Colo-Rectal Cancer

In Western countries, cancer of the large intestine and rectum (colorectal cancer) is the second most common type of cancer and the second leading cause of cancer death. The incidence of colorectal cancer begins to rise at age 40 and peaks between ages 60 and 75. Cancer of the large intestine (colon cancer) is more common in women; rectal cancer is more common in men. About 5 per cent of the people with colon or rectal cancer have more than one cancer of the colorectum at the same time.

People with a family history of colon cancer have a higher risk of developing the cancer themselves. A family history of familial polyposis or a similar disease also increases the risk of colon cancer. People with ulcerative colitis or Crohn's disease have a higher risk of developing cancer. The risk is related to the person's age when the condition developed and the length of time the person has had the condition.

Diet plays some role in the risk of colon cancer, but exactly how it affects risk is unknown. Throughout the world, people at highest risk tend to live in cities and eat a diet typical of affluent Westerners. Such a diet is low in fibre and high in animal protein, fats, and refined carbohydrates such as sugar. Risk seems to be reduced by a diet high in calcium, Vitamin D, and vegetables such as brussels sprouts, cabbage, and broccoli. Taking an aspirin every other day also seems to reduce the risk of colon cancer, but this measure can not be recommended until more information is available.

Colon cancer usually begins as a buttonlike swelling on the surface of the intestinal lining or on a polyp. As the cancer grows, it begins to invade the intestinal wall. Nearby lymph nodes also may be invaded. Because blood from the intestinal wall is carried to the liver, colon cancer usually spreads (metastasizes) to the liver soon after spreading to nearby lymph nodes.

Symptoms and Diagnosis
Colorectal cancer grows slowly and takes a long time before it's extensive enough to cause symptoms. Symptoms depend on the type, location, and extent of the cancer. The right (ascending) colon has a large diameter and a thin wall. Because its contents are liquid, it does not become obstructed until late in the course of the cancer. A tumor in the ascending colon may enlarge so much that a doctor can feel it through the abdominal wall. Yet fatigue and weakness from severe anemia may be the person's only symptoms. The left (descending) colon has a smaller diameter and a thicker wall, and the feces are semisolid. Cancer tends to encircle this part of the colon, causing alternating constipation and frequent bowel movements. Because the descending colon is narrower and its wall thicker, the cancer is more likely to cause an obstruction earlier. The person may seek medical treatment because of crampy abdominal pain or severe abdominal pain and constipation. The feces may be streaked or mixed with blood, but often the blood can not be seen; a laboratory test is needed to detect it.

Most cancers bleed, usually slowly. In rectal cancer, the most common first symptom is bleeding during a bowel movement. Whenever the rectum bleeds, even if the person is known to have hemorrhoids or diverticular disease, doctors consider cancer. With rectal cancer, the person may have painful bowel movements and a feeling that the rectum hasn't been completely emptied. Sitting may be painful. However, the person usually feels no pain from the cancer itself unless it spreads to tissue outside the rectum.

As with other cancers, regular screening tests aid in the early detection of colorectal cancer. The stool can be tested for microscopic amounts of blood simply and inexpensively. To help ensure accurate test results, the person eats a high-fiber diet free of red meat for three days before providing a stool sample. If this screening test indicates the possibility of cancer, further testing is required.

Before endoscopy, the intestine is emptied, often by using strong laxatives and several enemas. About 65 per cent of colorectal cancers can be seen with a flexible, fiber-optic sigmoidoscope. If a polyp that may be cancerous is seen, the entire large intestine is examined with a colonoscope, which has a longer reach. Some growths that appear cancerous are removed using surgical instruments passed through the colonoscope; others must be removed during regular surgery.

Blood tests can be helpful in making the diagnosis. Levels of carcinoembryonic antigen in the blood are high in 70 percent of the people with colorectal cancer. If carcinoembryonic antigen levels are high before an operation to remove cancer, they may be low after it. If so, they can be measured at subsequent checkups. A rise in the level suggests that the cancer has recurred. Two other antigens. CA 19-9 and CA 125, are similar to carcinoembryonic antigen and may also be measured.

Treatment and Prognosis
The main treatment for colorectal cancer is surgical removal of a large segment of the affected intestine and the associated lymph nodes. About 70 per cent of the people with colorectal cancer are good candidates for surgery. In the 30 per cent who can not tolerate an operation because of poor health, some tumors can be removed by electrocoagulation. This procedure may relieve symptoms and prolong life, but cure is unlikely.

In most cases of colon cancer, the cancerous segment of the intestine is removed surgically, and the remaining ends are joined. For rectal cancer, the type of operation depends on how far the cancer is from the anus and how deeply it has grown into the rectal wall. The complete removal of the rectum and anus leaves the person with a permanent colostomy (a surgically created opening between the large intestine and the abdominal wall).

With a colostomy, the contents of the large intestine empty through the abdominal wall into a bag, called a colostomy bag. If possible, only part of the rectum is removed, leaving a rectal stump and the anus intact. Then the rectal stump is rejoined to the end of the large intestine. Radiation therapy after surgical removal of visible rectal cancer may help control the growth of any residual tumors, delay a recurrence, and increase the chances of survival. People who have rectal cancer and one to four cancerous lymph nodes derive the most benefit from combined radiation and chemotherapy. In people with more than four cancerous lymph nodes, this treatment is less effective.

When colorectal cancer has spread and is not likely to be cured by surgery alone, chemotherapy with fluorouracil and levamisole after surgery may prolong the person's life, but cure is still rare. When colorectal cancer has spread so much that all of it can not be removed, surgery to relieve the intestinal obstruction may ease symptoms. However, survival time is typically only about seven months.

When the cancer has spread only to the liver, chemotherapy drugs can be injected directly into the artery supplying the liver.

A small pump inserted surgically beneath the skin or an external pump worn on a belt allows the person to be mobile during the treatment. Though expensive, this treatment may provide more benefit than ordinary chemotherapy; however, more research is needed. When cancer has spread beyond the liver, this approach has no advantage.

After colorectal cancer has been totally removed by surgery, most experts recommend two to five annual examinations of the remaining intestine, using colonoscopy. If these examinations don not detect any cancer, the person usually continues with follow-up examinations every two to three years thereafter.

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