Colorectal Cancer News:

Study: Conventional Colonoscopies Miss 10 Percent of Large Precancerous Polyps

Conventional colonoscopies miss about 10 percent of large precancerous polyps, but experts argue that the test, while not perfect, is the best available for detecting and preventing colorectal cancer.

As reported in the September 7 issue of the Annals of Internal Medicine, the study involved 1,233 adults without any symptoms of colorectal cancer who had same-day virtual colonoscopy and optical colonoscopy procedures.

In optical colonoscopy, doctors use a long flexible tube with a tiny camera on its tip to look for and remove polyps and early tumors. Virtual colonoscopy, a newer procedure, uses x-rays and computers to produce 3-dimensional images of the inside of the colon.

In the study, doctors were told the visual colonoscopy results. If the visual colonoscopy identified a polyp that was not seen with the optical colonoscopy, the doctors reexamined that section of the colon closely. The researchers then assessed how often the initial optical colonoscopy examination missed polyps that were seen at reexamination after the doctors knew the visual colonoscopy results.

Optical colonoscopy performed without knowledge of the virtual colonoscopy findings missed 55 of 511 polyps or 9.2 percent. Twenty one of these polyps were adenomas measuring six millimeters or greater. Adenomas missed by optical colonoscopy were usually on the proximal side of a fold or near the anal verge. Virtual colonoscopy missed 14% of the adenomas that measured six millimeters or greater that were detected by optical colonoscopy.

According to the researchers, the doctors who did the procedures were very experienced, while the visual colonoscopy technology quite sophisticated. Less experienced examiners and different VC techniques might miss more polyps.

Dr. Douglas Rex, the current president of the American College of Gastroenterology, said it has been clear for some time that colonoscopy is not a perfect test.

“On the other hand, based upon the literature to date, colonoscopy is still the best test and the current gold standard for colorectal cancer screening and prevention,” said Rex.

Rex said three studies have shown that colonoscopy prevents about 80 percent of colorectal cancers from developing by removing precancerous polyps.

Rex said the results of this new study emphasize the importance of colonoscopy being performed by skilled practitioners. “Patients undergoing colonoscopy should identify doctors trained to perform colonoscopy in gastroenterology fellowship or surgical residency programs whenever possible,” he added.

Source:Medical Week staff, September 24, 2004