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Virtual Colonoscopy Isn't Foolproof

New imaging device can miss 25 percent of lesions in the colon

MONDAY, Oct. 13, 2003 (HealthDayNews) -- Virtual colonoscopy may be the newest tool for detecting colon cancer but it's not the most effective -- at least not yet.

A virtual colonoscopy, which scans a person's colon with imaging machines from outside the body, offers a less invasive, less expensive and lower risk method of screening for colon polyps than does a colonoscopy, says Dr. Aaron Link of the University of Michigan.

But it's also less effective at finding potentially dangerous lesions.

A review of the new technology's effectiveness found it was only 73 percent successful at identifying lesions in the colon that could be cancerous polyps, compared to the 95 percent success rate afforded by a colonoscopy.

A colonoscopy, the recommended procedure for early detection of colon cancer, is an invasive procedure requiring sedation while a thin scope with a camera attached is inserted into the colon to search for cancer or precancerous lesions. It is recommended that all men and women over the age of 50 have colonoscopies to check for colon cancer, the third most common cancer in the United States, according to the American Cancer Society.

"As the technology improves and radiologists become more comfortable reading the results, they [virtual colonoscopies] will become better. But it's probably too early to say that virtual colonoscopies are accurate enough to replace colonoscopies as screening tools," says Link, a resident in internal medicine at the University of Michigan and author of the review.

Link presented his findings Oct. 13 at the American College of Gastroenterology annual meeting in Baltimore.

For his study, Link and his colleagues reviewed 25 studies of approximately 2,000 patients assessing the effectiveness of virtual colonoscopy.

He says he did the study because many patients are uncomfortable with the idea of a colonoscopy.

"The thought of a colonoscopy is unappealing. There is a fear of discomfort and the unknown. Patients are much more willing to consider screening when they know they won't have to undergo a colonoscopy," he says.

Also, Link adds, if a virtual colonoscopy could be as sensitive to lesions as a conventional colonoscopy, it would be a good alternative to a colonoscopy for people over 50 who have a low risk for colon cancer.

"It will never replace colonoscopies because if you have a lesion you have to have a colonoscopy to have it removed," he says. "But it could replace the use of colonoscopies for screening for those people at low risk."

The virtual colonoscopy is pretty accurate at detecting polyps larger than one centimeter, but much less so at finding the smaller lesions that are most important in the early detection of colon cancer, says Dr. Stanley Benjamin, chief of gastroenterology at Georgetown University Medical Center.

"The procedure adds to our ability in detection, but I don't think virtual colonoscopy should be advertised as a replacement or panacea for colonoscopy," he says. "People with small lesions could be walking around with a false sense of security."

Also at the conference, doctors presented two other papers on two groups of people prone to colon cancer.

The first paper found a high prevalence of colon cancer among blacks.

The second found a link between regular consumption of hard liquor and an increased risk for the disease.

Dr. Duane T. Smoot, of the Howard University College of Medicine, reports on the high prevalence of colon cancer among blacks.

According to the National Cancer Institute, black men and women suffer colon cancer at rates approximately 9 percent higher than whites, and they have a higher mortality rate than other racial groups.

Smoot studied 82 black men and women over 50 who were considered at average risk for colon cancer and who had colonoscopies to screen for colon cancer. He and his colleagues found that 26 of the participants, or approximately 30 percent, were found to have either colorectal cancer or pre-malignant polyps.

This high prevalence of disease underscores the need for greater diligence in screening blacks, Smoot reports.

In the other study, researchers from Stony Brook University's Division of Gastroenterology and Hepatology found those who drank at least nine glasses of hard liquor a week for more than 10 years had nearly three times the risk for colon cancer or precancerous colon polyps.

Dr. Gurvinder Sethi reports on approximately 2,000 symptom-free people who had colonoscopies. Cancer or suspicious polyps were found in 6.1 percent of the nondrinkers, and in 17.4 percent of those who drank hard liquor on a regular basis.

However, the researchers found moderate consumption of wine was associated with a reduced risk of colon cancer.

Sethi suggests regular drinkers of hard liquor may benefit from more intensive screening for colon cancer.

More information

To learn more about colon cancer, visit the National Cancer Institute and the American College of Gastroenterology.

SOURCES: Aaron Link, M.D., resident, internal medicine, University of Michigan, Ann Arbor; Stanley Benjamin, M.D., chief, gastroenterology, Georgetown University Medical Center, Washington, D.C.; Oct. 13, 2003, American College of Gastroenterology annual meeting, Baltimore
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