Colorectal Cancer

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Colorectal Cancer, malignancy of the large intestine, the lower portion of the intestinal tract, which consists of the colon and rectum. Although colon cancer can occur in any segment of the colon, it is most common in the sigmoid colon, the section closest to the rectum.
The American Cancer Society estimates that about 94,000 new cases of colon cancer and 36,000 cases of rectal cancer are diagnosed annually in the United States. An estimated 48,000 people with colon cancer and 8,600 with rectal cancer die from the diseases each year. These cancers are the third most common of all cancers, as well as the third most frequent cause of cancer death in both men and women. According to the Canadian Cancer Society, each year about 17,000 new cases of colorectal cancer are diagnosed in Canada, and 6,400 people die from the disease.




RISK FACTORS


The risk of colorectal cancer increases significantly with age. About 90 percent of all colorectal cancers are diagnosed in people over the age of 50. A family history of colorectal cancer, the presence of polyps (abnormal but usually benign growths) in the large intestine, or inflammatory bowel disease are also risk factors.
Mutated versions of several genes have been linked to colon cancer. For example, in their normal form the genes MSH2, MLH1, PMS1, and PMS2 correct tiny errors that occur when cells divide and grow. Mutated versions of these genes cannot make such repairs, and eventually an accumulation of many such errors interferes with a cell’s ability to resist the uncontrolled division and growth that characterize cancer.
Research has linked the consumption of certain foods to colorectal cancer. The more red meat and animal fat that people eat, the greater their risk of developing colorectal cancer. Conversely, some studies have indicated that diets high in fiber (indigestible roughage) may reduce the risk of the disease. However, this finding was disputed when two studies published in 2000 involving more than 3,500 people showed that a high-fiber diet does not prevent the polyps that can lead to colorectal cancer in people already at high risk for the disease. Physicians continue to recommend low-fat, high-fiber diets as part of a healthy lifestyle to reduce the risk of high blood pressure, heart disease, and diabetes mellitus.
Studies suggest that some drugs may decrease the risk of colorectal cancer. For instance, estrogen replacement therapy after menopause and the use of nonsteroidal anti-inflammatory drugs such as ibuprofen appear to reduce the chances of developing this cancer.




SYMPTOMS AND DIAGNOSIS

Colorectal cancer usually develops slowly and may not present apparent symptoms in its early stages. Some individuals with undiagnosed colorectal cancer may detect blood in their bowel movements (feces). They may also experience persistent constipation or diarrhea, abdominal pain, or unexplained weight loss.
Two simple tests can detect most colorectal tumors while they are still in an early, easy-to-treat stage. The first test is the digital rectal examination, during which the physician uses a gloved finger to gently check the smoothness of the rectal lining. The second test is the fecal occult blood test, in which a small sample of the patient’s feces is smeared on a card coated with a chemical called guaiac, which reacts with blood. The card is analyzed in a laboratory for occult (hidden) blood. A positive result does not necessarily indicate the presence of cancer. Although most colorectal cancers bleed, so do benign conditions such as hemorrhoids.
Another test is fiberoptic sigmoidoscopy, in which a flexible instrument is inserted into the lower intestinal tract through the anus. This instrument has light-conducting fibers that enable a physician to visually examine the interior of the colon and rectum. A biopsy (removal of tissue samples) can be performed simultaneously with a special biopsy tool attached to the end of the sigmoidoscope. The tissue is then examined under a microscope for signs of cancerous cells. However, two large studies published in July 2000 found that sigmoidoscopy, which only examines the lower colon, can miss precancerous growths that develop in the upper colon. The authors of the studies suggested that a more extensive test, known as colonoscopy, may be a more effective way to detect cancer.




TREATMENT


The primary treatment for colorectal cancer is surgery to remove the tumor. The surgery may be combined with radiation, chemotherapy, or both. Using a combination of high-dose radiation and chemotherapy prior to surgery now makes it possible to avoid permanent colostomies in many patients who previously would have needed this procedure. A colostomy is a surgical procedure to create an artificial opening through the abdominal wall to the exterior of the body for elimination of wastes into a plastic bag.
If cancer has spread from the colorectal area to the lymph nodes or liver, surgery or chemotherapy used in combination with three drugs—fluorouracil, leucovorin, and irinotecan—prolongs the lives of some patients.