The digestive system is made up of the esophagus (food pipe), stomach , and the small and large intestines. The upper 5–6 feet (1.5–1.8 m) of the large intestine is the colon, and the last 6–8 inches (15–20 cm) of the colon is the rectum. Colorectal cancer is a disease in which the cells of the tissues lining the colon and the rectum start to grow uncontrollably and form tumors.
Colorectal cancer is the second most common cancer for both men and women, and the second leading cause of cancer deaths. There are 150,000 new cases each year, with more than 55,000 people dying annually. The average age at first diagnosis is between 60 and 65 and appears to be a disease that affects the latter years of life. Since it is slow growing, it may take years before the disease manifests.
The primary function of the colon is to absorb water and the nutrients from the food that is already digested by the stomach and the small intestine . The waste material that remains moves into the rectum. From there, it is excreted out of the body through the anus. The colon has four sections. The ascending colon moves upward to the hepatic flexure. It then becomes the transverse colon, moving across to the liver . When it reaches the spleen, the colon continues as the descending colon and moves down to the pelvic area. It is then called the sigmoid colon and extends to the rectum. Cancer can develop in any of the four sections or in the rectum. Cancers beginning in the different sections have different symptoms.
Colorectal cancers have a very high cure rate if found early. Unfortunately, most colorectal cancers are silent tumors, which means they grow slowly and often do not produce symptoms until they reach a large size. Therefore, diagnosis is often delayed. The cancer usually begins as a benign growth (polyp) in the lining of the intestine. Although most polyps are not cancerous, virtually every colorectal cancer case begins with these polyps. There are two kinds of polyps: hyperplastic polyps, which are small, completely benign, and never develop into cancers, and adenomas, which are polyps that do have the potential to become cancerous.
Causes and symptoms
The current consensus among the medical community is that most colorectal cancers have a genetic link. Abnormal genes have been found in all inherited colorectal cancers and in most sporadic colon cancers. Dietary and environmental factors also seem to play a role in colorectal incidence.
Several risk factors may make a person more susceptible to colorectal cancer. They include:
- Family history: Some conditions such as familial adenomatous polyps (FAP) and Lynch syndrome (a genetic condition that predisposes certain families to colon cancer, even when polyps are not present) occur in certain families and may make an individual more likely to develop cancer of the colon or the rectum.
- History of colorectal cancer: Even when colorectal cancer has been completely removed, new cancers may still develop in other areas of the colon and the rectum. The incidence of recurrence is every 10 years.
- Recurrent intestinal polyps: These are polyps that increase the risk of colorectal cancer, especially if they are large and there are many of them.
- Inflammatory bowel disease: Chronic ulcerative colitis, a condition in which the colon is inflamed over a long period of time and causes ulcers in the lining, can increase the risk of colon cancer.
- Age: About 90% of colorectal cancers are found in people over the age of 50.
- Diet: Eating foods that are high in fat and low in fiber may increase the risk of colorectal cancer. It is estimated that diet accounts for 35%–45% of disease incidence.
- Physical inactivity: A sedentary lifestyle and not enough physical activity has been reported to be associated with a higher risk of colorectal cancer.
- Gender factors: Women have a 38% higher risk of having upper-colon cancer than men.
- Smoking: There is strong evidence that smoking increases the risk of colorectal cancer, possibly causing 12% of all colorectal cancer deaths. The frequency, amount, and duration of smoking over a lifetime are positively correlated with colon cancer. The more a person smokes over a long period of time, the greater the incidence of colon cancer.
- Ethnicity: Black, non-Hispanic people may have as much as a 24% increased risk in upper-colon cancer than other groups.
- Co-morbid illnesses: The presence of serious, life- threatening diseases like congestive heart failure , peptic ulcer, and diabetes mellitus may contribute up to a 28% increase in risk of colorectal cancer.
The earliest sign of colon cancer may be bleeding, though the amount is usually quite small. Blood can be detected by the fecal occult blood test (FOBT), which is a chemical testing of the feces for hidden (occult) blood.
When tumors grow to a large size, they may cause a change in bowel habits. Stools may be very narrow in diameter, and there may be diarrhea or constipation. Other symptoms of general stomach discomfort may be present, such as a feeling of fullness or bloating, stomach cramps, or gas pains. Sometimes, the patient complains of a feeling that the bowel does not empty completely. Constant tiredness and weight loss with no known reason may be other warning signs. Even though many of these symptoms can be caused by conditions other than cancer, they must be evaluated by a doctor without delay.
Usually, there are no signs of colorectal cancer at all. That is why screening is essential. Polyps may be detected before they develop into cancers, and are easily removed.
Regular screenings can identify colorectal cancer before symptoms manifest. Routinely, depending on the screening method used, this is done every one to five years, beginning at age 50. With higher risk populations (a family history of colorectal cancer or polyps, previous ulcerative colitis, or a specific ethnicity), screening may be initiated at an earlier age and conducted more often. Screening methods include a digital rectal examination, fecal occult blood testing (FOBT), a sigmoidoscopy , a colonoscopy , and a double-contrast barium enema .
If the physician suspects colon cancer, then a thorough physical examination will be conducted to check all symptoms and a complete medical history will be taken to assess any risk factors. A digital rectal examination will be done during the physical. In this procedure,
the physician inserts a gloved finger into the rectum to feel for anything abnormal. This simple test can help to detect many rectal cancers.
A fecal occult blood test may be ordered, in which a sample of stool is examined for blood. The test kit can be purchased at any local pharmacy. The test involves taking a sample of stool and smearing it on a slide. This is then sent to the laboratory or to the doctor's office to be chemically examined for the presence of red blood cells.
A sigmoidoscopy may be done to enable the physician to look inside the rectum and the lower half of the colon. In this procedure, a thin, flexible, hollow, lighted tube (sigmoidoscope) is inserted into the rectum. The physician then looks inside the scope for polyps. Since they may become cancerous, they are usually removed with the sigmoidoscope and examined for cancer cells. About half of all colon and rectal cancers are found using this procedure.
A colonoscopy will be ordered if the doctor wishes to examine the entire colon lining. A colonoscope is longer than a sigmoidoscope and is inserted through the rectum into the colon. It is connected to a video camera and a video display unit so that the physician can look at the inside of the colon. If a suspicious mass is detected, then the physician may cut out a small piece to examine it under a microscope for cancer cells. This procedure is called a biopsy.
Another test that is used to diagnose colon cancer is known as a double-contrast barium enema. The patient is given a barium sulfate enema through the anus. This is a chalky substance that partially fills and opens the colon. When the colon is about half full of barium, the patient is turned on the x-ray table so that the barium spreads throughout the colon. Air is then inserted into the colon to make it expand and x-ray films are taken. Usually, this procedure is done if the patient cannot tolerate a sigmoidoscopy, or a suspected mass prevents the penetration of the sigmoidoscope or the colonoscope.
Treatment for colon and rectal cancers depends on the stage of the cancer, which refers to the extent to which it has spread (metastasized). The standard modes of treatment are surgery, radiation therapy, and chemotherapy .
Surgery is the primary treatment for colon cancer. If the cancer is found at a very early stage, the physician may be able to remove the cancer without cutting into the abdomen. Instead, the physician may insert a tube through the rectum into the colon and cut the tumor out. This procedure is called a local excision. If the cancer is found in a polyp, however, the operation is called a polypectomy. When the cancer is large but confined to a portion of the colon, the abdomen is opened up and the cancerous growth and a small piece of normal tissue from either side of the cancer are removed. This procedure is called segmental resection. If there is any likeli- hood of the cancer having metastasized to the nearby lymph nodes, they may be removed as well. The remaining sections of the colon are then reattached.
When the physician is unable to reattach the colon, an opening called a stoma will be surgically created on the outside of the body for the waste material to pass from the body. This procedure is called a colostomy . Sometimes, the colostomy is temporary, lasting until the colon is healed, and then the colostomy can be reversed. However, if the surgery involves taking out the entire lower colon, a permanent colostomy is required. The patient will need to wear a special bag to collect body wastes. The disposable bag attaches to the body around the opening (stoma). Hospital personnel will teach patients how to take care of the stoma and maintain colostomy bags.
In the case of rectal cancer, different surgical methods are used. When the cancer is found in polyps, a polypectomy is performed. Local excision is a procedure that can be used to remove small superficial cancers. A small amount of adjoining tissue is also removed from the inner layer of the rectum. If the cancer is in the deeper layers of the rectum, local full thickness resection is used. A cut is made through all the layers of the rectum to remove the invasive cancer as well as some surrounding normal rectal tissue. Electrofulguration is a procedure in which the cancer is burned away by passing an electric current through it. All of these methods may be done without cutting through the abdomen. However, a colostomy may still be necessary if the cancer is too close to the anus, necessitating the removal of the sphincter muscles.
Radiation therapy involves the use of high-energy radiation to kill cancer cells. It can be applied to both colon and rectal cancers. External-beam radiation uses radiation from an external source that is focused on the tumor. Internal radiation therapy uses a small pellet of radioactive material that is implanted directly into the cancer. Radiation therapy is generally used as adjuvant therapy, that is, it is used after the surgery to destroy any cancerous material that may not have been removed during surgery. If the tumor is in a place that makes surgery difficult, then radiation may be used before surgery to shrink the tumor. In advanced cancers, in which surgery is not an option, radiation may be used to ease the symptoms such as pain , blockage, or bleeding.
In colorectal cancers, chemotherapy is generally used after surgery to destroy any cancerous cells that may have migrated from the original site and spread to other parts. The anti-cancer drugs are either given intravenously (through a vein) in the arm or orally in the form of pills. In the case of advanced cancers, chemotherapy may be given to alleviate symptoms.
The death rate from colorectal cancer has been going down for the past 20 years. This is due to advanced methods of early detection and improved treatment modes. If colorectal cancer is detected at an early stage and is treated appropriately, 92% of patients will survive five years or more. However, only a third of colorectal cancers are found at that early stage. Once the cancer has metastasized to nearby organs or lymph nodes, the five-year survival rate plummets to 64%. If the disease has metastasized to distant sites such as the liver or the lung, the outlook is bleak, with only 7% of the patients surviving five years after initial diagnosis. The American Cancer Society also notes that once colorectal cancer is detected and removed, another occurrence is highly probable in 10 years.
Health care team roles
Physicians, nurse practitioners, nurses, lab technicians, and radiology technicians all participate in the screening, diagnosing, and treating of colorectal cancers. Physicians and their nursing staff must educate patients in the necessity and urgency of complying with colorectal screening guidelines. Colorectal cancer, for many people, is a totally preventable disease. By exercising regularly, eating a high-fiber diet, and avoiding smoking many colorectal cancers can be prevented. For those with a family history of polyps or colorectal cancer, participation in a screening program can detect polyps, and they can have them removed before they turn into cancerous growths.
Subsequently, all members of the medical health team will need to educate patients about early screening, the procedures involved, and any possible side effects. They will also need to provide information about diet and exercise and anti-smoking support groups. Physicians may need to prescribe medications to cope with nicotine withdrawal.
When cancer is detected, the entire medical team will need to educate the patient about treatment options and procedures, outcomes, and aftercare. Physicians and radiology technicians will perform additional tests. The gastroenterologist and surgeon will prepare the patient physically and psychologically for surgery. The surgeon will remove the cancer and prepare a stoma, if necessary. The gastroenterologist will recommend radiation and/or chemotherapy as a preventative. The nursing staff will educate the patient on the care of the stoma and the colostomy equipment.
Many colon and rectal cancers may be prevented by avoiding risk factors and following screening guidelines. The number of colorectal cancer cases can be lowered and, by detecting the disease at an earlier stage, the death rate can be reduced.
The American Cancer Society recommends that, beginning at age 50, both men and women follow a screening schedule for the early detection of colorectal cancer. One or more of the following tests should be performed: a yearly fecal occult blood test and a digital rectal examination, a flexible sigmoidoscopy every five years, a colonoscopy every five to 10 years (depending on the patient's risk factors), or a barium enema x ray every five to 10 years.
Proper diet and exercise go a long way in preventing colorectal cancer. The American Cancer Society recommends eating at least five servings of fruits and vegetables every day and six servings of food from plant sources that contain fiber, such as breads, cereals, grain products, rice, pasta, or beans. Reducing the consumption of high-fat, low-fiber foods such as red meat and processed foods is also advised. Achieving and maintaining an ideal body weight are recommended, and participating in at least 30 minutes of physical activity every day is advocated.
The addition of mineral supplements may also be helpful in preventing colorectal cancer. Copper , selenium,
and calcium seem to be factors in colorectal cancer prevention. Eating foods rich in these minerals is recommended.
It is also recommended that individuals over 50 quit smoking as soon as possible. Besides the risks of other forms of cancer, there seems to be a correlation between the incidence of colorectal cancer and the amount of tobacco smoked and for how long.
It may not be possible to control risk factors such as a strong family history of colorectal cancer. However, by getting information about prevention and early detection, one can still beat the odds. People with a family history of colorectal cancer should start screening at a younger age, and the tests should be done more frequently. Certain genetic tests are now available that can help determine which members of certain families have inherited a high risk for developing colorectal cancer.
Adenomas —Polyp-like growths in the colon or the rectum that have the potential to turn cancerous.
Barium enema —An x-ray test of the bowel after receiving an enema of a white chalky substance that outlines the colon and the rectum, making them more visible in an x ray.
Benign —Tested tissue that is not cancerous and does not invade surrounding tissue or spread to other parts of the body.
Biopsy —Removal of a tissue sample for examination under the microscope to check for cancer cells.
Chemotherapy —Treatment with drugs that destroy cancerous tissue.
Colonoscopy —A medical procedure in which the physician looks at the colon through a flexible lighted instrument called a colonoscope.
Colostomy —An opening is created to provide a path for waste material to leave the body after the colon has been removed.
Crohn's disease —A chronic inflammatory disease in which the immune system starts attacking one's own body. The disease generally starts in the gastrointestinal tract.
Digital rectal examination —An exam to detect rectal cancer.
Familial adenomatous polyps (FAP) —An inherited condition in which hundreds of polyps develop in the colon and rectum.
Fecal occult blood test (FOBT) —A test in which the stool sample is chemically tested for hidden blood.
Flexible sigmoidoscopy —An examination in which the physician looks at the lower half of the colon.
Hyperplastic polyps —Benign polyps found in the colon or the rectum.
Lynch syndrome —A genetic condition that predisposes certain families to colon cancer, even when polyps are not present.
Polyp —An abnormal growth that develops on the inside of a hollow organ such as the colon.
Polypectomy —A surgical procedure that involves removal of the polyp.
Radiation therapy —Treatment using high-energy radiation from x-ray machines, cobalt, radium, or other sources.
Segmental resection —Surgical removal of a portion of the colon.
Stoma —The opening established in the abdominal wall by the colostomy procedure.
Ulcerative colitis —A chronic condition in which recurrent ulcers are found in the colon.
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Janie F. Franz