Colonoscopy: A screening test that works

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A new study, published yesterday in the Annals of Internal Medicine, suggests that screening colonoscopy may markedly reduce the risk of developing advanced colon cancer.

A team of researchers led by Dr. Chyke Doubeni, associate professor of family medicine and community health at the University of Pennsylvania, 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 (CRC). Although colonoscopy is widely used as a screening test for colon cancer, there is little research that proves it is effective in reducing colon cancer deaths, according to the study authors.

Researchers found that using colonoscopies to screen average-risk people can reduce the overall risk of a late-stage CRC diagnosis by about 70 percent. Further subgroup analysis showed that 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 CRC.

And as compared with flexible sigmoidoscopy, patients who had been screened thusly had a 50 percent reduction in overall risk for late-stage CRC, a 64 percent reduction in risk for left-sided CRC but only a 21 percent reduction in risk for right-sided colon cancer which was not a significant reduction, statistically. This made sense, as sigmoidoscopy cannot see the entire colon, only the last two feet (25 centimeters) or so.

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

The results of the new study may put to rest any doubts about colonoscopy's value as a screening tool for left- and right-sided cancer. "We knew colonoscopy was quite good as a diagnostic test in high-risk people, but we didn't know if it was effective in people at average risk," Dr. Doubeni said. "This study provides the average person without risk factors assurance that this test does work."

ACSH s Dr. Gilbert Ross added, We here at ACSH have been increasingly skeptical about the net benefits of many traditional screening tests. Studies over the past few years have called into question whether tests such as PSAs and even mammograms do more good than harm for normal-risk people as a screening method. Colonoscopy is clearly beneficial and life-saving for reducing the toll of CRC, however, which is the second leading cause of cancer death in the U.S.