LOS ANGELES — Millions of people have endured a colonoscopy, believing the dreaded exam might 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 research hasn’t previously shown that removing polyps would improve survival — the key measure of any cancer screening’s worth.
Some people skip the test because of the unpleasant preparation it requires.
“People complain to me all the time, ‘It’s horrible. It’s terrible,’ ” said Dr. Sidney Winawer, a gastroenterologist at Memorial Sloan-Kettering Cancer Center in New York who helped lead the study. “But look at the alternative.”
A second study in Europe found that colonoscopies did a better job of finding polyps than another common screening tool — tests that look for blood in stool. Both studies were published in Thursday’s New England Journal of Medicine.
Colorectal cancer is the second-leading cause of cancer death in the United States. More than 143,000 new cases of cancers of the colon or rectum are expected in the U.S. this year and nearly 52,000 people will die from it, according to the American Cancer Society.
Deaths from colorectal cancer have been declining for more than two decades, mostly because of screening including colonoscopies and other tests, the organization says. People at average risk of colon cancer ages 50 to 75 should get screened, but only about half in the U.S. do.
A government-appointed panel of experts recommends one of three methods: annual stool blood tests; a sigmoidoscopy (scope exam of the lower bowel) every five years, plus stool tests every three years; or a colonoscopy once a decade.
In a colonoscopy, a tube with a tiny camera is guided through the large intestine. Growths can be snipped off and checked for cancer. Patients are sedated, but many dread the test because it requires patients to eat a modified diet and drink solutions the day before to clear out the bowel.
Researchers at Sloan-Kettering previously showed that removing polyps during colonoscopy can prevent colon cancer from developing, but it was not clear whether it saved lives.
The new study followed 2,602 patients who had precancerous growths removed during colonoscopies for an average of 15 years. Their risk of dying from colon cancer was 53 percent lower than what would be expected among a similar group in the general population — 12 patients followed in the study died, versus 25 estimated deaths in the general population.