Virtual Colonoscopy Effective for Average Risk People

Regular colonoscopy's long-term value is also confirmed, studies report

WEDNESDAY, Sept. 17, 2008 (HealthDay News) -- For people with an average risk of colon cancer, two new studies offer good news on the colon cancer screening front.

First, one study found that virtual colonoscopy -- or CT colonography -- was effective in detecting 90 percent of precancerous lesions larger than 10 millimeters. And, the second study found that five years after having an initial standard colonoscopy, no cancers were found in people who repeated the test.

"CT colonography is a reasonable option for colon cancer screening," said Dr. Durado Brooks, director of prostate and colorectal cancer for the American Cancer Society. "It will miss some abnormalities, but even colonoscopy is not a perfect tool. Studies of back-to-back colonoscopy show miss rates of between 2 and 11 percent."

The second study, Brooks said, "reinforces the fact that colonoscopy screening does not need to be taking place at an every five-year interval." He said that, although the current cancer society recommendations for people with an average colon cancer risk are to have a colonoscopy every 10 years, some doctors feel that interval is too long and advise their patients to have a colonoscopy every three to five years. Since this new study found no cancers at all after five years, Brooks said this should "provide an additional level of comfort" to those who were concerned that the screening interval was too long.

Results of both studies are published in the Sept. 18 issue of the New England Journal of Medicine.

The first study included 2,531 people from 15 centers across the United States. All were over age 50 and had no known significant risk factors for colon cancer.

The study participants underwent CT colonography (virtual colonoscopy) and then a follow-up colonoscopy on the same day to verify the CT colonography findings. The preparation for CT colonography is the same as it is for colonoscopy and includes a limited diet the day before the test and the use of purging laxatives. (Brooks said there is ongoing research trying to devise a prep-less CT colonography, since the preparation for the test is what people often find most objectionable.)

CT colonography found nine out of 10 lesions that were 10 millimeters or larger. And, for smaller lesions -- those over 6 millimeters but less than 10 millimeters -- virtual colonoscopy found nearly eight out of 10.

In an accompanying editorial in the journal, Dr. Robert Fletcher, of Harvard Medical School, pointed out that while this study shows CT colonography is effective, there is a downside to this technology. If abnormalities are found, a patient still has to undergo colonoscopy, and CT colonography may find "extracolonic findings" that require further investigation. Of additional concern is that if someone used virtual colonoscopy exclusively and repeated the test every five years, the cumulative radiation dose might be too high, he said.

"These concerns do not rule out CT colonography as a screening test, but they need to be considered," Fletcher wrote.

The American Gastroenterological Association issued a news release discussing the study's findings. It said, in part, "Despite the perception that CT colonography is less invasive than traditional colonoscopy, it requires similar bowel preparation as for a colonoscopy. Patients need to understand that a prep is required for CT colonography, and if a polyp is found, it must be removed through a subsequent colonoscopy. Only colonoscopy can prevent colorectal cancer, by removing pre-cancerous polyps."

The second study included nearly 2,500 people with an average risk of colon cancer. The average age of the study participants was almost 57, and slightly more than half were men. Each had an initial colonoscopy, and then about half returned to be rescreened again an average of five years later.

"We found no colon cancer after five years, and the risk of advanced precancerous polyps was very low," said the study's lead author, Dr. Thomas F. Imperiale, a professor of medicine at Indiana University School of Medicine and a research scientist at the Regenstrief Institute in Indianapolis.

"The average person should be reassured by these findings if they've had a high quality colonoscopy, they need not be screened again for at least five years," he said.

More information

Learn more about colon cancer screening options from the American Cancer Society.

SOURCES: Thomas F. Imperiale, M.D., professor of medicine, Indiana University School of Medicine, and research scientist, the Regenstrief Institute, Indianapolis; Durado Brooks, M.D., director, prostate and colorectal cancer, American Cancer Society, Atlanta; Sept. 18, 2008, New England Journal of Medicine; American Gastroenterological Association, news release, Sept. 17, 2008
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