NEW YORK, NY. June 1, 1998 -- Researchers at the Columbia University College of Physicians & Surgeons have discovered that close relatives of individuals who have colon polyps (non-cancerous growths, or adenomas) face as high a risk of developing colorectal cancer as do people who have relatives with colorectal cancer itself. The research is reported in the June 1 issue of Annals of Internal Medicine.
"Our study may alter the screening approach to colorectal cancer, because it suggests that this population should get colonoscopy rather than sigmoidoscopy, which is more aggressive than previous recommendations," says Alfred I. Neugut, M.D., Ph.D., associate clinical professor of public health and medicine and co-author of the paper with Habibul Ahsan, MBBS; Gail Garbowski, MPH; Judith Jacobson, DrPH; Kenneth Forde, M.D.; Michael Treat, M.D.; and Jerome Waye, M.D.
Three tests are used to detect colorectal cancer and the polyps that often precede them -- a fecal occult blood test, sigmoidoscopy, and colonoscopy. Typically, sigmoidoscopy is used with fecal occult blood testing for screening the general population, with the more invasive colonoscopy reserved for people with a family history of colorectal cancer, who undergo it every three to five years. According to current guidelines, relatives of people with adenomas should have a yearly fecal occult blood test, with follow-up colonoscopy if results are positive. A family history of polyps or colon cancer can reflect genes that predispose to colorectal cancer, or shared dietary or other lifestyle habits that could contribute to developing the disorder.
"Over the last 20 to 30 years we have learned that by screening for colorectal cancer, both with fecal occult blood tests and sigmoidoscopy -- a flexible tube up the rectum -- we can lower mortality by 70 to 80 percent. Sigmoidoscopy screens only the distal half of the colon, so colonoscopy, which checks the entire colon, might decrease mortality further," says Dr. Neugut. But colonoscopy hasn't been more widely used because it is difficult to perform, has complications, and requires the patient to prepare for a day, he adds.
Would colonoscopy benefit people who have a relative with adenoma, rather than colorectal cancer? One previous investigation, the National Polyp Study, found that parents and siblings (first degree relatives) of people newly diagnosed with adenoma had an 80 percent increase in risk of developing colorectal cancer compared with their spouses. However, the study did not take into account the health status or family history of the spouses. Before screening recommendations can be amended to advise colonoscopy for first degree relatives of adenoma patients, the study would have to be replicated and designed to yield more specific information.
That's where the Columbia University project comes in. The researchers studied 1,554 first degree relatives of 244 patients newly diagnosed with adenoma and 2,173 relatives of 362 people who had been examined but did not have polyps. The patients were assessed between 1986 and 1988, so several years elapsed before the researchers obtained detailed information from the relatives. Results were strikingly like those of the National Polyp Study, revealing a relative risk of 1.74 for the relatives of adenoma patients. This means a slightly less than doubling of risk compared with the general population. Put a more meaningful way, the general population risk of developing colorectal cancer over a lifetime is 6 percent to 7 percent. If a person has a relative with adenoma, the risk rises to about 10 percent to 12 percent. The study also found that the risk was higher if the affected relative was diagnosed with polyps at a younger age. The relatives were not at increased risk for other types of cancer.
Dr. Neugut feels strongly that relatives of people with colon polyps should be offered colonoscopy. "The beauty of it is if you remove the adenomas, you prevent the cancer."
Journal
Annals of Internal Medicine