A: My father was recently diagnosed with colon cancer at age 71. Does this increase my risk of developing colon cancer? Is there anything I can do to avoid getting it?
Q: Like everyone else in this country, you have ample reason to worry about colon cancer, which is the second leading cause of cancer death among Americans; in 1993 there were 152,000 new cases and 57,000 deaths from colon cancer. On average, Americans have a 6 percent risk of developing colon cancer during their lifetime, and a 2.5 percent chance of dying from it. There has been no decrease in the frequency of colon cancer in recent years.
The use of proper screening measures might prevent as many as 90 percent of the deaths from colon cancer. That is because almost all cases of colon cancer develop over many years from an initially benign, small growth in the colon called a polyp or HTC adenoma. Early detection and removal of polyps eliminate the threat of cancer.
Three approaches work to screen for polyps: Tests for blood are the least expensive and invasive but also the least effective way to detect polyps or early cancer. Nonetheless, one study showed that annual tests for fecal blood reduced colon cancer deaths by 35 percent.
Sigmoidoscopy and colonoscopy are more accurate, and polyps can be removed during the procedure. Sigmoidoscopy examines only a limited portion of the colon so colonoscopy is better. But both procedures are expensive and uncomfortable.
Colon polyps and colon cancer can be identified by barium enemas, but any finding would need follow-up sigmoidoscopy or colonoscopy.
Screening tests are particularly important for people at higher risk for colon cancer, but relatively little is known about the risk factors for most cases of this disease. The most evident risk factor is increasing age -- the incidence of colon cancer rises precipitously after the age of 60 and is increased by about 70 percent in those with a parent or sibling with colon cancer. Other risk factors include a high-fat, low-fiber diet, excessive alcohol use, sedentary lifestyle and cigarette smoking.
The forms of colon cancer that run in families, which account for only a small percentage of cases, should be a concern if three or more first-degree relatives have developed colon cancer. Affected individuals in such families tend to develop the cancer at an early age and are more prone to other types of cancer as well. Since you have a close relative with colon cancer, you should ask your doctor whether a sigmoidoscopy would be of benefit if you are older than 40.
At this time, there is no proven way to prevent colon cancer, although one study showed a 50 percent reduction in colon cancer in those who took an aspirin tablet at least 15 days every month. More studies are needed to confirm aspirin's value.
The best approach is to remove polyps or treat cancer when it can still be cured. Experts agree that removing polyps with sigmoidoscopy will decrease the probability of developing advanced colon cancer. Some studies have shown that even a single sigmoidoscopy, particularly between the ages of 50 and 60, can prevent death from colon cancer. Sadly, few Americans take steps to detect polyps or early colon cancer; only 15 to 20 percent of Americans have had a sigmoidoscopy.
Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine.
