(AP) — Millions of people have endured a colonoscopy, believing the dreaded exam may help keep them from dying of colon cancer. For the first time, a major study offers clear evidence that it does.

Removing precancerous growths spotted during the test can cut the risk of dying from colon cancer in half, the study suggests. Doctors have long assumed a benefit, but until now research hasn’t shown that removing polyps would improve survival – the key measure of any cancer screening’s worth.

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