Study: Colonoscopies miss 4% of cancer cases

The gold-standard test to detect colon cancer is missing a "concerning" number of cases, according to a new Canadian study that evaluated the success rate of colonoscopies.
People naturally brace themselves for the probing fiber-optic exploration of their bowels. But now researchers say they should also brace themselves for the sobering fact that the invasive screening test is less than perfect.
Scientists with the Institute for Clinical Evaluative Sciences and the Universities of Toronto and Western Ontario conducted a study of Ontario patients and found that colonoscopies missed 4 percent of colon cancer cases.
"It is time to advise patients that there is a small chance a cancer may be missed," said ICES senior scientist Linda Rabeneck.
Rabeneck, senior author of the report published this month in the journal Gastroenterology, stressed that everyone over 50 should still undergo the exam because a colonoscopy remains the best screening tool available -- with an accuracy rate better than mammograms for breast cancer and Pap tests to detect cervical cancer.
But when early detection really can make a life or death difference, Rabeneck said even a 4-percent miss rate for colon cancer "is not what we would like see for any patient. We need to figure out why these cases are being missed, and pinpoint the causes so that we miss even fewer."
To perform a colonoscopy, doctors insert a flexible fiber-optic tube into the rectum and up through the muscular channel of the colon, which forms the major part of the large intestine. The tube then transmits magnified images of the inner colon to a screen.

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