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Colorectal Cancer

Colorectal cancer , also called colon cancer or bowel cancer , includes cancerous growths in the colon , rectum and appendix . It is the third most common form of cancer and in the United States and Europe, colorectal cancer is the second most common visceral neoplasm. Incidence is equally distributed between men and women.

Colorectal malignant tumors are almost always adenocarcinomas. About half of these are sessile lesions of the rectosigmoid area; the rest are polypoid lesions.

Many colorectal cancers are thought to arise from adenomatous polyps in the colon. These mushroom-like growths are usually benign, but some may develop into cancer over time. The majority of the time, the diagnosis of localized colon cancer is through colonoscopy. Therapy is usually through surgery, which in many cases is followed by chemotherapy .

Causes

The exact cause of colorectal cancer is unknown, but studies showing concentration in areas of higher economic development suggest a relation to diet (excess animal fat, particularly beef, and low fiber). Other factors that magnify the risk of developing colorectal cancer include:

• other diseases of the digestive tract .
• age (over 40) .
• history of ulcerative colitis (the average interval before onset of cancer is 11 to 17 years) .
• familial polyposis (cancer almost always develops by age 50).

Signs and symptoms

With proper screening, colon cancer should be detected BEFORE the development of symptoms, when it is most curable.

Most cases of colon cancer have no symptoms. The following symptoms, however, may indicate colon cancer:

• Diarrhea , constipation, or other change in bowel habits that does not resolve
• Blood in the stool
• Unexplained anemia (anemia in any adult who is not a menstruating woman should almost always be evaluated by a colonoscopy)
• Abdominal pain and tenderness in the lower abdomen
• Intestinal obstruction
• Weight loss with no known reason
• Stools narrower than usual

Diagnosis

Only a tumor biopsy can verify colorectal cancer, but the following tests help detect it:

• Digital examination can detect almost 15% of colorectal cancers.
• Hemoccult test (guaiac) can detect blood in stool.
• Proctoscopy or sigmoidoscopy can detect up to 66% of colorectal cancers.
• Colonoscopy permits visual inspection (and photographs) of the colon up to the ileocecal valve and gives access for polypectomies and biopsies of suspected lesions.
• Computed tomography scan helps to detect areas affected by metastasis.
• Barium X-ray, utilizing a dual contrast with air, can locate lesions that are undetectable manually or visually. Barium examination should follow endoscopy or excretory urography because the barium sulfate interferes with these tests.
• Carcinoembryonic antigen, although not specific or sensitive enough for an early diagnosis, is helpful in monitoring patients before and after treatment to detect metastasis or recurrence.

Treatment

The most effective treatment for colorectal cancer is surgery to remove the malignant tumor and adjacent tissues as well as any lymph nodes that may contain cancer cells. The type of surgery depends on the location of the tumor:

• Cecum and ascending colon: A right hemicolectomy (for advanced disease) is performed. It may include resection of the terminal segment of the ileum, cecum, ascending colon, and the right half of the transverse colon with corresponding mesentery.
• Proximal and middle transverse colon: A right colectomy is performed that includes the transverse colon and mesentery corresponding to midcolic vessels or segmental resection of the transverse colon and associated midcolic vessels.
• Sigmoid colon: Surgery is typically limited to the sigmoid colon and mesentery.
• Upper rectum: Anterior or low anterior resection is performed. A newer method, using a stapler, allows for resections much lower than were previously possible.
• Lower rectum: Abdominoperineal resection and permanent sigmoid colostomy is performed.

Chemotherapy is indicated for patients with metastasis, residual disease, or a recurrent inoperable tumor. Drugs used in such treatment commonly include fluorouracil with levamisole, leucovorin, methotrexate, or streptozocin. Patients whose tumor has extended to regional lymph nodes may receive fluorouracil and levamisole for 1 year postoperatively.

Prevention

Unfortunately, colon cancers can be well advanced before they are detected. The most effective prevention of colon cancer is early detection and removal of precancerous colon polyps before they turn cancerous.

If you are over age 50 talk to your doctor about your risks of colorectal cancer, and about what screening tests are appropriate. If screening tests do find polyps, have them removed promptly, to reduce the risk of cancer.

Dietary and lifestyle modifications are important. Some evidence suggests that low-fat and high-fiber diets may reduce your risk of colon cancer. However, even patients who follow strict diets can develop this disease and require colonoscopy.