Colonoscopy Best at Detecting Colon Cancer

Virtual Colonoscopy Misses More Polyps, Study Shows

From the WebMD Archives

Dec. 16, 2004 -- Recent headlines have touted virtual colonoscopy as a new, easier way to check for colon cancer. But not so fast, say researchers.

Colonoscopy does a better job of detecting colon cancer than virtual colonoscopy, a new study shows. The news reaffirms colonoscopy's reputation as the leading tool for colon cancer screening. Still, no method is perfect.

Colorectal cancer is the second leading cause of cancer deaths in the U.S., says the CDC. It's most often diagnosed in people age 50 or older, and the risk increases with age.

Early detection can save lives, so screening is crucial. But the thought of a colonoscopy leaves many people uneasy and too few people actually get screened.

During a colonoscopy, a long, thin, flexible tube with a scope is guided through the colon. Doctors then look for either cancer or growths, called polyps, which can turn into cancer.

Virtual colonoscopy is a newer, less-invasive technique. It uses CT scans to create computer-generated images of the colon. The scope used in traditional colonoscopy is not required. However, the tube does have to be inserted into the rectum to fill the colon with air.


A third method hunts for cancer on X-rays taken after the patient receives a barium enema and the colon is filled with air.

Which test is best? To find out, more than 600 people tried all three methods. All participants had a high risk of colon problems. They either had blood in their stools, a family history of colon cancer, or iron-deficiency anemia. The study appears in The Lancet's online edition. It's also scheduled to appear in the journal's Jan. 1 print edition.

The researchers, who included gastroenterologist Don Rickey, MD, of Duke University Medical Center, made sure the tests were performed by experienced doctors. That can make a difference, since some signs of cancer may be especially tiny or hidden.

Colonoscopy was the hands-down winner. It detected more signs of cancer than the other two methods.

For instance, for larger polyps, barium enema X-rays caught just under half of them. Virtual colonoscopy detected almost 60%. Colonoscopy outperformed both, flagging virtually all (98%) of that size of lesions.


When it came to finding smaller polyps, barium enema X-rays and virtual colonoscopy lost ground. Barium enema X-rays caught a little more than one-third. Virtual colonoscopy detected about one-half.

Colonoscopy did much better. It caught 99% of the tiny polyps. A study in April showed similar results. Researchers found that virtual colonoscopy detected only about 55% of growths of larger polyps and 39% of smaller growths. In contrast, conventional colonoscopy detected nearly 100%. This study appeared in The Journal of the American Medical Association.

The researchers don't dismiss the other methods. The study only included high-risk participants, so the results might not apply to other people, the researchers say. They also note that virtual colonoscopy, a newer technology, will "almost certainly" continue to improve.

Unfortunately, no method is foolproof. It's possible for any of these screening methods to miss cancer.

WebMD Health News


SOURCES: Rockey, D., The Lancet, online edition, Dec. 17, 2004. CDC, "Screen for Life: Colorectal Cancer -- Basic Facts on Screening." WebMD Medical News: "Virtual Colonoscopy Not Ready for Use Yet." News release, Duke University.
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