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(Ivanhoe Newswire) -- Colonoscopy has been credited with preventing many cases of colon cancer, but the test may not be catching as many pre-cancerous polyps as doctors thought.
According to researchers who reviewed health records of people who did and did not die of colorectal cancer, the test is clearly linked to a reduction in cancer deaths for left-sided colon cancers. But almost no effect was seen on cancers that developed on the right side of the colon.
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"Colonoscopy is an effective intervention," David F. Ransohoff, M.D., who wrote an editorial accompanying the study, was quoted as saying. "The study results, however, should caution physicians about saying that colonoscopy will reduce the risk of dying from colorectal cancer by 90 percent. A 60 to 70 percent risk-reduction rate seems more reasonable."
Why would colonoscopy be better at preventing left-sided cancers than right-sided cancers? The authors speculate some colonoscopies billed as "complete" may not actually be looking at the total right colon. Alternatively, it could be that bowel preparation isnt as good in the right colon, making it more difficult for doctors to spot pre-cancerous polyps, or polyps in the right colon might be flatter and thus more difficult to see and remove during the test. Right-sided polyps may also grow more quickly and thus be more dangerous.
"Although improvements in the quality of screening colonoscopy may improve detection at the right side, differences in tumor biology may limit the potential to prevent right-sided colorectal cancer deaths with current endoscopic technology," continues Dr. Baxter. "Nevertheless, this study clearly demonstrates that colonoscopy is an effective procedure for the prevention of death from colorectal cancer, it just may not be quite as effective as weve thought in the past."
SOURCE: Annals of Internal Medicine, published online December 15, 2008
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