Colonoscopy isn't just for high-risk people

Researchers analyzed the health records of 1,012 average-risk adults ages 55 to 85 to determine the effect of screening colonoscopy or sigmoidoscopy on the risk of being diagnosed with late-stage colorectal cancer. In addition to the 70 percent reduction in overall risk, people who had been screened using colonoscopy had a 74 percent reduction in risk for left-sided colorectal cancer and a 64 percent reduction in risk for right-sided colorectal cancer. (The right side of the colon, also known as the ascending colon, travels up the right side of the abdomen. The left side, or descending colon, travels down the left side of the abdomen.) Cancer in the right side of the colon accounts for about half of all new cases of colon cancer in the United States. By contrast, people who had been screened with sigmoidoscopy had a 50 percent reduction in overall risk for late-stage colorectal cancer, a 64 percent reduction in risk for left-sided colorectal cancer and a modest 21 percent reduction in risk for right-sided colon cancer.

Among the 474 people in the study who had advanced colorectal cancer, 251 (53 percent) had advanced cancer on the right side of the colon, which likely would not have been detected by sigmoidoscopy.

The study is published today (March 4) in the journal Annals of Internal Medicine.

Colonoscopy has been widely recommended as a screening tool for colorectal cancer since it allows a physician to detect and remove polyps that might turn into cancer, and find early-stage cancers that are more likely to respond to treatment. However, the test's ability to detect right-sided colorectal cancer has been questioned, said study leader Dr. Chyke Doubeni, presidential associate professor of family medicine and community health at the Perelman School of Medicine at the University of Pennsylvania.