Cancer

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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.