How accurate is a colonoscopy to screen for colon cancer?

Colonoscopies are considered the gold standard for colon cancer screening.

MedPage Today reports a recent study from the Annals of Internal Medicine, that suggests it’s much less accurate than initially thought. The problem was with detecting right-sided cancers, where “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 the 90+ percent improvement in mortality rate that’s commonly quoted, the authors suggest the number is closer to 60 percent to 70 percent.

That’s a surprising finding, and needs to be validated by future studies. If true, how will it change current recommendations? Will colonoscopies be recommended to be performed more frequently? Should fecal occult stool cards be performed in between colonoscopies? Will this affect the role of virtual colonoscopies?

First off, virtual, or CT, colonoscopies are not the answer. This test has its own accuracy issues, and is still considered less sensitive than the endoscopic route.

I still consider a colonoscopy the best test we have to screen for colon cancer, and continue to recommend it. With the data in flux, it may be reasonable to be more vigilant following up cases of rectal bleeding, or simply doing fecal occult cards, in between colonoscopies.