al. v. W.R. Grace & Co., et al. Six families alleged that chemicals dumped by the defendants caused leukemia in members of those families. Two closed municipal water wellswhich were the focus of the families' casewere found to be contaminated with EPA-listed hazardous substances, including trichloroethylene (TCE). Although the U.S. Department of Health and Human Services (HHS) lists TCE as "reasonably anticipated to be a human carcinogen," IARC has determined that trichloroethylene cannot currently be classified as such.

In any case, this action became a poster trial for the difficulty of linking certain events to a cluster of individual illnesses. The incredibly complex case involved thirty-three plaintiffs, two defendants, a mountain of conflicting geological and medical testimony, and multiple claims including negligence, nuisance, and emotional distress. A direct and incontrovertible connection between the pollution caused by W.R. Grace and the cancer cluster was never confirmed.

The prospect of a larger cancer cluster was investigated in New York State. The Breast Cancer and the Environment on Long Island Study was carried out in response to anecdotal reports that environmental toxins elevated breast cancer rates among women in the region. Chief among the suspects were polycyclic aromatic hydrocarbons (PAH), which are caused by incomplete combustion of various chemicals including diesel fuel and cigarette smoke, and organochlorine compounds, which are found in many pesticides. In August 2002 scientists reported that organochlorine compounds were not associated with the elevated rates of breast cancer on Long Island. However, the same investigators did suggest it was possible that risk in some individuals may be associated with organochlorine exposures because of individual differences in metabolism and the ability of one's body to repair DNA damage.

The researchers also found that PAHs were associated with a modest 50 percent increased risk for breast cancer in susceptible women exposed to high levels of the compounds. But for the population of women as a whole, no specific environmental factor could be tied to the incidence of breast cancer. Some have complained that the study failed to take into account the possible effects of leaks from a nearby nuclear reactor, and there have been public accusations that the study avoided the so-called "nuke connection" for political and financial reasons.

The thousands of individuals who were in and around the World Trade Center in lower Manhattan on and immediately after September 11, 2001, may constitute a cluster of future disease. Public safety personnel, rescue workers, and local residents were exposed to a lingering pall of dust and debris following the collapse of the twin towers and other buildings. Super-heated and aerosolized building materials created an incalculable number of toxic compounds. The full effects on the health of those exposed may not be known for decades.

In conclusion, the interplay between our environment and cancer is complex and not yet fully understood. It is increasingly clear that the unborn and very young children are particularly susceptible to environmental toxins such as endocrine-disrupting herbicides and insecticides. Adult cancer risk can be greatly reduced by avoiding tobacco products and limiting sun exposure. Known carcinogens often encountered in workplaces and homes include pesticides, asbestos, arsenic, uranium, and certain petroleum products.

see also Asbestos; Health, Human; PCBs (Polychlorinated Biphenyls); Radon; Risk.

Bibliography

Fackelmann, Kathleen. (1995). "Variations on a Theme: Interplay of Genes and Environment Elevates Cancer Risk." Science News 147(187):280.

"Extremely Low Frequency Electromagnetic FieldsW.H.O. Classifies The Cancer Risk (Update)." (2002). Journal of Environmental Health 65(5):47.

Munshi, A., and Jalali, R. (2002). "Cellular Phones and Their Hazards: The Current Evidence." National Medical Journal of India 15(5):275277.

Richter, E.D.; Berman, T.; and Levy, O. (2002). "Brain Cancer with Induction Periods of Less than 10 Years in Young Military Radar Workers." Archives of Environmental Health 57(4):270272.

Internet Resources

Asbestos Network Web site. Available from http://www.asbestosnetwork.com.

Harvard Medical School Web site. Available from http://www.intelihealth.com.

International Agency for Research on Cancer (IARC) Web site. Available from http://www.monographs.iarc.fr/.Int.

National Institutes of Health and National Cancer Institute Web site. Available from http://www.cis.nci.nih.gov.

U.S. Centers for Disease Control and Prevention Web site. Available from http://www.cdc.gov/nceh.

U.S. Environmental Protection Agency Web site. Available from http://www.epa.gov.

Bruce K. Dixon

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Cancer

Cancer

Cancer is a number of related diseases that are characterized by the uncontrolled proliferation and disorganized growth of cells. Tumor cells invade and destroy normal tissues and may spread throughout the body via the circulatory systems.

A Genetic Disease

Cancer is the result of changes in the genetic material of a cell that cause the cell to gradually lose the ability to grow in a regulated fashion. These changes can be brought about by contact with harmful environmental agents or by inheritance of genes leading to a genetic predisposition .

Cancer risk increases with age, as the probability of accumulating mutations in the DNA increases with time. Environmental factors include lifestyle (e.g., smoking), diet (e.g., saturated fats from red meat), and exposure to certain chemicals (e.g., asbestos, benzopyrenes), ionizing radiation (e.g., X-rays, radon gas), ultraviolet radiation (e.g., sun, tanning beds), and certain viruses (e.g., human papillomavirus, Epstein-Barr virus). Heredity also plays a role in oncogenesis , as mutations in certain genes increase the probability of developing certain types of cancer. For instance, women who inherit a mutated copy of the BRCA1 or BRCA2 gene have a greatly increased probability of developing breast cancer at a young age.

Classification of Cancer Types

The term "cancer" is general, in that it represents a large group of related diseases that arise from neoplasms . A neoplasm is classified by the type of tissue in which it arises and the stage to which it has progressed. Neoplasms are also called tumors. Not all tumors are cancerous. A tumor that grows in one place and does not invade surrounding tissue is called benign. In contrast, invasive tumors are called malignant. These are cancerous.

ESTIMATED NEW CANCER CASES AND DEATHS IN THE UNITED STATES 2000
Site of Origin New Cases* Deaths*
  Male Female Male Female
Breast 1,400 182,800 400 40,800
Colorectal 63,600 66,600 27,800 28,500
Esophagus 9,200 3,100 9,200 2,900
Kidney & Bladder 57,100 27,300 15,400 8,700
Leukemia 16,900 13,900 12,100 9,600
Liver 10,000 5,300 8,500 5,300
Lung 89,500 74,600 89,300 67,600
Lymphoid 35,900 26,400 14,400 13,100
Ovary - 23,100 - 14,000
Pancreas 13,700 14,600 13,700 14,500
Prostate 180,400 - 31,900 -
Skin 34,100 22,800 6,000 3,600
Stomach 13,400 8,100 7,600 5,400
Testis 6,900 - 300 -
Uterine - 48,900 - 11,100
*(the American Cancer Society's Clinical Oncology, Lenhard R.E., Osteen R.T., Gansler T., 2001)

Benign or Malignant Tumor

Whether a tumor is benign or malignant determines how potentially life-threatening it is. Benign tumors are usually harmless, although their location may be serious (if surgery to remove the tumor would carry significant risk). These tumors are not considered cancerous, are relatively slow-growing, and usually are encased within a fibrous capsule.

Malignant tumors (cancers) have great potential to spread, or metastasize, to other sites in the body. These tumors are fast-growing and aggressive, and they invade neighboring healthy tissue. They therefore are considered life threatening.

Type of Tissue

The body consists of many different organs, which in turn are composed of several different types of tissues. There are three major categories of tissue-related tumor types: carcinoma, sarcoma, and leukemia/lymphoma. There are also other specialized tumor categories, such as those of the central nervous system (e.g., brain tumors).

Carcinoma.

This is the largest category, containing about 90 percent of all cancers, and it consists of neoplasms derived from epithelial cells. Epithelial cells make up the outer layers of the skin. They also line the inner structures of organs such as the lungs, intestines and testes, as well as complex tissue such as the breast.

Sarcoma.

These are solid tumors derived from all connective tissues except the bloodforming tissues (these are the leukemias and lymphomas). These tumors account for about 2 percent of all cancers. They occur in such tissues as muscle, bone, and cartilage.

Leukemia and Lymphoma.

This group contains about 8 percent of all cancers, including blood cancers that originate from the marrow (leukemias) and from the lymphatic system (lymphomas). This group also includes other nonsolid tumors of the bone marrow and lymphatic system, such as myeloma, which affects plasma cellsa type of white blood cell found in the marrow and in other tissues.

Type of Cell

Classifying a tumor by the type of cell from which it is derived is slightly more complex than classifying it by the type of tissue, since there are so many cell types. The main cell types include adenomatous cells (which are ductal or glandular cells), basal cells (found at the base of the skin), myeloid blood cells (granulocytes, monocytes, and platelets), lymphoid cells (lymphocytes or macrophages), and squamous cells (flat cells). Therefore it is possible for a cancer classified by its site of origin to be broken up into one of several cell types. For example, a skin cancer could be either a squamous cell carcinoma, a basal cell carcinoma, or a melanoma (from a pigment-producing cell).

Site of Origin

Solid tumors are firm masses that develop from a neoplasm's originating organ, such as the brain, esophagus, kidney, liver, lung, ovary, pancreas, prostate, or testis. Tumors of the blood-forming tissues and lymphatic systems are not solid and tend to remain free and circulating even when malignant. Some of the common forms of cancer are listed in the table above.

Cancer Progression

There two main steps in cancer progression: the initial growth of the cancer and the subsequent spread via metastasis . Solid tumors are subject to the physiological constraints of biological systems: Without nutrients and oxygen, they will die. Therefore a solid tumor is initially limited in size to no larger than 1 to 2 millimeters in diameter (about the size of a small pea).

For a tumor to become aggressive, it needs to be able to nourish the cells at the center of its mass that are too far away from blood vessels. This is achieved by angiogenesis . Through mutation, a few cancer cells may gain the ability to produce angiogenic growth factors. These growth factors are proteins that are released by the tumor into nearby tissues, where they stimulate new blood vessels to grow into the tumor. This allows the tumor to rapidly expand in mass and invade surrounding tissue. It also provides a route for the cancer cells to escape into the new blood vessels and circulate throughout the body, where they can lodge in other organs forming metastases.

The most common way for a cancer to metastasize is through the lymphatic system. The lymphatic system is a network of channels throughout the body that carry a tissue fluid called lymph.

When a primary neoplasm metastasizes to another location, its cell type does not change. If leukemia metastasizes to the liver and develops a tumor, the tumor will display the characteristics of the leukemia, not those of a liver cancer. In some cases this can help physicians determine the original site of a tumor.

Genes Altered in Tumors

Although each cell in the body maintains itself and carries out its specific function, it is part of a large colony of collaborating cells that constitute the whole organism. A cell communicates with its surrounding cells by releasing chemical messages, in a process called signal transduction. These messages bind to specific receptor proteins on the surface of the surrounding cells. The gene expression of these cells is changed as a result of the messages.

A hyperplastic cell or a cancerous cell will stimulate neighboring cells to grow by secreting growth factors. Several types of genes can be mutated in tumor cells: oncogenes, tumor suppressor genes, DNA repair genes, and genes involved in cell mortality.

Oncogenes.

These genes are involved in signal transduction, and some are involved in the various phases of the cell cycle. Mutations in cell-cycle regulation or signal transduction can "push" the cell into dividing rapidly and without regard to its surroundings. Over 100 oncogenes have been identified so far. They include genes such as ABL1 (Abelson murine strain leukemia viral homolog) and EGFR (Epidermal Growth Factor Receptor).

Tumor Suppressor Genes.

These genes inhibit cell division, working in a manner opposite to that of the oncogenes. Surrounding cells secrete growth-inhibitory signals that help prevent proliferation. These growth-inhibitory signals work in conjunction with tumor suppressor genes. If a tumor suppressor gene is mutated, proliferating cells can ignore these inhibitory messages. This group includes the genes p53, BRCA1, and BRCA2.

DNA Repair Genes.

These are the genes that provide the cell with the ability to sense and correct damage to the DNA. Damage to the DNA can be caused by radiation, chemicals, ultraviolet light, or errors in transcription. If these errors are not corrected, they accumulate in the genome and can quickly increase the chance that a cell will become cancerous. Repair genes include those in the DNA-ligase and excision-repair gene families.

Genes Involved in Cell Mortality.

A normal cell can only undergo about forty divisions, after which it dies or enters senescence . If a tumor had this limitation it would be very limited in its size, as it would reach its forty divisions relatively quickly. This process is controlled by the enzyme telomerase, which maintains the telomeres (repetitive DNA sequences at the ends of chromosomes that shorten after each round of DNA replication, until they reach a length that causes the cell to die) by not allowing them to shorten. Some cancer cells become immortal as a result of mutations in the telomerase gene, causing the telomeres to be extended indefinitely, allowing the cell to continue dividing without limit. Other mutations affect the process of apoptosis .

Cancer does not usually arise by a single event. Instead, two or more "hits" are needed to convert a well-regulated cell to a cancer cell. This is the case because each cell contains two copies of each gene, one inherited from each parent. Most cancer-causing mutations cause a loss of function in the mutated gene. Often, having only one functional copy is enough to prevent disease. Thus, two mutations are needed.

This can be illustrated by looking at retinoblastoma, a common cancer of the retina. The affected gene (called the retinoblastoma gene) is a tumor suppressor. Spontaneous mutations are rare, but since there are many millions of cells in the retina, several will develop the appropriate gene mutation over the course of a lifetime. It would be very unlikely, though, for a single cell to develop two spontaneous mutations (at least in the absence of prolonged exposure to carcinogens), and thus spontaneous retinoblastoma is very rare.

If, however, a person inherits one copy of an already-mutated gene from one parent, every cell in the eye starts life with one "hit." The chances are very high that several cells will suffer another hit sometime during their life, and so the chances are very high that the person will develop retinoblastoma. Since inheriting a single copy of the mutated gene is so likely to lead to the disease, the gene is said to show a dominant inheritance pattern.

Future Directions in Diagnosis and Treatment

The increased knowledge of cancer at the biochemical and genetic level has led to many advances toward better diagnosis and treatment of cancer, including the design of more specific drugs that are less toxic to normal tissue. This includes the use of antisense molecules, which are nucleic acid sequences that are complementary to the mRNA of a target gene. As the two sequences are complementary, they anneal and thus the mRNA is blocked from being translated into a protein, resulting in less of that particular protein being produced (such as growth factor receptors). Drugs specific in blocking angiogenesis are able to control the growth and spread of tumors, especially when used in combination with other treatments.

see also Ames Test; Antisense Nucleotides; Apoptosis; Breast Cancer; Carcinogens; Cell Cycle; Colon Cancer; DNA Repair; Mutagen; Mutation; Oncogenes; Signal Transduction; Telomere; Tumor Suppressor Genes.

Giles Watts

Bibliography

Greider, C. W., and E. H. Blackburn. "Telomeres, Telomerase and Cancer." Scientific American 274 (1996): 80-85.

Kiberstis, Paula, and Jean Marx. "The Unstable Path to Cancer." Science 297, no. 5581 (2002): 543.

Lenherd, Raymond E., et al. Clinical Oncology. Atlanta, GA: American Cancer Society, 2001.

Rosenberg, S. A., and B. M. John. The Transformed Cell: Unlocking the Mysteries of Cancer. New York: Putnam, 1992.

Weinberg, R. A. Racing to the Beginning of the Road: The Search for the Origin of Cancer. New York: Putnam, 1998.

Weinberg, R. A. One Renegade Cell: How Cancer Begins. New York: Basic Books, 1999.

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Cancer

Cancer

Cancer is the uncontrolled growth of cells. This abnormal growth is the result of mutations in the genetic material of the cells, either spontaneous or brought on by environmental factors such as ultraviolet radiation or asbestos. This growth leads to a collection of mutated cells called a tumor. The tumor can be benign, meaning that it is comparatively harmless and restricted to one type of tissue. Alternately, it can be malignant, which means it can grow into surrounding tissue or migrate to different parts of the body. When a malignant tumor spreads to other tissues, this is known as metastasis.

Cell replication

Normally, animal cells grow with a variety of checkpoints. For example, when a person cuts her finger, skin cells will divide and grow to fill the opening, but they will stop growing once the cut is closed. The body has a number of mechanisms to prevent unchecked cell growth, and in order to become cancerous, abnormal cells must defeat several of them. Some of these mechanisms determine division rates; others manage DNA repair. Like any other controls in the body, these can go awry when a mistake arises in the DNA encoding them.

Excessive cell division.

Suppose, again, that a person gets cut. First, skin cells must decide when it is time to divide and when it is time to rest. Often cells will receive signals from outside their membranes instructing them what to do, and the signals must pass down a cascade of messengers inside the cell for them to be conveyed. Each step along the cascade, then, can be a control point: a surface molecule on a skin cell is told that it must divide to heal a cut, and the surface molecule sends a signal to a protein inside the cell, which sends the signal to a different protein, and so on, all the way to the nucleus, which then initiates DNA replication and cell growth. At each step, it is possible that a mistake might start or halt the cell replication process. For example, overexpression of ras, an intracellular messenger that resides in the pathway between the surface and the nucleus, can lead to excessive cell division.

Viruses and cancer.

There are a number of ways that a protein such as ras can be overexpressed, including the involvement of a virus or a genetic mutation. Certain viruses are associated with cancers: for example, sexually transmitted human papilloma virus has been known to increase rates of cervical cancer. Out of all cancers, 10 to 15 percent are thought to be virus-related. Alternately, the genetic mistake might be spontaneous in one of three ways. A gene encoding the protein could be accidentally copied more than once, and, as a result, each copy would churn out the protein when activated. The gene could be misplaced and put near a region of DNA that encourages protein expression. Lastly, a mutation inside the gene might make it unusually active or resistant to later degradation. When such errors initiate uncontrolled cell growth, the gene involved is called an onco-gene (onco is Greek for "tumor"). Before the mutation occurs, the gene may be called a proto-oncogene. Proto-oncogenes usually have the important function of controlling cell-cycle function, as is the case with ras, or may be involved in keeping the cell alive during times of stress, as in the case of Bcl-2, a molecule that prevents stressed or damaged cells from committing apoptosis (cell suicide). Certain viruses can cause these mutations and make oncogenes out of the protoncogenes.

How Cells Curb Their Own Growth

Mutations in cell-cycle control genes can obviously be a problem for an individual, so there are mechanisms in place to prevent this from happening. As mutations can happen during DNA replication, DNA copying is a tightly controlled process. Additionally, there are genes that have the task of DNA repair and mutation surveillance. One such gene is p53. If there is genetic damage, p53 will halt the cell cycle, may initiate DNA repair mechanisms, and may activate cell suicide if repair is not feasible. P53 and other genes that conduct DNA repair and damage surveillance are called "tumor suppressor genes."

Apoptosis.

Apoptosis is a way for damaged cells to prevent themselves from causing more problems. Once apoptosis is initiated, the cell cleaves its own DNA and falls apart in a tightly regulated fashion. The dying cell will pinch off into small pockets of membrane and organelles , known as apoptotic bodies, in order to prevent toxic cytosolic compounds from being released. Then the apoptotic bodies will be swept up and cleared from the area by macrophages or other cells.

"Slipperiness."

Aside from cell-cycle control and tumor suppressor genes, there are other means by which cells curb their own growth. For example, if one grows ordinary skin cells on a plate with growth media, the cells will grow until a bed covers the entire plate. But the cells will not grow beyond that; nor will they grow on top of one another. This is why a cut on one's finger will not grow into a huge lump after it closes. Normal cells will also adhere tightly to one another by secreting proteins that stick to other cell surfaces, whereas many cancer cells do not. Medical doctors use this lack of adhesion, this slipperiness, as one way of distinguishing cancerous tumors from other kinds of lumps.

Telomerases.

Another common mutation seen in cancers is the activation of telomerases. When DNA divides, the replication machinery moves down the nucleotide chain until the very end. It is unable to copy the very end of the molecule (the telomere), however, so with each successive round of replication, the DNA chain gets shorter. In mammals, the telomeres contain repetitive DNA sequences that encode no protein; the idea is that these useless nucleotides can be discarded as cells divide. As the telomeres get shorter, though, the cell will eventually start deleting useful DNA. Some scientists think this is a reason animals grow old: The more cells divide, the greater the likelihood that certain genes will be eliminated and that the new cells will be dysfunctional.

Cancer Cells

Cancer cells, on the other hand, have no such problem. They usually express telomerases, which are enzymes designed to prevent the elimination of the telomeres during cell division. Cancer cells can therefore divide many times and not delete any genetic information crucial to their survival.

Cells require more than one mutation to become cancerous. Mutations in cell-cycle control and tumor suppressor genes are usually required for a tumor to be considered a full-fledged cancer. While many of the tumor suppressor genes are dominant traits (requiring only one allelic deletion to deactivate), many proto-oncogenes are recessive , meaning that both alleles must be destroyed in order for the cells to grow improperly. Such a combination of mutations in a single cell is unlikely, which is why some scientists think that cancers do not begin to show in humans until late in life, when repeated cell division has had a chance to accumulate a number of mistakes in the DNA.

After p53 or other genes that screen DNA get deleted, the cells begin to spin out of control genetically and produce many different kinds of mutations. Like most mutations, the majority of these will simply kill off the cells possessing them. But as tumor cell division is unchecked, other cells will quickly replace them. As the tumor grows and accumulates more mutations, it may gain the ability to grow in different types of tissue.

Cancers may acquire a number of traits useful for their own growth. For example, certain tumors are angiogenic, meaning they draw blood vessels toward themselves to feed the growing tumor. The malignant cells do this by secreting certain hormones necessary for vessel formation. These new vessels also provide conduits for cancer cells to spread throughout the body. In the early twenty-first century, researchers also found that some tumor cells can create new lymphatic vessels, a process called lymphangio-genesis. These newly generated vessels may make it easier for the cancer to spread itself to other parts of the body.

Cancer Treatment

As one might predict, cancer treatment primarily seeks to stop the division of the cells. One method is radiation, which disrupts DNA replication entirely. Other pharmacological means seek to do the same. As cancers are usually the only collection of rapidly dividing cells in the body, halting replication can slow them down, although such treatments can impede healing or immune system function.

More recently, researchers have been using compounds designed to prevent angiogenesis to curb tumor growth. In the early twenty-first century, the National Cancer Institute was conducting clinical trials of anti-angiogenic compounds in a variety of cancers, including stomach, breast, prostate, lung, brain, and ovary, and in some leukemias and lymphomas.

Certain cancers produce tumor antigens, proteins recognizable by the body as hailing from a cancer. Prostate cancer, for example, generates tumor antigens specific enough to be used as a diagnostic tool in patients. Thus, it is theoretically possible to create a prostate cancer vaccine by teaching the body to recognize these antigens before cancer ever arrives and to fight off malignant cells, just as antivirus vaccines fight off virally infected cells. By the beginning of the twenty-first century, however, researchers had found vaccines to be of little use in specifically stimulating the body's immune system to reject tumors.

Cancers, ordinary cells gone wrong, defy normal biological conventions of regulation and homeostasis . As they can quickly reproduce and replace lost daughter cells, they are ripe for rapid mutation and evolution within the body. A variety of treatments exist, but cancers vary widely in origin and nature, as there are different regulatory mechanisms that control different cell types. A more detailed understanding of cell-cycle regulation and mutation surveillance may yet unlock the secrets to curing the disease.

see also Cells.

Ian Quigley

Bibliography

Scientific American. Special Topic Issue: "What You Need to Know about Cancer." September 1996.

Internet Resources

Cancernet. National Cancer Institute. <http://cancernet.nci.nih.gov/>.

HELA CELLS

Although Henrietta Lacks died of cancer in 1951, little bits of her are alive everywhere. She is the originator of the first immortal cell line, HeLa cells. These are cancer cells scraped from her cervix, and they grew so well that they proved ideal for study in laboratories all over the world. Unfortunately, they grew so well in culture that they invaded other cell lines and ruined countless experiments. It became such a problem that in 1968, the premier standard-bearer of cell lines in the world, the American Type Culture Collection, tested all thirty-four of its "pure" cell lines and found that twenty-four of them were HeLa cells instead.

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cancer

cancer The term ‘cancer’ refers to a diverse group of diseases, characterized by uncontrolled growth of cells, leading to a variety of pathological consequences and frequently death. It is typically a disease of the elderly — the incidence of all forms of cancer increases markedly with age. However, it also occurs occasionally in children. Often the abnormal cell growth results in the establishment of a macroscopic lump or tumour ‘oncos’ in Greek, hence the term ‘oncology’ for the study of cancer), which may grow to a large size and kill the patient by a local effect, e.g. occlusion of vital ducts — even the alimentary tract — or by compromising the functioning of some distant organ. Indeed, the very word ‘cancer’ derives from the appearance of solid tumours as noted on post mortem examination by early physicians, who likened their appearance to that of a crab (Cancer) because of the irregular and disorganized appearance of the threads of the tumour radiating from a central body. Some forms of cancer, however, do not grow as coherent lumps but as individual cells diffused through the vascular system; these diseases — leukaemias and lymphomas — are associated with quite a different pathological profile.

Not all tumours of the human body are cancerous, however. Everyone is familiar with the common wart, and probably other skin lesions that result from local proliferation of cells, and which are quite benign. What distinguishes cancerous tumours and renders them seriously life-threatening is the property of malignancy, which derives from the capacity of the cells to invade surrounding tissue and to break off from the parent lump, migrate around the body in the blood vessels or the lymphatic system, and set up secondary foci of cancerous growth at distant sites. It is the latter phenomenon, metastatic spread of the disease, which most frequently kills cancer patients. The secondary foci — metastases — often occur in the brain, lungs, or liver, because these organs have a large blood supply and a well-developed capillary bed of tiny vessels in which single cancer cells or clumps of cells can lodge. By contrast, many common skin cancers (with the singular exception of malignant melanoma) are invasive but not metastatic, so they can be cured by simple excision of the tumour together with a decent margin of surrounding tissue. This emphasizes the seriousness of metastasis in the pathology of cancer. It is also salutary that in many instances cancer patients present with clear evidence of metastatic disease, such as secondary tumours radiologically visible in the lung, but no sign of the primary lump. It may take all the skill of an experienced histopathologist to indicate the probable origin of the diseased cells, knowledge of which is likely to be crucial for any form of clinical management.

Cancer therapy involves four modalities which may be employed singly or in combination: surgery, radiotheraphy, chemotherapy, or a group of less well-defined treatments, of which immunotherapy is the chief example. It is common practice to employ surgery where applicable (to reduce the tumour burden if a single large mass has been detected e.g. by X-rays or magnetic resonance imaging), followed by localized or whole-body radiotherapy to attack residual disease, and/or chemotherapy to deal with distant metastases. If the disease is advanced, with obvious metastasis, chemotherapy with a cocktail of three or four powerfully cytotoxic drugs may be the only worthwhile option. Most of these drugs are DNA-reactive chemicals which directly attack the genetic blueprints of the rogue cells. Alternatively a massive dose of whole-body irradiation may be attempted, and the patient rescued from death due to destruction of his bone marrow by subsequent reimplantation of his own marrow cells, collected prior to treatment and ‘cleaned up’ in vitro (autologous bone marrow transplantation).

Cancer is increasingly seen as a lifestyle disease, caused at least partly by environmental influences, with important modulation by the genetic inheritance of the individual. Sometimes viral infections may start the process off. In other cases sunlight is to blame, particularly in causing skin cancers among fair-skinned Caucasians living in tropical countries or under the ozone hole of the Southern hemisphere. Sometimes it is diet which seems to trigger disease, especially of the gastrointestinal tract: here fats are held suspect, and a high-fibre diet rich in cereals and vegetables is to be recommended. But far and away the most serious, and preventable, environmental cause of cancer is tobacco smoking, which is inexorably linked to cancer of the lung. On this conclusion the epidemiological evidence is stark — witness the sharp continuing rise in lung cancer among women in the Western world, which correlates precisely with the changes in social attitudes to smoking over the last 50 years.

One of the hottest areas of cancer research by the end of the twentieth century was the identification of genes that impart an inherited susceptibility to cancer of particular organs, or to cancer in general. Early successes have been the discovery of BRCA1 and BRCA2, genes which predispose to breast cancer — still the most common form of malignancy in Western women — and there are more to come. Other cancer-prone individuals carry genes whose products are enzymes known to be intimately associated with the biological phenomena of cell signalling, gene transcription, or DNA repair. A picture is beginning to emerge of cancer development, starting with a single cell exposed to some external influence, which causes a mutation in one of a small number of critical genes, ‘initiating’ the process of escape from growth control. Other genetic changes, leading to aneuploidy (abnormalities in the nature or the number of chromosomes), follow over a period which may be as long as several years, while so-called ‘promoter’ substances exacerbate the multiplication of the abnormal cells into a small tumour, which begins to invade its surroundings and may start to metastasise. In the later stages of disease the cells enter a ‘progression’ phase, in which gross rearrangements of their genetic make-up occur — these, can be seen down the microscope as wholesale redistribution of chromosomes, involving deletions, translocations, breaks, duplications, and doubtless many more subtle changes. Genetic instability can proceed to a state of chromosomal chaos — a ‘point of no return’ whereby cells cannot revert to the normal karyotype (the characteristics of its chromosomes) and must be killed. At that stage the disease is rampant and only the most aggressive intervention, including treatment with drugs which have dire toxic side-effects, is likely to produce any relief or remission, and cure is most unlikely. Often the side-effects (hair loss, vomiting and diarrhoea, neurological disorders, or bone marrow suppression) are so serious as to be unacceptable to the sick patient, and palliative treatment with powerful opiates is all that can be recommended. The most recent scientific findings emphasize the importance in tumour control of programmed cell death (apoptosis) and shortening of the far end, of the ‘arms’ of chromosomes (the telomeres) during replication. Chemotherapeutic and radiotherapeutic strategies induce apoptosis, so escape from programmed death signals is important.

M. J. Waring


See also chemotherapy; radiotherapy.

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Cancer

CANCER

CANCER remains one of the most feared diseases of our times. Every year 500,000 Americans die from tumors of one sort or another, up from about 30,000 at the beginning of the twentieth century. Part of the increase is due to population growth and the fact that people now live longer—and cancer is, generally speaking, a disease of the elderly. A smaller fraction of the increase is due to the fact that previously undetected cancers are now more likely to be diagnosed. But cancer risks have also grown over time, due to increased exposures to carcinogenic agents—notably New carcinogens in food, air, and water, such as pesticides and asbestos; the explosive growth of tobacco use in the form of cigarettes, which were not widely used until World War I; and exposure to various forms of radiation, such as X-rays and radioisotopes. Tobacco alone still causes nearly a third of all American cancer deaths—including 90 percent of all lung tumors—making it the single most important cause of preventable cancers.

Cancer is actually a cluster of several different diseases, affecting different parts of the body and different kinds of tissue. Leukemia is a cancer of the blood, myeloma a cancer of the bone marrow, melanoma a cancer of the skin, and so forth. Cancer can be seen as "normal" tissue growing out of control or in places where it should not. In the case of breast cancer, for example, the danger is not from cancer cells confined to the breast, but rather from cancerous breast cells spreading to other parts of the body ("metastasis"), where they grow and eventually interfere with other parts of normal bodily function. Cancerous growths seem to begin when the body's normal cellular "suicide" functions break down; malignant cells are immortal in the sense that they continue to divide instead of periodically dying off as healthy cells should.

A great deal of research has gone into exploring the genetic mechanisms of carcinogenesis, with the hope of finding a way to halt the growth of cancerous cells. The difficulty has been that cancer cells look very much like normal cells, the difference typically being only a few minor mutations that give the cell novel properties. That is why cancer is so difficult to treat. It is not like the flu or malaria, where a living virus or bacterium has infected the body. Cancer cells are often not even recognized as foreign by the body's immune system—which is why they can grow to the point that normal physiological processes are obstructed, causing disability and, all too often, death.

Cancer also has to be understood as a historical disease, since the kinds of cancer that are common in a society will often depend on what people eat or drink, what kinds of jobs or hobbies or habits are popular, what kinds of environmental regulations are enforced, the environ-mental ethics of business leaders and labor activists, and many other things as well. Cancer is a cultural and political disease in this sense—but also in the sense that different societies (or different people within the same society) can suffer from very different kinds and rates of cancer.

Stomach cancer was the number one cause of cancer death in America in the early years of the twentieth century, for example, accounting for about half of all American cancer deaths. By the 1960s, however, stomach cancer had fallen to fifth place in the ranks of cancer killers, as a result of food refrigeration and the lowered consumption of high-salt, chemically colored, and poorly preserved foods. Cancers of the lung, breast, and ovary are now the more common causes of death for women, as are cancers of the lung, colon, prostate, and pancreas among men. Lung cancer has become the leading cause of cancer death among both men and women, in consequence of the rapid growth of smoking in the middle decades of the twentieth century. The twenty-to thirty-year time lag between exposure and death for most cancers explains why the decline of smoking in the 1970s and 1980s only began to show up at the end of the century in falling lung cancer rates.

It is important to distinguish cancer mortality (death rates) from cancer incidence (the rates at which cancers appear in the population). Some cancers are fairly common—they have a high incidence—but do not figure prominently in cancer mortality. Cancer of the skin, for example, is the most common cancer among both men and women, but since few people die from this ailment, it does not rank high in the mortality tables. Most skin cancers are quite easily removed by simple surgery. Lung cancer survival rates, by contrast, are quite low. Mortality rates are tragically close to incidence rates for this particular illness.

Worries over growing cancer rates led President Richard Nixon to declare a "war on cancer" in his State of the Union address of 1971. Funding for cancer research has increased dramatically since then, with over $35 billion having been spent by the National Cancer Institute alone. Cancer activists have also spurred increased attention to the disease, most notably breast cancer activists in the 1980s and prostate cancer activists in the 1990s. Attention was also drawn to Kaposi's sarcoma from its association with AIDS. Cancer researchers have discovered a number of genes that seem to predispose certain individuals to certain kinds of cancer; there are hopes that New therapies may emerge from such studies, though such knowledge as has been gained has been hard to translate into practical therapies. Childhood leukemia is one case where effective therapies have been developed; the disease is now no longer the death sentence it once was. From the point of view of both policy and personal behavior, however, most experts agree that preventing cancer is in principle easier than treating it. Effective prevention often requires changing deeply ingrained personal habits or industrial practices, which is why most attention is still focused on therapy rather than on prevention.

We already know enough to be able to prevent about half of all cancers. The problem has been that powerful economic interests continue to profit from the sale of carcinogenic agents—like tobacco. With heart disease rates declining, cancer will likely become the number one cause of American deaths by the year 2010 or 2020. Global cancer rates are rapidly approaching those of the industrialized world, largely as a result of the increasing consumption of cigarettes, which many governments use to generate tax revenue. The United States also contributes substantially to this global cancer epidemic, since it is the world's largest exporter of tobacco products. Only about two-thirds of the tobacco grown in the United States is actually smoked in the United States; the remainder is exported to Africa, Europe, Asia, and other parts of the world. Cancer must therefore be regarded as a global disease, with deep and difficult political roots. Barring a dramatic cure, effective control of cancer will probably not come until these political causes are taken seriously.

BIBLIOGRAPHY

Epstein, Samuel S. The Politics of Cancer Revisited. Fremont Center, N.Y.: East Ridge Press, 1998.

Patterson, James T. The Dread Disease: Cancer and Modern American Culture. Cambridge, Mass.: Harvard University Press, 1987.

Proctor, Robert N. Cancer Wars: How Politics Shapes What We Know and Don't Know About Cancer. New York: Basic Books, 1995.

Robert N.Proctor

See alsoCenters for Disease Control and Prevention ; Smoking ; Tobacco Industry .

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Cancer

Cancer

Normal tissue development depends on a balance between cell multiplication and cell death. When cells multiply faster than they die, the result is an abnormal tissue growth called a tumor (neoplasm). The study and treatment of tumors is a branch of medicine called oncology.

Not all tumors are cancerous. Benign tumors are surrounded by a fibrous capsule, grow slowly, and do not spread to other organs; although they are nevertheless sometimes fatal. A wart is a benign tumor. Malignant tumors have no capsule, grow rapidly, and shed cells that can "seed" new tumors in other organs, a phenomenon called metastasis . The word cancer refers only to malignant tumors. The word literally means "crab." It was coined by the ancient Greek physician Hippocrates when the tangle of blood vessels in a breast tumor reminded him of the legs of a crab.

Cancers are classified according to the type of tissues or cells in which they originate (see Table on page 112). A primary tumor is a tumor in the site of origin, and a secondary (metastatic) tumor is a tumor in a new site resulting from the spread of cells from the original tumor, for example, a brain tumor resulting from cells that originated in colon cancer.

Causes of Cancer

Most cancer is caused by environmental agents called carcinogens. Carcinogens include chemicals such as cigarette tar, nitrites (used as food preservatives), and many industrial chemicals; viruses such as the hepatitis B and herpes simplex 2 viruses; and ionizing radiation such as X rays and gamma rays. All of these agents are mutagens; that is, they cause mutations, or changes in deoxyribonucleic acid (DNA) and chromosome structure, which in turn result in uncontrolled cell division.

Cancer Genes

The risk of cancer is often hereditary, and many forms of cancer have been traced to two types of genes : oncogenes and tumor-suppressor genes.

Oncogenes. Oncogenes are mutated, "misbehaving" genes that normally code for growth factors or their receptors. Growth factors are chemical signals that trigger cell division. Some oncogenes cause excessive secretion of growth factors, and thus excessive cell division. Other oncogenes code for dysfunctional receptors that act like switches stuck in the "on" position, sending signals for cell division even when there is no growth factor bound to them. Many cases of breast and ovarian cancer are due to an oncogene called erbB2.

Tumor-Suppressor Genes. Tumor-suppressor (TS) genes normally inhibit cancer by opposing the action of oncogenes, promoting the repair of mutated DNA, or controlling tissue development. When TS genes are mutated, these protections are lost. A TS gene called p53 has been implicated in leukemia and colon, lung, breast, liver, brain, and esophageal cancer.


The top ten causes of cancer mortality in the United States, ranked from highest to lowest, are cancers of the lung, colon, breast, prostate, pancreatic, leukemic, ovarian, stomach, nervous system, and bladder.


Thus, oncogenes promote cancer and TS genes suppress it. They can be loosely compared to the accelerator and brake on a car, respectively. A defect in either one causes the "car," cell division, to run out of control. Cancers typically require more than one mutation before they develop; thus, colon cancer involves damage to at least three TS genes on chromosomes 5, 17, and 18, plus activation of an oncogene on chromosome 12. It may take many years for so many mutations to accumulate in a single cell, which is one reason cancer is more common among the elderly than among young people.

Type of cancer Site of origin
Carcinoma Epithelial cells
Melanoma Pigment-producing skin cells (melanocytes)
Sarcoma Bone, other connective tissues, or muscle
Leukemia Blood-producing tissues (bone marrow and lymphatic tissue)
Lymphoma Lymph nodes

Effects of Cancer

Cancer is almost always fatal if it is not treated. Four ways in which cancer can kill are:

  1. By displacing normal tissue, so the function of an organ deteriorates; an example of this is when a lung tumor replaces so much lung tissue that the blood can no longer get enough oxygen, or a brain tumor compresses and kills brain tissue
  2. By invading blood vessels, causing fatal hemorrhages
  3. By compressing vital passages, for example shutting off air flow into the lung or obstructing blood flow through a major vein or artery
  4. By competing with healthy tissues for nutrients, often causing the body to break down its own proteins (muscle, for example) to feed the "hungry" tumor, or failing to make enough red blood cells and platelets because stem cells are diverted into producing the abnormal white blood cells of leukemia.

Cancer is normally treated by surgery, chemotherapy, or both, depending on its location, type, and extent. Other approaches are radiotherapy (using radiation to destroy tumors) and immunotherapy (providing antibodies or immune cells to attack cancer cells). Some forms of cancer are highly treatable, such as skin cancer, whereas others offer much less hope of recovery, such as pancreatic cancer.

see also Cell Cycle; Genetic Diseases; Mutation; Oncogenes and Cancer Cells

Kenneth S. Saladin

Bibliography

American Cancer Society. <http://www.cancer.org/>.

Fauci, Anthony S., et al. Harrison's Principles of Internal Medicine, 14th ed. New York: McGraw-Hill, 1998.

McCance, Kathryn L., and Sue E. Huether. Pathophysiology, 3rd ed. St. Louis: Mosby, 1998.

Varmus, H., and R. A. Weinberg. Genes and the Biology of Cancer. San Francisco: W. H. Freeman and Company, 1993.

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Cancer

66. Cancer

See also 122. DISEASE and ILLNESS .

adenocele
a cystic tumor that may develop in the glands.
adenosarcoma
a malignant glandular tumor of the soft tissues of the body.
astroblastoma
a malignant tumor that may invade the brain and spinal cord, especially investing blood vessels.
astrocytoma
a brain tumor composed of large, star-shaped cells called astrocytes.
blastoma
a neoplasm arising in the blastema, i.e., tissue from which an organ or part is formed. Also blastocytoma.
cancericidal
of or pertaining to a chemical or process than can destroy malignant cells.
cancerophobia
carcinomophobia.
cancroid
1. of or pertaining to a lesion that resembles cancer.
2. a malignant skin cancer.
carcinectomy
the surgical removal of a cancer.
carcinogen
any natural or artificial substance that can produce or trigger cancer, as arsenic, asbestos, ionizing radiation, ultraviolet rays, x rays, and many derivatives of coal tar. carcinogenic, adj.
carcinoid
a small, yellow tumor that may develop from argentaffin cells in the gastrointestinal mucosa and spread widely throughout the body.
carcinolysis
the destruction of malignant cells, as by an antineoplastic drug.
carcinoma
1. a malignant tumor that may spread to surrounding tissue and distant areas of the body.
2. any kind of epithelial cancer. carcinomatous, adj.
carcinomatosis
carcinosis.
carcinomophobia, carcinomatophobia, carcinophobia
an abnormal fear of cancer. Also called cancerophobia.
carcinophilia
an afflnity for cancerous tissue, a property of certain chemical agents. carcinophilic, adj.
carcinosis
1. an abnormal condition characterized by the growth of numer-ous carcinomas throughout the body. Also carcinomatosis.
2. the process of development of carcinoma.
carcinostatic
of or pertaining to the slowing or stopping of the growth of a carcinoma.
celiothelioma
mesothelioma.
cerebroma
any abnormal mass of brain tissue, malignant or benign.
chemosurgery
a therapeutic procedure that uses chemicals to destroy pathogenic tissue, especially skin cancers.
chemotherapy
a procedure that uses radioisotopes of various elements, as iodine, phosphorus, and gold, to treat cancers of the thyroid gland, lungs, and other organs.
chloroma
a malignant, greenish tumor that invades myeloid tissue and fluoresces red under ultraviolet light.
chondrocarcinoma
a malignant cartilageous tumor of the epithelium.
chondrosarcoma
a malignant cartilageous tumor that most frequently invades the long bones, pelvis, and the scapula.
chordoma
a rare congenital tumor of the brain.
chorioblastoma
choriocarcinoma.
choriocarcinoma
a uterine malignancy that may develop shortly after conception, during pregnancy, or after an abortion. Also called chorioblastoma, chorionic epithelioma .
comedocarcinoma
a malignant tumor of the mammary ducts.
cystoma
any neoplasm or tumor that contains cysts, especially any such tumor that invades the ovaries.
cytotechnology
the study of human cells, especially to detect signs of cancer. cytotechnologist, n. cytotechnolqgic, adj.
erythroleukemia
a malignancy of the blood characterized by abnormally productive bone marrow and the development of oddly-shaped blood cells.
glioma
any of the predominant category of brain tumors composed of cancerous glial cells (a type of nerve cell).
hepatoma
a malignant tumor of the liver that most commonly occurs in association with hepatitis or cirrhosis,
leukemia
a malignancy of blood-producing tissues, characterized by proliferating immature white blood cells and infiltration of the spleen, liver, and other organs. Also leukocythemia. leukemie, leukemoid, adj.
leukocythemia
leukemia.
liposarcoma
a cancerous growth of primitive fat cells. Also called lipoma sarcomatode.
lymphoma
a growth of lymphoid tissue that is commonly cancerous and typically enlarges the lymph nodes.
medulloblastoma
a malignant tumor that commonly originates in the cere-bellum.
melanoma
any malignant growth, especially in the skin, that is composed of melanin-producing cells.
mesothelioma
a rare malignant tumor that may invade the linings of the lungs and the abdomen. Also called celiothelioma.
metastasis
the spread of malignancies, characterized by the cancerous invasion of the lymphatic system, the blood, and body organs. metastatic, adj. metastasize, v.
neoplasia
the abnormal proliferation of benign or malignant cells. neoplastic, adj.
neoplasm
the abnormal development of benign or cancerous tissue. neoplastic, adj.
neurinoma
a tumor that develops in a neural sheath and that may become malignant.
neuroblastoma
a highly malignant tumor that may develop from the neural plate in an embryo and spread to the bones, liver, and other organs.
neurosarcoma
a malignant growth composed of neural, connective, and vascular tissues. Also called malignant neuroma.
oncogenesis
the process by which a tumor develops. oncogenic, adj.
oncology
the field of medicine that specializes in the study of tumors.
osteoclastoma
a giant cell bone tumor that most commonly develops at the end of a long bone.
osteosarcoma
a malignant bone tumor. Also called osteogenic sarcoma .
retinoblastoma
a common childhood malignancy of the eye that develops from retinal cells.
sarcoma
a rare malignant tumor of the soft tissues that commonly develops in the lower extremities.
ulocarcinoma
a malignancy of the gums.

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Cancer

Cancer

Cancer is a disease of uncontrolled cell growth caused by exposure to carcinogens (cancer-causing substances), genetic defects, or viruses. Cancer cells can multiply and form a large mass of tissue called a tumor. Some tumors are limited to one location and can be surgically removed. These tumors may cause little harm and are therefore termed benign. Cancer cells of other tumors may spread, or metastasize (muh-TASS-tuh-size), to surrounding tissue or other organs of the body. Such aggressive tumors are termed malignant. Cancer is a word used usually to describe malignant, not benign, tumors. The study of cancer is called oncology.

How cancer cells are formed

The transformation of a normal cell into a cancer cell can occur when the genetic material (deoxyribonucleic acid or DNA) of a cell is changed, or mutated. A tumor is the result of multiple gene mutations within a single cell. Years or decades before a tumor forms, a cell can become weakened by various factors, making it more susceptible to later transformation into a cancer cell. Cancer is often a disease of age, with many occurring after age fifty.

Types of cancer

There are more than 200 different types of cancer, and they are named for the organ or tissue in which they begin to grow. Leukemia refers to cancer of white blood cells (also called leukocytes), and lymphoma is cancer of lymphoid tissue (a connective tissue containing white blood cells called lymphocytes). Melanomas are cancers that begin in melanocytes (skin pigment cells). Cancers that originate in epithelial tissue (cellular tissue that lines cavities such as the stomach or lung) are called carcinomas. Those that begin in connective tissue (such as bone and cartilage) or muscle are called sarcomas.

Words to Know

Carcinogen: A substance capable of causing cancer.

Chromosome: Organized strands of DNA in the nucleus of a cell.

DNA (deoxyribonucleic acid): The genetic material in the nucleus of cells that contains information for an organism's development.

Gene: A section of a chromosome that carries instructions for the formation, functioning, and transmission of specific traits from one generation to another.

Mutation: A change in the DNA in a cell.

Tumor: A mass of abnormal tissue that can be malignant or benign.

Causes of cancer

One of the most carcinogenic substances known is tobacco smoke. It is the major cause of lung cancer, which is the leading cause of cancer deaths in both men and women in the United States. In the year 2000, almost 160,000 people in the United States died from lung cancer. In comparison, cancer of the colon and rectum caused over 56,000 deaths that same year. Breast cancer claimed over 41,000 lives, while prostate cancer claimed almost 32,000.

Other carcinogens include certain chemicals, the Sun's ultraviolet light, and radiation. Some viruses can cause cancer by altering the DNA of a host cell and converting the cell's normal genes into cancer-causing genes, or oncogenes. Genetic factorssuch as chromosomal

abnormalities or the inheritance of faulty genes from a parentcan make some people more likely to develop certain cancers. For instance, people with Down syndrome, a chromosomal abnormality, are susceptible to leukemia.

Treatment

Cancer treatment consists of surgery to remove tumors and radiation to slow tumor growth. Chemotherapy, or drug therapy, is often used to treat cancers that have spread to other parts of the body. Another approach to treatment is to boost the immune system with immune-enhancing drugs or antibodies that can recognize and destroy abnormal cells. A new type of anticancer drug that homes in on cancer cellsleaving healthy ones alonewas introduced in the spring of 2001. The drug, Gleevec, works strikingly well against chronic myelogenous leukemia (one of the four main types of blood cancer) and gastrointestinal stromal tumor (GIST; a rare stomach tumor). Scientists believe the future of cancer treatment lies in the development of a wider range of anticancer drugs and in genetic engineering, whereby healthy genes would be manufactured to replace mutated DNA in transformed cells.

Prevention

Many cancers are preventable. It is estimated that avoidance of tobacco, overexposure to the Sun, high-fat diets, excessive alcohol, unsafe sex, and other known carcinogens could prevent more than 80 percent of all cancer cases. In addition, yearly testing can detect certain cancers and make early treatment possible, providing a better chance of survival.

[See also Carcinogen; Nucleic acid ]

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cancer

cancer Any disorder of cell growth that results in invasion and destruction of surrounding healthy tissue by abnormal cells. Cancer cells arise from normal cells whose nature is permanently changed. They multiply more rapidly than healthy body cells and do not seem subject to normal control by nerves and hormones. They may spread via the bloodstream or lymphatic system to other parts of the body, where they produce further tissue damage (metastases). Malignant tumour is another name for cancer. A cancer that arises in epithelium is termed a carcinoma; one that arises in connective tissue is called a sarcoma. Leukaemia is cancer of white blood cells; lymphoma is cancer of lymphoid tissue; and myeloma is cancer of plasma cells of the bone marrow. Causative agents (carcinogens) include various chemicals (including those in tobacco smoke), ionizing radiation, silica and asbestos particles, and oncogenic viruses. Hereditary factors and stress may also play a role. See oncogene.

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Cancer

Can·cer / ˈkansər/ 1. Astron. a constellation (the Crab), said to represent a crab crushed under the foot of Hercules. It is most noted for the globular star cluster of Praesepe (the Beehive cluster). ∎  [as genitive] (Can·cri / ˈkangkrē/ ) used with a preceding letter or numeral to designate a star in this constellation: the star Delta Cancri. 2. Astrol. the fourth sign of the zodiac, which the sun enters at the northern summer solstice (about June 21). ∎  (a Cancer) a person born when the sun is in this sign. PHRASES: tropic of Cancersee tropic1 . DERIVATIVES: Can·cer·i·an / kanˈsərēən; -ˈsi(ə)r-/ n. & adj. (in sense 2).

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cancer

cancer (kan-ser) n. any malignant tumour, including carcinoma and sarcoma. It arises from the abnormal and uncontrolled division of cells that then invade and destroy the surrounding tissues. The cancer cells spread (see metastasis), setting up secondary tumours (metastases) at sites distant from the original tumour. There are probably many causative factors, some of which are known; for example, cigarette smoking is associated with lung cancer, radiation with some sarcomas and leukaemia, and several viruses are implicated; genetic factors are involved in the development of many cancers. Treatment of cancer depends on the type of tumour, the site of the primary tumour, and the extent of spread.


www.cancerresearchuk.org Website of Cancer Research UK

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Cancer

CANCER

DEFINITION


Cancer is not just one disease, but a group of almost one hundred diseases. These diseases have two common characteristics. First, cells begin to grow out of control in the body. Second, those cells have the ability to travel from their original site to other locations in the body. If the spread is not controlled, cancer can result in death.

DESCRIPTION


Cancer is responsible for one out of every four deaths in the United States. It is second only to heart disease as a cause of death in this country. About 1.2 million Americans were diagnosed with cancer in 1998. Of that number, more than 500,000 are expected to die of the disease.

Cancer can attack anyone, but the chances of getting the disease increase with age. The most common forms of cancer are skin cancer, lung cancer, colon cancer, breast cancer (in women; see breast cancer entry), and prostate cancer (in men; see prostate cancer entry). Other major cancers that affect Americans include those of the kidneys, ovaries, uterus, pancreas, bladder, rectum, and blood and lymph nodes (see leukemia entry).

Cancer is a disorder that affects the genes. A gene is a small part of a deoxyribonucleic (pronounced dee-OK-see-RIE-bo-noo-KLEE-ik) acid (DNA) molecule. DNA molecules carry the master plan in cells that tells them how to behave. Genes carry the directions for making proteins. Proteins are involved in a wide number of functions in the body that make it possible to move, think, breathe, and carry out other activities.

Normally, cells go through a cycle in which they grow, divide, and die. Gene mutations (changes) can interrupt that cycle. Cells forget how to stop growing and reproduce over and over again, forming a lump of cells that gets bigger and bigger. The lump is known as a tumor or neoplasm ("new growth," pronounced NEE-o-plaz-um).

A healthy person's immune system can usually recognize and destroy neoplastic cells. Sometimes, though, mutant cells can escape detection. When they do, they can go on to become tumors. Tumors are of two types: benign ("harmless," pronounced bih-NINE) and malignant (harmful and possibly terminal, pronounced muh-LIG-nent). Benign tumors grow slowly and do not spread in the body. Once removed, they usually do not reappear. Malignant tumors, by contrast, invade surrounding tissue and spread through the body. If removed, a malignant tumor often grows back.

Most gene mutations are caused by environmental factors called carcinogens (pronounced car-SIN-o-genz). Carcinogens are things in our environment that cause cancer. Many kinds of carcinogens are known.

Cancer: Words to Know

Benign:
A growth that does not spread to other parts of the body, making recovery likely with treatment.
Biopsy:
Surgical removal and microscopic examination of tissue for diagnostic purposes.
Bone marrow:
Spongy material that fills the center of bones, from which blood cells are produced.
Carcinogen:
Any substance capable of causing cancer.
Chemotherapy:
Treatment of cancer that uses chemicals or drugs that destroy cancerous cells or tissues.
Epithelium:
The layer of cells covering the body's outer and inner surfaces.
Hormone therapy:
Treatment of cancer by slowing down the production of certain hormones.
Immunotherapy:
Treatment of cancer by stimulating the body's immune system.
Malignant:
Cancer cells that have broken loose from a tumor and spread to other parts of the body.
Metastasis:
The process by which cancer cells have spread from their original source to other parts of the body.
Radiation therapy:
Treatment that uses various forms of radiation to kill cancer cells.
Tumor:
An abnormal growth that has developed as cancer cells grow out of control.
X rays:
A kind of high-energy radiation that can be used to take pictures of the inside of the body, to diagnose cancer, or to kill cancer cells.

Some kinds of cancer are caused by genetic factors. Faulty genes can be passed from parents to children. When that happens, the children are at risk for cancer. In most such cases, a cancer is caused by some combination of genetic and environmental factors.

Normal body characteristics can increase the likelihood that a person will develop cancer. For example, people with fair skin are more likely to get skin cancer (see skin cancer entry) than those with darker skin.

Cancers can be classified according to the part of the body in which they occur:

  • Carcinomas. Carcinomas (pronounced car-sen-O-muhz) are cancers that arise in the epithelium (pronounced eh-peh-THEE-lee-um). The epithelium is the layer of cells that covers the outside (the skin) and the inside of the body. Carcinomas covering the exterior epithelium are called squamous (pronounced SKWAY-muss) cell carcinomas. Those that develop in an organ or gland are called adenocarcinomas (pronounced add-en-o-car-sen-O-muhz).
  • Melanomas. Melanomas are another form of skin cancer, and usually occur in cells that give skin their color (melanocytes).
  • Sarcomas. Sarcomas are cancers of the supporting tissues of the body, such as bone, muscle, and blood vessels.
  • Leukemias. Leukemias are cancers of the blood.
  • Lymphomas. Lymphomas are cancers of the lymph system.
  • Gliomas. Gliomas are cancers of nerve tissue.

CAUSES


The major risk factors for cancer are tobacco and alcohol use, diet, sexual and reproductive behavior, infectious agents, family history, occupation, radiation, and pollution.

The American Cancer Society estimates that about 40 percent of all cancer deaths in the United States are caused by tobacco and excessive alcohol use. An additional one-third of the deaths are caused by poor diet and nutrition. The vast majority of deaths from skin cancer are due to overexposure to ultraviolet light in the sun's rays.

Tobacco

Smoking is responsible for 80 to 90 percent of all cases of lung cancer (see lung cancer entry). Smoking is also a factor in other forms of cancer affecting the upper respiratory (breathing) tract, larynx, bladder, pancreas, and, probably, liver, stomach, and kidney. Secondhand smoke (smoke exhaled by smokers and inhaled by others nearby) can also increase the risk of developing cancer.

Alcohol

People who drink too much alcohol are at risk for certain forms of cancer, such as liver cancer. In combination with smoking, the use of alcohol can also increase the risk of developing cancer of the mouth, pharynx (pronounced FAHR-inks), larynx, and esophagus (pronounced SAH-fuh-guss).

Diet

One in three cancers can be traced to dietary factors. Obesity (see obesity entry) has been connected with cancers of the breast, colon, rectum, pancreas, prostate, gallbladder, ovaries, and uterus.

Sexual and Reproductive Behaviors

Some cancer-causing viruses can be transmitted by sexual activity. People who begin sexual activity early in their lives and have many partners appear to have a higher risk for developing cancer. Women who never have children or have them late in life may be at higher risk for developing ovarian and breast cancer.

Infectious Agents

Scientists believe that about 15 percent of all cancers are caused by viruses, bacteria, or parasites. A list of the most common cancer-causing infectious agents is shown in the table below.

Family History

Certain forms of cancer recur generation after generation in some families. These include breast, colon, ovarian, and uterine cancers.

COMMON PATHOGENS AND THE CANCERS ASSOCIATED WITH THEM
Causative Agent Type Of Cancer
Viruses
Papillomaviruses Cancer of the cervix
Hepatitis B virus Liver cancer
Hepatitis C virus Liver cancer
Epstein-Barr virus Burkitt's lymphoma
Cancers of the upper pharynx Hodgkin's lymphoma, Non-Hodgkin's lymphoma, Gastric cancers
Human immunodeficiency virus (HIV) Kaposi's sarcoma Lymphoma
Bacteria
Helicobacter pylori Stomach cancer Lymphomas

Occupational Hazards

About 4 percent of all cancers are thought to be connected with one's occupation. For example, people who work with asbestos have an increased chance of developing lung cancer. Asbestos is a naturally occurring mineral that was once used widely as insulation for housing and other buildings. Many other forms of occupational cancer have been identified. These include:

  • Bladder cancer, among dye, rubber, and gas workers
  • Skin and lung cancer, among those who work in smelters, with arsenic, and in gold mines
  • Leukemia, among glue and varnish workers
  • Liver cancer, among workers in the PVC (polyvinyl chloride plastics) industry
  • Lung, bone, and bone marrow cancer, among people who work with X rays and other forms of radiation, or with uranium

Radiation

Ultraviolet radiation is responsible for the majority of deaths from melanoma. Other sources of radiation include X rays, radon gas, and radiation from nuclear materials. These sources combined are thought to be responsible for about 1 to 2 percent of all cancer deaths.

Pollution

Experts think that roughly 1 percent of all cancer deaths are caused by air, land, and water pollution. Industries that release harmful chemicals into the environment are the primary source of these pollutants.

SYMPTOMS


Cancer is a progressive disease. That is, it goes through a series of stages that are progressively worse. The symptoms are different at each stage. One of the earliest symptoms of cancer is pain. As tumors grow, they push on organs, nerves, blood vessels, and other tissues around them, causing pain.

The earlier cancer is detected, the more effectively it can be treated. For this reason, the American Cancer Society has prepared a list of seven warning signs of cancer. They are:

  • Change in the size, color, or shape of a wart or mole
  • A sore that does not heal
  • Persistent cough, hoarseness, or sore throat
  • A lump or thickening in the breast or elsewhere
  • Unusual bleeding or discharge (release of fluids)
  • Chronic indigestion or difficulty in swallowing
  • Any change in bowel or bladder habits

Diseases other than cancer can also produce these symptoms, so the symptoms need to be checked as soon as possible. Many forms of cancer have no early warning signs at all. For that reason, regular medical tests may be important. For example, women should check their own breasts regularly and should have regular mammograms (X rays of the breasts).

DIAGNOSIS


The first steps in diagnosing cancer are doing a complete physical examination and getting a medical history. During the physical examination, the doctor looks at, feels, and palpates (applies pressure by touch) various parts of the body. He or she watches for unusual size, feel, or texture of organs or tissues.

Some of the specific symptoms a doctor looks for during such a physical examination are the following:

  • Thickening or sores in the lips, tongues, gums, throat, or roof of the mouth
  • Tenderness or lumps in the neck
  • Swelling or soreness of the lymph nodes in the neck, under the arms, and in the groin
  • Sores, itchiness, or bleeding on the skin
  • Sores or abnormal discharge from the ovaries, vagina, cervix, or uterus
  • Discharge, unevenness, or discoloration of the breasts
  • The presence of lumps or unusual masses in the breasts (in women) or in the rectum or testicles (in men)

If the doctor finds any of these signs, he or she may order tests. Some of the most common tests are the following:

  • Sputum (material coughed up from the lungs; pronounced SPYOO-tum) is studied under a microscope to look for lung cancer.
  • Blood tests can be used to look for tumor markers. A tumor marker is a special type of protein released by cancer cells. Blood tests are also used to follow the course of cancer and to see how well treatment is working.
  • Imaging tests help doctors find tumors deep within the body. Most imaging tests use a form of radiation (such as X rays) to look for abnormal masses inside the body.
  • A biopsy is the most reliable test for cancer. In a biopsy, the doctor removes a piece of tissue from an abnormal area of the body. The tissue is then studied under a microscope. A specialist can tell whether the tissue is normal or cancerous.

Screening tests are often helpful in detecting cancer at its earliest stages. A screening test is a relatively simple test that should be done regularly. A routine chest X ray is an example of a screening test. Some of the screening tests used for cancer include sigmoidoscopy (pronounced sig-moy-des-ca-pee; inspection of the colon) for colorectal cancer (see colorectal cancer entry), mammography for breast cancer, and a pap smear for cervical cancer.

Genetic testing is a relatively new form of screening that holds great promise. It can help doctors decide when people may be at risk for certain kinds of cancer because of their genetic makeup.

A TEAM EFFORT

Cancer treatment often requires the work of a team of doctors. At the head of the team is often an oncologist (pronounced on-KOLL-o-jist), a doctor who specializes in cancer care. Other doctors who may work with the oncologist include the following:

  • Radiation oncologists, who specialize in the use of radiation to treat cancer.
  • Gynecologist-oncologists who specialize in treatment of women with cancer of the reproductive organs.
  • Pediatric-oncologists who specialize in the treatment of children with cancer.
  • Radiologists, who use techniques such as X rays, ultrasound, and computed tomography (CT) scans to diagnose cancer.
  • Hematologists, who study blood disorders.
  • Pathologists, who analyze and identify the abnormal tissues that are present in tumors.

TREATMENT


Cancer treatment has two goals. First, as much of the original tumor as possible should be removed. Second, the tumor should be prevented from recurring or spreading to other parts of the body. One decision that often has to be made concerns the side effects of cancer treatments. Most cancer treatments are designed to kill cancer cells, but those treatments can also kill healthy cells. A patient undergoing cancer treatment can, therefore, become very ill from the treatments themselves.

In such cases, patients sometimes choose not to make use of treatments that try to cure the cancer. Instead, they are given other kinds of treatments designed to relieve their symptoms and make them more comfortable.

Many forms of cancer treatment are available. The form used with any one patient depends on many factors, including the patient's age, sex, general health, personal preferences, type and location of the cancer, and extent to which it has already metastasized (spread to other parts of the body, pronounced muh-TASS-tuh-sized). The major types of cancer treatment are surgery, radiation, chemotherapy, immunotherapy, hormone therapy, and bone marrow transplantation.

Surgery

Surgery involves the removal of a visible tumor and is the most common form of cancer treatment. Surgery is most effective when the tumor is small and confined to one area of the body. Surgery can be used for many purposes:

  • Treatment. When a tumor is removed surgically, a small amount of surrounding tissue is also removed. This ensures that no cancer cells are left in the area. Since cancer cells are often spread by means of the lymphatic system, nearby lymph nodes may also be removed.
  • Cytoreduction. In some cases, it may be impossible to completely remove all the cancer cells by surgery. Cytoreduction ("cell reduction"; pronounced SITE-o-ree-duk-shun) involves the removal of as much cancerous tissue as possible. Any remaining abnormal tissue is then treated with radiation, chemotherapy, or both.
  • Palliation. Tumors are sometimes so large that they cannot be removed completely by surgery. In such cases, palliative surgery is used to take out as much of the tumor as possible. This procedure often helps to relieve the symptoms of cancer even if it does not cure the disease itself. For example, a large tumor in the abdomen may press on and block a part of the intestine. The patient may be unable to digest food and feel constant pain and discomfort. Even if the whole tumor cannot be removed, some part of it can probably be taken out. The digestive system can then function normally again.
  • Prevention. Preventive surgery may be used even if no tumors exist. The presence of abnormal tissue may suggest that tumors could eventually form. To avoid that possibility, the tissue can be removed. Preventive surgery is often used, for example, to prevent ulcerative colitis (see ulcerative colitis entry). About 40 percent of the people with this form of cancer die from the disease. People with the disease may choose to have their colons removed rather than risk dying of ulcerative colitis.
  • Diagnosis. Whenever possible, biopsies are conducted with a needle. The needle is used to take out a small piece of tissue for study. Sometimes, a needle biopsy cannot be used. In those cases, surgery may be necessary to get the tissue needed for study.

Radiation

Radiation kills cancer cells. It can be used alone when a tumor cannot be removed surgically. More often, radiation is used in combination with surgery and chemotherapy. Radiation can be performed from either the outside or the inside of the body. An example of outside radiation is the use of X rays to treat a tumor. Inside radiation can be carried out by inserting pellets or liquids in a patient's body. Radiation given off by the pellets or liquid attacks and kills cancer cells.

Chemotherapy

Chemotherapy is the use of chemicals or drugs to kill cancer cells. It is used to destroy cells that have spread from the original tumor and are circulating in the body. The drugs used for chemotherapy can be given orally (by mouth) or by injection. They are used alone or in combination with surgery and radiation.

Chemotherapy is sometimes used before surgery or radiation because drugs are often able to kill cancer cells and reduce the size of a tumor. Surgery and radiation are likely to be more effective when used on smaller tumors. More often, chemotherapy is used after surgery or radiation treatments. In such cases, drugs may be able to destroy cancer cells remaining in the body after the initial treatment.

Immunotherapy

Immunotherapy is a relatively new form of cancer treatment. Its goal is to kill cancer cells by using chemicals that occur naturally in the body. Chemicals known as interferons are an example. Interferon can be given to a cancer patient to stimulate his or her own immune system to fight cancer more effectively.

Research is also being done to develop a cancer vaccine. A cancer vaccine is different from other kinds of vaccines. It is not being designed to prevent cancer. Instead, it will be given to patients who already have the disease. It is intended to help the patient's immune system fight cancer cells.

Hormone Treatment

Some forms of cancer grow faster when certain hormones are present. Examples of such cancers include cancer of the breast, prostate, and uterus. Hormone therapy involves the use of drugs that reduce the amount of hormones produced and their ability to cause changes in the body. These drugs can slow down the rate at which hormone-related cancers develop, extending the patient's life by months or years.

Bone Marrow Transplantation

Bone marrow is tissue found in the center of bones. It produces cells that develop into new blood cells. Radiation and chemotherapy often destroy bone marrow and the patient's body is no longer able to produce the amount of blood it needs to stay healthy.

Bone marrow transplantation involves the removal of some bone marrow from one person so that it can be given to another person. For the procedure to be successful, the two people must be closely related or have similar blood characteristics. Bone marrow transplantation can be important with patients who require very aggressive (serious) forms of treatment that are likely to destroy their own bone marrow.

Alternative Treatment

Many alternative forms of cancer treatment are available, however, patients should always seek the advice of trained health practitioners before trying alternative treatments. Treatment methods from other cultures can sometimes be effective in treating the symptoms of cancer or the side effects of radiation or chemotherapy. Two examples are acupuncture (a Chinese therapy technique where fine needles puncture the body) and Chinese herbal medicines. Body massage can help to ease muscle tension and reduce side effects such as nausea and vomiting.

Experts now believe that certain kinds of food, such as fruits, vegetables, and grains, can help protect against various forms of cancer. For example, a diet rich in fiber, which includes fruits and vegetables, seems to reduce the risk of colon cancer. Exercise and a diet low in fat can help control weight and reduce the risk of breast and colon cancers.

Scientists are not sure what is in foods that prevents cancer. Vitamins A, C, and E and the compound known as beta-carotene are likely prospects. So are two groups of compounds known as the isothiocyanates (pronounced I-so-THI-o-si-uh-nates) and the dithiolthiones (pronounced di-THI-ul-THI-ownz). These compounds are found in broccoli, cauliflower, cabbage, and carrots.

Some drugs used for cancer treatment may also help prevent the disease. Tamoxifen (pronounced tuh-MOK-sih-fen, trade name Nolvadex) is an example. Research is now being conducted to determine its effectiveness in preventing breast cancer. Compounds known as retinoids, obtained from vitamin A, are also being tested for use against head and neck cancers. The mineral selenium may also hold some promise for the prevention of some forms of cancer.

PROGNOSIS


"Lifetime risk" is the term used by cancer researchers to estimate the chance that a person will develop or die from cancer. In the United States, men have a 1 in 2 lifetime risk of developing cancer. For women, the risk is 1 in 3. African Americans have a higher lifetime risk than whites; they are also 30 percent more likely to die of cancer.

Most cancers can be cured if they are discovered and treated at an early stage. Prognosis depends on a number of factors, including the type of cancer, the stage at which it was detected, and how far it has already progressed. Personal factors, such as age, general health status, and treatment effectiveness also determine prognosis.

PREVENTION


Experts believe that the risk of getting cancer can be reduced by following some simple guidelines:

  • Eat plenty of vegetables and fruits.
  • Exercise vigorously for at least twenty minutes each day.
  • Avoid excessive weight gain.
  • Avoid tobacco, including secondhand smoke.
  • Decrease or avoid consumption of animal fats and red meat.
  • Avoid excessive amounts of alcohol.
  • Avoid overexposure to sunlight.
  • Avoid risky sexual practices.
  • Avoid known carcinogens in the environment and workplace.

See also: Breast cancer, colorectal cancer, Hodgkin's disease, lung cancer, prostate cancer, and skin cancer.

FOR MORE INFORMATION


Books

Buckman, Robert. What You Really Need to Know about Cancer: A Comprehensive Guide for Patients and Their Families. Baltimore: Johns Hopkins University Press, 1997.

Dollinger, Malin. Everyone's Guide to Cancer Therapy. Toronto: Somerville House Publishing, 1994.

Morra, Marion E. Choices. New York: Avon Books, 1994.

Murphy, Gerald P. Informed Decisions: The Complete Book of Cancer Diagnosis, Treatment and Recovery. Atlanta, GA: American Cancer Society, 1997.

Periodicals

"What You Need to Know about Cancer." Scientific American (September 1996).

Organizations

American Cancer Society. 1599 Clifton Road NE, Atlanta, GA 30329. (800) 2272345. http://www.cancer.org.

Cancer Care, Inc. 1180 Avenue of the Americas. New York, NY 10036. (800) 813HOPE. http://www.cancercareinc.org.

Cancer Research Institute. 681 Fifth Avenue, New York, NY 10022. (800) 9922623. http://www.cancerresearch.org.

National Cancer Institute. 31 Center Drive, Bethesda, MD 208922580. (800) 4CANCER. http://www.nci.nih.gov.

National Coalition for Cancer Survivorship. 1010 Wayne Avenue, 5th Floor, Silver Springs, MD 20910. (301) 6508868.

Web sites

Oncolink. [Online] University of Pennsylvania Cancer Center. http://cancer.med.upenn.edu. (accessed on October 13, 1999).

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Cancer (in astronomy)

Cancer [Lat.,=the crab], in astronomy, constellation lying on the ecliptic (the sun's apparent path through the heavens) between Gemini and Leo; it is a constellation of the zodiac. It contains the star cluster Praesepe, but no bright stars. The tropic of Cancer takes its name from this constellation, in which the summer solstice was located about 2,000 years ago. Now, because of the precession of the equinoxes, the summer solstice has moved westward into the constellation Gemini. Cancer reaches its highest point in the evening sky in March.

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cancer (in medicine)

cancer, in medicine, common term for neoplasms, or tumors, that are malignant. Like benign tumors, malignant tumors do not respond to body mechanisms that limit cell growth. Unlike benign tumors, malignant tumors consist of undifferentiated, or unspecialized, cells that show an atypical cell structure and do not function like the normal cells from the organ from which they derive. Cancer cells, unlike normal cells, lack contact inhibition; cancer cells growing in laboratory tissue culture do not stop growing when they touch each other on a glass or other solid surface but grow in masses several layers deep.

Loss of contact inhibition accounts for two other characteristics of cancer cells: invasiveness of surrounding tissues, and metastasis, or spreading via the lymph system or blood to other tissues and organs. Whereas normal cells have a limited lifespan controlled by the telomere gene, which signals the end of the cell line, cancer cells contain telomerase, an enzyme that alters the telomere gene and allows the cell to continue to divide. Cancer tissue, growing without limits, competes with normal tissue for nutrients, eventually killing normal cells by nutritional deprivation. Cancerous tissue can also cause secondary effects, in which the expanding malignant growth puts pressure on surrounding tissue or organs or the cancer cells metastasize and invade other organs.

Virtually all organs and tissues are susceptible to cancer. Cancers are usually named for their site of origin. Cancer cells that spread to other organs are similar to those of the original tumor, therefore these secondary (metastatic) cancers are still named for their primary site even though they may have invaded a different organ. For example, lung cancer that has spread to the brain is called metastatic lung cancer, rather than brain cancer. Carcinoma in situ refers to a cancer that has not spread. (See neoplasm for more on cancer nomenclature.)

Cancer is the second leading cause of death in the United States. Lung cancer is the leading cause of cancer death in adults; leukemia is the most common cancer in children. Other common types of cancer include breast cancer (in women), prostate cancer (in men), and colon cancer (see also Hodgkin's disease). The incidence of particular cancers varies around the world and sometimes according to ethnic group. For instance, African Americans have comparatively higher cancer rates and cancer mortality rates. It is unclear whether this is due to differences in exposure or to biological susceptibility. The number of diagnosed cases of cancer rose steadily in the United States for decades, but in 1998 it was announced that the number of new cases had begun to decline.

Causes of Cancer

Cancer results from mutations of certain genes that allow the cells to begin their uncontrolled growth. These mutations are either inherited or acquired. Acquired mutations are caused by repeated insults from triggers (e.g., cigarette smoke or ultraviolet rays) referred to as carcinogens. There is usually a latency period of years or decades between exposure to a carcinogen and the appearance of cancer. This, combined with the individual nature of susceptibility to cancer, makes it very difficult to establish a cause for many cancers.

The most significant avoidable carcinogens are the chemical components of tobacco smoke (see smoking). Dietary components, like excessive consumption of alcohol or of foods high in fat and low in fiber rather than fruits and vegetables that contain antioxidants and necessary micronutrients, have also been linked with various cancers. Some cancers may be triggered by hormone imbalances. For example, some daughters of mothers who had been given DES (diethylstilbestrol) during pregnancy to prevent miscarriage developed vaginal adenocarcinomas as young women. Aflatoxins are natural mold byproducts that can cause cancer of the liver.

Certain carcinogens present occupational hazards. For example, in the asbestos industry, workers have a high probability of developing lung and colon cancer or a particularly virulent cancer of the mesothelium (the lining of the chest and abdomen). Benzene and vinyl chloride are other known industrial carcinogens.

X rays and radioactive elements are also carcinogenic; the high incidence of leukemia and other cancers in Japanese survivors of the atomic bombing of Hiroshima and Nagasaki and the increased incidence of thyroid cancer after the Chernobyl nuclear disaster give evidence of this. Exposure to the ultraviolet radiation of sunlight is the leading cause of skin cancer.

Many other substances have been identified as carcinogenic to a greater or lesser extent, including chemicals in pesticides that leave residues on foods. The Delaney clause, an amendment (1958) to the U.S. Food, Drug, and Cosmetic Act that prohibits even minuscule amounts of carcinogens in the food supply, has provided the impetus for the investigation of many such chemicals but has also been a source of controversy between industry and environmentalists.

In the early 20th cent., the American virologist Peyton Rous showed that certain sarcomas affecting fowl could be transmitted by injection of an agent invisible under the microscope and later indentified as an RNA-containing virus. Other research uncovered oncogenic, or tumor-causing, viruses, first in experimental animals and then in humans. The Epstein-Barr virus, a member of the herpesvirus group, has been linked with a number of human cancers, including the lymphomas that often occur in immunosuppressed people, such as people with AIDS. Several human papillomaviruses (HPV) have also been shown to initiate cancers. For example, some types of HPV cause genital warts known as condylomata acuminata, which can lead to invasive cancer of the cervix, vulva, vagina, or penis, and another human papillomavirus has been associated with some forms of Kaposi's sarcoma. In addition, hepatitis B has been shown to increase the risk of liver cancer. Bacteria have also been associated with cancer. For example, the Helicobacter pylori bacterium that causes many ulcers is also associated with an increased risk of stomach cancer.

Cancer Susceptibility

Risk to humans from carcinogens depends upon the dose and a person's biologic susceptibility. Factors influencing a person's biological susceptibility to cancer include age, sex, immune status, nutritional status, genetics, and ethnicity. Only 5% of all cancers in the United States are thought to be explained by inherited genetic mutations. Known genes associated with hereditary cancer include the aberrant BRCA1 and BRCA2 genes that increase breast cancer risk and the HNPCC gene that is linked with colon cancer. In hereditary forms, it is often the normal gene of the allele that is injured or destroyed, leaving the abnormal inherited gene in control. Nonhereditary cancers sometimes involve the same gene mutations that hereditary forms have.

Tumor Development

Most bodily insults by carcinogens come to nothing because DNA has built-in repair mechanisms, but repeated insults can eventually result in mutations or altered gene expression in key genes called oncogenes and tumor-suppressor genes. Oncogenes produce growth factors, substances that signal a cell to grow and divide into daughter cells; tumor-suppressor genes (such as the p16, p53, and BRCA1 genes) normally produce a negative growth factor that tells a cell when to stop dividing. The abnormally inactivated tumor-suppressor gene or the abnormally activated oncogene is inherited by each of the cell's daughter cells, and a tumor develops. In many cases tumors remain small and in one place (in situ) for years, but some develop their own blood vessels (a process known as angiogenesis) and begin to grow and spread.

Symptoms

The classic symptoms of cancer are rapid weight loss; a change in a wart or mole; a sore that does not heal; difficulty swallowing; chronic hoarseness, blood in phlegm, urine, or stool (a consequence of angiogenesis); chronic abdominal pain; a change in size or shape of the testes; a change in bowel habits; a lump in the breast; and unusual vaginal bleeding. Many of these and other symptoms are often nonspecific, e.g., weakness, loss of appetite, and weight loss, and thus are not obvious in the early stages. Sometimes the side effects of tumor growth are more severe than the actual effects of the malignancy; for example, some tumors secrete materials such as serotonin and histamine that can cause drastic vascular changes. Conversely, cancers that destroy tissue may also have serious effects, e.g., malignant destruction of bone tissue may raise the blood level of calcium.

Prevention and Detection

As more has been learned about cancer, emphasis on prevention and early detection has increased. Cessation of smoking and other tobacco use is the most important controllable means of prevention; smoking causes about 30% of the cancer deaths in the United States. A diet low in fat and high in fiber, including a variety of fruits and vegetables (especially those high in antioxidants), is also recommended. Effective protection against the rays of the sun is recommended to avoid skin cancer. Another preventive approach is vaccination against cancer-causing viruses, such as the hepatitis B virus.

Cancers caught early, before metastasis, have the best cure rates. A number of screening tools are now available to allow early detection and treatment. Among these are monthly breast self-examinations and regular mammography and Pap tests for women, regular self-examination of the testes for young men, and, for older men, regular examination of the prostate gland with blood tests for prostate-specific antigen (PSA) tumor marker (a substance in the body that heralds an increased cancer risk). Colonoscopy plus physical examination and laboratory tests for carcinoembryonic antigen (CEA) are recommended for detection of colon cancer. Self-examination of the skin is important for the early detection of skin cancers. Suspicion of a tumor may be confirmed by X-ray study, endoscopy (see endoscope), blood tests for various tumor markers, and biopsy from which the cells are examined by a pathologist for malignancy.

Treatment

Developments in the treatment of cancer have led to greatly improved survival and quality of life for cancer patients in the past three decades. Traditionally, cancer has been treated by surgery, chemotherapy, and radiation therapy. In recent years immunotherapy has been added to that list. New drugs and techniques are constantly being researched and developed, such as antiangiogenic agents (e.g., angiostatin and endostatin), genetically engineered monoclonal antibodies, retinoid agents, and therapeutic vaccines (agents that stimulate the immune system to attack cancerous cells).

For most kinds of cancer, surgery remains the primary treatment. It is most effective if the cancer is caught while still localized. Some cancers that spread to the lymph system are sometimes treated by extensive surgical removal of tissue, but the trend is toward more conservative procedures (see mastectomy). Cryosurgery, the use of extreme cold, and electrodessication, the use of extreme heat, are also being used to kill cancerous tissue and the surrounding blood supply. If the cancer has metastasized, surgery is often replaced by or followed by radiation therapy (which is a localized therapy) and chemotherapy (which is a system-wide therapy).

For some cancers, radiation therapy—either from an external beam or from implanted radioactive pellets—is the primary treatment. The usual forms are X rays and gamma rays. Use of radioactive elements specific for particular target organs, such as radioactive iodine specific for the thyroid gland, is effective in treating malignancies of those organs.

Cytotoxic chemotherapy is used as a primary treatment for some cancers, such as lymphomas and leukemias or as an addition to surgery or radiation therapy. Cytotoxic drugs (drugs that are toxic to cells) are aimed at rapidly proliferating cells and interfere with nucleic acid and protein synthesis in the cancer cell, but they are often toxic to normal rapidly proliferating cells, such as bone marrow and hair cells. Often a combination of cytotoxic drugs is used. Drugs that reduce side effects may be added to the treatment, such as antinausea agents.

Hormonal chemotherapy is based upon the fact that the growth of some malignant tumors (specifically those of the reproductive organs) is influenced by reproductive hormones. Tamoxifen is a naturally occurring estrogen inhibitor used to prevent breast cancer recurrences. Flutamide is sometimes used in prostate cancer to inhibit androgen uptake. Sex-hormone related drugs such as DES and tamoxifen, which may be carcinogenic under some conditions, have proven to be protective under others.

More specifically targeted drug therapies have begun to be explored as a better understanding of the molecular biology of individual cancers has been developed. Such drugs are designed to kill only cancer cells while having fewer side effects. Gleevec (STI-571), which is used to treat chronic myelogenous leukemia and some other cancers, inhibits certain kinase receptors that become hyperactive in cancer cells, resulting in the cells' rapid reproduction.

Immunotherapy (sometimes called biological therapy) uses substances that help the body mobilize its immune defenses. Some attack the tumor itself, while others bolster the body's ability to withstand conventional chemotherapy treatment. Other new or experimental therapies include drugs that inhibit angiogenesis and photodynamic therapy, in which a patient is given a drug to make the tumor light-sensitive, after which the tumor is exposed to bright laser light. The best choice of treatment will increasingly be influenced by the growing field of molecular pathology, in which characteristics of individual cancers (e.g., virulence or resistance to a particular treatment) can be revealed by analysis of their genetic characteristics rather than by the microscope.

Besides treatment of the cancer itself, progress has been made in the management of the chronic pain that often accompanies cancer and in the education of patients and physicians in such techniques as biofeedback, acupuncture, and meditation and the appropriate use of narcotics and other medications. Because of improvements in early detection and treatment, many more people are now living with cancer. Over half of all people with cancer now survive for five or more years.

Bibliography

See C. N. Coleman, Understanding Cancer (2d ed. 2006); A. H. Ko et al., Everyone's Guide to Cancer Therapy (rev 5th ed. 2008); S. Mukherjee, The Emperor of All Maladies (2010); G. Johnson, The Cancer Chronicles (2013). See also publications of the National Cancer Institute and the American Cancer Society.

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Cancer

Cancer

An Ancient Affliction

What is Cancer?

How Does Cancer Begin?

How Does Cancer Spread?

What Causes Cancer?

How Do People Know They Have Cancer?

How is Cancer Diagnosed and Treated?

Will There Ever Be a Cure for All Cancers?

Can Cancer Be Prevented?

Living with Cancer

Resources

Cancer is a group of many related diseases in which abnormal celh grow out of control and spread.

KEYWORDS

for searching the Internet and other reference sources

Carcinogens

Carcinoma

Metastasis

Oncogenes

Oncology

Osteosarcoma

An Ancient Affliction

The disease we call cancer has been around as long as we have. Evidence of cancerous growths, or tumors, has been found among fossilized bones and in human mummies dating from ancient Egypt. The ancient Greek physician Hippocrates (hi-POK-ra-tees) was the first to use the word carcinoma (kar-si-NO-ma) to describe various kinds of tumors. Hippocrates noted that parts sticking out from some tumors looked like the limbs of a crab. The word cancer comes from the Latin word for crab. In 1913, only one in nine people had a chance of being alive five years after a diagnosis of cancer. Today, depending on the cancer, more than 50 percent of people with cancer will survive the disease. For many types of cancer, early detection and treatment result in a normal lifespan.

What is Cancer?

In all forms of cancer, cells grow out of control and may spread. In the United States, half of all men and one third of all women will develop one type of cancer or another during their lifetime. Almost everyone knows someone who has had cancer, and it is natural for children to worry that they might get it. But cancer in children is very rare. Some cancers are more common than others. The cancers that adults get most frequently are cancers of the skin, lungs, and colon and rectum. Breast cancer is a common cancer among women. Childhood cancers include leukemia (loo-KEE-mee-ya), lymphoma (lim-FO-ma), brain cancer, and osteosarcoma (os-tee-o-sar-KOME-a) (bone cancer). Cancer is sometimes referred to as a malignancy or a malignant tumor.

How Does Cancer Begin?

With more than 100 types of cancer, the disease can arise in almost any part of the body. Each cancer is different, but they all start the same way. A healthy body is home to more than 10 trillion cells (at least 100 times as many stars as there are in the entire Milky Way galaxy). Just as neighbors cooperate to maintain an orderly community, cells usually grow, divide, and die in a controlled fashion. But cancer cells are renegades, bad neighbors in the cellular community. Cancer begins when a single cell starts to multiply inappropriately.

What turns a good cell bad? The operating instructions for every-thing that our cells do are contained in the genes, packets of information that we inherit from our parents. Genes are made of a substance called DNA. The function of genes is to make proteins, the building blocks of life that carry out the work of the genes. When a gene inside a cell is switched on, the cell starts producing the required protein. Sometimes genes become altered, and we say they have mutated. Mutations in a gene can affect how the gene works; for example, a mutated gene might produce too much of a protein, or perhaps none at all.

Life proceeds by cell growth and division, and this process is directed by a collection of genes whose proteins work like traffic cops to encourage growth, or to halt it. When these genes become mutated, the proteins they make may erroneously tell cells to continue growing, like a traffic light stuck on green. The mutated genes are called oncogenes. Normal cells with damaged DNA die. But cancer cells with damaged DNA may not.

Many tumors need 30 to 40 years to develop, which explains why children rarely get cancer. But it is possible for a person to inherit a mutant cancer-causing gene. When that happens, people sometimes get cancer at an earlier age.

Genes can undergo mutations as a result of cancer-causing substances called carcinogens (kar-SIN-o-jens) in the environment as well as chemicals in our own cells. Another source of mutations is copying mistakes that occur when DNA is replicated during cell division. Cells normally have repair systems to correct such errors. But when the repair system slips up, the damage becomes a permanent part of that cell and of the cells descendants. If a person has a faulty repair system, mutations in the genes will build up rapidly, making the cells more likely to become cancerous. Faulty repair plays a role in certain kinds of colon, skin, and breast cancers.

The bodys defenses are impressive, and it is difficult for cancer to get started. But imagine that a renegade cell has managed to evade every one of the cells checkpoints and has formed a tumor. Now what? To grow larger than a millimeter (about the size of a pinhead), a tumor needs a blood supply, so it sends out a chemical signal to cause blood vessels to grow.

The U.S. and the World

  • The U.S. National Cancer Institute says that 8.4 million peopleabout 3 percent of the population in 1999 have a history of cancer. The death rates for most major cancers have declined since the 1970s, because of earlier detection and better treatment. About 2 million women are breast cancer survivors and 1 million men are prostate cancer survivors.
  • Still, cancers killed 539,577 Americans in 1997. This accounted for 23 percent of all deaths thatyear, making cancer the second leading cause of death after heart disease. Lung cancer caused the majority of the cancer deaths (29 percent), followed by stomach cancer (23.5 percent).
  • Each year, about 150 of every 1 million Americans under age 20 will be diagnosed with cancer. But the chances for surviving at least five years with cancer increased for children between the early 1980s (64 percent survived) and the early 1990s (74 percent). That is better than the five-year survival rate for all cancers, which was about 60 percent in the 1990s.
  • Worldwide, cancer caused an estimated 7.2 million deaths in 1998, which accounts for 13 percent of all deaths. Lung cancer was the leading cause, accounting for 17 percent of all cancer deaths.
  • Cancer deaths worldwide have increased slightly since 1993, when about 6 million people died of cancer. That represented 12 percent of all deaths worldwide in 1993.
  • About 81 million people worldwide were living with cancer in 1998. The World Health Organization (WHO) expects the prevalence of cancer cases to increase in the first 25 years of the twenty-first century in developing nations.
  • The World Health Organization estimates about 15 million new cases of cancer will develop in the year 2020, compared with 10 million new cases a year in the late 1990s. Reasons include increased smoking in developing nations, unhealthy diets, and more people living to old age, when cancer risk is higher.
  • The World Health Organization estimated in the mid-1990s that 15 percent of all cancers worldwide could be prevented by controlling infections. For example, more than 400,000 cases of liver cancer were tied to infection with hepatitis in the mid-1990s. Parasites in food also can lead to stomach cancers.
  • Other trends to watch between 1999 and 2025, according to WHO: Lung cancer and colorectal cancer cases and deaths will increase, largely because of increased smoking and unhealthy diet. Women will die in higher numbers from lung cancer in almost all industrialized countries. Stomach cancer is expected to become less common, because of improved food conservation, changes in diet, and declining infection. Cervical cancer is predicted to decrease in industrialized countries because of increased screening and it might decrease in the developed world if a vaccine is developed. And, finally, liver cancer will decrease as the rates of immunization and screenings for hepatitis increase.

How Does Cancer Spread?

Normal cells do not wander. But some types of cancer cells do, which is what makes them so dangerous. The process is called metastasis (meh-TAS-ta-sis). Although it may be fairly easy to remove the main, or primary, tumor in cancer, metastasis cannot usually be cured by surgery alone.

In order for cancer to spread to other parts of the body, it must detach from its original location, invade a blood vessel, travel through the circulation to a far-away site, and set up a new cellular colony. At every one of these steps, it must outsmart the many controls the body has to keep cells where they belong.

New techniques show that abnormal cells from a tumor often are circulating even when doctors can find no evidence of spread. We call this undetectable spread micrometastasis (MY-kro-meh-TAS-ta-sis). Once a cancer cell has found a new home, it must reverse all the steps it took in liberating itself. It has to attach to the inner lining of a blood vessel, cross through it, invade the tissue beyond, and multiply. Probably fewer than 1 in 1,000,000 of the cancer cells that make it into the bloodstream survive to take up residence elsewhere.

Cancer cells prefer small blood vessels, and the first small blood vessels a freed cancer cell encounters are those of the lungs. So the lungs are the most common site of spread for cancer, followed by the liver. Much of how cancer spreads is still a mystery. Some tissuesfor example, cartilage and brain tissueseem more resistant to cancer. And some animals almost never have cancer.

What Causes Cancer?

A risk factor is anything that increases a persons chance of getting a disease. But having a risk factor does not mean that a person will get the disease for sure. People get cancer as a result of a complex set of interactions between their genes and the environment. We are just beginning to understand these reactions.

Tobacco

Tobacco is a lethal cancer-causing substance. It causes 30 percent of total cancer deaths every year in the United States, affecting the lungs and other organs of the body. Almost all lung cancer is the result of smoking. The younger a person starts to smoke, the greater the risk of cancer.

Food and alcohol

In the United States, diet has been associated with certain cancers, particularly diets containing high amounts of animal (saturated) fat and red meat. After years of studies, coffee has not been proved to cause cancer, nor have artificial sweeteners. Eating insufficient quantities of fruits and vegetables appears to contribute to cancer, for reasons no one understands. It may be that fruits and vegetables help to block the cancer-causing effects of our own bodies. Drinking large amounts of alcohol increases the risk of cancer of the upper respiratory and digestive tracts, and alcoholic liver disease can lead to liver cancer. Even moderate drinking may contribute to breast and colon and rectal cancer.

Radiation

Some forms of radiation cause cancer. But most cancer deaths from radiation are caused by natural sources such as the suns ultraviolet rays. For example, sunburns during childhood are a key factor in causing a kind of skin cancer called melanoma (mel-a-NO-ma). But electric power lines, household appliances, and cellular telephones have so far not been proven to cause cancer. Radiation from nuclear materials and reactions does cause cancer, but most people are not exposed to levels high enough to harm them.

Chemicals

In the past, some people who worked with certain chemical substances such as asbestos (az-BES-tos) and benzene (BEN-zeen) had a greater chance of getting lung cancers and other kinds of cancers. But strict government regulations have limited the use of these substances and sharply reduced the numbers of these cancers.

How Do People Know They Have Cancer?

Many symptoms of cancer such as weight loss, fever, fatigue, and various kinds of lumps could also be caused by other diseases. Some cancers may cause no symptoms until they have spread. Based on the most commonly occurring cancers, the American Cancer Society publishes a list

American Cancer Society

The American Society for the Control of Cancer (ASCC) was founded in 1911 to educate the public about the dangers of cancer. In 1943, Mary Lasker, the wife of an advertising tycoon who himself would die of cancer, walked into the office of Clarence C. Little, the managing director of the ASCC, and asked him how much money the society was spending on research. Nothing, Little told her.

Lasker immediately began a campaign to raise funds for the renamed American Cancer Society (ACS). A granting program was begun in 1946. By 1948, the ACS had raised around $14 million. Today, the ACS has chartered divisions throughout the country and over 3,400 local units. ACS is the largest source of private, not-for-profit research funds in the United States, second only to the federal government in total dollars spent.

of seven warning signs of cancer. These symptoms do not mean that a person has cancer, but if they occur, a person should see the doctor:

Change in bowel or bladder habits (for instance diarrhea that does not go away or pain on urination)

A sore anywhere on the skin that does not heal

Unusual bleeding or discharge from the nose, mouth, skin, nipple, or vagina

A thickening or lump in the breast or elsewhere

Indigestion or difficulty in swallowing

Obvious changes in a wart or mole

Nagging cough, particularly if these symptoms occur in a cigarette smoker.

Eating for Health

The American Cancer Society recommends the following general nutritional guidelines to help people stay healthy:

  • Choosing most foods from plant sources such as vegetables, fruits, and grains
  • Limiting intake of high-fat foods, especially from animal sources
  • Staying physically active
  • Maintaining a healthy weight
  • Limiting consumption of alcoholic beverages

How is Cancer Diagnosed and Treated?

Diagnosis

Diagnosing cancer involves removing some tissue for evaluation. This procedure is called a biopsy (BY-op-see). Once the diagnosis is made, a treatment plan is put together. To do that, it is necessary to determine how widespread the disease is, and how serious. Staging the disease means assigning letters and numbers to it as a way of indicating whether it has spread and how far. There are several systems for staging, depending on the type of cancer. Generally speaking, the smaller the tumor, the more curable it is, although some cancer can be unpredictable. The outlook for some cancers, for example, leukemia and lymphoma, is judged according to other criteria. Cancer is classified by the part of the body in which it began and by how it looks under a microscope.

Treatment

Treatment for cancer includes surgery, radiation, and chemotherapy (kee-mo-THER-a-pee), alone or together. Because different types of cancer vary in how fast they grow, where they spread, and how they respond to treatment, treatment is specifically tailored to the kind of cancer a person has.

Surgery is the oldest form of treatment for cancer, and it still offers the greatest chance of cure for many kinds of cancer. About 60 percent of patients with cancer will have some type of surgery.

Radiation therapy uses high-energy particles or waves to damage cancer cells that surgery cannot catch because they are too small.

Chemotherapy uses anticancer drugs to treat cancer. Chemotherapy drugs are given through a vein (also called an intravenous or IV line) or by mouth as pills. These drugs enter the bloodstream and reach places in the body that surgery and radiation cannot reach. Chemotherapy is often given for cancer that has spread.

Another kind of therapy interferes with the production of substances in the blood called hormones (HOR-mones) that stimulate certain kinds of cells (for example, cells in the breast) to grow.

Will There Ever Be a Cure for All Cancers?

Every day researchers learn a little more about how the cell works, and many of these discoveries are being applied to cancer research. Many current therapies have side effects because they kill healthy cells as well as cancer cells or affect the function of other parts of the body. So one area of research scientists are working on is therapies that will kill only cancer cells and that will leave healthy cells alone. Another area of research is investigating ways of helping the bodys own defense system to fight cancer. Scientists are also exploring substances in food or drugs that will prevent cancer from developing in the first place.

Clinical Trials and New Cancer Treatments

Studies of new or experimental treatments in patients are known as clinical trials. Research in cancer could not move forward without them because drugs may work very differently in people than in the animals in which the drugs first proved successful.

Clinical trials seek to answer such questions as:

  • Does this new treatment work?
  • Does it work better than other treatments already available?
  • Do the benefits outweigh the risks, including side effects?

Although there are risks to new treatments, clinical trials are done only when there is some reason to believe that the treatment will be of value to the patient.

Participating in a clinical trial is completely up to the patient. The doctor may suggest it, or patients can request information about clinical trials from the U.S. National Cancer Institute.

Can Cancer Be Prevented?

In the United States, 1.2 million people are diagnosed with cancer each year. There is no way to prevent cancers children get. But many cancers that occur in adults could be prevented by changes in a persons lifestyle. For example, cancers caused by cigarette smoking and drinking a lot of alcohol could be prevented completely. Limiting certain kinds of foods, such as red meats and animal fats, and eating lots of fruits and legumes (such as peas and lentils) may help reduce the risk of getting many cancers. Physical activity helps to avoid obesity and may have other protective effects against cancer. Most of the one million skin cancers that are diagnosed each year could be avoided by staying out of the sun.

Regular cancer checks, called screenings, for cancer of the breast, colon, rectum, cervix, prostate, testes, mouth, and skin are an effective way of detecting cancer early enough to be treated successfully. In addition, self-examination for breast and skin cancers also helps to detect tumors at earlier stages. The American Cancer Society estimates that if all Americans participated in regular cancer screenings, survival would be dramatically improved.

Living with Cancer

A cancer diagnosis is usually shocking and frightening. A persons life is suddenly disrupted by surgery, treatment, visits to the doctors, and changing personal relationships. Children with cancer may have to miss school for a time or to give up sports or other activities. A person may feel anger at themselves or others, or at God. Children especially may feel that something they did caused the cancer, especially if it is a brother or sister who is sick. Family, physician, friends and organizations, religious groups and clergy, and self-help groups all may be an important source of support. Each persons way of dealing with cancer is unique. Even with cancers that will cause death, a person may live for many years. And more than 70 percent of children and adolescents with cancer are successfully treated.

Alternative and complementary therapies

Many patients seek out other kinds of therapies during their treatment. Cancer is a frightening word, and some people will do anything, no matter how unlikely to work. A number of alternative treatments are themselves dangerous, and can distract from effective treatment. Some can be costly as well. These therapies generally are of two kinds:

  • Alternative therapies are often promoted in the mass media as cancer cures. Patients should be aware that these therapies have either not been tested for safety and effectiveness, or have been tested and found to be ineffective.
  • Complementary therapies, on the other hand, are used in addition to standard therapy. They may help to relieve symptoms of the disease or side effects of treatment, or they just may make patients feel better. Examples of complementary therapies are meditation to relieve stress and peppermint tea to combat nausea (stomach upset) from chemotherapy.

Patients who are thinking of using alternative or complementary therapies should first discuss it with their health care team.

See also

Bladder Cancer

Brain Tumor

Breast Cancer

Colorectal Cancer

Hepatitis

Kidney Cancer

Leukemia

Lung Cancer

Mouth Cancer

Pancreatic Cancer

Polyps

Prostate Cancer

Stomach Cancer

Skin Cancer

Testicular Cancer

Tumor

Viral Infections

Resources

U.S. National Cancer Institute, Bethesda, MD 20892. The NCI coordinates the governments cancer research program, and provides information about cancer to patients, their families, and the public. Its Cancer Information Service posts a What You Need to Know About Cancer series of fact sheets at its website, and its kidscontents fact sheet When Someone in Your Family Has Cancer can help with resources and referrals. Telephone 800-4-CANCER http://www.nci.nih.gov/wyntk_pubs/index.html http://rex.nci.nih.gov/NCI_Pub_Interface/guide_for_kids/kidscon-tents.html

American Cancer Society (ACS), 1599 Clifton Road NE, Atlanta GA 30329-4251. ACS is a national, not-for-profit society that provides upto-date health information about cancer. Telephone 800-ACS-2345 http://www.cancer.org

KidsHealth.org and the Nemours Foundation publish Childhood Cancer and What is Cancer and What Happens When Kids Get It?, offering practical, straightforward advice for parents and children on the kinds of cancer children get. http://www.KidsHealth.org

University of Pennsylvania Cancer Center. The OncoLink website at the University of Pennsylvania posts information about all aspects of cancer. http://www.cancer.med.upenn.edu

The World Health Organization posts information at its website about cancer and other noncommunicable diseases worldwide. http://www.who.org

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cancer

cancer A wide variety of diseases characterized by uncontrolled growth of tissue. Dietary factors may be involved in the initiation of some forms of cancer, and a high‐fat diet has been especially implicated. There is some evidence that antioxidant nutrients such as carotene, vitamins C and E, and the mineral selenium may be protective. See also carcinogen.

Patients with advanced cancer are frequently malnourished, the condition of cachexia.

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cancer

can·cer / ˈkansər/ • n. the disease caused by an uncontrolled division of abnormal cells in a part of the body. ∎  a malignant growth or tumor resulting from such a division of cells: skin cancers. ∎ fig. a practice or phenomenon perceived to be evil or destructive and hard to contain or eradicate. DERIVATIVES: can·cer·ous / ˈkansərəs/ adj.

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Cancer

Cancer Northern constellation between Gemini and Leo. It contains two open clusters: M44, the Praesepe or Beehive Nebula (NGC 2632), and M67 (NGC 2692). The brightest star is Beta Cancri.

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cancer

cancer Group of diseases featuring the uncontrolled proliferation of cells (tumour formation). Malignant (cancerous) cells spread (metastasize) from their original site to other parts of the body. There are many different cancers. Known causative agents (carcinogens) include smoking, certain industrial chemicals, asbestos dust and radioactivity. Viruses are implicated in the causation of some cancers. Some people have a genetic tendency towards particular types of cancer. Treatments include surgery, chemotherapy with cell-destroying drugs and radiotherapy (or sometimes a combination of all three). Early diagnosis holds out the best chance of successful treatment.

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cancer

cancer zodiacal constellation of the Crab XIV; malignant tumour XVII. — L. cancer crab, creeping ulcer, after Gr. karkínos crab, karkinōma CARCINOMA.

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Cancer

Cancer in astrology, the fourth sign of the zodiac, which the sun enters at the northern summer solstice (about 21 June).

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cancer

canceramasser, gasser, macassar, Makassar, Mombasa, Nasser •relaxer, waxer •salsa •cancer, romancer •piazza • necromancer • madrasa •Kinshasa, Lhasa, passer, Tarrasa, Vaasa •advancer, answer, chancer, dancer, enhancer, lancer, prancer •tazza •addresser, aggressor, assessor, compressor, confessor, contessa, depressor, digresser, dresser, guesser, intercessor, lesser, Odessa, oppressor, possessor, professor, represser, successor, transgressor, Vanessa •Alexa, flexor, vexer •Elsa, Kielce •censer, censor, dispenser, fencer, Mensa, sensor, Spenser •seltzer •Faenza, Henze •indexer • hairdresser • predecessor •microprocessor, processor •acer, bracer, chaser, debaser, embracer, facer, macer, mesa, pacer, placer, racer, spacer, tracer •Ailsa • steeplechaser •greaser, Lisa, Nerissa, piecer, Raisa, releaser •pizza

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Cancer

Cancer


A malignant tumor, cancer comprises a broad spectrum of malignant neoplasms classified as either carcinomas or sarcomas. Carcinomas originate in the epithelial tissues, while sarcomas originate from connective tissues and structures that have their origin in mesodermal tissue. Cancer is an invasive disease that spreads to various parts of the body. It spreads directly to those tissues immediately surrounding the primary site of the cancer and may spread to remote parts of the body through the lymphatic and circulatory systems.

Cancer occurs in most, if not all, multicellular animals. Evidence from fossil records reveal bone cancer in dinosaurs, and sarcomas have been found in the bones of Egyptian mummies. Hippocrates is credited with coining the term carcinoma, the Greek word for crab. Why the word for crab was chosen enjoys much speculation, but may have had to do with the sharp, biting pain and invasive, spreading nature of the disease.

A carcinogen is any substance or agent that produces or induces the development of cancer. Carcinogens are known to affect and initiate metabolic processes at the level of DNA (the information-storing molecules in cells). DNA damage (mutation )is the development of cancer after exposure to a carcinogen. This kind of mutation is actually reversible; our bodies continually experience DNA damage, which is continually being corrected. It is only when promoter cells intervene during cell proliferation that tumors begin to develop. Although several agents can induce cell division, only promoters induce tumor development.

An example of this process would be what happens in an epidermal cell, when its DNA undergoes rapid, irreversible alteration or mutation after exposure to a carcinogen. The cell undergoes proliferation, producing altered progeny, and it is at this point that the cell may proceed on one of two pathways. The cell may undergo interrupted exposure to promoters and experience early reversible precancerous lesions. Or it may experience continuous exposure to the promoters, thereby causing malignant cell changes. During the late phase of promotion, the primary epidermal cell becomes tumorous and begins to invade normal cells; then it begins to spread. It is at this stage that tumors are identified as malignant.

The spread of tumors throughout the body is believed to be governed by several processes. One possible mechanism is direct invasion of contiguous organs. This mechanism is poorly understood, but it involves multiplication, mechanical pressure, release of lytic enzymes, and increased motility of individual tumor cells. A second process is metastasis. This is the spread of cancer cells from a primary site of origin to a distant site, and it is the life-threatening aspect of malignancy. At present there are many procedures available to surgeons for successfully eradicating primary tumors; however, the real challenge in reducing cancer mortality is finding ways to control metastasis.

Clinical manifestations of cancer take on many forms. Usually little or no pain is associated with the early stages of malignant disease, but pain does affect 6080% of those terminally ill with cancer. General mechanisms causing pain associated with cancer include pressure, obstruction, invasion of a sensitive structure, stretching of visceral surfaces, tissue destruction, and inflammation. Abdominal pain is often caused by severe stretching from the tumor invasion of the hollow viscus, as well as tumors that obstruct and distend the bowel. Tumor compression of nerve endings against a firm surface also creates pain. Brain tumors have very little space to grow without compressing blood vessels and nerve endings between the tumor and the skull. Tissue destruction from infection and necrosis can also cause pain. Frequently infection occurs in the oral area, in which a common cause of pain is ulcerative lesions of the mouth and esophagus.

Cancer treatments involve chemotherapy, radiotherapy, surgery, immunotherapy, and combinations of these

Frequency of Cancer-Related Death
Cancer Site Number of Deaths Per Year
Lung 160,100
Colon and rectum 56,500
Breast 43,900
Prostate 39,200
Pancreas 28,900
Lymphoma 26,300
Leukemia 21,600
Brain 17,400
Stomach 13,700
Liver 13,000
Esophagus 11,900
Bladder 12,500
Kidney 11,600
Multiple myeloma 11,300


modalities. Chemotherapy and its efficacy is related to how the drug enters the cell cycle; the design of the therapy is to destroy enough malignant cells so that the body's own immune system can destroy the remaining cells naturally. Smaller tumors with rapid growth rates seem to be most responsive to chemotherapy. Radiation therapy is commonly used to eradicate tumors without excessive damage to surrounding tissues. Radiation therapy attacks the malignant cell at the DNA level, disrupting its ability to reproduce. Surgery is the treatment of choice when it has been determined that the tumor is intact and has not metastasized beyond the limits of surgical excision. Surgery is also indicated for benign tumors that could progress into malignant tumors. Premalignant and in situ tumors of epithelial tissues, such as skin, mouth, and cervix, can be removed.

Chemotherapy and radiation treatments are the most commonly used therapies for cancer. Unfortunately, both methods produce unpleasant side effects; they often suppress the immune system, making it difficult for the body to destroy the remaining cancer even after the treatment has been successful. In this regard, immunotherapy holds great promise as an alternative treatment, because it makes use of the unique properties of the immune system.

Immunotherapies for the treatment of cancer are generally referred to as biological response modifiers (BRMs). BRMs are defined as mammalian gene products, agents, and clinical protocols that affect biologic responses in host-tumor interactions. Immunotherapies have a direct cytotoxic effect on cancer cells, initiation or augmentation of the host's tumor-immune rejection response, and modification of cancer cell susceptibility to the lytic or tumor static effects of the immune system. As with other cancer therapies immunotherapies are not without their own side effects. Most common are flu-like symptoms, skin rashes, and vascular-leak syndrome. At their worst, these symptoms are usually less severe than those of current chemotherapy and radiation treatments.

See also Hazardous material; Hazardous waste; Leukemia; Radiation sickness

[Brian R. Barthel ]


RESOURCES

BOOKS

Aldrich, T., and J. Griffith. Environmental Epidemiology. New York: Van Nostrad Reinhold, 1993.

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Cancer

Cancer

Definition

Cancer is characterized by uncontrolled growth of cells in the body and the ability of these malignant cells to spread (metastasize) to distant sites within the body. If the spread is not controlled, cancer can result in death. Cancer is not just one disease but a group of almost one hundred different types of malignant diseases.

Description

Cancer, by definition, is a disease of the genes. A gene is a small part of DNA, which is the instruction manual of the cell. Genes hold the instructions to make proteins, which carry out many of the body's functions. It is these proteins that allow the human body to carry out all the processes that permit people to breathe, think, move, etc.

Throughout people's lives the cells in their bodies grow, divide, and replace themselves. Many genes produce proteins that are involved in controlling the processes of cell growth and division. An alteration (mutation) to the DNA molecule can disrupt some of the genes on the DNA molecule and produce faulty proteins. This causes a cell to loose restraint on growth. The abnormal cell begins to divide uncontrollably and eventually forms a new growth known as a tumor or neoplasm (medical terms for cancer meaning new growth). In a healthy body the immune system can recognize neoplastic (abnormal) cells and destroy them before they get a chance to divide. Even so, some mutant cells may escape immune detection and survive to develop into cancerous growths.

Tumors are divided into two general categories: benign or malignant. A benign tumor is slow growing and does not spread or invade surrounding tissue. Once it is removed it does not usually recur. A malignant tumor, on the other hand, invades surrounding tissue and can spread to other parts of the body. Malignant tumors can be removed; however, if the cancer cells have spread to the surrounding tissues, the tumor is likely to recur.

A majority of cancers are caused by changes in the cell's DNA that are due to the environment. Environmental factors that are responsible for causing the initial mutation in the DNA are called carcinogens. Internal factors can cause cancer as well. Certain hormones have been shown to have an effect the growth or control of a particular cell line. Hormones are substances made by one organ and passed through the bloodstream to perform a function in another organ.

While there is scientific evidence that both environmental and genetic factors play a role in most cancers, approximately 5-10% of all cancers are classified as hereditary (genetic). This means a faulty gene that leads to a cancer is passed from parent to child. This poses a greater risk for that particular type of cancer in certain descendants of the family. However, having a cancer-causing gene does not necessarily mean that person will automatically get cancer. Rather, it means that person is predisposed to a type of cancer, or more likely to get this cancer when compared to the general population. Cancers known to have a hereditary tendency in some cases include breast cancer, colon cancer, ovarian cancer, skin cancer, and prostate cancer.

Aside from genes, certain inherited physiological traits can contribute to cancers. For example, inheriting fair skin makes a person more likely to develop skin cancer, but only if they also have prolonged exposure to intensive sunlight.

There are many different types of cancers. Some of the most common types include:

  • Carcinomas. These cancers arise in the epithelium (layers of cells in the skin covering the body's surface and lining the internal organs and various glands). About 80% of human cancers fall into this category. Carcinomas can be subdivided into two subtypes: adenocarcinomas, which are cancers that develop in an organ or a gland; and squamous cell carcinomas, cancers that originate in the skin.
  • Melanomas. This form also originates in the skin, usually in the pigment cells (melanocytes), and can quickly metastasize to internal organs.
  • Sarcomas. Cancers of the supporting tissues of the body, such as bone, muscle, cartilage, and fat.
  • Leukemias. Cancers of the blood or blood-forming organs.
  • Lymphomas. Cancer of the lymphatic system, the network of vessels and nodes that acts as a filtration system, distributing nutrients to blood and tissue and preventing bacteria and other foreign substances from entering the bloodstream.
  • Gliomas. Cancers of nerve tissue.

The most common cancers are skin cancer, lung cancer, colon and rectal (colorectal) cancer, breast cancer (in women), and prostate cancer (in men). In addition, cancer of the kidneys, ovaries, uterus, pancreas, bladder, and blood and lymph-node cancer (leukemias and lymphomas) are also included among the 12 major cancers that affect most Americans.

Almost every tissue can give rise to cells that cause cancer and each of these cancers is very different in its symptoms and prognosis. However, there are basic and similar genetic processes that lead to tumor growth in the human body. Genes are responsible for producing proteins that regulate cell growth and division. When these genes do not function properly, the proteins are abnormal and cells can grow uncontrollably. This results in the formation of a tumor. As more genetic mutations (changes) occur in this tumor, it becomes more life-threatening and has a greater chance of spreading to other parts of the body.

Three classes of genes appear to play a role in the development of cancer:

  • Proto-oncogenes encourage and promote the normal growth and division of cells. When they are defective, they become oncogenes. Oncogenes are overactive proto-oncogenes that cause excessive cell multiplication that can lead to tumors.
  • Tumor suppressor genes act as brakes on cell growth. They prevent cells from multiplying uncontrollably. If these genes are defective there is no control over cell growth and tumors can result.
  • DNA repair genes ensure that each strand of DNA is correctly copied during cell division. When these genes do not function properly, the replicated DNA is likely to have errors. This causes defects in other genes and can lead to tumor formation in some cases.

Approximately 5-10% of cancers have a hereditary component. In these cancers a child does not inherit cancer from the parents. Rather, a predisposition to cancer is inherited. For example, a faulty tumor suppressor gene may be inherited. This gene is not able to control cell growth but the corresponding gene inherited from the other parent is still functional. Cell growth is under control. However, as a child grows up, radiation, pollution, or any other environmental factor could change the functional gene, making it defective as well. Now, neither of these tumor suppressor genes are functioning, and it is likely that a tumor will develop. Defects in proto-oncogenes and DNA repair genes can be inherited, as well, leaving a person more vulnerable to cancer than the general population.

Some cancers seem to run in families. In these cancers there is no specific gene responsible for the clustering of cancer in a family. However, a particular type of cancer may be seen more often than in the general population. It is suggested that this is due to a combination of genetic and environmental factors.

Cancer kills one out of every four Americans. As of 2001 it was the second leading cause of death in the United States, surpassed only by heart disease. More than 1.2 million new cases of cancer are diagnosed every year in the United States. The National Cancer Institute estimates that approximately 8.4 million Americans alive in 2001 had a history of cancer. Some of these people were cured while others were still affected with the disease and possibly undergoing treatment.

Anyone is at risk for developing cancer. Since the occurrence of cancer increases as a person ages, most cases are seen in adults middle-aged or older. Nearly 80% of cancers are diagnosed in people 55 years of age and older.

Lifetime risk is the term used to refer to the probability that an individual will develop cancer over the course of his or her lifetime. In the United States men have a one-in-two lifetime risk of developing cancer. For women, the risk is one in three. Overall, African Americans are more likely to develop cancer than Caucasians and are 33% more likely to die of cancer than Caucasians.

The major risk factors for cancer are tobacco, alcohol, diet, sexual and reproductive behavior, infectious agents, family history, occupation, environment, and pollution.

Tobacco

Eighty-to-ninety percent of lung cancer cases occur in smokers. Smoking has also been shown to be a contributory factor in cancers of mouth, pharynx, larynx, esophagus, pancreas, uterine cervix, kidney, and bladder. Smoking accounts for at least 30% of all cancer deaths. Scientists have shown that inhaling secondhand smoke (passive smoking) can increase one's risk of developing cancer.

Alcohol

Excessive consumption of alcohol is a risk factor in certain cancers such as liver and breast cancer. Alcohol, in combination with tobacco, significantly increases the chances that an individual will develop mouth, pharynx, larynx, and esophageal cancers. The combined effect of tobacco and alcohol is greater than the sum of their individual effects. This is called synergy.

Diet and physical activity

One-third of all cancer deaths are due to a poor adult diet. High-fat diets have been associated with cancers of the colon and rectum, prostate, endometrium, and possibly breast. Consumption of meat, especially red meat, has been associated with increased cancer at various sites such as the colon and prostate. Additionally, a high-calorie diet and low level of physical activity can lead to obesity, which increases the risk for cancer at various sites including the breast, colon and rectum, prostate, kidney, and endometrium.

Sexual and reproductive behavior

The human papilloma virus, a sexually transmitted disease, has been shown to cause cancer of the cervix. Having many sexual partners and becoming sexually active early has been shown to increase one's chances of contracting this disease and, therefore, developing cervical cancer. In addition, it has also been shown that women who do not have children or those who have children late in life have an increased risk for both ovarian and breast cancer.

Hormone replacement therapy

As women go through menopause, a physician may recommend hormone replacement therapy. This involves taking female hormones (called estrogen and progesterone) to control certain symptoms such as hot flashes and vaginal dryness that occur during this time of a woman's life. Taking estrogen alone can increase the risk for uterine cancer. However, progesterone is often prescribed at the same time to counteract the cancerous effects of estrogen. There is a questionable relationship between hormone replacement therapy and breast cancer as well. As of 2001, this relationship was not fully understood.

Family history

Certain cancers tend to occur more commonly among members of a family. Much of the time this seems to happens by chance, or is due to a common family habit such as cigarette smoking or extended sun exposure. However, certain cancers can occur in excess in some families due to a genetic predisposition that is passed from generation to generation. For example, if the BRCA1 gene is defective in a family, members of that family may have an increased risk to develop breast, colon, ovarian, or prostate cancer. Other defective genes can make persons susceptible to other types of cancer. Therefore, inheriting particular genes can increase a person's chance of developing cancer.

Occupational hazards

There is ample evidence that occupational hazards account for 4% of all cancer deaths. For example, asbestos workers have an increased incidence of lung cancer. Similarly, bladder cancer is associated with dye, rubber, and gas workers; skin and lung cancer with people who are smelters, gold miners and arsenic workers; leukemia is seen more frequently in people who work with glue and varnish; liver cancer is more prevalent in PVC manufacturers; and lung, bone, and bone marrow cancer is associated with radiologists and uranium miners.

Environment

High-frequency radiation has been shown to cause human cancer. Ultraviolet radiation from the sun accounts for a majority of melanoma cases. Other sources of radiation are x rays, radioactive substances, and rays that enter the earth's atmosphere from outer space. Virtually any part of the body can be affected by these types of radiation, especially bone marrow and the thyroid gland.

Additionally, being exposed to substances such as certain chemicals, metals, or pesticides, can increase the risk of cancer. Asbestos is an example of a well-known carcinogen, increasing the risk for lung cancer. This risk is increased even further for a smoker who is exposed to asbestos over a period of time.

Common pathogens and the cancers associated with them
Causative agent Type of cancer
Viruses
PapillomavirusesCancer of the cervix
Hepatitis B virusLiver cancer
Hepatitis C virusLiver cancer
Epstein-Barr virusBurkitt's lymphoma
Cancers of the upper pharynxHodgkin's lymphoma, non-Hodgkin's lymphoma, gastric cancers
Human immunodeficiency virus (HIV)Kaposi's sarcoma, lymphoma
Bacteria
Helicobacter pyloriStomach cancer, lymphomas

Causes and symptoms

Cancer is a progressive disease and goes through several stages. Each stage can produce a number of symptoms. Unfortunately, many types of cancer do not display any obvious symptoms or cause pain until the disease has progressed to an advanced stage. Early signs of cancer are often subtle and are easily mistaken for signs of other less-dangerous diseases.

Despite the fact that there are several hundred different types of cancers producing very different symptoms, the American Cancer Society (ACS) has established the following seven symptoms as possible warning signals of cancer:

  • changes in the size, color, or shape of a wart or a mole
  • a sore that does not heal
  • persistent cough, hoarseness, or sore throat
  • a lump or thickening in the breast or elsewhere
  • unusual bleeding or discharge
  • chronic indigestion or difficulty in swallowing
  • any change in bowel or bladder habits

Other diseases can produce similar symptoms. However, it is important to have these symptoms checked as soon as possible, especially if they linger. The earlier a cancer is diagnosed and treated, the better the chance of it being cured. Many cancers, for example breast cancer, may not have any early symptoms. Therefore, it is important to undergo routine screening tests, such as breast self-exams and mammograms.

Diagnosis

If a person has symptoms of cancer, a physician will begin with a complete medical history and a thorough physical examination. The doctor will examine different parts of the body in order to identify any variations from the normal size, feel, and texture of the organ or tissue. In addition to the physical exam, the doctor may order various tests.

Laboratory tests on blood and urine are often used to obtain information about a person's health. If cancer is suspected, a special test can be done that measures the amount of certain substances, called tumor markers, in the blood, urine, or particular tissues. These proteins are released from some types of cancer cells. Thus, the levels of these substances may be abnormal when certain cancers are present. However, laboratory tests alone cannot be used to make a definitive diagnosis of cancer. Blood tests are generally more useful in monitoring the effectiveness of the treatment or in following the course of the disease and detecting any signs of recurrence.

A doctor may look for tumors by examining images of areas inside the body. The most common way to obtain these images is by using x rays. Other techniques used to examine the insides of the body include computed tomography (CT scan), magnetic resonance imaging (MRI), and ultrasonography.

The most definitive diagnostic test is a biopsy. In this technique a piece of tissue is surgically removed for examination under a microscope. A biopsy provides information about the cellular nature of an abnormality: the stage it has reached, the aggressiveness of the cancer, and the extent of its spread. Further analysis of the tissue obtained by biopsy defines the cause of the abnormality. Since a biopsy provides the most accurate analysis, it is considered the gold standard of diagnostic tests for cancer.

Regular screening examinations conducted by healthcare professionals can result in the early detection of various types of cancer. Early detection means treatment is more likely to succeed. For example, the American Cancer Society recommends an annual mammogram (x ray of the breast) for women over the age of 40 years, to screen for breast cancer. It also recommends a sigmoidoscopy, in which a thin, lighted tube with a tiny camera is used to view the inside of the colon, every five years for people over the age of 50. This technique can assess the presence of colorectal cancer. Self-examinations for cancers of the breast, testes, mouth, and skin can also help in detecting tumors before the symptoms become serious.

Evolutions in molecular biology and the genetics of cancer have led to the development of several tests designed to assess one's risk of getting certain types of cancer. Genetic testing involves looking closely at certain genes that have been linked to particular cancers. As of 2001 there were many limitations to genetic testing. Tests could be uninformative and to a very small proportion of individuals tested. Additionally, concerns exist about insurance coverage and employment discrimination for someone who has an increased risk for cancer. As of 2001 these tests were reserved only for very specific individuals. A hereditary cancer clinic can help assess who may benefit from this type of testing.

Treatment

The aim of cancer treatment is to remove all or as much of the tumor as possible and to prevent the recurrence or spread of the primary tumor. While devising a treatment plan for cancer, the likelihood of curing the cancer must be weighed against the side effects of the treatment. If the cancer is aggressive and a cure is not possible, then treatment should be aimed at relieving the symptoms and controlling the cancer for as long as possible.

Cancer treatment can take many different forms, and it is always tailored to an individual. The decision on which type of treatment is the most appropriate depends upon the type and location of the cancer and the extent to which it has already spread. A physician will also consider an affected person's age, sex, general health status, and personal treatment preferences. Treatment can be local, meaning that it affects cancer cells in the tumor and the surrounding area only. Surgery and radiation are local treatments. Treatment can also be systemic, meaning that the treatment travels through the bloodstream and affects cancer and other cells throughout the entire body. Chemotherapy, immunotherapy, and hormone therapy are examples of systemic treatments.

Surgery

Surgery can be used for many purposes:

  • Treatment. Treatment of cancer by surgery involves removal of the tumor to cure the disease. This is typically done when the cancer is localized to a discrete area. Along with the cancer, some of the surrounding tissue is also removed to ensure that no cancer cells remain in the area. Since cancer usually spreads via the lymphatic system, lymph nodes near the tumor site may be removed for examination.
  • Prevention. Preventive or prophylactic surgery involves removal of an abnormal-looking area that is likely to become malignant over time. For example, 40% of people with a colon disease called ulcerative colitis ultimately die of colon cancer. Rather than live with the fear of developing colon cancer, these people may choose to have their colons removed in order to reduce their risk of colorectal cancer.
  • Diagnosis. The most definitive tool for diagnosing cancer is a biopsy. Sometimes a biopsy can be performed by inserting a needle through the skin and aspirating a small amount of fluid or tissue. At other times the only way to obtain a tissue sample is through surgery.
  • Cytoreductive surgery. This is a surgical procedure in which the surgeon removes as much of the cancer as possible. The remaining cancer cells are then treated with radiation therapy, chemotherapy, or both.
  • Palliative surgery. This type of surgery is intended to relieve cancer symptoms or slow the progression of disease. It is not designed to cure the cancer. For example, if the tumor is very large or has spread to many places in the body, removing the entire tumor may not be an option. However, by decreasing the size of the tumor, pain may be alleviated. This is known as debulking surgery.

Radiation therapy

Radiation uses high-energy rays to kill cancer cells. This technique may be used instead of surgery. It also may be utilized before surgery to shrink a tumor or after surgery to destroy any remaining cancer cells.

Radiation can be either external or internal. In the external form, the radiation comes from a machine that aims the rays at the tumor. In internal radiation (also known as brachytherapy), radioactive material is sealed in needles, seeds, or wires and placed directly in or near the tumor. Radiation may lead to various side effects, such as fatigue, hair loss, and a susceptibility to infections. However, these side effects can usually be controlled.

Chemotherapy

Chemotherapy is the use of drugs to kill cancer cells. The entire body is exposed to the drugs (systemic therapy) in an effort to destroy the hard-to-detect cancer cells that have spread and are circulating in the body. The cancer cells are affected more dramatically than normal cells because they are rapidly dividing. Chemotherapeutic drugs can be injected into a vein, the muscle, or the skin, or they may be taken by mouth.

When chemotherapy is used before surgery, it is known as primary, or neoadjuvant chemotherapy. Its purpose is usually to reduce the size of the tumor. The more common use of chemotherapy is in adjuvant therapy. In this technique, chemotherapy is given after surgery to destroy any remaining cancer cells and to help prevent cancer from recurring. Chemotherapy can also be used in conjunction with radiation.

Side effects of chemotherapy vary but can include susceptibility to infections, fatigue, poor appetite, weight loss, nausea, diarrhea, and hair loss. Decreased fertility can be a long-term side effect in some instances.

Bone marrow failure is a complication of chemotherapy. When high-dose chemotherapy is utilized, bone marrow failure is anticipated. Bone marrow transplantation (BMT) or peripheral stem cell transplantation (PSCT) are techniques used to treat this complication. Both techniques provide healthy stem cells for an affected person. Stem cells are immature cells that mature into blood cells. Transplanted stem cells replace the patient's stem cells that have been damaged or destroyed by chemotherapy or radiation. This procedure allows an individual to undergo very aggressive treatment for cancer. Those who receive BMT or PSCT have an increased risk of infection, bleeding, and other side effects due to the chemotherapy and radiation. Graft-versus-host disease may also occur. This complication develops when the donated marrow reacts against the recipient's tissues. It can occur any time after the transplant. Drugs may be given to reduce the risk of graft-versus-host disease and to treat the problem if it occurs.

Immunotherapy

Immunotherapy, also called biological therapy, is the use of treatments that promote or support the body's immune system response to cancer. The side effects of immunotherapy are variable but include flulike symptoms, weakness, loss of appetite, and skin rash. These symptoms will subside after the treatment is completed.

Hormone therapy

Hormone therapy is used to fight certain cancers that depend on hormones for their growth. Drugs can be used to block the production of hormones or change the way they work. Additionally, organs that produce hormones may be removed. As a result of this therapy, the growth of the tumor slows and survival may be extended for several months or years.

Alternative and complementary therapies

There are certain cancer therapies that have not been scientifically tested and approved. If these unproven treatments are used instead of the standard therapy, this is known as alternative therapy. If they are used along with standard therapy, this is known as complementary therapy. Alternative therapy is considered dangerous because some of these unproven treatments might have life-threatening side effects. Additionally, persons who use alternative therapy may lose the opportunity to benefit from standard, proven therapy. However, some complementary therapies may help to relieve symptoms of cancer, decrease the magnitude of side effects from treatment, or improve a patient's sense of well being. The ACS recommends that anyone considering alternative or complementary therapy consult a health care team before doing so.

Palliative care

Palliative care, which focuses on the terminally ill, is an extremely important aspect of care. Its goal is to prevent and relieve pain and suffering through symptom management, and addresses not only the physical, but the practical, emotional, and spiritual needs of patients, their families, and caregivers. By viewing dying as a natural process, palliative care helps facilitate what can be termed a "good" death, free from suffering and stress. Many patients and their families are unaware that suffering at the end of life is no longer necessary. Health care professionals can relieve a patient and their loved ones of much anxiety by informing them that appropriate symptom management is readily available.

Hospice care

Hospice care is the environment in which palliative care is given to terminally ill patients. Hospice care can be provided either at home, or in a home-like facility called a hospice. Hospice care focuses on providing the best possible palliative care for the patient until the patient dies.

Prognosis

Most cancers are curable if detected and treated in their early stages. The prognosis for a person with cancer is affected by many factors, particularly the type of cancer and stage of the cancer, the extent to which it has metastasized, and its aggressiveness. In addition, a person's age, general health status, and effectiveness of the treatment being pursued are important factors.

Recommendations for cancer screening
Procedure Frequency
Source: U.S. Preventative Services Task Force, Dept. of Health and Human Services.
Chest x rayNot recommended on a routine basis
Sputum cytologyNot recommended on a routine basis
Fecal occult blood testing (FOBT) or sigmoidoscopyYearly after age 50
Papanicolaou (Pap) smearEvery 3 years from onset of sexual activity to age 65
Mammography alone or mammography and breast physical examinationEvery 1-2 years at ages 50-69; starting at ages 40-49 may be recommended if high-risk

To help predict the outcome of cancer and the likelihood of recovery from the disease, five-year survival rates are used. In the United States, as of 2001, the five-year survival rate for all cancers combined was 59%. This means that 59% of people with cancer are expected to be alive five years after they are diagnosed. These people may be free of cancer, or they may be undergoing treatment. It is important to note that, while this statistic can give some information about the average survival of people with cancer in a given population, it cannot be used to predict the course of cancer for an individual. No two people are exactly alike. The five-year survival rate does not account for differences in detection methods, types of treatments, additional illnesses, and personal behavior of the individual.

Health care team roles

Family physicians, internists, gynecologists, or pediatricians generally make an initial diagnosis of cancer. Other physicians, notable radiologists, and oncologists provide chemotherapeutic and radiologic treatment. Nurses provide emotional and educational support, home care, home hospice care, and case management. Counselors and psychologists may provide emotional support to patients and their families. Epidemiologists collect and maintain data related to cancer.

KEY TERMS

Benign— A growth that does not spread to other parts of the body. Recovery is favorable with treatment.

Biopsy— The surgical removal and microscopic examination of living tissue for diagnostic purposes.

Bone marrow— Spongy material that fills the inner cavities of the bones. The progenitors of all the blood cells are produced in this bone marrow.

Carcinogen— Any substance capable of causing cancer by mutating a cell's DNA.

Chemotherapy— Treatment with anticancer drugs.

Epithelium— Layer of cells covering the body's surface and lining the internal organs and various glands.

Hormone therapy— Treatment of cancer by changing the hormonal environment, such as testosterone and estrogen.

Immunotherapy— Treatment of cancer by stimulating the body's immune system.

Malignant— A general term for cells that can break loose from an original tumor, invade, and then destroy other tissues and organs.

Metastasis— The spread of cancer from one part of the body to another.

Radiation therapy— Treatment using high-energy radiation from x-ray machines, cobalt, radium, or other sources.

Sore— An open wound or a bruise or lesion on the skin.

Tumor— An abnormal growth resulting from a cell that lost its normal growth control restraints and started multiplying uncontrollably.

X rays— High energy radiation used in high doses, either to diagnose or treat disease.

Prevention

According to experts from leading universities in the United States, a person can reduce the chances of getting cancer by following these guidelines:

  • eating plenty of fruits and vegetables
  • exercising vigorously for at least 20 minutes every day
  • avoiding excessive weight gain
  • avoiding tobacco (including second hand smoke)
  • decreasing or avoiding consumption of animal fats and red meats
  • avoiding excessive amounts of alcohol
  • avoiding the midday sun (between 11 am and 3 pm) when the sun's rays are the strongest
  • avoiding risky sexual practices
  • avoiding known carcinogens in the environment or work place

Certain drugs being used for treatment can also be suitable for prevention. For example, tamoxifen (Nolvadex) has been very effective against recurrence of breast cancer and is now thought to be helpful in the prevention of breast cancer. Similarly, retinoids derived from vitamin A are being tested for their ability to slow the progression of, or prevent, head and neck cancers.

Resources

BOOKS

Armstrong-Dailey, Ann, and Sarah Zarbhock. Hospice Care for Children. New York: Oxford, 2001.

Bragg, Rubin. Oncologic Imaging, 2nd ed. Philadelphia: Saunders, 2001.

Crist, William M, et al. "Neoplastic Diseases and Tumors." In Nelson Textbook of Pediatrics. 16th ed. Ed. Richard E. Behrman et al. Philadelphia: Saunders, 2000, 1531-1573.

Eyre, Harmon J., Dianne Lange, and Lois B. Morris. Informed Decisions: The Complete Book of Cancer Diagnosis, Treatment, and Recovery. Washington: American Cancer Society, 2001.

Hudson, Christopher N. Textbook of Ovarian Cancer, 2nd ed. New York: Oxford, 2001.

Ihde, Daniel C., and Dan L. Longo. "Presentations of the Patient with Cancer." In Harrison's Principles of Internal Medicine, 14th ed. Ed. Anthony S. Fauci, et al., New York: McGraw-Hill, 1998, 360-362.

Kantoff, Philip. Prostate Cancer: Principles and Practice. Philadelphia: Lippincott Williams & Wilkins, 2001.

Lippman, Marc E. "Evaluation of Breast Masses in Men and Women." In Harrison's Principles of Internal Medicine, 14th ed. Ed. Anthony S. Fauci, et al., New York: McGraw-Hill, 1998, 362-365.

Longo, Dan L., et al. "Oncology." In Harrison's Principles of Internal Medicine, 14th ed. Ed. Anthony S. Fauci, et al., New York: McGraw-Hill, 1998, 493-633.

Rosenbaum, Ernest H. Supportive Cancer Care: The Complete Guide for Patients and Families. Naperville, IL: Sourcebooks Trade, 2001.

Simone, Joseph M., et al., "Oncology." In Cecil Textbook of Medicine, 21st ed. Ed. Lee Goldman and J. Claude Bennett. Philadelphia: W.B. Saunders, 2000, 1029-1081.

PERIODICALS

Feldt-Rasmussen U. "Iodine and Cancer." Thyroid 11, no. 5 (2001): 483-486.

Izquierdo-Porrera, A.M., J. Trelis-Navarro, X. GomezBatiste. "Predicting Place of Death of Elderly Cancer Patients Followed by a Palliative Care Unit." Journal of Pain Symptom Management 21, no. 6 (2001): 481-490.

Kutner, J.S., C.T. Kassner, and D.E. Nowels. "Symptom Burden at the End of Life. Hospice Providers' Perceptions." Journal of Pain Symptom Management 21. no. 6 (2001): 473-480.

Messmann, H., and K. Schlottmann. "Role of Endoscopy in the Staging of Esophageal and Gastric Cancer." Seminars in Surgical Oncology 20, no. 2 (2001): 78-81.

Nelson, R.L. "Iron and Colorectal Cancer Risk: Human Studies." Nutrition Review 59, no. 5 (2001): 140-148.

Skarin, A.T., R.S., Herbst, T.L. Leong, A. Bailey, and D. Sugarbaker. "Lung Cancer in Patients Under 40." Lung Cancer 32, no. 3 (2001): 255-264.

ORGANIZATIONS

American Academy of Physical Medicine and Rehabilitation. One IBM Plaza, Suite 2500, Chicago, IL 60611-3604. (312) 464-9700. 〈http://www.aapmr.org/consumers/public/amputations.htm〉.

American College of Occupational and Environmental Medicine. 55 West Seegers Road, Arlington Heights, IL 60005. (708) 228-6850. 〈http://www.acoem.org〉.

American College of Radiology. 1891 Preston White Drive, Reston, VA 20191. (703) 648-8900. 〈http://www.acr.org〉.

American College of Surgeons. 633 North St. Clair Street, Chicago, IL 60611-32311. (312) 202-5000. 〈http://www.facs.org/〉.

American Lung Association. 1740 Broadway, New York, NY 10019. (212)-315-8700. 〈http://www.lungusa.org/diseases/lungtb.html〉.

American Melanoma Foundation. 3914 Murphy Canyon Road, Suite A132, San Diego, CA 92123. (858) 277-4426. 〈http://www.melanomafoundation.org/homepage.html〉.

National Alliance of Breast Cancer Organizations. 9 East 37th Street, New York, NY 10016. (212) 889-0606. 〈http://www.nabco.org/〉.

National Cancer Institute. Building 31, Room 10A31, 31 Center Drive, MSC 2580, Bethesda, MD 20892-2580. (800) 422-6237, or (301) 435-3848. 〈http://www.nci.nih.gov/〉.

Skin Cancer Foundation. 245 5th Avenue, Suite #1403, New York, NY 10016. (800) 754-6490. 〈http://www.skincancer.org/melanoma/〉.

OTHER

American Cancer Society. 〈http://www2.cancer.org/contact/〉.

Canadian Cancer Society. 〈http://www.cancer.ca/〉.

Cancer Care. 〈http://www.cancercare.org/〉.

Cancer Guide. 〈http://www.cancerguide.org/〉.

Memorial Sloan-Kettering Cancer Center. 〈http://www.mskcc.org/〉.

National Breast Cancer Coalition. 〈http://www.natlbcc.org/〉.

National Cancer Institute. 〈http://cancernet.nci.nih.gov/〉.

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Cancer

Cancer

Definition

Description

Demographics

Causes and symptoms

Diagnosis

Treatment

Nutrition/Dietetic concerns

Therapy

Prognosis

Prevention

Resources

Definition

Cancer is a group of diseases characterized by uncontrolled growth of cells in the human body and the ability of these cells to travel from the original site and spread to distant sites. Another name for cancer cells is malignant cells. Diet and nutrition play an important role in cancer prevention and cancer treatment.

Description

By definition, cancer is a disease of the genes. A gene is a small part of DNA, which is the master molecule of the cell. Genes make proteins, which serve as the workhorses of the body’s cells. These proteins allow the body to carry out all of the many processes that permit breathing, thinking, moving, and others often taken for granted.

Throughout people’s lives, the cells in their bodies are growing, dividing, and replacing themselves. Many genes produce proteins that are involved in controlling the processes of cell growth and division. Any alteration, or mutation, to the DNA molecule can disrupt the genes and produce faulty proteins. This causes the cell to become abnormal and lose the restraints on its growth. The abnormal cell will begin to divide uncontrollably. The new growth it forms will be called a tumor or neoplasm. Not all tumors are cancerous. Those that are cancerous spread to other parts of the body near the original cancer site or to distant sites. Cancerous tumors are called malignancies. A tumor that is not cancerous is called benign.

Cancer can occur in anyone and is the second leading cause of death in the United States. Although cancer may be inherited, it also may occur due to certain environmental risk factors or behaviors. For example, it is well known that smoking can lead to lung cancer or that unprotected sun exposure is a risk factor for skin cancer. Diet and physical activity also play a role in cancer risk.

Demographics

The American Cancer Society (ACS) estimated that almost one and one-half million new cases of cancer would be diagnosed in 2007 in the United States. And more than 1,500 people a day were projected to die of cancer in 2007. Lung cancer remains the leading cause of cancer deaths among U.S. men and women. Prostate cancer is the second-leading cause of cancer deaths among men and breast cancer is the second-leading cause of death among U.S. women. Colon and rectal cancer is the third-leading.

Most prevalent cancer-related deaths, 2002 .

Male cancers Deaths Female cancers Deaths (000)
Trachea/brounchus/lung886Breast Trache/474
Stomach523bronchus/lung353
Liver428Stomach326
Colon/rectum321Colon/rectum299
Oesophagus284Cervix Uteri239
Prostate268Liver191

source: The World Health Repor 2003.

(illustration by GGS I2nformation Services/Thomson Gale).

cause of cancer death among U.S. men and women. There are various racial and ethnic differences in incidence of cancer and deaths from cancer in the United States. Some of these differences may be due to cultural factors such as behaviors or access to care. Others may be related to genetics. Survival rates for all races and types of cancer combined continue to increase substantially. From 1996-2002, 66% of cancer survivors lived five years or longer, combined with only 50% between 1975 and 1977.

Causes and symptoms

There are numerous risk factors and causes of cancer. Among them are age, sex, and family medical history. Some risk factors depend on the type of cancer. In some cases, a person may have more than one risk factor for the disease. Another person may be diagnosed with cancer and have no apparent risk factor. Genetic causes can’t be controlled by an individual, but people who know they are at risk because a close relative had a particular cancer should follow all recommendations for screening and prevention.

Often, physicians cannot explain what causes cancer. In addition to a family history of cancer, overall risk factors for cancer include aging, tobacco or alcohol use, exposure to sunlight or ionizing radiation, exposure to certain chemicals or substances, and exposure to some viruses and bacteria. Poor diet, lack of physical activity, or being overweight also are risk factors for cancers. Not all of these risk factors pertain to all cancers. For example, exposure to sunlight is a risk factor for skin cancer, while certain hormones increase the risk of breast cancer.

Cancer may not produce pain. And many symptoms may be due to a condition that is not cancer. But any signs similar to those for a particular cancer or that show a change in health should be checked by a physician. Symptoms vary depending on the type of.

KEY TERMS

Benign —Mild, does not threaten health or life. When referring to a tumor, it generally means noncancerous.

Malignant —Unfavorable, tending to produce deterioration or death. For a tumor, it generally means cancerous.

Radiopharmaceutical —A drug that is radioactive. It is used for diagnosing or treating diseases.

cancer, but some common symptoms of cancer include:

  • feeling weak or very tired
  • a lump in the breast or any other part of the body
  • a new mole or changes in an existing mole
  • changes to bowel or bladder habits
  • hoarseness or a cough that won’t go away
  • a sore that doesn’t heal
  • difficulty swallowing
  • unexplained weight loss or weight gain
  • unusual discharge or bleeding

Diagnosis

Generally, the earlier cancer is found, the better. Many cancer types have screening methods to help find them early. For example, screening mammography helps detect breast cancer before symptoms occur. A Pap test screens for cervical cancer. Several tests, such as colonoscopy, are recommended for people of certain ages or with certain risk factors, to screen for colon and rectal cancer. It is important to follow the guidelines of organizations such as the American Cancer Society concerning recommended screening for cancers.

Physicians use a combination of family and medical history, screening examination results, laboratory examinations, imaging examinations, and other procedures to diagnose cancer. Family and medical history are important to look for hereditary links to many cancers. Medical history helps to determine if a person may have behaviors, such as smoking, that increase risk for many cancers.

Laboratory examinations may test a person’s blood, urine, or other fluids. These tests often are conducted to search for levels of substances called tumor markers. Laboratory tests alone cannot diagnose cancer, but can help lead a physician toward or away from a suspected diagnosis.

X rays are traditional imaging and may be the first type of imaging performed. Mammography is a form of x ray; it is the screening and diagnostic examination used to detect breast cancer. Chest x rays may be used to detect lung cancer. Other types of x rays may be used in cancer diagnosis.

Computed tomography (CT) scanning. Because the use of the computer can generate finer, cross-sectional detail in combination with x rays, CT scans often are used to image a particular area. And CT scans have been used to screen for lung cancer, though the practice still is in debate. CT colonography can screen for polyps and other lesions in the large intestine, much like a colono-scopy. But CT is noninvasive, meaning it does not penetrate the skin or enter the body. CT may involve use of contrast that is injected to help make certain fluids or tissues more visible on the image for the radiologist.

Nuclear medicine or radionuclide scans involve injection of a small amount of a radiopharmaceutical into a vein. The agent flows through the bloodstream and collects in certain areas or organs. When a special camera is used to take images, the agent will show in “hot spots,” which the radiologist will use to interpret the results. Often, nuclear medicine scans will be used to check for spread of cancer to bone, but they also have other uses. Most of the radiopharmaceutical passes out of the body in urine or stool and the rest disappears through natural loss of radioactivity over time. Reaction to the agent is rare.

Ultrasound is an imaging examination that does not use radiation. Instead, high-frequency sound waves are used to produce images. Ultraound often is used to follow up in suspicious mammogram findings. Ultrasound images show fluids and soft tissues very well and often help radiologists determine if a mass is most likely a benign cyst or a malignant (cancerous) solid mass. Other common areas that ultrasound is used to image when diagnosing cancer are the thyroid, the abdomen, the pelvic area (ovaries, uterus), and the prostate.

Magnetic resonance imaging (MRI) also does not require use of radiation. Instead, a strong magnetic field and radio waves provide clear and detailed pictures through a computer display. MRI has proven to be the most sensitive examination for brain tumors. MRI also has become increasingly useful in breast cancer imaging in recent years, as well as for many other suspected cancers.

Positron emission tomography, or PET, scanning is a nuclear medicine procedure that acquires images based on detection of radiation, as in a radionuclide scan, but through emission of positrons. Positrons are tiny particles emitted from a radioactive substance administered to the patient. Cancer cells sometimes show up as areas of high activity. In recent years, physicians have been able to combine these images with CT images, fusing them with one another to show superb detail of the anatomy from CT scans along with the functional details gained from PET. These images improve diagnosis, staging, and tracking of treatment progress for cancer patients.

In most cases, at least for cancers that are solid tumors, a biopsy is the only definite method for confirming cancer diagnosis. Before many of the imaging methods discussed above were developed, a biopsy only could be performed through surgery, where a small sample of the tissue was cut out and sent to a laboratory for evaluation by a pathologist. Today, these samples can be extracted using small needles. The physician can be guided to the site of the suspected cancer by use of ultrasound, CT, MRI, or other imaging methods. The biopsy method often is called fine needle aspiration biopsy or core needle biopsy. Biopsies also may be performed during surgery, particularly to verify and stage cancer when a mass is removed as part of treatment. Removal and biopsy of the entire tumor is called excisional biopsy, while removal of only a portion of the tumor is called incisional biopsy.

Treatment

Planning treatment for cancer first involves staging of the cancer. Once the physician has gathered the information needed to determine the cancer”s stage, the physician will communicate with the patient about treatment options. The most common treatments for cancer are chemotherapy, radiation, and surgery. A cancer patient may receive one or all of these treatments or a combination of them in any order. The particular use and details of each treatment depend on the type of cancer, the stage, and many other factors individual to each patient.

Staging

Cancer staging determines the extent of the cancer in the body. It usually is based on the size of the original tumor, whether the cancer has spread to the lymph nodes, and whether the cancer has spread to organs of the body that are distant from the original site. Each cancer has its own staging system using letters and numbers. The T in cancer staging describes the original tumor and the N stands for whether the cancer has spread to nearby lymph nodes. The M stands for metastases, or distant spread of the cancer. Numbers area assigned along with the letters. Stage I cancers are the least advanced and have the best outlook for survival. Stage IV is the most advanced level. A cancer’s stage does not change, even if cancer recurs or distant spread develops.

Chemotherapy

Cancer can spread, even early in the cancer cells” development. Chemotherapy uses cancer-killing drugs that are given to the patient by mouth or by intravenous injection. The drugs travel through the bloodstream to try to kill cancer cells throughout the body, not just at the original tumor site. Usually, the drugs are given in cycles and treatment can last up to six months. Chemotherapy may cause side effects, including fatigue, nausea, and increased susceptibility to colds and infections.

Radiation therapy

Also called radiotherapy or radiation treatment, radiation therapy usually is used to shrink or control growth of a tumor. The radiation destroys the cancer cells” ability to reproduce and the body naturally gets rid of the cells. In the past, radiation only came from external beam radiation therapy, where x-ray beams were directed toward the tumor from a machine outside the patient’s body. But patients also may receive brachy-therapy, a procedure in which radioactive sources, sometimes called seeds, are placed inside the body at the tumor site. Radiation therapy techniques have improved dramatically in recent years. Using computers and 3-D imaging, radiation oncologists and radiation therapists can precisely target the tumor area, sparing healthy tissues. Newer techniques even take into account natural movements such as breathing to better target the cancer cells. Radiation can produce some side effects, such as skin changes. Most of the effects are short term.

Surgery

When a surgeon removes cancerous tissue, he or she often removes a little bit of the tissue around it. This is to ensure that all of the cancer cells were removed, to help minimize chance of recurrence. Surgery may require a hospital stay and recovery time, depending on the type and extent of the surgery. The belief that surgery for cancer leads to spreading of the disease is untrue.

Nutrition/Dietetic concerns

Diet also is an important part of cancer treatment. It is important to eat the right kinds of foods before treatment, during treatment, and after treatment.

The American Cancer Society says that according to scientific evidence, about one-third of the cancer deaths that occur in the United States each year are due to nutrition and physical activity factors. These factors include excess weight. In 2006, the ACS recommended that Americans maintain a healthy weight throughout life, adopt a physically active lifestyle as adults and children, and consume a healthy diet with an emphasis on plant sources. The physical activity suggestions include at least 30 minutes of moderate to vigorous physical activity for adults five or more days a week, with 45 to 60 minutes of activity preferred. Children and adolescents should engage in at least 60 minutes of activity at least five days a week.

The ACS recommends choosing food and beverages that help to achieve and maintain a healthy weight. The society also recommends eating nine or more servings of a variety of fruits and vegetables per day. Whole grains should replace processed grains and the recommendations say to limit consumption of processed and red meats. Scientific evidence shows that populations with diets rich in vegetables and fruits but low in animal fat, meat, and calories have reduced risk of some common cancers.

Diet also is important during cancer treatment. Cancer and its treatment can cause nutritional deficiencies. Many cancer treatments can cause loss of appetite, and chemotherapy can additionally cause nausea. Radiation also can affect appetite, depending on the location of the tumor and treatment. Other nutritional needs for cancer patients arise because of a tendency to lose weight and muscle mass. When cancer is diagnosed, many patients will be placed on high-protein and high-calorie diets for a period of time to help maintain muscle and weight.

During treatment, the physician may recommend diet strategies to help soothe side effects. If patients are having trouble chewing or difficulty swallowing, thick liquids such as milkshakes may be suggested. Other semi-solid foods such as mashed potatoes may be helpful until swallowing or chewing ability improves. Other patients may have pain, nausea, vomiting, or diarrhea. Eating a meal before treatment may ease nausea. Eating small meals several times a day and choosing bland foods are some suggestions caregivers will offer patients to deal with nausea caused by cancer treatment. Diarrhea can be treated by eating broth, soups, sports drinks, or bananas and avoiding greasy foods. Loss of appetite can be overcome by eating small snacks that contain plenty of calories and protein and eating foods with odors that are appealing, as well as by trying new foods. Sometimes, cancer treatment alters the taste of foods. Rinsing the mouth before eating, using plastic utensils if foods taste metallic and adding spices to foods may help ease the symptoms.

After cancer treatment, it is important to resume healthy eating habits, following the recommendations of the American Cancer Society to maintain a healthy weight, be as physically active as possible, and to eat a balanced diet that leans toward whole grains and plant-based foods instead of red meats and processed foods.

Therapy

Some cancer patients will need nutrition therapy to restore nutrients and remain nourished, particularly if they experience malnutrition because of their cancer or cancer treatment. Nutrition therapy may consist of enteral nutrition, also known as tube feeding. Enteral nutrition is food given in liquid form directly through a tube that is inserted into the stomach or small intestine. Parenteral nutrition is delivered into the blood stream through a thin tube, or catheter, inserted into a vein. Eating by mouth always is preferred to these methods, and patients are encouraged to eat as soon as they can following these nutrition therapies.

Some patients may receive palliative care for cancer. Palliative care is not treatment of the cancer, but steps taken to improve the patient’s quality of life and symptom side effects. Hospice is a program of special care for patients who are at the end of their life. It may be provided in a hospital, special hospice facility, or in cooperation with the patient’s family and other care-givers in the patient’s home.

Prognosis

Cancer prognosis depends on the type and stage of cancer at diagnosis, the person’s overall health at diagnosis, and treatment success. Studies show that physicians sometimes are reluctant to provide information about prognosis, so it is important for cancer patients to ask specific questions about their likelihood of survival if they want detailed information.

Prevention

In addition to following the American Cancer Society guidelines concerning diet, nutrition, and activity, it is important to follow recommendations from the ACS, family physicians, and other credible health sources regarding behaviors that might lead to cancer. Examples of these behaviors include tobacco use and exposure to ultraviolet rays (sunshine) without protection. Anyone who has a first-degree relative with cancer should speak with their physician about their risk for the same type of cancer and participate in recommended screening as recommended. In cancer,early detection is essential to treatment and good prognosis.

Resources

BOOKS

American Cancer Society’s Health Eating Cookbook. 3rd Edition. American Cancer Society, 2005.

Good for You! Reducing Your Risk of Developing Cancer. American Cancer Society, 2002.

ORGANIZATIONS

American Cancer Society. P.O. Box 22718, Oklahoma City, OK 73213-1718 or contact the office in closest city. 800-227-2345. <http://www.cancer.org>

National Cancer Institute. 6116 Executive Blvd, Room 3036A, Bethesda, MD 20892. 800-422-6237. <http://www.cancer.gov>

Teresa G. Odle

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Cancer

Cancer

The history of cancer as a known disease

The genetics of cancer

Types of cancers

Causes and symptoms

Diagnosis

Treatment

Prognosis

Prevention

Resources

Cancer is not just one disease, but a large group of almost 100 diseases. Its two main characteristics are uncontrolled growth of the cells in the human body and the ability of these cells to migrate from the original site and spread to distant sites. If the spread is not controlled, cancer can result in death.

Of all premature deaths, one out of every four deaths in the United States is from cancer. It is second only to heart disease as a cause of death in the United States. According to the American Cancer Society (ACS), as of 2006, over 550 million people in the United States die of cancer each year. Annually, about 1.4 million new cases of cancer will be diagnosed, excluding preinvasive cancer (but including urinary bladder cancer) and nonmelanoma skin cancer (in which about one million cases will be diagnosed).

Cancer can attack anyone. Since the occurrence of cancer increases as people age, most of the cases are seen in adults, middle-aged or older. The most common cancers are skin cancer, lung cancer, colon cancer, breast cancer (in women), and prostate cancer (in men). In addition, cancer of the kidneys, ovaries, uterus, pancreas, bladder, rectum, and blood and lymph node cancer (leukemia and lymphomas) are also included among the 12 major cancers that affect most Americans.

The history of cancer as a known disease

The term cancer derives from the observation by Hippocrates in 400 BC that the veins radiating from a breast cancer resembled the legs of a crab, hence karkinoma in Greek and cancer in Latin. Cancer is not a single disease, but is many different diseases that all share common biological and pathological characteristics. In most western societies, cancer is a leading cause of death. The disease may develop in any body tissue or organ and over one hundred different types of cancer can occur in adults. Cancer also occurs in children and may even be present at birth.

The first clues to the cause of cancer came over two hundred years ago from an observation by Percivall Pott, a London doctor, who in 1775 found a high incidence of scrotal cancer in men who had worked as chimney sweeps. Later, radiation was found to cause skin cancer and tragically Marie Curie (18671934), the discoverer of x rays, died of a cancer caused by prolonged exposure to radiation. During the second half of the twentieth century, epidemiologists (those who study disease in populations) linked exposure to certain environmental toxins and particular types of cancer. Most notably, cigarette smoking and lung cancer, sunlight and skin cancer, and certain industrial chemicals were linked as the cause of bladder and liver cancer. Finally several viruses were also been implicated in causing cancer, such as the hepatitis B virus and cancer of the liver, the Epstein Barr virus and lymphoma, and the human papilloma virus and cancer of the cervix. These important observations all suggested that specific external environmental agents could cause specific cancers.

How then could a diverse range of external agents such as chemicals, radiation, and viruses, all lead to the development of cancer?. The answer to this question has come over the last 30 years from two different lines of investigation: studies on cancer causing viruses and research into the genetics of some rare cancers in children.

In 1910, Frances Peyton Rous (18791970) isolated a virus from a cancer in chickens (a sarcoma) that caused new sarcomas to develop when infected into healthy chickens. Rouss work languished for over 50 years until he was awarded a Nobel Prize in 1966. By this time, methods for the study of viruses and cancer had improved considerably and many new animal derived viruses were found to cause cancer in a range of species. These viruses could also induce cancer-like changes when introduced into normal cells grown in the laboratory. A genetic study of these cancer causing viruses identified a small number of genes termed viral onco-genes (v-oncogenes) which, when introduced into cells, could transform the normal cells into malignant cells.

The presence of viral oncogenes led to the search for endogenous cellular oncogenes, which might cause cancer. In a crucial experiment in the late 1970s, DNA (deoxyribonucleic acid) from mouse cells that had been transformed by a chemical carcinogen, was transfected into normal mouse cells. The normal mouse cells became malignant suggesting that a gene within the cancer (a proto-oncogene) had been mutated by exposure to the chemical and was able to induce cancer. Surprisingly, when these endogenous cellular oncogenes were eventually isolated they were found to be homologous to virally derived oncogenes.

In the early 1970s, American pediatrician and scientist Alfred Knudson at the Fox Chase Cancer Center studied retinoblastoma, a rare childhood eye cancer that is sometimes inherited but is most often sporadic. He observed that children who had inherited retinoblastoma often had the cancer at birth, and were at high risk of developing multiple cancers in both eyes. Children with later onset retinoblastoma usually had no family history and developed isolated tumors. Knudson reasoned that children with inherited retinoblastoma had a germline mutation in one allele of a recessive cancer gene. The germline mutation was the first of two hits in knocking out a recessive cancer gene. This is known as Knudsons two hit hypothesis. Later genetic studies found the first hit in children with inherited retinoblastoma to be a partial deletion of the long arm of chromosome 13 causing loss of the tumor suppressor gene, RB1.

These two directions of study independently identified two different classes of cancer gene, the oncogene and tumor suppressor gene, that when mutated in a given cell can set in train the sequence of events leading to the development of a cancer.

The genetics of cancer

Cancer, by definition, is a disease of the genes. Cancer is also the most common genetic disease in humans, but only rarely is it inherited. A gene is a small part of DNA, which is the master molecule of the cell. Genes make proteins, which are the ultimate workhorses of the cells. It is these proteins that allow human bodies to carry out all the many processes that permit people to breathe, think, move, etc.

Throughout peoples lives, the cells in their bodies are growing, dividing, and replacing themselves. Many genes produce proteins that are involved in controlling the processes of cell growth and division. An alteration (mutation) to the DNA molecule can disrupt the genes and produce faulty proteins. This causes the cell to become abnormal and lose its restraints on growth. The abnormal cell begins to divide uncontrollably and eventually forms a new growth known as a tumor or neoplasm (which is the medical term for cancer meaning new growth).

In a healthy individual, the immune system can recognize the neoplastic cells and destroy them before they get a chance to divide. However, some mutant cells may escape immune detection and survive to become tumors or cancers.

Tumors are of two types: benign or malignant. A benign tumor is slow growing, does not spread or invade surrounding tissue, and once it is removed, it does not usually recur. A malignant tumor, on the other hand, invades surrounding tissue and spreads to other parts of the body. The hallmark of a malignant cancer is the uncontrolled clonal proliferation and spread of abnormal cancer cells. If the cancer cells have spread to the surrounding tissues, then, even after the malignant tumor is removed, it generally recurs.

Many cancers are caused by changes in the cells DNA because of damage due to the environment. Environmental factors that are responsible for causing the initial mutation in the DNA are called carcinogens. There are many types of carcinogens, such as asbestos and noitrosonornicotine (in cigarettes).

There are some cancers that have a genetic basis. In other words, an individual could inherit faulty DNA from his/her parents, which could predispose that person to getting cancer. While there is scientific evidence that both factors (environmental and genetic) play a role, less than 10% of all cancers are purely hereditary. Cancers that are known to have a hereditary link are breast cancer, colon cancer, ovarian cancer, and uterine cancer. Besides genes, certain physiological traits could be inherited and could contribute to cancers. For example, inheriting fair skin makes a person more likely to develop skin cancer, but only if they also have prolonged exposure to intensive sunlight.

Most cancers are sporadic and arise in a particular tissue such as the colon, breast, lung, or skin when normal cells acquire mutations in one or more onco-genes or tumor suppressor genes. The acquisition of multiple new genetic changes is what sets the cancer cell apart from the normal cells in its surrounding tissues.

The cancer cell develops when a normal cell in an organ or tissue acquires the capacity to divide in an uncontrolled fashion. Over time the developing cancer cell starts to multiply in a clonal fashion, begins to appear different (anaplastic or undifferentiated), and progressively acquires other characteristics, such as the capacity metastasise while losing cell-to-cell adhesion. The continued acquisition of new biologic characteristics is the key to many aggressive cancers evading the host defenses, and to the resisting some treatments such chemotherapy and radiotherapy.

It is important to appreciate that oncogenes and tumor suppressor genes are in fact normal cellular genes with vital functions within normal cells. It is only when they are mutated in some way that these genes become cancer causing.

The Ha-ras gene is a good example of an onco-gene. Located on chromosome 11 at the normal cellular Ha-ras gene is one of a family of ras genes and encodes a small protein that is involved in intracellular signaling. Mutations in the ras oncogenes disrupt processing of cell signals and contribute to cell transformation. Mutations in ras oncogenes are found in approximately 10% of cancers especially cancer of the colon and lung.

The most important tumor suppressor gene is the p53 gene. This gene which is known as the guardian of the genome encodes for a protein with multiple intracellular functions related to the detection of DNA damage. When DNA is damaged by exposure to a mutagen such as UV (ultraviolet) irradiation the p53 gene is expressed. The p53 protein causes the cell to stop dividing so DNA mismatch repair genes can repair the DNA. If the DNA is successfully repaired, the cell resumes normal cell functions and the p53 gene is down regulated. However, if the DNA damage is beyond repair the p53 protein switches on a process called apoptosis (programmed cell death) leading to the death of the cell. For example, sunburn to the skin causes UV induced DNA damage, which often cannot be repaired. Expression of the p53 gene induces apoptosis the skin cells die and peel off.

Mutations in the p53 gene occur in approximately 50% of all cancersparticularly cancer of the breast, colon, lung, and brain. The mutant p53 protein is unable to stop uncontrolled cell division or switch on apoptosis, and can no longer protect the cell from acquiring additional mutation in other genes. The result is an unstable cell genome liable to further progressive DNA damage. The inherited cancer condition, Li-Fraumeni syndrome, is an autosomal dominant disorder caused by inherited mutations in the p53 gene. Individuals affected with Li-Fraumeni syndrome may develop breast cancer, brain tumors, leukemia, prostate cancer and various sarcomas at a young age.

Mismatch repair genes are another class of cancer gene contributing to instability of the cancer cell genome. Damaged DNA is repaired by an active DNA mismatch repair mechanism that identifies damaged DNA, then cuts out and repairs the damaged DNA bases. Mutations in these repair genes are common in cancer cancers of the colon.

Oncogenes, tumor suppressor genes and other cancer causing genes can become mutated in any number of different ways. Most oncogenes become activated by specific mutations within their DNA sequence that causes the gene protein to function abnormally. Some oncogenes such MYCN are activated by DNA amplification. Oncogene amplification occurs commonly in neuroblastoma an aggressive cancer in children. These tumors can acquire hundreds of copies of this gene by DNA amplification making the cancer very resistant to treatment. Another means of oncogene activation is by its translocation from one chromosome to another. In the Burkitt lymphoma the c-myc oncogene is translocated from chromosome 8 to chromosome 14 where it becomes activated by an immunoglobulin gene. Only one allele of an oncogenes need to be activated for it to participate in cell transformation.

Tumor suppressor genes on the other hand are recessive and normally act to suppress cell replication. Cell transformation occurs when both gene alleles are inactivated (knocked out). Most commonly, inactivation of one gene allele occurs by a chromosome deletion. The second event may be an inactivating gene mutation, a second deletion or methylation of the genes promoter.

Regardless of the actual mutations involved, a crucial concept in the development of most cancers is that more than one gene is usually involved in the process. Indeed in the development of cancer of the colon at least six or more separate oncogenes and tumor suppressor genes are involved in a progressive multi-step process to transform a normal colon cell into an aggressive, self replicating and invading cancer.

More recently, the application of gene expression arrays (microarrays) to the study of cancer has found that in addition to multiple gene mutations, the expression of many hundreds of non-mutant genes is affected in the process of cell transformation.

Microarray analysis of cancers of the breast and soft tissues has also identified distinctive patterns of gene expression that can be used to aid diagnosis and predict the clinical behavior of individual tumors.

This type of genetic analysis will also aid the development of new cancer therapies directed specifically at the molecular biology of the cancer.

Types of cancers

There are several different types of cancers:

  • Carcinomas are cancers that arise in the epithelium (the layers of cells covering the bodys surface and lining the internal organs and various glands). Ninety percent of human cancers fall into this category. Carcinomas can be subdivided into two subtypes: adenocarcinomas and squamous cell carcinomas. Adenocarcinomas are cancers that develop in an organ or a gland, while squamous cell carcinomas refer to cancers that originate in the skin.
  • Melanomas also originate in the skin, usually in the pigment cells (melanocytes).
  • Sarcomas are cancers of the supporting tissues of the body, such as bone, muscle and blood vessels.
  • Cancers of the blood and lymph glands are called leukemia and lymphomas respectively.
  • Gliomas are cancers of the nerve tissue.

Causes and symptoms

The major risk factors for cancer are: tobacco, alcohol, diet, sexual and reproductive behavior, infectious agents, family history, occupation, environment and pollution.

According to the estimates of the American Cancer Society (ACS), just over 40% of the cancer deaths in 2004 were due to tobacco and excessive alcohol use. An additional one-third of the deaths were related to diet and nutrition. Many of the one million skin cancers that each year were due to over-exposure to ultraviolet light from the Suns rays.

Tobacco

Eighty to ninety percent of the lung cancer cases occur in smokers. Smoking has also been shown to be a contributory factor in cancers of upper respiratory tract, esophagus, larynx, bladder, pancreas, and probably liver, stomach, and kidney as well. Recently, scientists have also shown that second-hand smoke (or passive smoking) can increase ones risk of developing cancer.

Alcohol

Excessive consumption of alcohol is a risk factor in certain cancers, such as liver cancer. Alcohol, in combination with tobacco, significantly increases the chances that an individual will develop mouth, pharynx, larynx, and esophageal cancers.

Diet

Thirty five percent of all cancers are due to dietary causes. Excessive intake of fat leading to obesity has been associated with cancers of the breast, colon, rectum, pancreas, prostate, gall bladder, ovaries, and uterus.

Sexual and reproductive behavior

The human papilloma virus, which is sexually transmitted has been shown to cause cancer of the cervix. Having too many sex partners and becoming sexually active early has been shown to increase ones chances of contracting this disease. In addition, it has also been shown that women who do not have children or have children late in life, have an increased risk for both ovarian and breast cancer.

Infectious agents

In the later decades of the twentieth century, scientists obtained evidence to show that approximately 15% of the worlds cancer deaths can be traced to viruses, bacteria, or parasites. The most common cancer-causing pathogens and the cancers associated with them are shown in table form.

Family history

Certain cancers like breast, colon, ovarian and uterine cancer, recur generation after generation in some families. A few cancers, such as the eye cancer retinoblastoma, a type of colon cancer, and a type of breast cancer known as early-onset breast cancer, have been shown to be linked to certain genes that can be tracked within a family. It is therefore possible that inheriting particular genes makes a person susceptible to certain cancers.

Occupational hazards

There is evidence to prove that certain occupational hazards account for at least 4% of all cancer deaths. For example, asbestos workers have an increased incidence of lung cancer. Similarly, a higher likelihood of getting bladder cancer is associated with dye, rubber and gas workers; skin and lung cancer with smelters, gold miners, and arsenic workers; leukemia with glue and varnish workers; liver cancer with PVC (polyvinyl chloride) manufacturers; and lung, bone and bone marrow cancer with radiologists and uranium miners.

Environment

Radiation is believed to cause 1 to 2% of all cancer deaths. Ultra-violet radiation from the sun accounts for a majority of melanoma deaths. Other sources of radiation are x rays, radon gas, and ionizing radiation from nuclear material.

Pollution

Several studies have shown that there is a well-established link between asbestos and cancer. Chlorination of water may account for a small rise in cancer risk. However, the main danger from pollution occurs when dangerous chemicals from industries escape into the surrounding environment. It has been estimated that approximately 1% of cancer deaths are due to air, land and water pollution.

Cancer is a progressive disease, and goes through several stages. Each stage may produce a number of symptoms. Some symptoms are produced early and may occur due to a tumor that is growing within an organ or a gland. As the tumor grows, it may press on the nearby nerves, organs and blood vessels. This causes pain and some pressure which may be the earliest warning signs of cancer.

Despite the fact that there are several hundred different types of cancers, producing very different symptoms, the ACS has established the following seven symptoms as possible warning signals of cancer:

  • Changes in the size, color, or shape of a wart or a mole;
  • A sore that does not heal;
  • Persistent cough, hoarseness, or sore throat;
  • A lump or thickening in the breast or elsewhere;
  • Unusual bleeding or discharge;
  • Chronic indigestion or difficulty in swallowing; and
  • Any change in bowel or bladder habits.

Many other diseases, besides cancer, could produce the same symptoms. However, it is important to have these symptoms checked, as soon as possible, especially if they linger. The earlier a cancer is diagnosed and treated, the better the chance of it being cured. Many cancers such as breast cancer may not have any early symptoms. Therefore, it is important to undergo routine screening tests such as breast self-examinations and mammograms.

Diagnosis

Diagnosis begins with a thorough physical examination and a complete medical history. The doctor will observe, feel, and palpate (apply pressure by touch) different parts of the body in order to identify any variations from the normal size, feel and texture of the organ or tissue.

As part of the physical examination, the doctor will inspect the oral cavity or the mouth. By focusing a light into the mouth, the physician will look for abnormalities in color, moisture, surface texture, or presence of any thickening or sore in the lips, tongue, gums, the hard palate on the roof of the mouth, and the throat. To detect thyroid cancer, the doctor will observe the front of the neck for swelling. He/she may gently manipulate the neck and palpate the front and side surfaces of the thyroid gland (located at the base of the neck) to detect any nodules or tenderness. As part of the physical examination, the doctor will also palpate the lymph nodes in the neck, under the arms and in the groin. Many illnesses and cancers cause a swelling of the lymph nodes.

The doctor may conduct a thorough examination of the skin to look for sores that have been present for more than three weeks and that bleed, ooze, or crust; irritated patches that may itch or hurt, and any change in the size of a wart or a mole.

Examination of the female pelvis is used to detect cancers of the ovaries, uterus, cervix, and vagina. In the visual examination, the doctor looks for abnormal discharges or the presence of sores. Then, using gloved hands the physician palpates the internal pelvic organs such as the uterus and ovaries to detect any abnormal masses. Breast examination includes visual observation where the doctor looks for any discharge, unevenness, discoloration, or scaling. The doctor palpates both breasts to feel for masses or lumps.

For males, inspection of the rectum and the prostate is also included in the physical examination. The doctor inserts a gloved finger into the rectum and rotates it slowly to feel for any growths, tumors, or other abnormalities. The doctor also conducts an examination of the testis, where the doctor observes the genital area and looks for swelling or other abnormalities. The testicles are palpated to identify any lumps, thickening or differences in the size, weight, and firmness.

If the doctor detects an abnormality on physical examination, or the patient has some symptom that could be indicative of cancer, the doctor may order diagnostic tests.

Laboratory studies of sputum (sputum cytology), blood, urine, and stool can detect abnormalities that may indicate cancer. Sputum cytology is a test where the phlegm that is coughed up from the lungs is microscopically examined. It is often used to detect lung cancer. A blood test for cancer is easy to perform, usually inexpensive and risk-free. The blood sample is obtained by a laboratory technician or a doctor, by inserting a needle into a vein and is relatively painless. Blood tests can be either specific or non-specific. Often times, in certain cancers, the cancer cells release particular proteins (called tumor markers) and blood tests can be used to detect the presence of these tumor markers. However, with a few exceptions, tumor markers are not used for routine screening of cancers, because several non-cancerous conditions also produce positive results. Blood tests are generally more useful in monitoring the effectiveness of the treatment, or in following the course of the disease and detecting recurrent disease.

Imaging tests such as computed tomography (CT) scans, magnetic resonance imaging (MRI), ultrasound, and fiberoptic scope examinations help the doctors determine the location of the tumor even if it is deep within the body. Conventional x-rays are often used for initial evaluation, because they are relatively cheap, painless, and easily accessible. In order to increase the information obtained from a conventional x ray, air or a dye (such as barium or iodine) may be used as a contrast medium to outline or highlight parts of the body.

The most definitive diagnostic test is the biopsy, wherein a piece of tissue is surgically removed for microscope examination. Besides, confirming a cancer, the biopsy also provides information about the type of cancer, the stage it has reached, the aggressiveness of the cancer and the extent of its spread. Since a biopsy provides the most accurate analysis, it is considered the gold standard of diagnostic tests.

Screening examinations, conducted regularly by healthcare professionals can result in the detection of cancers of the breast, colon, rectum, cervix, prostate, testis, tongue, mouth, and skin at early stages, when treatment is more likely to be successful. Some of the routine screening tests recommended by the ACS are sigmoidoscopy (for colorectal cancer), mammography (for breast cancer), pap smear (for cervical cancer), and the PSA (prostate-specific antigen) test (for prostate cancer). Self-examinations for cancers of the breast, testes, mouth and skin can also help in detecting the tumors before the symptoms become serious.

A recent revolution in molecular biology and cancer genetics has contributed a great deal to the development of several tests designed to assess ones risk of getting cancers. These new techniques include genetic testing, where molecular probes are used to identify mutations in certain genes that have been linked to particular cancers.

Treatment

The aim of cancer treatment is to remove all or as much of the tumor as possible and to prevent the recurrence or spread of the primary tumor. While devising a treatment plan for cancer, the likelihood of curing the cancer has to be weighed against the side effects of the treatment. If the cancer is very aggressive and a cure is not possible, then the treatment should be aimed at relieving the symptoms and controlling the cancer for as long as possible.

Cancer treatment can take many different forms, and it is always tailored to the individual patient. The decision on which type of treatment is the most appropriate depends on the type and location of cancer, the extent to which it has already spread, the patients age, sex, general health status and personal treatment preferences. The major types of treatment are: surgery, radiation, chemotherapy, immunotherapy, hormone therapy, and bone-marrow transplantation.

Surgery

Surgery is the removal of a visible tumor and is the most frequently used cancer treatment. It is most effective when a cancer is small and confined to one area of the body.

Surgery can be used for many purposes. The following list describes the major reasons.

  • Treatment: Treatment of cancer by surgery involves removal of the tumor to cure the disease. This is typically done when the cancer is localized to a discrete area. Along with the cancer, some part of the normal surrounding tissue is also removed to ensure that no cancer cells remain in the area. Since cancer usually spreads via the lymphatic system, adjoining lymph nodes may be examined and sometimes they are removed as well.
  • Preventive surgery: Preventive or prophylactic surgery involves removal of an abnormal looking area that is likely to become malignant over time. For example, about 40% of the people with a colon disease known as ulcerative colitis, ultimately die of colon cancer. Rather than live with the fear of developing colon cancer, these people may choose to have their colons removed and reduce the risk significantly.
  • Diagnostic purposes: The most definitive tool for diagnosing cancer is a biopsy. Sometimes a biopsy can be performed by inserting a needle through the skin. However, at other times, the only way to obtain some tissue sample for biopsy, is by performing a surgical operation.
  • Cytoreductive surgery: is a procedure where the doctor removes as much of the cancer as possible, and then treats the remaining with radiation therapy or chemotherapy or both.
  • Palliative surgery: is aimed at curing the symptoms, not the cancer. Usually, in such cases, the tumor is so large or has spread so much that removing the entire tumor is not an option. For example, a tumor in the abdomen may be so large, that it may press on and block a portion of the intestine, interfering with digestion and causing pain and vomiting. Debulking surgery may remove a part of the blockage and relieve the symptoms. In tumors that are dependent on hormones, removal of the organs that secrete the hormones is an option. For example, in prostate cancer, the release of testosterone by the testicles stimulates the growth of cancerous cells. Hence, a man may undergo an orchiectomy (removal of testicles) to slow the progress of the disease. Similarly, in a type of aggressive breast cancer, removal of the ovaries (oophorectomy) in women will stop the synthesis of hormones from the ovaries and slow the progression of the cancer.

Radiation

Radiation kills cells. Radiation is used alone in cases where a tumor is unsuitable for surgery. More often, it is used in conjunction with surgery and chemotherapy. Radiation can be either external or internal. In the external form, the radiation is aimed at the tumor from outside the body. In internal radiation (also known as brachytherapy), a radioactive substance, in the form of pellets or liquid is placed at the cancerous site by means of a pill, injection, or insertion in a sealed container.

Chemotherapy

Chemotherapy is the use of drugs to more specifically kill cancer cells. It destroys the hard-to-detect cancer cells that have spread and are circulating in the body. Chemotherapeutic drugs can be taken either orally (by mouth) or intravenously, and may be given alone or in conjunction with surgery, radiation, or both.

When chemotherapy is used before surgery or radiation, it is known as primary chemotherapy or neoadjuvant chemotherapy. An advantage of neoadjuvant chemotherapy is that since the cancer cells have not been exposed to anti-cancer drugs, they are especially vulnerable. It can therefore be used effectively to reduce the size of the tumor for surgery or target it for radiation. However, the toxic effects of neoadjuvant chemotherapy are severe. In addition, it may make the body less tolerant to the side effects of other treatments that follow such as radiation therapy. The more common use of chemotherapy is adjuvant therapy, which is given to enhance the effectiveness of other treatments For example, after surgery, adjuvant chemotherapy is given to destroy any cancerous cells that still remain in the body.

Immunotherapy

Immunotherapy uses the bodys own immune system to destroy cancer cells. This form of treatment is being intensively studied in clinical trials and is not yet widely available to most cancer patients. The various immunological agents being tested include substances produced by the body (such as the interferons, inter-leukins, and growth factors), monoclonal antibodies, and vaccines. Unlike traditional vaccines, cancer vaccines do not prevent cancer. Instead, they are designed to treat people who already have the disease. Cancer vaccines work by boosting the bodys immune system and training the immune cells to specifically destroy cancer cells.

Hormone therapy

Hormone therapy is standard treatment for some types of cancers that are hormone-dependent and grow faster in the presence of particular hormones. These include cancer of the prostate, breast, and uterus. Hormone therapy involves blocking the production or action of these hormones. As a result the growth of the tumor slows down and survival may be extended for several months or years.

Bone marrow transplantation

The bone marrow is the tissue within the bone cavities that contains blood-forming cells. Healthy bone marrow tissue constantly replenishes the blood supply and is essential to life. Sometimes, the amount of drugs or radiation needed to destroy cancer cells also destroys bone marrow. Replacing the bone marrow with healthy cells counteracts this adverse effect. A bone marrow transplant is the removal of marrow from one person and the transplant of the blood-forming cells either to the same person or to some one else. Bone-marrow transplantation, while not a therapy in itself, is often used to rescue a patient, by allowing those with cancer to undergo very aggressive therapy.

Many different specialists generally work together as a team to treat cancer patients. An oncologist is a physician who specializes in cancer care. The oncologist provides chemotherapy, hormone therapy, and any other non-surgical treatment that does not involve radiation. The oncologist often serves as the primary physician and coordinates the patients treatment plan.

The radiation oncologist specializes in using radiation to treat cancer, while the surgical oncologist performs the operations needed to diagnose or treat cancer. Gynecologist-oncologists and pediatric-oncologists, as their titles suggest, are physicians involved with treating womens and childrens cancers respectively. Many other specialists may also be involved in the care of a cancer patient. For example, radiologists specialize in the use of x-rays, ultrasounds, CT scans, MRIs, and other techniques that are used to diagnose cancer. Hematologists specialize in disorders of the blood and are consulted in case of blood cancers and bone marrow cancers. The samples that are removed for biopsy are sent to a laboratory, where a pathologist examines them to determine the type of cancer and extent of the disease. Only some of the specialists who are involved with cancer care have been mentioned above. There are many other specialties, and virtually any type of medical or surgical specialist may become involved with care of the cancer patient should it become necessary.

Alternative treatment

There are a multitude of alternative treatments available to help the person with cancer. They can be used in conjunction with, or separate from, surgery, chemotherapy, and radiation therapy. Alternative treatment of cancer is a complicated arena and a trained health practitioner should be consulted.

The effectiveness of complementary therapies such as acupuncture in alleviating cancer pain has not been clinically proven. Bodywork therapies such as massage and reflexology ease muscle tension and may alleviate the side effects such as nausea and vomiting. Homeopathy and herbal remedies used in Chinese traditional herbal medicine have also been reported to alleviate some of the side effects of radiation and chemotherapy and are being recommended by many doctors.

Certain foods including many vegetables, fruits, and grains are believed to offer protection against various cancers. However, isolation of the individual constituent of vegetables and fruits that are anti-cancer agents has proven difficult. In laboratory studies, vitamins such as A, C and E, as well as compounds such as isothiocyanates and dithiolthiones found in broccoli, cauliflower, and cabbage, and beta-carotene found in carrots have been shown to protect against cancer. Studies have shown that eating a diet rich in fiber as found in fruits and vegetables reduces the risk of colon cancer. Exercise and a low fat diet help control weight and reduce the risk of endometrial, breast, and colon cancer.

Certain drugs, which are currently being used for treatment, could also be suitable for prevention. For example, the drug tamoxifen (Nolvadex®), that has been very effective against breast cancer, is currently being tested by the National Cancer Institute, for its ability to prevent cancer. Similarly, retinoids derived from vitamin A are being tested for their ability to slow the progression or prevent head and neck cancers. Certain studies have suggested that cancer incidence is lower in areas where soil and foods are rich in the mineral selenium. More trials are needed to explain these intriguing connections.

Prognosis

Life-time risk is the term that cancer researchers use to refer to the probability that an individual, over the course of a lifetime will develop cancer or die from it. In the United States, men have a 1 in 2 lifetime risk of developing cancer, and for women the risk is 1 in 3. Overall, African-Americans are more likely to develop cancer than whites. African-Americans are also 30% more likely to die of cancer than whites.

Many cancers are curable if detected and treated at their early stages. A cancer patients prognosis is affected by many factors, particularly the type of cancer the patient has, the stage of the cancer, the extent to which it has metastasized and the aggressiveness of the cancer. In addition, the patients age, general health status, and the effectiveness of the treatment being pursued are also important factors.

KEY TERMS

Benign A growth that does not spread to other parts of the body. Recovery is favorable with treatment.

Biopsy The surgical removal of a small part of a tumor. The excised tissue is studied under the microscope to determine whether it is benign or malignant.

Bone marrow A spongy tissue located in the hollow centers of certain bones, such as the skull and hip bones. Bone marrow is the site of blood cell generation.

Carcinogen Any substance capable of causing cancer by mutating the cells DNA.

Chemotherapy Use of powerful drugs to kill cancer cells in the human body.

Epithelium The layer of cells that covers external and internal surfaces of the body. The many types of epithelium range from flat cells to long cells to cubed cells.

Hormone therapy Treatment of cancer by inhibiting the production of hormones, such as testosterone and estrogen.

Immunotherapy Treatment of cancer by stimulating the body s immune defense system.

Malignant A general term for cells that can dislodge from the original tumor, invade and destroy other tissues and organs.

Metastasis The spread of cancer from one part of the body to another.

Radiation therapy Treatment using high-energy radiation from x-ray machines, cobalt, radium, or other sources.

Sore An open wound or a bruise or lesion on the skin.

Tumor An uncontrolled growth of tissue, either benign (noncancerous) or malignant (cancerous).

X ray Electromagnetic radiation of very short wavelength, and very high energy.

To help predict the future course and outcome of the disease and the likelihood of recovery from the disease, doctors often use statistics. The five-year survival rates are the most common measures used. The number refers to the proportion of people with cancer who are expected to be alive, five years after initial diagnosis, compared with a similar population that is free of cancer. It is important to note that while statistics can give some information about the average survival experience of cancer patients in a given population, it cannot be used to indicate individual prognosis, because no two patients are exactly alike.

Prevention

According to nutritionists and epidemiologists from leading universities in the United States, a person can reduce the chances of getting cancer by following some simple guidelines:

  • Eating plenty of vegetables and fruits,
  • Exercising regularly,
  • Avoiding excessive weight gain,
  • Avoiding tobacco (including second hand smoke),
  • Avoiding excessive amounts of alcohol,
  • Avoiding the midday sun (between 11 a.m. and 3 p.m.) when the suns rays are the strongest,
  • Avoiding risky sexual practices, and
  • Avoiding known carcinogens in the environment or work place.

In addition, a vaccine (Guardasil) is now (as of 2007) available for young women against HPV (human papilloma virus). HPV infection is responsible for the eventual development of over two-thirds of cervical cancer cases.

See also Gene therapy; Immunology; Nuclear medicine; Radioisotopes in medicine; Stem cells.

Resources

BOOKS

Haskell, Charles M. Cancer Treatment, 5th ed. Philadelphia, PA: W.B. Saunders, 2001.

King, Roger, J.B., and Mike W. Robins. Cancer Biology. Harlow, UK, and New York: Pearson/Prentice Hall, 2006.

Rosenbaum, Ernst H. MD, et al. Everyones Guide to Cancer Therapy, 4th ed. Riverside, NJ: Andrews McMeel Publishing, 2002.

Souhami, Robert L. Oxford Textbook of Oncology. Oxford, UK, and New York: Oxford University Press, 2002.

Tannock, Ian F., ed. The Basic Science of Oncology. New York: McGraw-Hill Medical Publishing Division, 2005.

PERIODICALS

Brookes, Anthony, Rethinking Genetic Strategies to Study Complex Diseases, Trends in Molecular Medicine (November 2001):5126.

OTHER

National Institutes of Health. National Cancer Institute. cancer.gov <http://www.nci.nih.gov/> (accessed November 28, 2006).

Lata Cherath Micheal Sullivan

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Cancer

Cancer

Definition

Cancer is not just one disease, but a large group of almost 100 diseases. Its two main characteristics are uncontrolled growth of the cells in the human body and the ability of these cells to migrate from the original site and spread to distant sites. If the spread is not controlled, cancer can result in death .

Description

One out of every four deaths in the United States is from cancer. About 1.4 million Americans are diagnosed with cancer annually. More than 550,000 people in the United States were anticipated to die of cancer in 2008. This equates to more than 1,500 deaths from cancer per day. Overall, cancer death

Percentage of people in the United States age 65 and over who reported having cancer, by sex and by race, 2005–2006
Sex Percent
Data is based on a 2-year average from 2005–2006.
source: National Health Interview Survey, National Center for
Health Statistics, Centers for Disease Control and Prevention,
U.S. Department of Health and Human Services
(Illustration by GGS Information Services. Cengage Learning, Gale)
Men23.6%
Women19.3%
Total 21.1%
Race Percent
White23.4%
Black11.5%
Hispanic or Latino12.1%

rates for both men and women have decreased since 2004. However, cancer ranks as the number one cause of death in persons under the age of 85 and ranks second only to heart disease as a cause of death overall in the United States.

Cancer, by definition, is a disease of the genes. A gene is a small part of DNA, which is the master molecule of the cell. Genes make proteins, which are the ultimate workhorses of the cells. these proteins allow the body to carry out all the many processes that permits an individual function, to breathe, think, and move.

Throughout people's lives, the cells in their bodies are growing, dividing, and replacing themselves. Many genes produce proteins that are involved in controlling the processes of cell growth and division. An alteration (mutation) to the DNA molecule can disrupt the genes and produce faulty proteins. This causes the cell to become abnormal and lose its restraints on growth. The abnormal cell begins to divide uncontrollably and eventually forms a new growth known as a tumor or neoplasm (medical term for cancer meaning “new growth”).

In a healthy individual, the immune system can recognize the neoplastic cells and destroy them before

Number of deaths from cancer in the U.S. by age, 2004
Age Number of Deaths
source: National Vital Statistics Reports, Vol. 55. No. 19,
National Center for Health Statistics, Centers for Disease Control
and Prevention, U.S. Department of Health and Human Services
(Illustrationby GGS Information Services. Cengage Learning, Gale)
45−5449,520
55−6496,958
65−74139,417
75−84166,085
85+80,345

they get a chance to divide. However, some mutant cells may escape immune detection and survive to become tumors or cancers.

Tumors are of two types, benign or malignant. A benign tumor is not considered cancer. It is slow growing, does not spread or invade surrounding tissue, and once it is removed, does not usually recur. A malignant tumor, by contrast, is cancer. It invades surrounding tissue and spreads to other parts of the body. If the cancer cells have spread to the surrounding tissues, even after the malignant tumor is removed, it generally recurs.

A majority of cancers are caused by changes in the cell's DNA because of damage due to the environment. Environmental factors that are responsible for causing the initial mutation in the DNA are called carcinogens, and there are many types.

Some cancers have a genetic basis. In other words, individuals can inherit faulty DNA from a parent, which could predispose the person to getting cancer. While there is scientific evidence that both factors (environmental and genetic) play a role, less than 10% of all cancers are strictly hereditary. Cancers that are known to have a hereditary link are breast cancer , colon cancer , ovarian cancer , and uterine cancer. Besides genes, certain physiological traits could be inherited and could contribute to cancers. For example, inheriting fair skin makes a person more likely to develop skin cancer , but only if that person also has prolonged exposure to intensive sunlight.

There are several different types of cancers:

  • Carcinomas are cancers that arise in the epithelium (the layer of cells covering the body's surface and lining the internal organs and various glands). Ninety percent of human cancers fall into this category. Carcinomas can be subdivided into two types: adenocarcinomas (those that develop in an organ or a gland) and squamous cell carcinomas (those that originate in the skin).
  • Melanomas also originate in the skin, usually in the pigment cells (melanocytes).
  • Sarcomas are cancers of the supporting tissues of the body, such as bone, muscle, and blood vessels.
  • Cancers of the blood and lymph glands are called leukemias and lymphomas respectively.
  • Gliomas are cancers of the nerve tissue.

Demographics

Cancer can attack anyone. Since the occurrence of cancer increases as individuals age, most of the cases are seen in adults, middle-aged or older. Sixty percent of all cancers are diagnosed in people who are older than 65 years of age. The probability of an American male developing an invasive cancer or dying from cancer in his lifetime is 1 in 2; for American females the probability is 1 in 3. The most common cancers are skin cancer, lung cancer , colon cancer, breast cancer (in women), and prostate cancer (in men). In addition, cancer of the kidneys, ovaries, uterus, pancreas, bladder, rectum, and blood and lymph node cancer (leukemias and lymphomas) are also included among the 12 major cancers that affect most Americans.

Causes and symptoms

The major risk factors for cancer are: tobacco, alcohol, diet , sexual and reproductive behavior, infectious agents, family history, occupation, and environment and pollution.

According to estimates of the American Cancer Society (ACS), approximately 40% of cancer deaths in 2008 were anticipated to be due to tobacco and excessive alcohol use. An additional one-third of the deaths were expected to be related to being overweight, being obese, lacking physical activity, and having poor nutrition . Many of the one million skin cancers diagnosed in 2008 were believed to be a direct result of overexposure to ultraviolet light from the sun's rays.

Tobacco

Eighty to 90% of lung cancer cases occur in smokers. Smoking has also been shown to be a contributory factor in cancers of the upper respiratory tract, esophagus, larynx, bladder, pancreas, and probably liver, stomach, breast, and kidney as well. In the 2000s, scientists also showed that second-hand smoke (or passive smoking) can increase one's risk of developing cancer.

Alcohol

Excessive consumption of alcohol is a risk factor in certain cancers, such as liver cancer . Alcohol, in combination with tobacco, significantly increases the chances that an individual will develop mouth, pharynx, larynx, and esophageal cancers.

Diet

Thirty-five percent of all cancers are due to dietary causes. Excessive intake of fat leading to obesity has been associated with cancers of the breast, colon, rectum, pancreas, prostate, gall bladder, ovaries, and uterus.

Sexual and reproductive behavior

The human papillomavirus, which is sexually transmitted, has been shown to cause cancer of the cervix. Having too many sex partners and becoming sexually active early has been shown to increase one's chances of contracting this disease. In addition, it has also been shown that women who do not have children or have children late in life have an increased risk for both ovarian and breast cancer.

Infectious agents

Between 1985 and 2005, scientists obtained evidence to show that approximately 15% of the world's cancer deaths can be traced to viruses , bacteria, or parasites.

Family history

Certain cancers such as breast, colon, ovarian, and uterine cancer recur generation after generation in some families. A few cancers, such as the eye cancer retinoblastoma, a type of colon cancer, and a type of breast cancer known as early-onset breast cancer, have been shown to be linked to certain genes that can be tracked within a family. It is, therefore, possible that inheriting particular genes makes a person susceptible to certain cancers.

Occupational hazards

There is evidence to show that certain occupational hazards account for 4% of all cancer deaths. For example, asbestos workers have an increased incidence of lung cancer. Similarly, a higher likelihood of getting bladder cancer is associated with dye, rubber, and gas workers; skin and lung cancer with smelters, gold miners, and arsenic workers; leukemia with glue and varnish workers; liver cancer with PVC manufacturers; and lung, bone, and bone marrow cancer with radiologists and uranium miners.

Environment

Radiation is believed to cause 1–2% of all cancer deaths. Ultra-violet radiation from the sun accounts for a majority of melanoma deaths. Other sources of radiation are x rays, radon gas, and ionizing radiation from nuclear material.

Pollution

Several studies have shown a link between asbestos and cancer. Chlorination of water may account for a small rise in cancer risk. However, the main danger from pollution occurs when dangerous chemicals from the industries escape into the surrounding environment. It has been estimated that 1% of cancer deaths are due to air, land, and water pollution.

Symptoms

Cancer is a progressive disease and goes through several stages. Each stage may produce a number of symptoms. Some symptoms are produced early and may occur due to a tumor that is growing within an organ or a gland. As the tumor grows, it may press on the nearby nerves, organs, and blood vessels. This causes pain and some pressure, which may be the earliest warning signs of cancer.

Despite the fact that there are several hundred different types of cancers, producing very different symptoms, the ACS has established the following seven symptoms as possible warning signals of cancer:

  • changes in the size, color, or shape of a wart or a mole
  • a sore that does not heal
  • persistent cough, hoarseness, or sore throat
  • a lump or thickening in the breast or elsewhere
  • unusual bleeding or discharge
  • chronic indigestion or difficulty in swallowing
  • any change in bowel or bladder habits

Many other diseases besides cancer can produce the same symptoms. However, it is important to have these symptoms checked, as soon as possible, especially if they linger. The earlier a cancer is diagnosed and treated, the better the chance of it being cured. Many cancers such as breast cancer may not have any early symptoms. Therefore, it is important to undergo routine screening tests such as breast self-exams and mammograms.

Diagnosis

Diagnosis begins with a thorough physical examination and a complete medical history. The doctor will observe, feel, and palpate (apply pressure by touch) different parts of the body in order to identify any variations from the normal size, feel, and texture of the organ or tissue.

As part of the physical exam, the doctor will inspect the patient's mouth. By focusing a light into the mouth, he will look for abnormalities in color, moisture, surface texture, or presence of any thickening or sores in the lips, tongue, gums, the hard palate on the roof of the mouth, and the throat. To detect thyroid cancer , the doctor will observe the front of the neck for swelling. He may gently manipulate the neck and palpate the front and side surfaces of the thyroid gland (located at the base of the neck) to detect any nodules or tenderness. As part of the physical examination, the doctor will also palpate the lymph nodes in the neck, under the arms, and in the groin. Many illnesses and cancers cause a swelling of the lymph nodes.

The doctor may conduct a thorough examination of the skin to look for sores that have been present for more than three weeks and that bleed, ooze, or crust; irritated patches that may itch or hurt; and any change in the size of a wart or a mole.

Examination of the female pelvis is used to detect cancers of the ovaries, uterus, cervix, and vagina. In the visual examination, the doctor looks for abnormal discharges or the presence of sores. Then, using gloved hands the physician palpates the internal pelvic organs such as the uterus and ovaries to detect any abnormal mass. Breast examination includes visual observation where the doctor looks for any discharge, unevenness, discoloration, or scaling. The doctor palpates both breasts to feel for masses or lumps.

For males, inspection of the rectum and the prostate is also included in the physical examination. The doctor inserts a gloved finger into the rectum and rotates it slowly to feel for any growths, tumors, or other abnormalities. The doctor also conducts an examination of the testes, in which the doctor observes the genital area and looks for swelling or other abnormalities. The testicles are palpated to identify any lumps, thickening, or differences in the size, weight and firmness.

If the doctor detects an abnormality on physical examination, or the patient has some symptom that could be indicative of cancer, the doctor may order diagnostic tests.

Laboratory studies of sputum (sputum cytology), blood, urine, and stool can detect abnormalities that may indicate cancer. Sputum cytology is a test in which the phlegm that is coughed up from the lungs is microscopically examined. It is often used to detect lung cancer. A blood test for cancer is easy to perform, usually inexpensive and risk-free. The blood sample is obtained by a lab technician or a doctor by inserting a needle into a vein and is relatively painless. Blood tests can be either specific or non-specific. Often, in certain cancers, the cancer cells release particular proteins (called tumor markers) and blood tests can be used to detect the presence of these tumor markers. However, with a few exceptions, tumor markers are not used for routine screening of cancers, because several non-cancerous conditions also produce positive results. Blood tests are generally more useful in monitoring the effectiveness of the treatment, or in following the course of the disease and detecting recurrent disease.

Imaging tests such as computed tomography scans (CT scans ), magnetic resonance imaging (MRI), ultrasound and fiberoptic scope examinations help the doctors determine the location of the tumor even if it is deep within the body. Conventional x rays are often used for initial evaluation because they are relatively cheap, painless, and easily accessible. In order to increase the information obtained from a conventional x ray, air or a dye (such as barium or iodine) may be used as a contrast medium to outline or highlight parts of the body.

The most definitive diagnostic test is the biopsy, wherein a piece of tissue is surgically removed for microscope examination. Besides confirming a cancer, the biopsy also provides information about the type of cancer, the stage it has reached, the aggressiveness of the cancer, and the extent of its spread. Since a biopsy provides the most accurate analysis, it is considered the gold standard of diagnostic tests.

Screening examinations conducted regularly by healthcare professionals can result in the detection of cancers of the breast, colon, rectum, cervix, prostate, testis, tongue, mouth, and skin at early stages, when treatment is more likely to be successful. Some of the routine screening tests recommended by the ACS are sigmoidoscopy (for colorectal cancer), mammography (for breast cancer), pap smear (for cervical cancer ), and the PSA test (for prostate cancer). Self-examinations for cancers of the breast, testes, mouth, and skin can also help in detecting the tumors before the symptoms become serious.

A revolution in molecular biology and cancer genetics has contributed a great deal to the development of several tests designed to assess the risk of getting cancers. These new techniques include genetic testing, in which molecular probes are used to identify mutations in certain genes that have been linked to particular cancers. As of 2008, however, there were a lot of limitations to genetic testing and its utility appeared ambiguous, emphasizing the need to develop better strategies for early detection.

Treatment

Treatment and prevention of cancers continued to be the focus of a great deal of research as of 2008. Research into new cancer therapies included cancer-targeting gene therapy, cancer vaccines, and other targeted therapies such as monoclonal antibodies. However, all of these new therapies take years of clinical testing and research.

The aim of cancer treatment is to remove all or as much of the tumor as possible and to prevent the recurrence or spread of the primary tumor. While devising a treatment plan for cancer, the likelihood of curing the cancer has to be weighed against the side effects of the treatment. If the cancer is very aggressive and a cure is not possible, then the treatment should be aimed at relieving the symptoms and controlling the cancer for as long as possible.

Cancer treatment can take many different forms, and it is typically tailored to the individual patient. The decision on which type of treatment is the most appropriate depends on the type and location of cancer, the extent to which it has already spread, the patient's age, sex, general health status, and personal treatment preferences. The major types of treatment are: surgery, radiation, chemotherapy , biological therapy, targeted therapy, hormone therapy, and bone-marrow and stem cell transplantation.

Surgery

Surgery is the removal of a visible tumor and is the most frequently used cancer treatment. It is most effective when a cancer is small and confined to one area of the body.

Surgery can be used for many purposes.

  • Treatment. Treatment of cancer by surgery involves removal of the tumor to cure the disease. This is typically done when the cancer is localized to a discrete area. Along with the cancer, some part of the normal surrounding tissue is also removed to ensure that no cancer cells remain in the area. Since cancer usually spreads via the lymphatic system, adjoining lymph nodes may be examined and sometimes are removed as well.
  • Preventive surgery. Preventive or prophylactic surgery involves removal of an abnormal looking area that is likely to become malignant over time. For example, 40% of people with a colon disease known as ulcerative colitis ultimately die of colon cancer. Rather than live with the fear of developing colon cancer, these people may choose to have their colons removed and reduce the risk significantly.
  • Diagnostic purposes. The most definitive tool for diagnosing cancer is a biopsy. Sometimes, a biopsy can be performed by inserting a needle through the skin. At other times, the only way to obtain a tissue sample for biopsy is by performing a surgical operation.
  • Cytoreductive surgery is a procedure in which the doctor removes as much of the cancer as possible and then treats the remaining area with radiation therapy or chemotherapy or both.
  • Palliative surgery is aimed at curing the symptoms, not the cancer. Usually, in such cases, the tumor is so large or has spread so much that removing the entire tumor is not an option. For example, a tumor in the abdomen may be so large that it may press on and block a portion of the intestine, interfering with digestion and causing pain and vomiting. Debulking surgery removes a part of the blockage and relieves the symptoms. In tumors that are dependent on hormones, removal of the organs that secrete the hormones is an option. For example, in prostate cancer, the release of testosterone by the testicles stimulates the growth of cancerous cells. Hence, a man may undergo an orchiectomy (removal of testicles) to slow the progress of the disease. Similarly, in a type of aggressive breast cancer, removal of the ovaries (oophorectomy) stops the synthesis of hormones from the ovaries and slows the progression of the cancer.

Radiation therapy

Radiation kills tumor cells. Radiation is used alone in cases in which a tumor is unsuitable for surgery. More often, it is used in conjunction with surgery and chemotherapy. Radiation can be either external or internal. In the external form, the radiation is aimed at the tumor from outside the body. In internal radiation (also known as brachytherapy), a radioactive substance in the form of pellets or liquid is placed at the cancerous site by means of a pill, injection, or insertion in a sealed container.

Chemotherapy

Chemotherapy is the use of drugs to kill cancer cells. It destroys the hard-to-detect cancer cells that have spread and are circulating in the body. Chemotherapeutic drugs can be taken either orally (by mouth) or intravenously and may be given alone or in conjunction with surgery, radiation, or both.

When chemotherapy is used before surgery or radiation, it is known as primary chemotherapy or neoadjuvant chemotherapy. An advantage of neoadjuvant chemotherapy is that since the cancer cells have not been exposed to anti-cancer drugs, they are especially vulnerable. It can, therefore, be used effectively to reduce the size of the tumor for surgery or target it for radiation. However, the toxic effects of neoadjuvant chemotherapy are severe. In addition, it may make the body less tolerant to the side effects of other treatments that follow, such as radiation therapy. The more common use of chemotherapy is adjuvant therapy, which is given to enhance the effectiveness of other treatments. For example, after surgery, adjuvant chemotherapy is given to destroy any cancerous cells that still remain in the body.

Biological and targeted therapies

Biological and targeted therapies use the body's own immune system to destroy cancer cells. As of 2008, this form of treatment was being intensively studied in clinical trials and many newer agents were commonly in use to treat a variety of cancers. The various agents being tested included substances produced by the body (such as the interferons, interleukins, and growth factors), monoclonal antibodies, and vaccines. Unlike traditional vaccines, cancer vaccines do not prevent cancer. Instead, they are designed to treat people who already have the disease. Cancer vaccines work by boosting the body's immune system and training the immune cells to specifically destroy cancer cells.

Hormone therapy

Hormone therapy is standard treatment for some types of cancers that are hormone-dependent and grow faster in the presence of particular hormones. These include cancer of the prostate, breast, and uterus. Hormone therapy involves blocking the production or action of these hormones. As a result, the growth of the tumor slows, and survival may be extended for several months or years.

QUESTIONS TO ASK YOUR DOCTOR

  • What are my specific risk factors for cancer?
  • How can I minimize or eliminate those risks?
  • What foods should I increase or reduce or eliminate in my diet?
  • What are the most current guidelines for nutrition and physical activity as recommended by the American Cancer Society?
  • What annual cancer screening tests are recommended for my age and gender?

Bone marrow, stem cell, and cord blood transplantation

The bone marrow is the tissue within the bone cavities that contains blood-forming cells. Healthy bone marrow tissue constantly replenishes the blood supply and is essential to life. Sometimes, the amount of drugs or radiation needed to destroy cancer cells also destroys bone marrow. Replacing the bone marrow with healthy cells counteracts this adverse effect. A bone marrow transplant is the removal of marrow from one person and the transplant of the blood-forming cells either to the same person or to someone else. Bone-marrow transplantation, while not a therapy in itself, is often used to rescue patients, by allowing those with cancer to undergo aggressive therapy. Stem cell transplants have been performed to replace bone marrow that has been destroyed by cancer, chemotherapy, or radiation therapy. Stem cells are specialized cells in the bone marrow from which the body receives a constant source of blood cells. Stem cells may also be harvested from umbilical cords, a process which is referred to as cord blood transplant. Some cancers in which stem cell transplants may be used include leukemia, lymphoma, and multiple myeloma .

Alternative treatment

There are a multitude of alternative treatments available to help the person with cancer. They can be used in conjunction with, or separate from, surgery, chemotherapy, and radiation therapy. Alternative treatment of cancer is a complicated arena and a trained health practitioner should be consulted.

Although the effectiveness of complementary therapies such as acupuncture in alleviating cancer pain has not been clinically proven, many cancer patients find it safe and beneficial. Bodywork therapies such as massage and reflexology ease muscle tension and may alleviate side effects such as nausea and vomiting. Homeopathy and herbal remedies used in Chinese traditional herbal medicine also have been shown to alleviate some of the side effects of radiation and chemotherapy and are recommended by many doctors.

Cancer treatment team

Many different specialists generally work together as a team to treat cancer patients. An oncologist is a physician who specializes in cancer care. The oncologist provides chemotherapy, hormone therapy, and any other non-surgical treatment that does not involve radiation. The oncologist often serves as the primary physician and coordinates the patient's treatment plan.

The radiation oncologist specializes in using radiation to treat cancer, whereas the surgical oncologist performs the operations needed to diagnose or treat cancer. Gynecologist-oncologists and pediatric-oncologists, as their titles suggest, are physicians involved with treating women's and children's cancers, respectively. Many other specialists also may be involved in the care of a cancer patient. For example, radiologists specialize in the use of x rays, ultrasounds, CT scans, MRI imaging and other techniques that are used to diagnose cancer. Hematologists specialize in disorders of the blood and are consulted in case of blood cancers and bone marrow cancers. The samples that are removed for biopsy are sent to a laboratory, where a pathologist examines them to determine the type of cancer and extent of the disease. There are many other specialties, and virtually any type of medical or surgical specialist may become involved with care of the cancer patient should it become necessary.

Nutrition/Dietetic concerns

Certain foods, including many vegetables, fruits, and grains, are believed to offer protection against various cancers. However, isolation of the individual constituent of vegetables and fruits that are anti-cancer agents has proven difficult. In laboratory studies, vitamins such as A, C, and E, as well as compounds such as isothiocyanates and dithiolthiones found in broccoli, cauliflower, and cabbage, and beta-carotene found in carrots have been shown to protect against cancer. Studies have shown that eating a diet rich in fiber as found in fruits and vegetables reduces the risk of colon cancer. Exercise and a low fat diet help control weight and reduce the risk of endometrial, breast, and colon cancer.

KEY TERMS

Benign —Mild, nonmalignant. Recovery is favorable with treatment.

Biopsy —The surgical removal and microscopic examination of living tissue for diagnostic purposes.

Bone marrow —Spongy material that fills the inner cavities of the bones. The progenitors of all the blood cells are produced in this bone marrow.

Carcinogen —Any substance capable of causing cancer by mutating the cell's DNA.

Chemotherapy —Treatment with certain anticancer drugs.

Epithelium —The layer of cells covering the body's surface and lining the internal organs and various glands.

Hormone therapy —Treatment of cancer by inhibiting the production of hormones such as testosterone and estrogen.

Immunotherapy —Treatment of cancer by stimulating the body's immune defense system.

Malignant —A general term for cells and the tumors they form that can invade and destroy other tissues and organs.

Metastasis —The spread of cancer from one part of the body to another.

Radiation therapy —Treatment using high-energy radiation from x-ray machines, cobalt, radium, or other sources.

Sore —An open wound, bruise, or lesion on the skin.

Tumor —An abnormal growth resulting from a cell that lost its normal growth control restraints and started multiplying uncontrollably.

X rays —High-energy radiation used in high doses, either to diagnose or treat disease.

Prognosis

Lifetime risk is the phrase that cancer researchers use to refer to the probability that an individual over the course of a lifetime will develop cancer or die from it. In the United States, men have a one in two lifetime risk of developing cancer, and for women the risk is one in three. Overall, African Americans are more likely to develop cancer than whites. African Americans are also 30% more likely to die of cancer than whites.

Most cancers are curable if detected and treated at their early stages. A cancer patient's prognosis is affected by many factors, particularly the type of cancer the patient has, the stage of the cancer, the extent to which it has metastasized, and the aggressiveness of the cancer. In addition, the patient's age, general health status, and the effectiveness of the treatment being pursued are important factors.

To help predict the future course and outcome of the disease and the likelihood of recovery from the disease, doctors often use statistics. The five-year survival rates are the most common measures used. The number refers to the proportion of people with cancer who are expected to be alive five years after initial diagnosis compared with a similar population that is free of cancer. It is important to note that while statistics can give some information about the average survival experience of cancer patients in a given population, they cannot be used to indicate individual prognosis because no two patients are exactly alike.

Prevention

According to nutritionists and epidemiologists from leading universities in the United States, a person can reduce the chances of getting cancer by following some simple guidelines:

  • eating plenty of vegetables and fruits
  • exercising vigorously for at least 30 minutes on 5 or more days every week, forty-five to sixty minutes of moderate to vigorous physical activity is preferable
  • avoiding excessive weight gain
  • avoiding tobacco (even secondhand smoke)
  • decreasing or avoiding consumption of animal fats and red meats
  • avoiding excessive amounts of alcohol
  • avoiding the midday sun (between 11 a.m. and 3 p.m.) when the sun's rays are the strongest
  • avoiding risky sexual practices
  • avoiding known carcinogens in the environment or work place

Resources

BOOKS

Quillan, Patrick. Beating Cancer with Nutrition. Tulsa, OK: Nutrition Times Press, 2005.

Walsh, Patrick C., and Janet Farrar Worthington. Dr. Patrick Walsh's Guide to Surviving Prostate Cancer, 2nd ed. Petalulma, CA: Wellness Central, 2007.

PERIODICALS

“Cancer Statistics 2008.” CA: A Cancer Journal for Clinicians (March 2008): 71–96.

ORGANIZATIONS

American Cancer Society, PO Box 22718, Oklahoma City, OK, 73123-1718, (800) ACS-2345, https://www.cancer.org/.

National Cancer Institute, 6116 Executive Blvd., Room 3036A, Bethesda, MD, 20892-8322, (800) 422-6237, http://www.cancer.gov.

National Coalition for Cancer Survivorship, 1010 Wayne Avenue, 5th Floor, Suite 300, Silver Spring, MD, 20910, (888) 650-9127, http://www.canceradvocacy.org/.

Rosalyn Carson-DeWitt MD

Teresa G. Odle

Melinda Oberleitner R.N., D.N.S.

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Cancer

CANCER


Cancer is the common name for a group of 100 or more chronic, progressive diseases, all characterized by abnormal and continuous multiplication of cells in a particular tissue or organ without reference to the needs of the body. This commonly gives rise to a solid mass or tumor composed of such cells (e.g., in the lung, breast, or brain), but it can also affect almost any tissue or organ, including the blood-forming cells of the bone marrow (leukemias), the immune defense system (lymphomas), and the soft tissues, such as muscles, cartilage, or blood vessels (sarcomas). Invasion of the organ or tissue of origin by a malignant tumor–called a neoplasm, or new growth–can itself be fatal, but cancer mortality arises mainly from the tendency of most cancers to metastasize elsewhere in the body and to disable or destroy vital organs such as the brain, lung, liver, or bone marrow.

Cancer afflicts all animals as well as humans. The ultimate cause of all cancers is failed control of the growth, reproduction, or senescence (aging) of cells. This is due in turn to inherited and/or acquired damage to cellular DNA, giving rise to a malignant clone comprising all the descendant cells of the original cancerous cell. Inherited susceptibility can greatly increase the risk of developing cancer, but it appears to account for only a small proportion of all cancers, and congenital malignancy is extremely rare. Cumulative genetic damage acquired over the course of life accounts for the occurrence of most cancers. Knowledge in this domain is likely to increase rapidly with further progress in cancer genetics following the completion of the Human Genome Project.

Among the known environmental causes of cancer, use of tobacco (smoking, chewing, sucking, or inhaling) is the most important and most widely recognized. Tobacco use probably accounted for up to a third of all cancers in 2000, and a higher proportion of all cancer deaths, since it is a cause of some of the most fatal cancers–lung, larynx, pharynx, esophagus, and pancreas. Other causes include:

  • Exposure to certain chemicals and other substances. For example, benzene exposure is a cause of leukemias, and exposure to asbestos produces mesothelioma of the lung lining and abdomen.
  • Ionizing radiation. X-rays and γ-radiation cause solid tumors as well as leukemias.
  • Solar or artificial ultraviolet radiation. Exposure produces skin cancers including melanoma.
  • Obesity. Obesity increases the risk of breast and colon cancers.
  • Infection by certain bacteria. For example, Helicobacter pylori is a cause of stomach cancer.
  • Infection by certain viruses. Certain human papilloma viruses (HPV) cause cervical cancer; some hepatitis viruses cause liver cancer; human immunodeficiency virus (HIV) causes Kaposi sarcoma and other cancers.
  • Infection by certain parasites. For example, some liver flukes can cause biliary tract cancers, and schistosomes are a cause of bladder cancer.

Many cancers can be prevented by avoidance of exposure to the underlying cause or risk factor. Thus, 90 percent of lung cancers that are directly attributable to tobacco use would not occur in the absence of exposure; almost all mesotheliomas would be avoided if asbestos exposure were eliminated. Vaccination against hepatitis B can prevent associated liver cancers, and vaccination against HPV will almost certainly prevent cervical cancers. Mass population screening, in which selected groups of the entire population are systematically invited for regular diagnostic tests, has been shown to reduce mortality from some cancers by detecting tumors at an early stage before they are clinically detectable or give rise to symptoms, and when treatment is more effective for most cancers. The cancers most widely screened for are breast cancer in women aged 50 to 69 (using mammography), and cervical cancer in women of reproductive age and up to age 60 (using a cervical smear or direct visualization). Screening for bowel cancer by detection of occult blood in the stool is also likely to reduce mortality. Mortality from cancers that do occur would be greatly reduced if all patients were diagnosed earlier, investigated thoroughly, and treated appropriately.

Around the turn of the twenty-first century, the International Agency for Research on Cancer (part of the World Health Organization) estimated that about 10 million people worldwide developed cancer every year, and that 6.9 million cancer deaths occurred in 2000, or 12.4 percent of the global death toll. Estimates of global mortality from the most common cancers are shown in Table 1. The economic cost of cancer is huge: over $100 billion dollars a year in medical expenditure and lost productivity in the U.S. alone in 2000. The human cost is incalculable.

The total number of cancers arising in a population depends on the size of the population, its age and sex structure, and the age- and sex-specific risks of developing cancer. All three components differ

TABLE 1

between countries and populations, and over time. Population growth and aging both lead to an increase in the annual number of new cancers. About half of all cancers in 2000 arose in developed countries, with just a quarter of the world's population, but the proportion of cancers arising in developing countries is set to rise substantially as the relatively young populations in those countries increase and become older. About half of all cancers occur over the age of 65 years. Primary prevention to reduce the risk of developing cancer at any given age is, and will remain, the most effective long-term strategy for cancer control.

See also: Diseases, Chronic and Degenerative; Tobacco-Related Mortality.

bibliography

Coleman, Michel, Jacques Estève, Philippe Damiecki, Annie Arslan, and Hélène Renard. 1993. Trends in Cancer Incidence and Mortality (IARC Scientific Publications No. 121). Lyon: International Agency for Research on Cancer.

Miller, Anthony, Jocelyn Chamberlain, Nick Day, Matti Hakama, and Philip Prorok. 1990. "Report on a Workshop of the UICC Project on Evaluation of Screening for Cancer." International Journal of Cancer 46: 761–69.

Peckham, Michael, Herbert Pinedo, and Umberto Veronesi, eds. 1995. Oxford Textbook of Oncology. Oxford, Eng.: Oxford Medical Publications.

Peto, Julian. 2001. "Cancer Epidemiology in the Last Century and the Next Decade." Nature 411: 390–395.

Tomatis, Lorenzo, A. Aitio, Nick Day, Elisabeth Heseltine, John Kaldor, Anthony Miller, et al., eds.1990. Cancer: Causes, Occurrence and Control (IARC Scientific Publications No. 100). Lyon: International Agency for Research on Cancer.

World Health Organization. 2001. The World Health Report 2001. Geneva: World Health Organization.

Michel P. Coleman

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Cancer

Cancer

Definition

Cancer is characterized by uncontrolled growth of cells in the body and the ability of these malignant cells to spread (metastasize) to distant sites within the body. If the spread is not controlled, cancer can result in death. Cancer is not just one disease but a group of almost one hundred different types of malignant diseases.

Description

Cancer, by definition, is a disease of the genes. A gene is a small part of DNA, which is the instruction manual of the cell. Genes hold the instructions to make proteins , which carry out many of the body's functions. It is these proteins that allow the human body to carry out all the processes that permit people to breathe, think, move, etc.

Throughout people's lives the cells in their bodies grow, divide, and replace themselves. Many genes produce proteins that are involved in controlling the processes of cell growth and division. An alteration (mutation) to the DNA molecule can disrupt some of the genes on the DNA molecule and produce faulty proteins. This causes a cell to loose restraint on growth. The abnormal cell begins to divide uncontrollably and eventually forms a new growth known as a tumor or neoplasm (medical terms for cancer meaning new growth). In a healthy body the immune system can recognize neoplastic (abnormal) cells and destroy them before they get a chance to divide. Even so, some mutant cells may escape immune detection and survive to develop into cancerous growths.

Tumors are divided into two general categories: benign or malignant. A benign tumor is slow growing and does not spread or invade surrounding tissue. Once it is removed it doesn't usually recur. A malignant tumor, on the other hand, invades surrounding tissue and can spread to other parts of the body. Malignant tumors can be removed; however, if the cancer cells have spread to the surrounding tissues, the tumor is likely to recur.

A majority of cancers are caused by changes in the cell's DNA that are due to the environment. Environ- mental factors that are responsible for causing the initial mutation in the DNA are called carcinogens. Internal factors can cause cancer as well. Certain hormones have been shown to have an effect the growth or control of a particular cell line. Hormones are substances made by one organ and passed through the bloodstream to perform a function in another organ.

While there is scientific evidence that both environ- mental and genetic factors play a role in most cancers, approximately 5–10% of all cancers are classified as hereditary (genetic). This means a faulty gene that leads to a cancer is passed from parent to child. This poses a greater risk for that particular type of cancer in certain descendants of the family. However, having a cancer- causing gene does not necessarily mean that person will automatically get cancer. Rather, it means that person is predisposed to a type of cancer, or more likely to get this cancer when compared to the general population. Cancers known to have a hereditary tendency in some cases include breast cancer , colon cancer, ovarian cancer, skin cancer, and prostate cancer .

Aside from genes, certain inherited physiological traits can contribute to cancers. For example, inheriting fair skin makes a person more likely to develop skin cancer, but only if they also have prolonged exposure to intensive sunlight.

There are many different types of cancers. Some of the most common types include:

  • Carcinomas. These cancers arise in the epithelium (layers of cells in the skin covering the body's surface and lining the internal organs and various glands). About 80% of human cancers fall into this category. Carcinomas can be subdivided into two subtypes: adenocarcinomas, which are cancers that develop in an organ or a gland; and squamous cell carcinomas, cancers that originate in the skin.
  • Melanomas. This form also originates in the skin, usually in the pigment cells (melanocytes), and can quick- ly metastasize to internal organs.
  • Sarcomas. Cancers of the supporting tissues of the body, such as bone, muscle, cartilage, and fat.
  • Leukemias. Cancers of the blood or blood-forming organs.
  • Lymphomas. Cancer of the lymphatic system , the network of vessels and nodes that acts as a filtration system, distributing nutrients to blood and tissue and preventing bacteria and other foreign substances from entering the bloodstream.
  • Gliomas. Cancers of nerve tissue.

The most common cancers are skin cancer, lung cancer , colon and rectal (colorectal) cancer, breast cancer (in women), and prostate cancer (in men). In addition, cancer of the kidneys , ovaries, uterus, pancreas , bladder, and blood and lymph-node cancer (leukemias and lymphomas) are also included among the 12 major cancers that affect most Americans.

Almost every tissue can give rise to cells that cause cancer and each of these cancers is very different in its symptoms and prognosis. However, there are basic and similar genetic processes that lead to tumor growth in the human body. Genes are responsible for producing proteins that regulate cell growth and division. When these genes do not function properly, the proteins are abnormal and cells can grow uncontrollably. This results in the formation of a tumor. As more genetic mutations (changes) occur in this tumor, it becomes more life-threatening and has a greater chance of spreading to other parts of the body.

Three classes of genes appear to play a role in the development of cancer:

  • Proto-oncogenes encourage and promote the normal growth and division of cells. When they are defective, they become oncogenes. Oncogenes are overactive proto-oncogenes that cause excessive cell multiplication that can lead to tumors.
  • Tumor suppressor genes act as brakes on cell growth. They prevent cells from multiplying uncontrollably. If these genes are defective there is no control over cell growth and tumors can result.
  • DNA repair genes ensure that each strand of DNA is correctly copied during cell division . When these genes do not function properly, the replicated DNA is likely to have errors. This causes defects in other genes and can lead to tumor formation in some cases.

Approximately 5–10% of cancers have a hereditary component. In these cancers a child does not inherit caner

from the parents. Rather, a predisposition to cancer is inherited. For example, a faulty tumor suppressor gene may be inherited. This gene is not able to control cell growth but the corresponding gene inherited from the other parent is still functional. Cell growth is under control. However, as a child grows up, radiation, pollution, or any other environmental factor could change the functional gene, making it defective as well. Now, neither of these tumor suppressor genes are functioning, and it is likely that a tumor will develop. Defects in proto-oncogenes and DNA repair genes can be inherited, as well, leaving a person more vulnerable to cancer than the general population.

Some cancers seem to run in families. In these cancers there is no specific gene responsible for the clustering of cancer in a family. However, a particular type of cancer may be seen more often than in the general population. It is suggested that this is due to a combination of genetic and environmental factors.

Cancer kills one out of every four Americans. As of 2001 it was the second leading cause of death in the United States, surpassed only by heart disease. More than 1.2 million new cases of cancer are diagnosed every year in the United States. The National Cancer Institute estimates that approximately 8.4 million Americans alive in 2001 had a history of cancer. Some of these people were cured while others were still affected with the dis- ease and possibly undergoing treatment.

Anyone is at risk for developing cancer. Since the occurrence of cancer increases as a person ages, most cases are seen in adults middle-aged or older. Nearly 80% of cancers are diagnosed in people 55 years of age and older.

Lifetime risk is the term used to refer to the probability that an individual will develop cancer over the course of his or her lifetime. In the United States men have a one-in-two lifetime risk of developing cancer. For women, the risk is one in three. Overall, African Americans are more likely to develop cancer than Caucasians and are 33% more likely to die of cancer than Caucasians.

The major risk factors for cancer are tobacco, alcohol, diet, sexual and reproductive behavior, infectious agents, family history, occupation, environment, and pollution.

Tobacco

Eighty-to-ninety percent of lung cancer cases occur in smokers. Smoking has also been shown to be a contributory factor in cancers of mouth, pharynx, larynx, esophagus, pancreas, uterine cervix, kidney, and bladder. Smoking accounts for at least 30% of all cancer deaths. Scientists have shown that inhaling secondhand smoke (passive smoking) can increase one's risk of developing cancer.

Alcohol

Excessive consumption of alcohol is a risk factor in certain cancers such as liver and breast cancer. Alcohol, in combination with tobacco, significantly increases the chances that an individual will develop mouth, pharynx, larynx, and esophageal cancers. The combined effect of tobacco and alcohol is greater than the sum of their individual effects. This is called synergy.

Diet and physical activity

One-third of all cancer deaths are due to a poor adult diet. High-fat diets have been associated with cancers of the colon and rectum, prostate, endometrium, and possibly breast. Consumption of meat, especially red meat, has been associated with increased cancer at various sites such as the colon and prostate. Additionally, a high-calorie diet and low level of physical activity can lead to obesity , which increases the risk for cancer at various sites including the breast, colon and rectum, prostate, kidney, and endometrium.

Sexual and reproductive behavior

The human papilloma virus, a sexually transmitted disease, has been shown to cause cancer of the cervix. Having many sexual partners and becoming sexually active early has been shown to increase one's chances of contracting this disease and, therefore, developing cervical cancer. In addition, it has also been shown that women who do not have children or those who have children late in life have an increased risk for both ovarian and breast cancer.

Hormone replacement therapy

As women go through menopause , a physician may recommend hormone replacement therapy. This involves taking female hormones (called estrogen and progesterone) to control certain symptoms such as hot flashes and vaginal dryness that occur during this time of a woman's life. Taking estrogen alone can increase the risk for uterine cancer. However, progesterone is often prescribed at the same time to counteract the cancerous effects of estrogen. There is a questionable relationship between hormone replacement therapy and breast cancer as well. As of 2001, this relationship was not fullyunderstood.

Family history

Certain cancers tend to occur more commonly among members of a family. Much of the time this seems to happens by chance, or is due to a common family habit such as cigarette smoking or extended sun exposure. However, certain cancers can occur in excess in some families due to a genetic predisposition that is passed from generation to generation. For example, if the BRCA1 gene is defective in a family, members of that family may have an increased risk to develop breast, colon, ovarian, or prostate cancer. Other defective genes can make persons susceptible to other types of cancer. Therefore, inheriting particular genes can increase a person's chance of developing cancer.

Occupational hazards

There is ample evidence that occupational hazards account for 4% of all cancer deaths. For example, asbestos workers have an increased incidence of lung cancer. Similarly, bladder cancer is associated with dye, rubber, and gas workers; skin and lung cancer with people who are smelters, gold miners and arsenic workers; leukemia is seen more frequently in people who work with glue and varnish; liver cancer is more prevalent in PVC manufacturers; and lung, bone, and bone marrow cancer is associated with radiologists and uranium miners.

Environment

High-frequency radiation has been shown to cause human cancer. Ultraviolet radiation from the sun accounts for a majority of melanoma cases. Other sources of radiation are x rays, radioactive substances, and rays that enter the earth's atmosphere from outer space. Virtually any part of the body can be affected by these types of radiation, especially bone marrow and the thyroid gland .

Additionally, being exposed to substances such as certain chemicals, metals, or pesticides, can increase the risk of cancer. Asbestos is an example of a well-known carcinogen, increasing the risk for lung cancer. This risk is increased even further for a smoker who is exposed to asbestos over a period of time.

Causes and symptoms

Cancer is a progressive disease and goes through several stages. Each stage can produce a number of symptoms. Unfortunately, many types of cancer do not display any obvious symptoms or cause pain until the disease has progressed to an advanced stage. Early signs of cancer are often subtle and are easily mistaken for signs of other less-dangerous diseases.

Despite the fact that there are several hundred different types of cancers producing very different symptoms, the American Cancer Society (ACS) has established the following seven symptoms as possible warning signals of cancer:

  • changes in the size, color, or shape of a wart or a mole
  • a sore that does not heal
  • persistent cough, hoarseness, or sore throat
  • a lump or thickening in the breast or elsewhere
  • unusual bleeding or discharge
  • chronic indigestion or difficulty in swallowing
  • any change in bowel or bladder habits

Other diseases can produce similar symptoms. However, it is important to have these symptoms checked as soon as possible, especially if they linger. The earlier a cancer is diagnosed and treated, the better the chance of it being cured. Many cancers, for example breast cancer, may not have any early symptoms. Therefore, it is important to undergo routine screening tests, such as breast self-exams and mammograms.

Diagnosis

If a person has symptoms of cancer, a physician will begin with a complete medical history and a thorough physical examination . The doctor will examine different parts of the body in order to identify any variations from the normal size, feel, and texture of the organ or tissue. In addition to the physical exam, the doctor may order various tests.

Laboratory tests on blood and urine are often used to obtain information about a person's health. If cancer is suspected, a special test can be done that measures the amount of certain substances, called tumor markers, in the blood, urine, or particular tissues. These proteins are released from some types of cancer cells. Thus, the levels of these substances may be abnormal when certain cancers are present. However, laboratory tests alone cannot be used to make a definitive diagnosis of cancer. Blood tests are generally more useful in monitoring the effectiveness of the treatment or in following the course of the disease and detecting any signs of recurrence.

A doctor may look for tumors by examining images of areas inside the body. The most common way to obtain these images is by using x rays. Other techniques used to examine the insides of the body include computed tomography (CT scan), magnetic resonance imaging (MRI), and ultrasonography.

The most definitive diagnostic test is a biopsy. In this technique a piece of tissue is surgically removed for examination under a microscope . A biopsy provides information about the cellular nature of an abnormality: the stage it has reached, the aggressiveness of the cancer, and the extent of its spread. Further analysis of the tissue obtained by biopsy defines the cause of the abnormality. Since a biopsy provides the most accurate analysis, it is considered the gold standard of diagnostic tests for cancer.

Regular screening examinations conducted by healthcare professionals can result in the early detection of various types of cancer. Early detection means treatment is more likely to succeed. For example, the ACS recommends an annual mammogram (x ray of the breast) for women over the age of 40 years, to screen for breast cancer. It also recommends a sigmoidoscopy , in which a thin, lighted tube with a tiny camera is used to view the inside of the colon, every five years for people over the age of 50. This technique can assess the presence of colorectal cancer . Self-examinations for cancers of the breast, testes, mouth, and skin can also help in detecting tumors before the symptoms become serious.

Evolutions in molecular biology and the genetics of cancer have led to the development of several tests designed to assess one's risk of getting certain types of cancer. Genetic testing involves looking closely at certain genes that have been linked to particular cancers. As of 2001 there were many limitations to genetic testing. Tests could be uninformative and to a very small proportion of individuals tested. Additionally, concerns exist about insurance coverage and employment discrimination for someone who has an increased risk for cancer. As of 2001 these tests were reserved only for very specific individuals. A hereditary cancer clinic can help assess who may benefit from this type of testing.

Treatment

The aim of cancer treatment is to remove all or as much of the tumor as possible and to prevent the recur- rence or spread of the primary tumor. While devising a treatment plan for cancer, the likelihood of curing the cancer must be weighed against the side effects of the treatment. If the cancer is aggressive and a cure is not possible, then treatment should be aimed at relieving the symptoms and controlling the cancer for as long as possible.

Cancer treatment can take many different forms, and it is always tailored to an individual. The decision on which type of treatment is the most appropriate depends upon the type and location of the cancer and the extent to which it has already spread. A physician will also consider an affected person's age, sex, general health status, and personal treatment preferences. Treatment can be local, meaning that it affects cancer cells in the tumor and the surrounding area only. Surgery and radiation are local treatments. Treatment can also be systemic, meaning that the treatment travels through the bloodstream and affects cancer and other cells throughout the entire body. Chemotherapy , immunotherapy, and hormone therapy are examples of systemic treatments.

Surgery

Surgery can be used for many purposes:

  • Treatment. Treatment of cancer by surgery involves removal of the tumor to cure the disease. This is typically done when the cancer is localized to a discrete area. Along with the cancer, some of the surrounding tissue is also removed to ensure that no cancer cells remain in the area. Since cancer usually spreads via the lymphatic system, lymph nodes near the tumor site may be removed for examination.
  • Prevention. Preventive or prophylactic surgery involves removal of an abnormal-looking area that is likely to become malignant over time. For example, 40% of people with a colon disease called ulcerative colitis ultimately die of colon cancer. Rather than live with the fear of developing colon cancer, these people may choose to have their colons removed in order to reduce their risk of colorectal cancer.
  • Diagnosis. The most definitive tool for diagnosing cancer is a biopsy. Sometimes a biopsy can be performed by inserting a needle through the skin and aspirating a small amount of fluid or tissue. At other times the only way to obtain a tissue sample is through surgery.
  • Cytoreductive surgery. This is a surgical procedure in which the surgeon removes as much of the cancer as possible. The remaining cancer cells are then treated with radiation therapy, chemotherapy, or both.
  • Palliative surgery. This type of surgery is intended to relieve cancer symptoms or slow the progression of disease. It is not designed to cure the cancer. For example, if the tumor is very large or has spread to many places in the body, removing the entire tumor may not be an option. However, by decreasing the size of the tumor, pain may be alleviated. This is known as debulking surgery.

Radiation therapy

Radiation uses high-energy rays to kill cancer cells. This technique may be used instead of surgery. It also may be utilized before surgery to shrink a tumor or after surgery to destroy any remaining cancer cells.

Radiation can be either external or internal. In the external form, the radiation comes from a machine that aims the rays at the tumor. In internal radiation (also known as brachytherapy), radioactive material is sealed in needles, seeds, or wires and placed directly in or near the tumor. Radiation may lead to various side effects, such as fatigue, hair loss, and a susceptibility to infections. However, these side effects can usually be controlled.

Chemotherapy

Chemotherapy is the use of drugs to kill cancer cells. The entire body is exposed to the drugs (systemic therapy) in an effort to destroy the hard-to-detect cancer cells that have spread and are circulating in the body. The cancer cells are affected more dramatically than normal cells because they are rapidly dividing. Chemotherapeutic drugs can be injected into a vein, the muscle, or the skin, or they may be taken by mouth.

When chemotherapy is used before surgery, it is known as primary, or neoadjuvant chemotherapy. Its purpose is usually to reduce the size of the tumor. The more common use of chemotherapy is in adjuvant therapy. In this technique, chemotherapy is given after surgery to destroy any remaining cancer cells and to help prevent cancer from recurring. Chemotherapy can also be used in conjunction with radiation.

Side effects of chemotherapy vary but can include susceptibility to infections, fatigue, poor appetite, weight loss, nausea, diarrhea , and hair loss. Decreased fertility can be a long-term side effect in some instances.

Bone marrow failure is a complication of chemotherapy. When high-dose chemotherapy is utilized, bone

Recommendations for cancer screening
Procedure Frequency
SOURCE: U.S. Preventative Services Task Force, Dept. of Health and Human Services.
Chest x rayNot recommended on a routine basis
Sputum cytologyNot recommended on a routine basis
Fecal occult bloodYearly after age 50
testing (FOBT) or
sigmoidoscopy
Papanicolaou (Pap)Every 3 years from onset of sexual activity to
smearage 65
Mammography aloneEvery 1–2 years at ages 50–69; starting at ages
or mammography40–49 may be recommended if high-risk
and breast physical
examination

marrow failure is anticipated. Bone marrow transplantation (BMT) or peripheral stem cell transplantation (PSCT) are techniques used to treat this complication. Both techniques provide healthy stem cells for an affected person. Stem cells are immature cells that mature into blood cells. Transplanted stem cells replace the patient's stem cells that have been damaged or destroyed by chemotherapy or radiation. This procedure allows an individual to undergo very aggressive treatment for cancer. Those who receive BMT or PSCT have an increased risk of infection , bleeding, and other side effects due to the chemotherapy and radiation. Graft-versus-host dis- ease may also occur. This complication develops when the donated marrow reacts against the recipient's tissues. It can occur any time after the transplant. Drugs may be given to reduce the risk of graft-versus-host disease and to treat the problem if it occurs.

Immunotherapy

Immunotherapy, also called biological therapy, is the use of treatments that promote or support the body's immune system response to cancer. The side effects of immunotherapy are variable but include flu- like symptoms, weakness, loss of appetite, and skin rash. These symptoms will subside after the treatment is completed.

Hormone therapy

Hormone therapy is used to fight certain cancers that depend on hormones for their growth. Drugs can be used to block the production of hormones or change the way they work. Additionally, organs that produce hormones may be removed. As a result of this therapy, the growth of the tumor slows and survival may be extended for several months or years.

COMMON PATHOGENS AND THE CANCERS ASSOCIATED WITH THEM
Causative Agent Type Of Cancers
Viruses
PapillomavirusesCancer of the cervix
Hepatitis B virusLiver cancer
Hepatitis C virusLiver cancer
Epstein-Barr virusBurkitt's lymphoma
Cancers of the upper pharynxHodgkin's lymphoma, Non-Hodgkin's lymphoma, Gastric cancers
Human immunodeficiency virus (HIV)Kaposi's sarcoma Lymphoma
Bacteria
Helicobacter pyloriStomach cancer Lymphomas

Alternative and complementary therapies

There are certain cancer therapies that have not been scientifically tested and approved. If these unproven treatments are used instead of the standard therapy, this is known as alternative therapy. If they are used along with standard therapy, this is known as complementary therapy. Alternative therapy is considered dangerous because some of these unproven treatments might have life- threatening side effects. Additionally, persons who use alternative therapy may lose the opportunity to benefit from standard, proven therapy. However, some complementary therapies may help to relieve symptoms of cancer, decrease the magnitude of side effects from treatment, or improve a patient's sense of well being. The American Cancer Society recommends that anyone considering alternative or complementary therapy consult a health care team before doing so.

Palliative care

Palliative care, which focuses on the terminally ill, is an extremely important aspect of care. Its goal is to prevent and relieve pain and suffering through symptom management, and addresses not only the physical, but the practical, emotional, and spiritual needs of patients, their families, and caregivers. By viewing dying as a natural process, palliative care helps facilitate what can be termed a "good" death, free from suffering and stress . Many patients and their families are unaware that suffering at the end of life is no longer necessary. Health care professionals can relieve a patient and their loved ones of much anxiety by informing them that appropriate symptom management is readily available.

Hospice care

Hospice care is the environment in which palliative care is given to terminally ill patients. Hospice care can be provided either at home, or in a home-like facility called a hospice. Hospice care focuses on providing the best possible palliative care for the patient until the patient dies.

Prognosis

Most cancers are curable if detected and treated in their early stages. The prognosis for a person with cancer is affected by many factors, particularly the type of cancer and stage of the cancer, the extent to which it has metastasized, and its aggressiveness. In addition, a person's age, general health status, and effectiveness of the treatment being pursued are important factors.

To help predict the outcome of cancer and the likeli- hood of recovery from the disease, five-year survival rates are used. In the United States, as of 2001, the five- year survival rate for all cancers combined was 59%. This means that 59% of people with cancer are expected to be alive five years after they are diagnosed. These people may be free of cancer, or they may be undergoing treatment. It is important to note that, while this statistic can give some information about the average survival of people with cancer in a given population, it cannot be used to predict the course of cancer for an individual. No two people are exactly alike. The five-year survival rate does not account for differences in detection methods, types of treatments, additional illnesses, and personal behavior of the individual.

Health care team roles

Family physicians, internists, gynecologists, or pediatricians generally make an initial diagnosis of cancer. Other physicians, notable radiologists, and oncologists provide chemotherapeutic and radiologic treatment. Nurses provide emotional and educational support, home care , home hospice care, and case management. Counselors and psychologists may provide emotional support to patients and their families. Epidemiologists collect and maintain data related to cancer.

Prevention

According to experts from leading universities in the United States, a person can reduce the chances of getting cancer by following these guidelines:

  • eating plenty of fruits and vegetables
  • exercising vigorously for at least 20 minutes every day
  • avoiding excessive weight gain
  • avoiding tobacco (including second hand smoke)
  • decreasing or avoiding consumption of animal fats and red meats
  • avoiding excessive amounts of alcohol
  • avoiding the midday sun (between 11 a.m. and 3 p.m.) when the sun's rays are the strongest
  • avoiding risky sexual practices
  • avoiding known carcinogens in the environment or work place

Certain drugs being used for treatment can also be suitable for prevention. For example, tamoxifen (Nolvadex) has been very effective against recurrence of breast cancer and is now thought to be helpful in the prevention of breast cancer. Similarly, retinoids derived from vitamin A are being tested for their ability to slow the progression of, or prevent, head and neck cancers.


KEY TERMS


Benign —A growth that does not spread to other parts of the body. Recovery is favorable with treatment.

Biopsy —The surgical removal and microscopic examination of living tissue for diagnostic purposes.

Bone marrow —Spongy material that fills the inner cavities of the bones. The progenitors of all the blood cells are produced in this bone marrow.

Carcinogen —Any substance capable of causing cancer by mutating a cell's DNA.

Chemotherapy —Treatment with anticancer drugs.

Epithelium —Layer of cells covering the body's surface and lining the internal organs and various glands.

Hormone therapy —Treatment of cancer by changing the hormonal environment, such as testosterone and estrogen.

Immunotherapy —Treatment of cancer by stimulating the body's immune system.

Malignant —A general term for cells that can break loose from an original tumor, invade, and then destroy other tissues and organs.

Metastasis —The spread of cancer from one part of the body to another.

Radiation therapy —Treatment using high-energy radiation from x-ray machines, cobalt, radium, or other sources.

Sore —An open wound or a bruise or lesion on the skin.

Tumor —An abnormal growth resulting from a cell that lost its normal growth control restraints and started multiplying uncontrollably.

X rays —High energy radiation used in high doses, either to diagnose or treat disease.


Resources

BOOKS

Armstrong-Dailey, Ann, and Sarah Zarbhock. Hospice Care for Children. New York: Oxford, 2001.

Bragg, Rubin. Oncologic Imaging. 2nd ed. Philadelphia: Saunders, 2001.

Crist, William M, et al. "Neoplastic Diseases and Tumors." In Nelson Textbook of Pediatrics. 16th ed. Ed. Richard E. Behrman et al., Philadelphia: Saunders, 2000, 1531-1573.

Eyre, Harmon J. Dianne Lange, and Lois B. Morris. Informed Decisions: The Complete Book of Cancer Diagnosis, Treatment, and Recovery. Washington: American Cancer Society, 2001.

Hudson, Christopher N. Textbook of Ovarian Cancer. 2nd ed. New York: Oxford, 2001.

Ihde, Daniel C., and Dan L. Longo. "Presentations of the Patient with Cancer." In Harrison's Principles of Internal Medicine. 14th ed. Ed. Anthony S. Fauci, et al., New York: McGraw-Hill, 1998, 360-362.

Kantoff, Philip. Prostate Cancer: Principles and Practice. Philadelphia: Lippincott Williams & Wilkins, 2001.

Lippman, Marc E. "Evaluation of Breast Masses in Men and Women." In Harrison's Principles of Internal Medicine, 14th ed. Ed. Anthony S. Fauci, et al., New York: McGraw-Hill, 1998, 362-365.

Longo, Dan L., et al. "Oncology." In Harrison's Principles of Internal Medicine. 14th ed. Ed. Anthony S. Fauci, et al., New York: McGraw-Hill, 1998, 493-633.

Rosenbaum, Ernest H. Supportive Cancer Care: The Complete Guide for Patients and Families. Naperville: Sourcebooks Trade, 2001.

Simone, Joseph M., et al., "Oncology." In Cecil Textbook of Medicine 21st ed. Ed. Lee Goldman and J. Claude Bennett, Philadelphia: W.B. Saunders, 2000, 1029-1081.

PERIODICALS

Feldt-Rasmussen U. "Iodine and Cancer." Thyroid 11, no. 5 (2001): 483-486.

Izquierdo-Porrera, A.M., J. Trelis-Navarro, X. Gomez-Batiste. "Predicting Place of Death of Elderly Cancer Patients Followed by a Palliative Care Unit." Journal of Pain Symptom Management 21, no. 6 (2001): 481-490.

Kutner J.S., C.T. Kassner, and D.E. Nowels. "Symptom Burden at the End of Life. Hospice Providers' Perceptions." Journal of Pain Symptom Management 21. no. 6 (2001): 473-480.

Messmann, H., and K. Schlottmann. "Role of Endoscopy in the Staging of Esophageal and Gastric Cancer." Seminars in Surgical Oncology 20, no.2 (2001): 78-81.

Nelson, R.L. "Iron and Colorectal Cancer Risk: Human Studies." Nutrition Review 59, no. 5 (2001): 140-148.

Skarin, A.T., R.S., Herbst, T.L. Leong, A. Bailey, and D. Sugarbaker. "Lung Cancer in Patients Under 40." Lung Cancer 32, no. 3 (2001): 255-264.

ORGANIZATIONS

American Academy of Physical Medicine and Rehabilitation. One IBM Plaza, Suite 2500, Chicago, IL 60611-3604.(312) 464-9700. <http://www.aapmr.org/consumers/public/amputations.htm>.

American College of Occupational and Environmental Medicine. 55 West Seegers Road, Arlington Heights, IL60005. (708) 228-6850. <http://www.acoem.org>.

American College of Radiology. 1891 Preston White Drive, Reston, VA 20191. (703) 648-8900.<http://www.acr.org>.

American College of Surgeons. 633 North St. Clair Street, Chicago, IL 60611-32311. (312) 202-5000. <http://www.facs.org/>.

American Lung Association. 1740 Broadway, New York, NY 10019.(212)-315-8700. <http://www.lungusa.org/diseases/lungtb.html>.

American Melanoma Foundation. 3914 Murphy Canyon Road, Suite A132, San Diego, CA 92123. (858) 277-4426. <http://www.melanomafoundation.org/homepage.html>.

National Alliance of Breast Cancer Organizations. 9 East 37th Street, New York, NY 10016. (212) 889-0606. <http://www.nabco.org/>.

National Cancer Institute. Building 31, Room 10A31, 31 Center Drive, MSC 2580, Bethjesda, MD 20892-2580.(800) 422-6237, or (301) 435-3848. <http://www.nci.nih.gov/>.

Skin Cancer Foundation. 245 5th Avenue, Suite #1403, New York, NY 10016. (800) 754-6490. <http://www.skincancer.org/melanoma/>.

OTHER

American Cancer Society. <http://www2.cancer.org/contact/>.

Canadian Cancer Society. <http://www.cancer.ca/>.

Cancer Care. <http://www.cancercare.org/>.

Cancer Guide. <http://www.cancerguide.org/>.

Memorial Sloan-Kettering Cancer Center. <http://www.mskcc.org/>.

National Breast Cancer Coalition. <http://www.natlbcc.org/>.

National Cancer Institute. <http://cancernet.nci.nih.gov/>.

L. Fleming Fallon, Jr., M.D., Dr.P.H.

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Cancer

Cancer

Cancer is not a single disease, but rather a monster with many faces. Doctors and scientists have listed more than 200 varieties of cancer, each having different degrees of mortality, different means of prevention, different hopes for a cure. Carcinomas hit mucous membranes or the skin, sarcomas attack the tissues under the skin, and leukemia strikes at the marrow—and these are just a few varieties of cancer. Cancers are all characterized by an uncontrolled proliferation of cells under pre-existing tissues, producing abnormal growths. Yet popular attitudes toward cancer have been less bothered with medical distinctions than with providing a single characterization of the disease, evoking a slow and painful process of decay that comes as a sort of punishment for the patient. "Cancerphobia" is, as Susan Sontag and James T. Patterson have shown, deeply rooted in American culture.

Cancer is a very ancient disease, dating back to pre-historic times. Archeological studies have allowed scientists to detect breast cancer in an Egyptian mummy, while precise descriptions of different cases of cancer started in the eighteenth century. The word cancer comes from the Latin "cancer-cancri" and the Greek karkinos (used by Hippocrates in the fifth century B.C.), meaning both cancer and crab. The two words are linked via images of creeping, voracity, and obliqueness. Just like crabs, cancers creep inside the organism and eat away at it. The association of cancers and crabs has lasted throughout the centuries: Rudyard Kipling used the expression "Cancer the Crab," and an American cartoon booklet from the 1950s shows a giant crab crushing its victims with its huge pincers, the words "Cancer the killer" appearing above the scene. Adopting a typically apocalyptic mood, Michael Shimkin claimed that American citizens had defeated the "pale rider of pestilence" and the "cadaverous rider of hunger," but that they now had to face two different riders—"one in shape of a mushroom cloud and one in the shape of a crab".

In the United States, cancer made its first big public appearance with the illness and death in 1884-1885 of the national hero who had led the Union troops to victory in the Civil War: Ulysses S. Grant. Public use of the word cancer, as James Patterson has pointed out, had been uncommon until then. Grant's cancer received exceptional newspaper coverage and the readers of the age were fascinated by it. Unofficial remedies and healers came to the forefront, positing for the first time what would be a recurrent dichotomy in the history of cancer research: the orthodox medicine of the "cancer establishment" versus the unorthodox medicine of the "cancer counter-culture." Cancer, with its slow but unrelenting progression, seemed the very denial of several developments taking place during the late nineteenth century (such as higher life expectancy and economic growth) which contributed to the people's perception of the United States as the land of progress and opportunity for a well-to-do life. The denial of death played an important part in this quest for a well-to-do life, and James Patterson explains that this particular attitude "account[s] for many responses to cancer in the United States during the twentieth century, including a readiness to entertain promises of 'magic bullets.' In no other nation have cancerphobia and 'wars' against cancer been more pronounced than in the United States." Since the late 1970s, the war on cancer has been coupled with a fierce battle against smoking (which medical specialists have singled out as the main cause of lung cancer), a battle featuring scientific researchers pitted against tobacco lobbies and their powerful advertising experts.

Military metaphors have been widely used in the battle against cancer. One of the posters of the American Society for Control of Cancer from the 1930s urges us to "fight cancer with knowledge"; the message appears below a long sword, the symbol of the Society. As part of the growing pressure for a national war on the disease during the 1960s, cancer activists asked for more money to be devoted to research and prevention by claiming that cancer was worse than the Vietnam War; the latter had killed 41,000 Americans in four years, while the former had killed 320,000 in a single year. Nixon was the first president of the United States to declare war on cancer. In January 1971, he declared in his State of the Union message that "the time has come when the same kind of concentrated effort that split the atom and took the man on the moon should be turned toward conquering this dread disease." Later in the same year, two days before Christmas, Nixon signed the National Cancer Act (which greatly increased the funds of the National Cancer Institute, or NCI) and called for a national crusade to be carried out by 1976, the two hundredth anniversary of the birth of the United States. And yet this program revealed itself to be too optimistic and the association of cancer and Vietnam reappeared. People started to compare the inability of the NCI to deliver a cure to the disastrous outcome of the Vietnam War. Dr. Greenberg, a cancer researcher, declared in 1975 that the war on cancer was like the Vietnam War: "Only when the public realized that things were going badly did pressure build to get out." Gerald Markle and James Petersen, comparing the situation to the fight against polio, concluded that "the war on cancer is a medical Vietnam."

The military rhetoric of wars and crusades has also been applied to drugs, poverty, and other diseases in our society. Susan Sontag has claimed that military metaphors applied to illnesses function to represent them as "alien." Yet the stigmatization of cancer leads inevitably to the stigmatization of the patients as well. Many scientific attempts to explain the causes of cancer implicitly blame patients. As late as the 1970s, Lawrence LeShan and Carl and Stephanie Simonton claimed that stress, emotional weakness, self-alienation, depression, and consequent defeatism were the distinctive features of a "cancer personality" and could all be causes of cancer. Sontag maintained that the theory that there was "a forlorn, self-hating, emotionally inert creature" only helped to blame the patient. This particular focus on stress was also based on a traditionally American distrust of modern industrialized civilization and urban life, which were to be blamed for the intensification of the pace of living and the consequent rise in anxiety for human beings. The wide circulation of these ideas pointed to popular dissatisfaction with most official medical explanations of cancer. Not surprisingly, cancer itself has become a powerful metaphor for all that is wrong in our society. Commentators often talk about the cancer of corruption effecting politics or about the spreading cancer of red ink in the federal budget. No other disease has provided metaphors for such a wide range of social and economic issues.

"Cancerphobia" has been a constant source of inspiration for popular literature, cinema, and television. While cancer was mainly a disease for supporting actors (Paul Newman's father in Cat on a Hot Tin Roof, 1958) in the 1950s and 1960s, since the 1970s cancer movies have often served as vehicles for stars such as Ali McGraw and Ryan O'Neal in Love Story (1970), James Caan in Brian's Song (1972), Debra Winger in Terms of Endearment (1983), Julia Roberts in Dying Young (1991), Jack Lemmon in Dad (1989), Tom Hanks and Meg Ryan in Joe Versus the Volcano (1990), Michael Keaton in My Life (1993), and Susan Sarandon and Julia Roberts in Stepmom (1998). Most of these few-days-to-live-stories are melodramatic, tear-jerking accounts of cancer which rely on the popular perception of the illness as mysterious and deceiving. In Terms of Endearment, Debra Winger discovers she has cancer almost by chance and dies shortly after having declared that she feels fine. In Dad, Jack Lemmon's cancer disappears, giving everyone false hopes, only to reappear fatally after a short while. These stories are often told with a moralizing intent: cancer is perceived as providing opportunities for the redemption of the characters involved in the drama—in Terms of Endearment, Winger and her husband Jeff Daniels, who have both been unfaithful, reconcile at her deathbed; in Dad, cancer brings Jack Lemmon and his son Ted Danson closer together after years of estrangement; and in Stepmom the disease rekindles female bonds that had been obscured by misunderstandings and rivalries over men. And in Love Story and Dying Young, cancer serves as the medium through which two young people from different economic backgrounds are brought together despite their parents' opposition.

The (melo)drama of cancer in American culture is characterized by an enduring dichotomy of hope and fear. The official optimism for a cure, such as that placed in the 1980s on interferon, a protein able to stop the reproduction of cancerous cells, has always been countered by obstinate popular skepticism. Medical progress has been unable to discourage popular faith in unorthodox approaches to the disease. On the contrary, as James Patterson has argued, popular skepticism has often been fostered by "the exaggerated claims for science and technological medicine" and still makes cancer retain its malignant grip on the American popular imagination as "an alien, surreptitious, and voracious invader."

—Luca Prono

Further Reading:

LeShan, Lawrence. You Can Fight For Your Life: Emotional Factors in the Causation of Cancer. New York, M. Evans & Co., 1977.

Markle, Gerald, and James Petersen, editors. Politics, Science and Cancer. New York, AAAS, 1980.

Patterson, James T. The Dread Disease: Cancer and Modern American Culture. Cambridge, Harvard University Press, 1987.

Shimkin, Michael. Science and Cancer. Bethesda, Maryland, National Institute of Health, 1980.

Simonton, Carl and Stephanie. Getting Well Again. Los Angeles, J.P.Tarcher, 1978.

Sontag, Susan. Illness as Metaphor. New York, Farrar, Strauss, and Giroux, 1978.

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Cancer

Cancer

Cancer is not just one disease , but a large group of almost 100 diseases. Its two main characteristics are uncontrolled growth of the cells in the human body and the ability of these cells to migrate from the original site and spread to distant sites. If the spread is not controlled, cancer can result in death.

One out of every four deaths in the United States is from cancer. It is second only to heart disease as a cause of death in the states. About 1.2 million Americans are expected to be diagnosed with cancer in 1998, of which, more than 500,000 are expected to die.

Cancer can attack anyone. Since the occurrence of cancer increases as individuals age, most of the cases are seen in adults, middle-aged or older. The most common cancers are skin cancer, lung cancer, colon cancer, breast cancer (in women), and prostate cancer (in men). In addition, cancer of the kidneys, ovaries, uterus, pancreas, bladder, rectum, and blood and lymph node cancer (leukemia and lymphomas) are also included among the 12 major cancers that affect most Americans.


The history of cancer as a known disease

The term cancer derives from the observation by Hippocrates in 400 b.c. that the veins radiating from a breast cancer resembled the legs of a crab, hence karkinoma in Greek and cancer in Latin. Cancer is not a single disease, but is many different diseases that all share common biological and pathological characteristics. In most western societies, cancer is a leading cause of death. The disease may develop in any body tissue or organ and over one hundred different types of cancer can occur in adults. Cancer also occurs in children and may even be present at birth .

The first clues to the cause of cancer came over two hundred years ago from an observation by Percivall Pott, a London doctor, who in 1775 found a high incidence of scrotal cancer in men who had worked as chimney sweeps. Later, radiation was found to cause skin cancer and tragically Marie Curie (1867–1934) the discoverer of x rays , died of a cancer caused by prolonged exposure to radiation. During the second half of the twentieth century, epidemiologists (those who study disease in populations) linked exposure to certain environmental toxins and particular types of cancer. Most notably, cigarette smoking and lung cancer, sunlight and skin cancer, and certain industrial chemicals to the cause of bladder and liver cancer. Finally several viruses were also been implicated in causing cancer, such as the hepatitis B virus and cancer of the liver, the Epstein Barr virus and lymphoma, and the human papilloma virus and cancer of the cervix. These important observations all suggested that specific external environmental agents could cause specific cancers.

How then could a diverse range of external agents such as chemicals, radiation and viruses, all lead to the development of cancer? The answer to this question has come over the last 25 years from two different lines of investigation; studies on cancer causing viruses and research into the genetics of some rare cancers in children.

In 1910, Frances Peyton Rous (1879–1970) isolated a virus from a cancer in chickens (a sarcoma) that caused new sarcomas to develop when infected into healthy chickens. Rous's work languished for over 50 years until he was awarded a Nobel Prize in 1966. By this time, methods for the study of viruses and cancer had improved considerably and many new animal derived viruses were found to cause cancer in a range of species . These viruses could also induce cancer-like changes when introduced into normal cells grown in the laboratory. A genetic study of these cancer causing viruses identified a small number of genes termed viral oncogenes (v-oncogenes) which, when introduced into cells, could transform the normal cells into malignant cells.

The presence of viral oncogenes led to the search for endogenous cellular oncogenes, which might cause cancer. In a crucial experiment in the late 1970s, DNA from mouse cells which had been transformed by a chemical carcinogen , was transfected into normal mouse cells. The normal mouse cells became malignant suggesting that a gene within the cancer (a proto-oncogene) had been mutated by exposure to the chemical and was able to induce cancer. Surprisingly, when these endogenous cellular oncogenes were eventually isolated they were found to be homologous to virally derived oncogenes.

In the early 1970s the American pediatrician and scientist, Alfred Knudson at the Fox Chase Cancer Center studied retinoblastoma, a rare childhood eye cancer that is sometimes inherited but is most often sporadic. He observed that children who had inherited retinoblastoma often had the cancer at birth, and were at high risk of developing multiple cancers in both eyes. Children with later onset retinoblastoma usually had no family history and developed isolated tumors. Knudson reasoned that children with inherited retinoblastoma had a germline mutation in one allele of a recessive cancer gene. The germline mutation was the first of two hits in knocking out a recessive cancer gene. This is known as Knudson's two hit hypothesis. Later genetic studies found the first hit in children with inherited retinoblastoma to be a partial deletion of the long arm of chromosome 13 causing loss of the tumor suppressor gene, RB1.

These two directions of study independently identified two different classes of cancer gene, the oncogene and tumor suppressor gene, that when mutated in a given cell can set in train the sequence of events leading to the development of a cancer.

The genetics of cancer

Cancer, by definition, is a disease of the genes. Cancer is also our most common genetic disease, but only rarely is it inherited. A gene is a small part of DNA, which is the master molecule of the cell. Genes make "proteins," which are the ultimate workhorses of the cells. It is these proteins that allow our bodies to carry out all the many processes that permit us to breathe, think, move, etc.

Throughout people's lives, the cells in their bodies are growing, dividing, and replacing themselves. Many genes produce proteins that are involved in controlling the processes of cell growth and division. An alteration (mutation) to the DNA molecule can disrupt the genes and produce faulty proteins. This causes the cell to become abnormal and lose its restraints on growth. The abnormal cell begins to divide uncontrollably and eventually forms a new growth known as a "tumor" or neoplasm (medical term for cancer meaning "new growth").

In a healthy individual, the immune system can recognize the neoplastic cells and destroy them before they get a chance to divide. However, some mutant cells may escape immune detection and survive to become tumors or cancers.

Tumors are of two types, benign or malignant. A benign tumor is slow growing, does not spread or invade surrounding tissue, and once it is removed, it doesn't usually recur. A malignant tumor, on the other hand, invades surrounding tissue and spreads to other parts of the body. The hallmark of a malignant cancer is the uncontrolled clonal proliferation and spread of abnormal cancer cells. If the cancer cells have spread to the surrounding tissues, then, even after the malignant tumor is removed, it generally recurs.

A majority of cancers are caused by changes in the cell's DNA because of damage due to the environment. Environmental factors that are responsible for causing the initial mutation in the DNA are called carcinogens, and there are many types.

There are some cancers that have a genetic basis. In other words, an individual could inherit faulty DNA from his parents, which could predispose him to getting cancer. While there is scientific evidence that both factors (environmental and genetic) play a role, less than 10% of all cancers are purely hereditary. Cancers that are known to have a hereditary link are breast cancer, colon cancer, ovarian cancer, and uterine cancer. Besides genes, certain physiological traits could be inherited and could contribute to cancers. For example, inheriting fair skin makes a person more likely to develop skin cancer, but only if they also have prolonged exposure to intensive sunlight.

Most cancers are sporadic and arise in a particular tissue such as the colon, breast, lung, or skin when normal cells acquire mutations in one or more oncogenes or tumor suppressor genes. The acquisition of multiple new genetic changes is what sets the cancer cell apart from the normal cells in its surrounding tissues.

The cancer cell develops when a normal cell in an organ or tissue acquires the capacity to divide in an uncontrolled fashion. Over time the developing cancer cell starts to multiply in a clonal fashion, begins to appear different (anaplastic or undifferentiated), and progressively acquires other characteristics, such as the capacity metastasise while losing cell-to-cell adhesion. The continued acquisition of new biologic characteristics is the key to many aggressive cancers evading the host defenses, and to the resisting some treatments such chemotherapy and radiotherapy.

It is important to appreciate that oncogenes and tumor suppressor genes are in fact normal cellular genes with vital functions within normal cells. It is only when they are mutated in some way that these genes become cancer causing.

The Ha-ras gene is a good example of an oncogene. Located on chromosome 11 at the normal cellular Ha-ras gene is one of a family of ras genes and encodes a small protein that is involved in intracellular signaling. Mutations in the ras oncogenes disrupt processing of cell signals and contribute to cell transformation. Mutations in ras oncogenes are found in approximately 10% of cancers especially cancer of the colon and lung.

The most important tumor suppressor gene is the p53 gene. This gene which is known as the guardian of the genome encodes for a protein with multiple intracellular functions related to the detection of DNA damage. When DNA is damaged by exposure to a mutagen such as UV irradiation the p53 gene is expressed. The p53 protein causes the cell to stop dividing so DNA mismatch repair genes can repair the DNA. If the DNA is successfully repaired, the cell resumes normal cell functions and the p53 gene is down regulated. However, if the DNA damage is beyond repair the p53 protein switches on a process called apoptosis (programmed cell death ) leading to the death of the cell. For example, sunburn to the skin causes UV induced DNA damage, which often cannot be repaired. Expression of the p53 gene induces apoptosis the skin cells die and peel off.

Mutations in the p53 gene occur in approximately 50% of all cancers—particularly cancer of the breast, colon, lung, and brain . The mutant p53 protein is unable to stop uncontrolled cell division or switch on apoptosis, and can no longer protect the cell from acquiring additional mutation in other genes. The result is an unstable cell genome liable to further progressive DNA damage. The inherited cancer condition, Li-Fraumeni syndrome , is an autosomal dominant disorder caused by inherited mutations in the p53 gene. Individuals affected with Li-Fraumeni syndrome may develop breast cancer, brain tumors, leukemia, prostate cancer and various sarcomas at a young age.

Mismatch repair genes are another class of cancer gene contributing to instability of the cancer cell genome. Damaged DNA is repaired by an active DNA mismatch repair mechanism that identifies damaged DNA, then cuts out and repairs the the damaged DNA bases. Mutations in these repair genes are common in cancer cancers of the colon.

Oncogenes, tumor suppressor genes and other cancer causing genes can become mutated in any number of different ways. Most oncogenes become activated by specific mutations within their DNA sequence that causes the gene protein to function abnormally. Some oncogenes such MYCN are activated by DNA amplification. Oncogene amplification occurs commonly in neuroblastoma an aggressive cancer in children. These tumors can acquire hundreds of copies of this gene by DNA amplification making the cancer very resistant to treatment. Another means of oncogene activation is by its translocation from one chromosome to another. In the Burkitt lymphoma the c-myc oncogene is translocated from chromosome 8 to chromosome 14 where it becomes activated by an immunoglobulin gene. Only one allele of an oncogenes need to be activated for it to participate in cell transformation.

Tumor suppressor genes on the other hand are recessive and normally act to suppress cell replication. Cell transformation occurs when both gene alleles are inactivated (knocked out). Most commonly, inactivation of one gene allele occurs by a chromosome deletion. The second event may be an inactivating gene mutation , a second deletion or methylation of the genes promoter.

Regardless of the actual mutations involved a crucial concept in the development of most cancer is that more than one gene is usually involved in the process. Indeed in the development of cancer of the colon at least six or more separate oncogenes and tumor suppressor genes are involved in a progressive multi-step process to transform a normal colon cell into an aggressive, self replicating and invading cancer.

More recently, the application of gene expression arrays (microarrays) to the study of cancer has found that in addition to multiple gene mutations, the expression of many hundreds of non-mutant genes is affected in the process of cell transformation.

Microarray analysis of cancers of the breast and soft tissues has also identified distinctive patterns of gene expression which can be used to aid diagnosis and predict the clinical behavior of individual tumors.

This type of genetic analysis will also aid the development of new cancer therapies directed specifically at the molecular biology of the cancer.


Types of cancers

There are several different types of cancers:

  • Carcinomas are cancers that arise in the epithelium (the layers of cells covering the body's surface and lining the internal organs and various glands ). Ninety percent of human cancers fall into this category. Carcinomas can be subdivided into two subtypes: adenocarcinomas and squamous cell carcinomas. Adenocarcinomas are cancers that develop in an organ or a gland, while squamous cell carcinomas refer to cancers that originate in the skin.
  • Melanomas also originate in the skin, usually in the pigment cells (melanocytes).
  • Sarcomas are cancers of the supporting tissues of the body, such as bone, muscle and blood vessels.
  • Cancers of the blood and lymph glands are called leukemia and lymphomas respectively.
  • Gliomas are cancers of the nerve tissue.

Causes and symptoms

The major risk factors for cancer are: tobacco, alcohol , diet, sexual and reproductive behavior, infectious agents, family history, occupation, environment and pollution .

According to the estimates of the American Cancer Society (ACS), approximately 40% of the cancer deaths in 1998 were due to tobacco and excessive alcohol use. An additional one-third of the deaths were related to diet and nutrition . Many of the one million skin cancers that are expected to be diagnosed each year are due to overexposure to ultraviolet light from the sun's rays.

Tobacco

Eighty to ninety percent of the lung cancer cases occur in smokers. Smoking has also been shown to be a contributory factor in cancers of upper respiratory tract, esophagus, larynx, bladder, pancreas, and probably liver, stomach, and kidney as well. Recently, scientists have also shown that second-hand smoke (or passive smoking) can increase one's risk of developing cancer.


Alcohol

Excessive consumption of alcohol is a risk factor in certain cancers, such as liver cancer. Alcohol, in combination with tobacco, significantly increases the chances that an individual will develop mouth, pharynx, larynx, and esophageal cancers.


Diet

Thirty five percent of all cancers are due to dietary causes. Excessive intake of fat leading to obesity has been associated with cancers of the breast, colon, rectum, pancreas, prostate, gall bladder, ovaries, and uterus.


Sexual and reproductive behavior

The human papilloma virus, which is sexually transmitted has been shown to cause cancer of the cervix. Having too many sex partners and becoming sexually active early has been shown to increase one's chances of contracting this disease. In addition, it has also been shown that women who do not have children or have children late in life, have an increased risk for both ovarian and breast cancer.


Infectious agents

In the later decades of the twentieth century, scientists have obtained evidence to show that approximately 15% of the world's cancer deaths can be traced to viruses, bacteria , or parasites . The most common cancer-causing pathogens and the cancers associated with them are shown in table form.


Family history

Certain cancers like breast, colon, ovarian and uterine cancer, recur generation after generation in some families. A few cancers, such as the eye cancer "retinoblastoma," a type of colon cancer, and a type of breast cancer known as "early-onset breast cancer," have been shown to be linked to certain genes that can be tracked within a family. It is therefore possible that inheriting particular genes makes a person susceptible to certain cancers.


Occupational hazards

There is evidence to prove that certain occupational hazards account for 4% of all cancer deaths. For example, asbestos workers have an increased incidence of lung cancer. Similarly, a higher likelihood of getting bladder cancer is associated with dye, rubber and gas workers; skin and lung cancer with smelters, gold miners, and arsenic workers; leukemia with glue and varnish workers; liver cancer with PVC manufacturers; and lung, bone, and bone marrow cancer with radiologists and uranium miners.


Environment

Radiation is believed to cause 1-2% of all cancer deaths. Ultra-violet radiation from the sun accounts for a majority of melanoma deaths. Other sources of radiation are x rays, radon gas, and ionizing radiation from nuclear material.


Pollution

Several studies have shown that there is a well-established link between asbestos and cancer. Chlorination of water may account for a small rise in cancer risk. However, the main danger from pollution occurs when dangerous chemicals from the industries escape into the surrounding environment. It has been estimated that 1% of cancer deaths are due to air, land and water pollution .

Cancer is a progressive disease, and goes through several stages. Each stage may produce a number of symptoms. Some symptoms are produced early and may occur due to a tumor that is growing within an organ or a gland. As the tumor grows, it may press on the nearby nerves, organs and blood vessels. This causes pain and some pressure which may be the earliest warning signs of cancer.

Despite the fact that there are several hundred different types of cancers, producing very different symptoms, the ACS has established the following seven symptoms as possible warning signals of cancer:

  • changes in the size, color , or shape of a wart or a mole
  • a sore that does not heal
  • persistent cough, hoarseness, or sore throat
  • a lump or thickening in the breast or elsewhere
  • unusual bleeding or discharge
  • chronic indigestion or difficulty in swallowing
  • any change in bowel or bladder habits.

Many other diseases, besides cancer, could produce the same symptoms. However, it is important to have these symptoms checked, as soon as possible, especially if they linger. The earlier a cancer is diagnosed and treated, the better the chance of it being cured. Many cancers such as breast cancer may not have any early symptoms. Therefore, it is important to undergo routine screening tests such as breast self-exams and mammograms.


Diagnosis

Diagnosis begins with a thorough physical examination and a complete medical history. The doctor will observe, feel, and palpate (apply pressure by touch ) different parts of the body in order to identify any variations from the normal size, feel and texture of the organ or tissue.

As part of the physical exam, the doctor will inspect the oral cavity or the mouth. By focusing a light into the mouth, he will look for abnormalities in color, moisture, surface texture, or presence of any thickening or sore in the lips, tongue, gums, the hard palate on the roof of the mouth, and the throat. To detect thyroid cancer, the doctor will observe the front of the neck for swelling. He may gently manipulate the neck and palpate the front and side surfaces of the thyroid gland (located at the base of the neck) to detect any nodules or tenderness. As part of the physical examination, the doctor will also palpate the lymph nodes in the neck, under the arms and in the groin. Many illnesses and cancers cause a swelling of the lymph nodes.

The doctor may conduct a thorough examination of the skin to look for sores that have been present for more than three weeks and that bleed, ooze, or crust; irritated patches that may itch or hurt, and any change in the size of a wart or a mole.

Examination of the female pelvis is used to detect cancers of the ovaries, uterus, cervix, and vagina. In the visual examination, the doctor looks for abnormal discharges or the presence of sores. Then, using gloved hands the physician palpates the internal pelvic organs such as the uterus and ovaries to detect any abnormal masses. Breast examination includes visual observation where the doctor looks for any discharge, unevenness, discoloration, or scaling. The doctor palpates both breasts to feel for masses or lumps.

For males, inspection of the rectum and the prostate is also included in the physical examination. The doctor inserts a gloved finger into the rectum and rotates it slowly to feel for any growths, tumors, or other abnormalities. The doctor also conducts an examination of the testis, where the doctor observes the genital area and looks for swelling or other abnormalities. The testicles are palpated to identify any lumps, thickening or differences in the size, weight, and firmness.

If the doctor detects an abnormality on physical examination, or the patient has some symptom that could be indicative of cancer, the doctor may order diagnostic tests.

Laboratory studies of sputum (sputum cytology ), blood, urine, and stool can detect abnormalities that may indicate cancer. Sputum cytology is a test where the phlegm that is coughed up from the lungs is microscopically examined. It is often used to detect lung cancer. A blood test for cancer is easy to perform, usually inexpensive and risk-free. The blood sample is obtained by a lab technician or a doctor, by inserting a needle into a vein and is relatively painless. Blood tests can be either specific or non-specific. Often times, in certain cancers, the cancer cells release particular proteins (called tumor markers) and blood tests can be used to detect the presence of these tumor markers. However, with a few exceptions, tumor markers are not used for routine screening of cancers, because several non-cancerous conditions also produce positive results. Blood tests are generally more useful in monitoring the effectiveness of the treatment, or in following the course of the disease and detecting recurrent disease.

Imaging tests such as computed tomography scans (CT scans), magnetic resonance imaging (MRI) , ultrasound, and fiberoptic scope examinations help the doctors determine the location of the tumor even if it is deep within the body. Conventional x rays are often used for initial evaluation, because they are relatively cheap, painless and easily accessible. In order to increase the information obtained from a conventional x ray, air or a dye (such as barium or iodine) may be used as a contrast medium to outline or highlight parts of the body.

The most definitive diagnostic test is the biopsy, wherein a piece of tissue is surgically removed for microscope examination. Besides, confirming a cancer, the biopsy also provides information about the type of cancer, the stage it has reached, the aggressiveness of the cancer and the extent of its spread. Since a biopsy provides the most accurate analysis, it is considered the gold standard of diagnostic tests.

Screening examinations, conducted regularly by healthcare professionals can result in the detection of cancers of the breast, colon, rectum, cervix, prostate, testis, tongue, mouth, and skin at early stages, when treatment is more likely to be successful. Some of the routine screening tests recommended by the ACS are sigmoidoscopy (for colorectal cancer), mammography (for breast cancer), pap smear (for cervical cancer), and the PSA test (for prostate cancer). Self-examinations for cancers of the breast, testes, mouth, and skin can also help in detecting the tumors before the symptoms become serious.

A recent revolution in molecular biology and cancer genetics has contributed a great deal to the development of several tests designed to assess one's risk of getting cancers. These new techniques include genetic testing , where molecular probes are used to identify mutations in certain genes that have been linked to particular cancers.


Treatment

The aim of cancer treatment is to remove all or as much of the tumor as possible and to prevent the recurrence or spread of the primary tumor. While devising a treatment plan for cancer, the likelihood of curing the cancer has to be weighed against the side effects of the treatment. If the cancer is very aggressive and a cure is not possible, then the treatment should be aimed at relieving the symptoms and controlling the cancer for as long as possible.

Cancer treatment can take many different forms, and it is always tailored to the individual patient. The decision on which type of treatment is the most appropriate depends on the type and location of cancer, the extent to which it has already spread, the patient's age, sex, general health status and personal treatment preferences. The major types of treatment are: surgery , radiation, chemotherapy, immunotherapy, hormone therapy, and bone-marrow transplantation.


Surgery

Surgery is the removal of a visible tumor and is the most frequently used cancer treatment. It is most effective when a cancer is small and confined to one area of the body.

Surgery can be used for many purposes.

  • Treatment: Treatment of cancer by surgery involves removal of the tumor to cure the disease. This is typically done when the cancer is localized to a discrete area. Along with the cancer, some part of the normal surrounding tissue is also removed to ensure that no cancer cells remain in the area. Since cancer usually spreads via the lymphatic system , adjoining lymph nodes may be examined and sometimes they are removed as well.
  • Preventive surgery: Preventive or prophylactic surgery involves removal of an abnormal looking area that is likely to become malignant over time. For example, about 40% of the people with a colon disease known as ulcerative colitis, ultimately die of colon cancer. Rather than live with the fear of developing colon cancer, these people may choose to have their colons removed and reduce the risk significantly.
  • Diagnostic purposes: The most definitive tool for diagnosing cancer is a biopsy. Sometimes a biopsy can be performed by inserting a needle through the skin. However, at other times, the only way to obtain some tissue sample for biopsy, is by performing a surgical operation.
  • Cytoreductive surgery: is a procedure where the doctor removes as much of the cancer as possible, and then treats the remaining with radiation therapy or chemotherapy or both.
  • Palliative surgery: is aimed at curing the symptoms, not the cancer. Usually, in such cases, the tumor is so large or has spread so much, that removing the entire tumor is not an option. For example, a tumor in the abdomen may be so large, that it may press on and block a portion of the intestine, interfering with digestion and causing pain and vomiting. "Debulking surgery" may remove a part of the blockage and relieve the symptoms. In tumors that are dependent on hormones , removal of the organs that secrete the hormones is an option. For example, in prostate cancer, the release of testosterone by the testicles stimulates the growth of cancerous cells. Hence, a man may undergo an "orchiectomy" (removal of testicles) to slow the progress of the disease. Similarly, in a type of aggressive breast cancer, removal of the ovaries (oophorectomy) will stop the synthesis of hormones from the ovaries and slow the progression of the cancer.

Radiation

Radiation kills cells. Radiation is used alone in cases where a tumor is unsuitable for surgery. More often, it is used in conjunction with surgery and chemotherapy. Radiation can be either external or internal. In the external form, the radiation is aimed at the tumor from outside the body. In internal radiation (also known as brachytherapy), a radioactive substance, in the form of pellets or liquid is placed at the cancerous site by means of a pill, injection, or insertion in a sealed container.


Chemotherapy

Chemotherapy is the use of drugs to more specifically kill cancer cells. It destroys the hard-to-detect cancer cells that have spread and are circulating in the body. Chemotherapeutic drugs can be taken either orally (by mouth) or intravenously, and may be given alone or in conjunction with surgery, radiation, or both.

When chemotherapy is used before surgery or radiation, it is known as primary chemotherapy or "neoadjuvant chemotherapy." An advantage of neoadjuvant chemotherapy is that since the cancer cells have not been exposed to anti-cancer drugs, they are especially vulnerable. It can therefore be used effectively to reduce the size of the tumor for surgery or target it for radiation. However, the toxic effects of neoadjuvant chemotherapy are severe. In addition, it may make the body less tolerant to the side effects of other treatments that follow such as radiation therapy. The more common use of chemotherapy is adjuvant therapy, which is given to enhance the effectiveness of other treatments For example, after surgery, adjuvant chemotherapy is given to destroy any cancerous cells that still remain in the body.


Immunotherapy

Immunotherapy uses the body's own immune system to destroy cancer cells. This form of treatment is being intensively studied in clinical trials and is not yet widely available to most cancer patients. The various immunological agents being tested include substances produced by the body (such as the interferons , interleukins, and growth factors), monoclonal antibodies, and vaccines. Unlike traditional vaccines, cancer vaccines do not prevent cancer. Instead, they are designed to treat people who already have the disease. Cancer vaccines work by boosting the body's immune system and training the immune cells to specifically destroy cancer cells.


Hormone therapy

Hormone therapy is standard treatment for some types of cancers that are hormone-dependent and grow faster in the presence of particular hormones. These include cancer of the prostate, breast, and uterus. Hormone therapy involves blocking the production or action of these hormones. As a result the growth of the tumor slows down and survival may be extended for several months or years.


Bone marrow transplantation

The bone marrow is the tissue within the bone cavities that contains blood-forming cells. Healthy bone marrow tissue constantly replenishes the blood supply and is essential to life. Sometimes, the amount of drugs or radiation needed to destroy cancer cells also destroys bone marrow. Replacing the bone marrow with healthy cells counteracts this adverse effect. A bone marrow transplant is the removal of marrow from one person and the transplant of the blood-forming cells either to the same person or to some one else. Bone-marrow transplantation, while not a therapy in itself, is often used to "res cue" a patient, by allowing those with cancer to undergo very aggressive therapy.

Many different specialists generally work together as a team to treat cancer patients. An oncologist is a physician who specializes in cancer care. The oncologist provides chemotherapy, hormone therapy, and any other non-surgical treatment that does not involve radiation. The oncologist often serves as the primary physician and co-ordinates the patient's treatment plan.

The radiation oncologist specializes in using radiation to treat cancer, while the surgical oncologist performs the operations needed to diagnose or treat cancer. Gynecologist-oncologists and pediatric-oncologists, as their titles suggest, are physicians involved with treating women's and children's cancers respectively. Many other specialists may also be involved in the care of a cancer patient. For example, radiologists specialize in the use of x rays, ultrasounds, computed tomography scans (CT scans), MRI imaging, and other techniques that are used to diagnose cancer. Hematologists specialize in disorders of the blood and are consulted in case of blood cancers and bone marrow cancers. The samples that are removed for biopsy are sent to a laboratory, where a pathologist examines them to determine the type of cancer and extent of the disease. Only some of the specialists who are involved with cancer care have been mentioned above. There are many other specialties, and virtually any type of medical or surgical specialist may become involved with care of the cancer patient should it become necessary.


Alternative treatment

There are a multitude of alternative treatments available to help the person with cancer. They can be used in conjunction with, or separate from, surgery, chemotherapy, and radiation therapy. Alternative treatment of cancer is a complicated arena and a trained health practitioner should be consulted.

The effectiveness of complementary therapies such as acupuncture in alleviating cancer pain has not been clinically proven. Bodywork therapies such as massage and reflexology ease muscle tension and may alleviate the side effects such as nausea and vomiting. Homeopathy and herbal remedies used in Chinese traditional herbal medicine have also been reported to alleviate some of the side effects of radiation and chemotherapy and are being recommended by many doctors.

Certain foods including many vegetables , fruits , and grains are believed to offer protection against various cancers. However, isolation of the individual constituent of vegetables and fruits that are anti-cancer agents has proven difficult. In laboratory studies, vitamins such as A, C and E, as well as compounds such as isothiocyanates and dithiolthiones found in broccoli, cauliflower, and cabbage, and beta-carotene found in carrots have been shown to protect against cancer. Studies have shown that eating a diet rich in fiber as found in fruits and vegetables reduces the risk of colon cancer. Exercise and a low fat diet help control weight and reduce the risk of endometrial, breast, and colon cancer.

Certain drugs, which are currently being used for treatment, could also be suitable for prevention. For example, the drug tamoxifen (Nolvadex), that has been very effective against breast cancer, is currently being tested by the National Cancer Institute, for its ability to prevent cancer. Similarly, retinoids derived from vitamin A are being tested for their ability to slow the progression or prevent head and neck cancers. Certain studies have suggested that cancer incidence is lower in areas where soil and foods are rich in the mineral selenium. More trials are needed to explain these intriguing connections.


Prognosis

"Life-time risk" is the term that cancer researchers use to refer to the probability that an individual, over the course of a lifetime will develop cancer or die from it. In the United States, men have a one in two lifetime risk of developing cancer, and for women the risk is one in three. Overall, African-Americans are more likely to develop cancer than whites. African-Americans are also 30% more likely to die of cancer than whites.

Most cancers are curable if detected and treated at their early stages. A cancer patient's prognosis is affected by many factors, particularly the type of cancer the patient has, the stage of the cancer, the extent to which it has metastasized and the aggressiveness of the cancer. In addition, the patient's age, general health status, and the effectiveness of the treatment being pursued are also important factors.

To help predict the future course and outcome of the disease and the likelihood of recovery from the disease, doctors often use statistics . The five-year survival rates are the most common measures used. The number refers to the proportion of people with cancer who are expected to be alive, five years after initial diagnosis, compared with a similar population that is free of cancer. It is important to note that while statistics can give some information about the average survival experience of cancer patients in a given population, it cannot be used to indicate individual prognosis, because no two patients are exactly alike.


Prevention

According to nutritionists and epidemiologists from leading universities in the United States, a person can reduce the chances of getting cancer by following some simple guidelines:

  • Eating plenty of vegetables and fruits
  • Exercising regularly
  • Avoiding excessive weight gain
  • Avoiding tobacco (including second hand smoke)
  • Avoiding excessive amounts of alcohol
  • Avoiding the midday sun (between 11 a.m. and 3 p.m.) when the suns rays are the strongest
  • Avoiding risky sexual practices
  • Avoiding known carcinogens in the environment or work place.

See also Gene therapy; Immunology; Nuclear medicine; Radioisotopes in medicine; Stem cells.


Resources

books

Haskell, Charles M. Cancer Treatment. 5th. ed. Philadelphia: W.B. Saunders, 2001.

Rosenbaum, Ernst H. MD, et al. Everyone's Guide to Cancer Therapy. 4th. ed. Andrews McMeel Publishing, 2002.

Steingraber, Sandra. Living Downstream: A Scientist's Personal Investigation of Cancer and the Environment. Vintage Books, 1998.


periodicals

Brookes, Anthony, "Rethinking Genetic Strategies to Study Complex Diseases," Trends in Molecular Medicine (November 2001): 512–6.


other

National Institutes of Health. "National Cancer Institute." (February 5, 2003).<http://www.nci.nih.gov/>.

Lata Cherath

Micheal Sullivan

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Benign

—A growth that does not spread to other parts of the body. Recovery is favorable with treatment.

Biopsy

—The surgical removal of a small part of a tumor. The excised tissue is studied under the microscope to determine whether it is benign or malignant.

Bone marrow

—A spongy tissue located in the hollow centers of certain bones, such as the skull and hip bones. Bone marrow is the site of blood cell generation.

Carcinogen

—Any substance capable of causing cancer by mutating the cell's DNA.

Chemotherapy

—Use of powerful drugs to kill cancer cells in the human body.

Epithelium

—The layer of cells that covers external and internal surfaces of the body. The many types of epithelium range from flat cells to long cells to cubed cells.

Hormone therapy

—Treatment of cancer by inhibiting the production of hormones, such as testosterone and estrogen.

Immunotherapy

—Treatment of cancer by stimulating the body s immune defense system.

Malignant

—A general term for cells that can dislodge from the original tumor, invade and destroy other tissues and organs.

Metastasis

—The spread of cancer from one part of the body to another.

Radiation therapy

—Treatment using high-energy radiation from x-ray machines, cobalt, radium, or other sources.

Sore

—An open wound or a bruise or lesion on the skin.

Tumor

—An uncontrolled growth of tissue, either benign (noncancerous) or malignant (cancerous).

X ray

—Electromagnetic radiation of very short wavelength, and very high energy.

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Cancer

CANCER

During the twentieth century wealthy countries underwent a transition in mortality from acute, infectious diseases such as pneumonia to chronic diseases such as cancer. By the late twentieth century the lifetime risk of a person receiving a cancer diagnosis in the United States had climbed above one-in-three. The quest for an elusive "cure" for cancer became a policy imperative, and by the first decade of the twenty-first century U.S. government expenditures on cancer research had reached three billion dollars per year. Notwithstanding decades of heavy research funding, advances in long-term survival for many of the common types of cancer have remained insignificant, and critics have charged that research funding has been too narrowly focused.


Etiologies

The ancient Greeks and Romans understood cancer and other diseases in terms of the bodily humors of phlegm, blood, black bile, and yellow bile (Rather 1978). When the humors were out of balance, such as an excess of black bile in the case of cancer, a disease could erupt. Similar humoral approaches characterized other Old World medical systems, such as the traditional medicines of east and south Asia. Although the rise of scientific biology displaced humoral thinking from the medical sciences, humoral approaches to disease can still be found in some complementary and alternative medicine (CAM) approaches to cancer, such as macrobiotic, Ayurvedic, and other traditional Asian medical systems, as well as in general notions of rebalancing the body. Ancient physicians also identified diet and trauma as two possible environmental sources of cancer, and those ideas continue to be relevant to thinking on the etiology (causes) of cancer in the early-twenty-first century.

By the beginning of the twentieth century medical researchers were pursuing diverse approaches to cancer etiology. In the wake of the bacteriological revolution, many researchers thought that cancer was an infectious, bacterial disease. Although bacterial theories and therapies were on the wane by the 1920s, throughout the twentieth century a marginal network of researchers kept the approach alive, and they developed dietary and vaccine-based therapies (Hess 1997). At the end of the twentieth century, bacteria were gaining some general recognition as a risk factor for digestive tract cancers. Viral oncology, which had a peak of popularity during the 1960s, had also won general acceptance for viruses as the cause of some human and animal cancers.

At a popular level, laypeople in early-twentieth-century Western countries frequently believed that trauma was a significant cause of cancer (Clow 2001), and the belief is still widespread in some countries. The medical profession recognized a related risk factor of tissue irritation from sources such as tobacco or childbirth. The interest in tissue irritation gradually developed into research programs on chemical carcinogenesis. In the eighteenth century the relationship between creosote tar and scrotal cancer in chimney sweeps had been identified. By the end of the twentieth century, a wide range of chemicals, as well as some forms of electromagnetic radiation, were acknowledged as risk factors, including especially the carcinogens in cigarette smoke.

At the beginning of the twentieth century, some medical researchers also drew attention to the role of internal biological processes in cancer etiology. One theory assumed that embryonic cells remained embedded in differentiated tissues and that they could develop into cancer under some conditions. The theory did not win widespread acceptance, but therapies based on enzymes and other dietary modifications continued as part of the field of CAM cancer care. Furthermore the theory drew attention to the role of growth hormones in cancer, which became part of mainstream cancer research. By the middle decades of the twentieth century, research programs were also emerging on the role of sex hormones in some cancers.

Another development during the twentieth century was research on inherited susceptibility to cancer, which developed from longstanding beliefs about heredity and cancer. Animal experiments in the early decades of the twentieth century confirmed the role of heredity, and by the late-twentieth century it became clear that some types of inherited gene variations (alleles) carried very high risk for some types of cancer, such as the BRCA1 and BRCA2 genes for breast cancer. However, epidemiologists at the end of the twentieth century generally believed that heredity explained only a minor percentage of the variation in the aggregate incidence of cancer and in its growth in incidence.

The development of molecular biology in the second half of the twentieth century allowed a synthesis of various risk factors (for example viruses, chemical carcinogens, radiation) at the molecular level of genetic damage and the expression of genes related to cancer (oncogenes and tumor suppressor genes). However, heredity as a risk factor needs to be distinguished from the understanding of carcinogenesis at a molecular level. Epidemiologists have increasingly given priority to environmental and lifestyle factors, of which diet and exposure to carcinogenic chemicals are generally seen as the central risk factors. In the early-twenty-first century, other recognized risk factors include reproductive behavior, obesity, viral infection, and excessive exposure to sunlight.


Ethics in the Clinical Setting

Most discussions of ethics and cancer focus on the doctor-patient relationship and the various types of ethical problems that emerge in cancer diagnosis and treatment (Angelos 1999). A key issue involves the communication of information to the patient. In some countries physicians have historically informed family members of the diagnosis but have concealed the diagnosis from the patient, even if the patient asks for the information. The practice appears to be changing, but other questions remain. For example, should a physician inform the patient of the diagnosis and/or prognosis, even if the patient asks not to be informed? Likewise should a clinician volunteer statistical information about prognosis even when only more general information is requested?

A related but in a sense inverted problem involves the disclosure to kin of a known genetic mutation that is related to cancer, such as the BRCA1/2 mutation. Patients who undergo such testing often do not expect to benefit personally from it, but they hope that the information will be helpful to kin. As a result, questions have been raised about informed consent regarding the autonomy of the patients who undergo testing, who may feel compelled by responsibility toward kin as a reason for undertaking the testing, as well as the autonomy of kin, who may not want to know such information or may fear genetic discrimination (Hallowell et al. 2003).

A second issue in the doctor-patient relationship involves the ethics of physician reactions to decisions by patients to withdraw from treatment. Sometimes patients decide that the side effects of conventional treatments, such as chemotherapy, are too severe in comparison with the potential benefits (long-term remission) for their particular type of cancer. Patients may combine the decision to withdraw from treatment with a decision to opt for a CAM treatment, but sometimes they simply forego chemotherapy for reasons other than pursuing a successful treatment. For example, patients may decide that there is no hope for recovery and that they are ready to die, or they may feel healthy and may want to work until they no longer can. However oncologists may not recognize nonmedical reasons as good reasons for refusing treatment, or they may reject the patient's assessment of the relative risks and benefits of various options, and consequently a communication gap may emerge when oncologists refuse to continue to monitor patients who refuse treatment (Huijer and Leeuwen 2000).

When parents make similar decisions for children, the cases can end in bitter conflicts. In some cases doctors have called in state agencies to take children away from their parents and forcibly deliver conventional therapies. Presumably some calculation of the benefits and risks of both the proposed conventional therapy (including no treatment) and the alternative treatment option (including no treatment) pursued by the parents inform decisions about whether to support the parents or take their child away. As a result, in some cases doctors may support the parents' decision. For example, a child was diagnosed with a type of brain tumor for which conventional therapies offered no possibility of cure. The parents decided to try antineoplastons, an experimental therapy that had only limited supporting evidence at the time but held some risk associated with the insertion of an intravenous catheter. In this case the doctors and hospital opted to insert the catheter and follow the patient, but they also informed the parents of their skepticism that the therapy would be beneficial (Jackson 1994).


Ethics and Research Funding

Ethical issues have also emerged around the politics of funding. One key area has been research funding on chemical carcinogenesis. For years, evidence that smoking is a substantial risk factor for lung cancer (as well as some other types of cancer) was suppressed, and epidemiologists who sought funds for and produced evidence on the role of smoking faced a long battle for recognition. In the early-twenty-first century a younger generation of epidemiologists faces a similar battle to gain acceptance for claims that military and industrial pollution is a major risk factor (Davis and Webster 2002). Historically researchers who have attempted to document risks from industrial pollutants such as ionizing radiation have faced suppression, and industry support groups also have produced scientific dissensus by funding studies that questioned the risks associated with industrial pollutants (Proctor 1995).

In addition to the politics of funding for research on etiology, ethical issues also have emerged around funding choices for research that evaluates or develops therapies. In the early twentieth century surgery was the only mainstream therapy for cancer, but radium-based therapies gained currency by the 1920s, and chemotherapy emerged after World War II. Surgeons and physicians who owned radium or advocated chemotherapy actively opposed the vaccine-oriented therapies developed by researchers who adopted immunological or biological approaches (Hess 1997). Similar suppression has been documented for nutritional therapies and a range of other CAM approaches to cancer (Moss 1995).

As cancer treatment developed during the twentieth century, medical subspecialties and cancer-related treatment industries opposed radical changes in treatment that threatened to undercut the profits of surgery, radiation therapy, and patented drugs. Although biological/immunological therapies for cancer (such as the use of interleukins and drugs that block the formation of blood vessels) are gaining ground in the early-twenty-first century, those developments take place through the mechanism of patented drug development. Researchers who investigate therapies that rely on unpatented products derived from plant or animal substances have been unable to obtain the level of private sector investment that is necessary to become competitors in the field of cancer therapy, which after the early 1960s involved a very costly drug approval process. As a result, a wide range of potentially lifesaving therapies has remained underinvestigated. Public funding agencies in the United States and other countries that could have stepped in to provide research funding for orphaned, unpatented therapies did not do so until the late-twentieth century, and even then the funding remained very minimal. (The term "orphaned" refers to therapies that lack sufficient research funding to be brought to market, because private firms cannot recuperate research costs in future sales due to lack of patentability or size of market.)

Another way in which research on unpatented products can hit a dead end is due to the way that the ethics of clinical trials has developed. Ethicists have argued in favor of equipoise, that is, the condition that study and treatment arms in a clinical trial have equal risk/benefit profiles. As a result, in cancer research placebo controls are rarely used; instead an experimental treatment is compared to the treatment standard. Frequently the experimental treatment is the standard treatment plus an additional drug. The standard of equipoise protects patients with life-threatening diseases from research that would put them at risk of receiving completely inefficacious treatment. However because funding is absent to generate preliminary human data, unpatented therapies can be locked in a limbo that prevents head-to-head testing against standard therapies. In this way ethical considerations at one level (patient rights) can negatively impact ethical considerations at another level (investigation of orphaned or unpatented therapies).

In short, significant ethical issues remain unaddressed regarding research funding for both etiology and treatment. Industrial interests external to cancer research and treatment, such as industries that generate significant pollution with suspected carcinogens, have opposed research that might lead to costly changes in materials or production processes. Likewise industrial interests internal to cancer research and treatment, such as medical subspecialties and the pharmaceutical/biotechnology industries, have opposed research that might open the door to competition from unpatented products. After decades of publicly supported research that have followed President Nixon's declaration of the war on cancer in 1971, for many patients therapeutic options remain limited and long-term prognosis remains dismal.


DAVID HESS

SEE ALSO Death and Dying; Health and Disease; Medical Ethics.

BIBLIOGRAPHY

Angelos, Peter. (1999). Ethical Issues in Cancer Patient Care. Dordrecht, The Netherlands: Kluwer. Good survey of the bedside ethical dimensions of conventional cancer care.

Clow, Barbara. (2001). Negotiating Disease. Montreal McGill-Queen's University Press. Survey of popular and academic understandings of cancer etiology in the twentieth-century.

Davis, Devra Lee, and Pamela Webster. (2002). "Epidemiology and Science: The Social Context of Science." Annals of the American Academy of Political and Social Science 584(13): 13–34. Example of the younger generation of epidemiologists that is developing the case for environmental etiologies.

Hallowell, Nina; Foster, C.; Eeles, R., et al. (2003). "Balancing Autonomy and Responsibility: The Ethics of Generating and Disclosing Genetic Information. Journal of Medical Ethics 29(2): 74–79. A leading journal for those interested in medical ethics.

Hess, David. (1997). Can Bacteria Cause Cancer? New York: New York University Press. A multidisciplinary analysis of the history of one type of alternative theory and therapy for cancer, analysis of its suppression, evaluation of the evidence, and discussion of policy remedies.

Huijer, Marli, and Evert van Leeuwen. (2000). "Personal Values and Cancer Treatment Refusal." Journal of Medical Ethics 26(5): 358–362.

Jackson, Jennifer. (1994). "Unproven Treatment in Childhood Oncology: How Far Should Pediatricians Co-Operate? Commentary." Journal of Medical Ethics 20: 77–79.

Moss, Ralph. (1995). The Cancer Industry. Brooklyn, NY: Equinox Press. Classic study of the suppression of alternative cancer therapies and researchers.

Proctor, Robert. (1995). Cancer Wars. New York: Basic Books. Review of research controversies surrounding environmental etiologies of cancer.

Rather, L. J. (1978). The Genesis of Cancer: A Study of the History of Ideas. Baltimore, MD: Johns Hopkins University Press. Examples the early theories of cancer.

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Cancer

Cancer

Definition

Cancer is not just one disease, but a large group of diseases characterized by uncontrolled and abnormal growth of the cells in the human body and the ability of these cells to spread to distant sites (metastasis). If the spread is not controlled, cancer can result in death.

Description

Cancer, by definition, is a disease of the genes. Genes are formed from deoxyribonucleic acid (DNA ) and located on chromosomes. They carry the hereditary instructions for the cell to make the proteins required for many body functions. Proteins are special chemical compounds that mostly contain carbon, hydrogen, oxygen, and nitrogen and that are required by our bodies to carry out all the processes that allow us to breathe, think, move, etc.

Throughout people's lives, the cells in their bodies are growing, dividing, and replacing themselves. Many genes produce proteins that are involved in controlling the processes of cell growth and division. A change (mutation) occurring in the DNA molecules can disrupt the genes and produce faulty proteins and cells. Abnormal cells can start dividing uncontrollably, eventually forming a new growth known as a "tumor" or "neoplasm" (medical term for cancer meaning "new growth"). In a healthy individual, the immune system can recognize the neoplastic cells and destroy them before they get a chance to divide. However, some abnormal cells may escape immune detection and survive to become cancerous.

Tumors are of two types, benign or malignant. A benign tumor is slow growing and does not spread or invade surrounding tissue. Once the tumor is removed, it will not usually start growing again. A malignant tumor, on the other hand, invades surrounding tissue and can spread to other parts of the body, often very distant from the location of the first tumor. Malignant tumors can be removed, but if the cancer cells have spread too much, the cancer becomes very difficult, if not impossible, to treat.

Most cancers are caused by changes in the cell's DNA that result from exposure to a harmful environment. Environmental factors responsible for causing the initial mutation in the DNA are called carcinogens. Other factors can cause cancer as well. For example, certain hormones have been shown to have an effect on the growth or control of a particular cell line. Hormones are substances made by one organ and passed through the bloodstream to affect the function of other cells in another organ.

While there is scientific evidence that both environmental and genetic factors play a role in most cancers, only 5-10% of all cancers are classified as hereditary. This means that a faulty gene that may cause cancer is passed from parent to child. This results in a greater risk for that type of cancer in the offspring of the family. However, if someone has a cancer-causing gene, this doesn't mean they will automatically get cancer. Rather, this person is thought to be "predisposed" to a type of cancer, or more likely to get this cancer when compared to the general population. Various cancers are known to have a hereditary component in some cases. A few examples are breast cancer , colon cancer, ovarian cancer , skin cancer and prostate cancer .

Aside from genes, certain physiological traits that are inherited can contribute to cancers as well. For example, fair skin makes a person more likely to develop skin cancer, but only if they also have prolonged exposure to intensive sunlight.

There are several different types of cancers. Some of the most common types include:

  • Carcinomas These cancers arise in the epithelium (the layers of cells covering the body's surface and lining the internal organs and various glands). About 80% of human cancers fall into this category. Carcinomas can be subdivided into two subtypes: adenocarcinomas and squamous cell carcinomas. Adenocarcinomas are cancers that develop in an organ or a gland, while squamous cell carcinomas refer to cancers that originate in the skin.
  • Melanomas This form also originates in the skin, usually in the pigment cells (melanocytes).
  • Sarcomas These are cancers of the supporting tissues of the body, such as bone, muscle, cartilage, and fat.
  • Leukemias Cancers of the blood or blood-forming organs.
  • Lymphomas This type affects the lymphatic system, a network of vessels and nodes that acts as a filter in the body. It distributes nutrients to blood and tissue and prevents bacteria and other foreign substances from entering the bloodstream.
  • Gliomas Cancers of the nerve tissue.

The most common cancers are skin cancer, lung cancer, colon and rectal (colorectal) cancer, breast cancer (in women), and prostate cancer (in men). In addition, cancer of the kidneys, ovaries, uterus, pancreas, bladder, and blood and lymph node cancer (leukemias and lymphomas) are also included among the 12 major cancers that affect most Americans.

Genetic profile

Three classes of genes are believed to play roles in the development of cancer. These are:

  • Proto-oncogenes. These genes encourage and promote the normal growth and division of cells. When they are defective, they become oncogenes. Oncogenes are overactive proto-oncogenes and they cause excessive cell multiplication that can lead to tumors.
  • Tumor suppressor genes. These act as brakes on cell growth. They prevent cells from multiplying uncontrollably. If these genes are defective, there is no control over cell growth and tumors can result.
  • DNA repair genes. These genes ensure that each strand of DNA is correctly copied during cell division. When these genes do not function properly, the replicated DNA is likely to have mistakes. This causes defects in other genes and can also lead to tumor formation.

As stated above, approximately 5-10% of cancers have a hereditary component. In these cancers, a child does not inherit cancer from his parents. Rather, he inherits a predisposition to cancer. For example, he may inherit a faulty tumor suppressor gene. This gene is not able to control cell growth but the corresponding gene inherited from the other parent is still functional. Cell growth is then under control. However, as this child grows up, radiation, pollution, or any other harmful environmental factor could change the healthy gene, making it abnormal as well. When both of these tumor suppressor genes are not functioning, a tumor is most likely to develop. Defects in proto-oncogenes and DNA repair genes can be inherited as well, leaving a person more vulnerable to cancer than the general population.

Additionally, some cancers seem to be familial. In these cancers, there is not a specific gene that is responsible for the clustering of cancer in a family. However, a particular type of cancer may be seen more often than expected. It is suggested that this is due to a combination of genetic and environmental factors.

Demographics

One out of every four Americans will die from cancer. It is the second leading cause of death in this country, surpassed only by heart disease. Over 1.2 million new cases of cancer are diagnosed every year. The National Cancer Institute estimated that approximately 8.4 million Americans alive in 2001 had a history of cancer. Some of these people had been cured of their cancer while others were still affected with the disease and were undergoing treatment.

Anyone is at risk for developing cancer. Since the occurrence of cancer increases as a person ages, most of the cases are seen in adults who are middle-aged or older. Nearly 80% of cancers are diagnosed in people who are 55 years of age and older.

"Lifetime risk" is the term that cancer researchers use to refer to the probability that an individual will develop cancer over the course of their lifetime. In the United States, men have a one in two lifetime risk of developing cancer, and for women the risk is one in three. Overall, African-Americans are more likely to develop cancer than caucasians. They are also 33% more likely to die of cancer than caucasians.

The major risk factors for cancer are: tobacco, alcohol, diet, sexual and reproductive behavior, infectious agents, family history, occupation, environment, and pollution.

Tobacco

Eighty to ninety percent of the lung cancer cases occur in smokers. Smoking has also been shown to be a contributory factor in cancers of the mouth, pharynx, larynx, esophagus, pancreas, uterine cervix, kidney, and bladder. Smoking accounts for at least 30% of all cancer deaths. Recently, scientists have also shown that secondhand smoke (or passive smoking) can increase one's risk of developing cancer.

Alcohol

Excessive consumption of alcohol is a risk factor in some cancers, such as liver cancer and breast cancer. Alcohol, in combination with tobacco, significantly increases the chances that an individual will develop mouth, pharynx, larynx, and esophageal cancers. The combined effect of tobacco and alcohol is greater than the sum of their individual effects.

Diet and physical activity

One-third of all cancer deaths are due to a poor adult diet. High-fat diets have been associated with cancers of the colon and rectum, prostate, endometrium, and possibly breast. Consumption of meat, especially red meat, has been associated with increased cancer at various sites, such as the colon and prostate. Additionally, a high calorie diet and low level of physical activity can lead to obesity. This increases the risk for cancer at various sites including the breast, colon and rectum, prostate, kidney, and endometrium.

Sexual and reproductive behavior

The human papilloma virus, which is a sexually transmitted disease, has been shown to cause cancer of the cervix. Having many sexual partners and becoming sexually active early has been shown to increase a woman's chances of contracting this disease and, therefore, developing cervical cancer. In addition, it has also been shown that women who do not bear any children or those who become pregnant late in life have an increased risk for both ovarian and breast cancer.

Hormone replacement therapy

As women go through menopause, a doctor may recommend hormone replacement therapy. This involves taking female hormones (called estrogen and progesterone) to control certain symptoms that occur during this time of a woman's life, such as hot flashes and vaginal dryness. Taking estrogen alone can increase the risk for uterine cancer. However, progesterone is often prescribed at the same time to counteract the cancerous effects of estrogen. There is a questionable relationship between hormone replacement therapy and breast cancer as well. This relationship is not fully understood.

Family history

Some types of cancers tend to occur more frequently among members of a family. In most cases, this happens by chance or due to common family habits such as cigarette smoking or excessive sun exposure. However, this can also be due to a genetic predisposition that is passed from generation to generation. For example, if a certain gene called BRCA1 is defective in a given family, members of that family may have an increased risk to develop breast, colon, ovarian and prostate cancer. Other defective genes have been identified that can make a person susceptible to various types of cancer. Therefore, inheriting particular genes can increase a person's chance to develop cancer.

Occupational hazards

There is strong evidence proving that occupational hazards account for 4% of all cancer deaths. For example, asbestos workers have an increased incidence of lung cancer. Similarly, bladder cancer is associated with dye, rubber and gas workers; skin and lung cancer with smelters, gold miners and arsenic workers; leukemia with glue and varnish workers; liver cancer with PVC manufacturers; and lung, bone and bone marrow cancer with radiologists and uranium miners.

Environment

High-frequency radiation has been shown to cause human cancer. Ultra-violet radiation from the sun accounts for a majority of melanoma. Other sources of radiation are x rays, radioactive substances, and rays that enter the Earth's atmosphere from outer space. Virtually any part of the body can be affected by these types of radiation, especially the bone marrow and the thyroid gland.

Additionally, being exposed to substances such as certain chemicals, metals, or pesticides can increase the risk of cancer. Asbestos is an example of a well-known carcinogen. It increases the risk for lung cancer. This risk is increased even further for a smoker who is exposed to asbestos over a period of time.

Signs and symptoms

Almost every tissue of the body can give rise to abnormal cells that cause cancer and each of these cancers is very different in symptoms and prognosis.

Cancer is also a progressive disease and goes through several stages. Each stage can produce a number of symptoms. Unfortunately, many types of cancer do not display any obvious symptoms or cause pain until the disease has progressed to an advanced stage. Early signs of cancer are often subtle and are easily mistaken for signs of other less-dangerous diseases.

Despite the fact that there are several hundred different types of cancers producing very different symptoms, the American Cancer Society (ACS) has established the following seven symptoms as possible warning signs of cancer:

  • changes in the size, color, or shape of a wart or a mole
  • a sore that does not heal
  • persistent cough, hoarseness, or sore throat
  • a lump or thickening in the breast or elsewhere
  • unusual bleeding or discharge
  • chronic indigestion or difficulty in swallowing
  • any change in bowel or bladder habits

Many other diseases can produce similar symptoms. However, it is important to have these symptoms checked as soon as possible, especially if they do not stop. The earlier a cancer is diagnosed and treated, the better the chance of a cure. Many cancers, such as breast cancer, may not have any early symptoms. Therefore, it is important to undergo routine screening tests, such as breast self-exams and mammograms.

Childhood cancers associated with congenital syndromes or malformations

Syndrome or Anomaly Tumor
AniridiaWilms tumor
HemihypertrophyWilms tumor, hepatoblastoma, adrenocortical carcinoma
Genito-urinary abnormalities (including testicle maldescent)Wilms tumor, Ewing sarcoma, nephroblastoma, testicular carcinoma
Beckwith-Wiedmann syndromeWilms tumor, neuroblastoma, adrenocortical carcinoma
Dysplastic naevus syndromeMelanoma
Nevoid basal cell carcinoma syndromeBasal cell carcinoma, medulloblastoma, rhabdomyosarcoma
Poland syndromeLeukemia
Trisomy-21 (Down syndrome)Leukemia, retinoblastoma
Bloom syndromeLeukemia, gastrointestinal carcinoma
Severe combined immune deficiency diseaseEBV-associated B-lymphocyte lymphoma/leukemia
Wiscott-Aldridge syndromeEBV-associated B-lymphocyte lymphoma
Ataxia telangiectasiaEBV-associated B-lymphocyte lymphoma, gastric carcinoma
RetinoblastomaWilms tumor, osteosarcoma, Ewing sarcoma
Fanconi anemiaLeukemia, squamous cell carcinoma
Multiple endocrine neoplasia syndromes (MEN I, II, III)Adenomas of islet cells, pituitary, parathyroids, and adrenal glands Submucosal neuromas of the tongue, lips, eyelids
Pheochromocytomas, medullary carcinoma of the thyroid, malignant schwannoma, non-appendiceal carcinoid
Neurofibromatosis (von Recklinghausensyndrome)Rhabdomyosarcoma, fibrosarcoma, pheochromocytomas, opticglioma, meningioma

Diagnosis

If a person has symptoms of cancer, the doctor will begin with a complete medical history and a thorough physical examination. Different parts of the body will be examined to identify any variations from the normal

size, feel and texture of the organ or tissue. Additionally, the doctor may order various other tests.

Laboratory tests on blood and urine are often used to obtain information about a person's health. If cancer is suspected, a special test can be done that measures the amount of certain substances, called tumor markers, in the blood, urine, or particular tissues. These proteins are released from some types of cancer cells. Thus, the levels of these substances may be abnormal when certain cancers are present. However, laboratory tests alone cannot be used to make a definitive diagnosis of cancer. Blood tests are generally more useful in monitoring the effectiveness of the treatment or in following the course of the disease and detecting any signs of recurrence.

The doctor may also look for tumors by examining pictures of areas inside the body. The most common way to obtain these images is by using x rays. Other techniques used to obtain pictures of the inside of the body include computed tomography scanning (CT scan), magnetic resonance imaging (MRI), and ultrasonography.

The most definitive diagnostic test is the biopsy. In this technique, a piece of tissue is surgically removed for examination under a microscope. A biopsy provides information about the cellular nature of the abnormality, the stage it has reached, the aggressiveness of the cancer, and the extent of its spread. Further analysis of the tissue obtained by biopsy defines the cause of the abnormality. Since a biopsy provides the most accurate analysis, it is considered the gold standard of diagnostic tests for cancer.

Regular screening examinations conducted by healthcare professionals can result in the early detection of various types of cancer. If detected at an early stage, treatment is more likely to be successful. For example, the American Cancer Society recommends an annual mammogram (x ray of the breast) for women over the age of 40 to screen for breast cancer. It also recommends a sigmoidoscopy (procedure using a thin, lighted tube to view the inside of the colon) every five years for people over the age of 50. This technique can check for colorectal cancer. Self-examinations for cancers of the breast, testes, mouth and skin can also help in detecting tumors.

Recent progress in molecular biology and cancer genetics have led to the development of several tests designed to assess one's risk of developing certain types of cancer. This genetic testing involves looking closely at certain genes that have been linked to particular cancers. If these genes are abnormal, a person's risk for certain types of cancer increases. At present, there are many limitations to genetic testing. The tests may be uninformative and they are useful to a very small number of people. Additionally, there are concerns about insurance coverage and employment discrimination for someone who has an increased risk for cancer. These tests are reserved only for very specific people. A hereditary cancer clinic can help to assess who may benefit from this type of testing.

Treatment and management

The aim of cancer treatment is to remove all or as much of the tumor as possible and to prevent the metastasis of the primary tumor. While devising a treatment plan for cancer, the likelihood of curing the cancer must be weighed against the side effects of the treatment. For example, if the cancer is very aggressive and a cure is not possible, then the treatment should be aimed at relieving the symptoms and controlling the cancer for as long as possible.

Cancer treatment can take many different forms and it is always tailored to the individual patient. The decision on which type of treatment to use depends on the type and location of cancer and the extent to which it has already spread. The doctor will also consider the patient's age, sex, general health status, and personal treatment preferences. Treatment can be local, meaning that it seeks to destroy cancer cells in the tumor and the surrounding area. It can also be systemic, meaning that the treatment drugs will travel through the bloodstream and reach cancer cells all over the body. Surgery and radiation are local treatments. Chemotherapy, immunotherapy, and hormone therapy are examples of systemic treatments.

Surgery

Surgery can be used for many purposes in cancer therapy.

  • Treatment surgery: This involves removal of the tumor to cure the disease. It is typically performed when the cancer is localized to a discrete area. Along with the cancer, some of the surrounding tissue may also be removed to ensure that no cancer cells remain in the area. Since cancer usually spreads via the lymphatic system, lymph nodes that are near the tumor site may be examined and removed as well.
  • Preventive surgery: Preventive or prophylactic surgery involves removal of an abnormal area that is likely to become malignant over time. For example, 40% of people with a colon disease called ulcerative colitis ultimately die of colon cancer. Rather than live with the fear of developing colon cancer, these people may choose to have their colons removed in order to reduce their risk of cancer.
  • Diagnostic purposes: The most definitive tool for diagnosing cancer is a biopsy. Sometimes a biopsy can be performed by inserting a needle through the skin. In other cases, the only way to obtain a tissue sample for biopsy is by performing a surgical operation.
  • Cytoreductive surgery: This is a procedure in which the doctor removes as much of the cancer as possible. He then treats the remaining cancer cells with radiation therapy, chemotherapy, or both.
  • Palliative surgery: This type of surgery is aimed at relieving cancer symptoms or slowing the progression of disease. It is not designed to cure the cancer. For example, if the tumor is very large or has spread to many places in the body, removing the entire tumor may not be an option. However, by decreasing the size of the tumor, pain may be alleviated. This is known as "debulking surgery."

Radiation therapy

Radiation uses high-energy rays to kill cancer cells. This treatment may be used instead of surgery. It also may be used before surgery to shrink a tumor or after surgery to destroy any remaining cancer cells.

Radiation can be either external or internal. In the external form, the radiation comes from a machine that aims the rays at the tumor. In internal radiation (also known as brachytherapy), radioactive material is sealed in needles, seeds, or wires and placed directly in or near the tumor. Radiation may lead to various side effects, such as fatigue, hair loss, and a susceptibility to infections. However, these side effects can usually be controlled.

Chemotherapy

Chemotherapy is the use of drugs to kill cancer cells. The anticancer drugs are usually released into the entire body (systemic therapy) so as to destroy the hard-to-detect cancer cells that have spread and are circulating in the body. Chemotherapy is based on the principle that cancer cells are affected more dramatically than the normal cells because they are rapidly dividing. Chemotherapeutic drugs can be injected into a vein, the muscle, or the skin or they may be taken by mouth.

When chemotherapy is used before surgery, it is known as primary chemotherapy or "neoadjuvant chemotherapy." Its purpose is usually to reduce the size of the tumor. The more common use of chemotherapy is in "adjuvant therapy." In this form of treatment, chemotherapy is given after surgery to destroy any remaining cancer cells and to help prevent cancer from recurring. Chemotherapy can also be used in conjunction with radiation therapy.

The side effects of chemotherapy vary but can include susceptibility to infections, fatigue, poor appetite, weight loss, nausea, diarrhea, and hair loss. Decreased fertility can be a long-term side effect in some patients who undergo chemotherapy.

Immunotherapy

Immunotherapy, also called biological therapy, is the use of treatments that promote or support the body's immune system response to cancer. The side effects of this immunotherapy are variable but include flu-like symptoms, weakness, loss of appetite, and skin rash. These symptoms will subside after the treatment is completed.

Bone marrow failure is a complication of chemotherapy. When high dose chemotherapy is used, this failure is anticipated. Bone marrow transplantation (BMT) or peripheral stem cell transplantation (PSCT) are techniques used to treat this complication. Both techniques provide healthy stem cells for the patient. Stem cells are immature cells that mature into blood cells. They can replace the patient's own stem cells that have been damaged or destroyed by chemotherapy or radiation. It allows a patient to undergo very aggressive treatment for their cancer. Patients who receive BMT or PSCT have an increased risk of infection, bleeding, and other side effects due to the chemotherapy and radiation. Graft-versus-host disease may also occur as well. This complication occurs when the donated marrow reacts against a patient's tissues. It can occur any time after the transplant. Drugs may be given to reduce the risk of graft-versus-host disease and to treat the problem if it occurs.

Hormone therapy

Hormone therapy is used to fight certain cancers that depend on hormones for their growth. Drugs can be used to block the production of hormones or change the way they work. Additionally, organs that produce hormones may be removed. As a result of this therapy, the growth of the tumor slows and survival may be extended for several months or years.

Alternative and complementary therapies

There are certain cancer therapies that have not been scientifically tested and approved. If these unproven treatments are used instead of the standard therapy, this is known as "alternative therapy." If used along with standard therapy, this is known as "complementary therapy." The use of alternative therapies must be carefully considered because some of these unproven treatments may have life-threatening side effects. Additionally, if someone uses alternative therapy, they may lose the opportunity to benefit from the standard, proven therapy. However, some complementary therapies may help to relieve symptoms of cancer, decrease the magnitude of side effects from treatment, or improve a patient's sense of well-being. The American Cancer Society recommends that anyone considering alternative or complementary therapy consult a health care team.

Prevention

According to experts from leading universities in the United States, a person can reduce the chances of getting cancer by following these guidelines:

  • eating plenty of fruits and vegetables
  • exercising vigorously for at least 20 minutes every day
  • avoiding excessive weight gain
  • avoiding tobacco (including second hand smoke)
  • decreasing or avoiding consumption of animal fats and red meats
  • avoiding excessive amounts of alcohol
  • avoiding the midday sun (between 11 a.m. and 3 p.m.) when the sun's rays are the strongest
  • avoiding risky sexual practices
  • avoiding known carcinogens in the environment or work place

Certain drugs that are currently being used for treatment can also be suitable for prevention. For example, the drug tamoxifen, also called Nolvadex, has been very effective against breast cancer and is now thought to be helpful in the prevention of breast cancer. Similarly, retinoids derived from vitamin A are being tested for their ability to slow the progression or prevent head and neck cancers.

Prognosis

Most cancers are curable if detected and treated at their early stages. A cancer patient's prognosis is affected by many factors, particularly the type of cancer the patient has, the stage of the cancer, the extent to which it has metastasized and the aggressiveness of the cancer. In addition, the patient's age, general health status and the effectiveness of the treatment being pursued are also important factors.

To help predict the future outcome of cancer and the likelihood of recovery from the disease, five-year survival rates are used. The five-year survival rate for all cancers combined is 59%. This means that 59% of people with cancer are expected to be alive five years after they are diagnosed. These people may be free of cancer or they may be undergoing treatment. It is important to note that while this statistic can give some information about the average survival of cancer patients in a given population, it cannot be used to predict individual prognosis. No two patients are exactly alike. For example, the five-year survival rate does not account for differences in detection methods, types of treatments, additional illnesses, and behaviors.

Resources

BOOKS

American Cancer Society. Cancer Facts & Figures 2000. American Cancer Society, 2000.

Buckman, Robert. What You Really Need to Know about Cancer: A Comprehensive Guide for Patients and Their Families. Johns Hopkins University Press, 1997.

Murphy, Gerald P. Informed Decisions: The Complete Book of Cancer Diagnosis, Treatment and Recovery. American Cancer Society, 1997.

PERIODICALS

Ruccione, Kathy. "Cancer and Genetics: What We Need to Know." Journal of Pediatric Oncology Nursing 16 (July 1999): 156-171.

"What You Need to Know about Cancer." Scientific American 275, no. 3 (September 1996).

ORGANIZATIONS

American Cancer Society. 1599 Clifton Rd. NE, Atlanta, GA 30329. (800) 227-2345. <http://www.cancer.org>.

American Foundation for Urologic Disease, Inc. 1128 North Charles St., Baltimore, MD 21201-5559. (410)468-1808. <http://www.afud.org>.

American Liver Foundation. 75 Maiden Lane, Suite 603, New York, NY 10038. (800) 465-4837 or (888) 443-7222. <http://www.liverfoundation.org>.

National Cancer Institute. Office of Communications, 31 Center Dr. MSC 2580, Bldg. 1 Room 10A16, Bethesda, MD 20892-2580. (800) 422-6237. <http://www.nci.nih.gov>.

National Familial Pancreas Tumor Registry. Johns Hopkins Hospital, Weinberg Building, Room 2242, 401 North Broadway, Baltimore, MD 21231-2410. (410) 955-9132. <http://www.path.jhu.edu/pancreas>.

University of Texas M.D. Anderson Cancer Center. 1515 Holcombe Blvd., Houston, TX 77030. (800) 392-1611. <http://www.mdanderson.org>.

WEBSITES

American Cancer Society. Cancer Resource Center. <http://www3.cancer.org/cancerinfo/>.

National Cancer Institute. CancerNet. <http://cancernet.nci.nih.gov>.

University of Pennsylvania Cancer Center. Oncolink. <http://cancer.med.upenn.edu>.

Mary E. Freivogel, MS

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