SOURCE: American College of Physicians

December 17, 2008 17:00 ET

Colonoscopy Significantly Reduces Death From Left-Sided Colon Cancer but Not From Right-Sided Colon Cancer

Physicians Should Advise Patients of Test Limitations

PHILADELPHIA, PA--(Marketwire - December 17, 2008) - Colorectal cancer is the second-leading cause of cancer death in North America. Colonoscopy is the "gold standard" for evaluation of the colon. Now, a new study published in Annals of Internal Medicine finds colonoscopy may not be as effective as previously believed.

Researchers reviewed health records for persons aged 52 to 90 who received a colorectal cancer diagnosis between 1996 and 2001 and died of colorectal cancer by 2003. When researchers compared these patients to a control group, they found that complete colonoscopy was strongly associated with fewer deaths from left-sided colorectal cancer. Conversely, the data showed that colonoscopy seemed to have almost no mortality prevention benefit for right-sided colorectal cancer.

The researchers suggest several reasons why colonoscopy may be less effective in preventing death from right-sided colorectal cancer. First, some colonoscopies considered "complete" may not evaluate the entire right colon. Second, bowel preparation may be worse in the right colon. Third, right and left colonic cancers and polyps may differ biologically. Right-sided growths may be less likely to have a fleshy stalk and are occasionally flat, which makes them harder to identify and remove, or they may grow more rapidly.

Patients who have had a prior colonoscopy with no abnormalities should report to their physician any unusual bowel symptoms, such as blood in the stool.

Annals of Internal Medicine ( is one of the most widely cited peer-reviewed medical journals in the world. The journal has been published for 81 years and accepts only 7 percent of the original research studies submitted for publication. Annals of Internal Medicine is published by the American College of Physicians, the nation's largest medical specialty society.

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