How often should you have a colonoscopy to test for colon cancer if you’re over age 50? The editor of the Johns Hopkins Medical Letter: Health After 50 answers this important question.
Colon cancer is the third leading cause of cancer in the United States: Estimates suggest that 146,000 people were diagnosed with colon cancer in 2005 and 56,000 died from it. Screening tests, such as colonoscopy, are very effective in detecting the disease, and the chance of surviving colon cancer is greatest when it is caught early.
Yet, according to a consumer survey reported by the American Cancer Society, Americans have a poor grasp on when and why to get tested for colon cancer. The survey of 1,004 adults was conducted over the Internet in February 2005. The most startling result was that 38% of people over age 50 were able to name a judge on the hit television show “American Idol,” yet only 34% knew they were at risk for colon cancer. Women were less likely than men to believe they were at risk for colon cancer, although the risk of colon cancer is equal in men and women. Seventy percent of those over age 50 believed that getting tested for colon cancer could reduce their risk of colon cancer, but less than half (44%) knew when they should start testing (the answer is age 50).
Q. I recently had a colonoscopy during which a nonmalignant polyp was removed. My doctor recommends that I have the colonoscopy again in five years. However, several friends who’ve also had polyps removed were advised to have another colonoscopy in three years. Which recommendation is correct?
A. A few factors may account for the different advice. Your doctor is following recently revised guidelines, issued in 2003 by the U.S. Multisociety Task Force on Colorectal Cancer, which recommend that most patients who have had a polyp removed (a polypectomy) undergo a follow-up colonoscopy at five years, rather than every three years as previously recommended. Yet according to a survey of specialists published in August 2004 in the Annals of Internal Medicine, many physicians prescribe a follow-up colonoscopy after polyp removal more frequently than the current guidelines recommend, even in low-risk patients. The recommended frequency of repeat colonoscopy also depends on the likelihood a polyp will recur and become cancerous, which is influenced by the type, size, and number of polyps discovered during the initial exam.
There are two major types of polyps: adenomatous polyps, which have the potential to become malignant; and hyperplastic polyps, which are benign. Patients who have had a hyperplastic polyp removed have the same risk of colon cancer as the general population and can adhere to the same screening schedule—colonoscopy every 10 years after age 50. Patients with one or two small (less than 1 cm) adenomas are considered at low risk for colon cancer, and it’s recommended that they have their first follow-up colonoscopy at five years. People with large (more than 1 cm), multiple (three or more), or villous adenomas (frondlike lesions attached to the colonic mucosa at their base) are at increased risk for developing advanced adenomas or colon cancer and should have colonoscopy repeated at three years. Almost three quarters of the people whose lesions are identified during screening colonoscopy have only one or two small adenomas, so their risk of developing colon cancer is low. Overuse of colonoscopy for monitoring such patients not only exposes them to unnecessary inconvenience and the risk of complications, but also places unnecessary strain on the nation’s health care system.
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