Colonoscopies Miss Many Cancers, Study Finds

Then, last spring, researchers reported the test may miss a type of polyp, a flat lesion or an indented one that nestles against the colon wall. And now, a Canadian study, published Tuesday in the journal Annals of Internal Medicine, found the test, while still widely recommended, was much less accurate than anyone expected.

In the new study, the test missed just about every cancer in the right side of the colon, where cancers are harder to detect but about 40 percent arise. And it also missed roughly a third of cancers in the left side of the colon.

Instead of preventing 90 percent of cancers, as some doctors have told patients, colonoscopies might actually prevent more like 60 percent to 70 percent.