As Good as it Gets

January 2nd, 2009 | Sources: Annals of Int'l Medicine, NY Times

Colonoscopy isn’t as good we thought as a screening test for colon cancer, but it’s a lot better than nothing and people ought to be getting it as per existing guidelines, according to a report in the Annals of Internal Medicine.

In a case-controlled study of 10,292 Canadians who died of colon cancer, scientists found that colonoscopy missed nearly all cancers of the right colon and a third of those on the left. Overall, it prevents 60-70% of colon cancer deaths.

Physicians usually tell patients the procedure prevents 90%.

For comparison’s sake, mammograms prevent 25% of breast cancer deaths and the PSA test has never been shown to reduce prostate cancer mortality.

Internists and family practitioners performed a third of the colonoscopies in this study. Many of them perform the procedure infrequently. The study did not compare their yields against gastroenterologists or those with more experience.

The study also did not address the role played by bowel preparation in determining colonoscopy yields.

Scientists attributed the near complete failure to detect right-sided cancer to location-specific attributes of colon polyps, the cancer-precursor lesions sought after and removed by colonoscopists. In the right colon, these polyps are flat and hard to see.

Left-sided polyps are easier to spot because they tend to be raised and have stalks.

After the study was published, the American Cancer Society said it will not alter its screening guidelines, adding that the procedure’s risk and cost mitigate against more frequent testing.

 “If I was to provide one main message, it would be that colonoscopies are the way that colon cancer mortality gets reduced,” David Ransohoff told the New York Times.

The UNC gastroenterologist added that “colonoscopy is a good test, but it isn’t completely effective. And you know what? We ought to be happy with that.”


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