Colonoscopy, a screening procedure that saves lives by detecting colon cancer, may not be as effective as previously thought. A new study demonstrates that while colonoscopy is very effective at locating cancer in the left portion of the colon, it has more trouble finding cancer on the right side of the colon.

The study, published today on the website of the Annals of Internal Medicine, showed that screening for colorectal cancer by colonoscopy seems to prevent about two-thirds of deaths from colon cancer, rather than 90 percent as has been widely claimed. The vast majority of deaths were prevented by detecting cancers located on the left or descending side of the colon. Colonoscopy seemed to have almost no benefit in preventing deaths from cancers located on the right side or ascending portion of the colon.

A colonoscopy uses a flexible camera to look inside the colon for signs of colon cancer. The researchers propose several possible reasons why cancers of the right side of the colon are not detected. One possibility is that some colonoscopies may not actually examine the full length of the colon. The right or ascending portion of the colon is the furthest portion, and precancerous growths such as polyps in this area may be missed if the colonoscopy is incomplete.

Another possible reason for the difference is that the biology of polyps and other precancerous changes may be different in the left and right colon. Researchers already know that right-sided growths are likely to be flat, which makes them harder to see.

Despite the findings that colonoscopies are less than perfect, the study does provide evidence that the procedure is a lifesaver for many people. Colorectal cancer is the third leading cause of cancer deaths in both men and women and will claim the lives of an estimated 50,000 Americans this year. Even so, fewer than 10 percent of the subjects in the study had ever had a colonoscopy.

What is your risk for colon cancer? Find out by talking to your doctor. He or she may recommend a colonoscopy every 10 years or more frequently depending on your risk factors. There are also other tests that can help detect colon cancer including annual fecal occult blood testing, which examines the stool for blood, flexible sigmoidoscopy, which examines the portion of the colon adjacent to the rectum, double-contrast barium enemas, and virtual colonoscopies using CT scanners.

For more information about colorectal cancer, join the Healia Health Community for Colorectal Cancer.

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