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Colonoscopy Can Miss Some Cancers

Study finds specialists are best at spotting malignancies

TUESDAY, May 17, 2005 (HealthDay News) -- Colonoscopy may be the best way to detect colon cancer and remove suspicious growths, but the procedure can still miss some cancers, Canadian researchers report.

Both patient factors and physician factors contribute to these oversights during colonoscopy, explained researcher Dr. Linda Rabeneck, a professor of medicine and director of the division of gastroenterology at the University of Toronto.

"If you're a physician doing colonoscopies, we ought to take extra special care that we don't miss a cancer," she said.

To determine the cancer miss rate and the factors that predict it, Rabeneck's team collected data on nearly 13,000 patients with colon cancer. The researchers identified all patients who had received a colonoscopy within three years of diagnosis. They then divided the patients into two groups: those whose cancer had been picked up during a colonoscopy, and those whose cancer had been missed.

Rabeneck's team found that the site of the cancer in the colon had a lot to do with whether it was likely to be overlooked. The miss rate varied from 6.2 percent to 2.1 percent by location, according to the report, which was presented Tuesday at Digestive Disease Week 2005, an annual meeting of gastroenterologists in Chicago.

Other factors that can predict missing a cancer during a colonoscopy fell into two categories: patient factors and physician factors.

Patient factors included being older, being female, a prior history of abdominal or pelvic surgery and a history of diverticular disease (inflammation of the colon).

When it came to doctors, specialists were less likely to miss cancers than were generalists, the Toronto team found.

"When the colonoscopy was done by an internist or family physician, the miss rate was higher than if it were done by a gastroenterologist," Rabeneck said. "If the colonoscopy was done in an office setting or a nonacademic hospital, the miss rate was higher than if it was done in an academic hospital."

The findings are important, she said, since many patients may not know that colonoscopy can still leave cancers undetected.

These results probably apply in the United States as well as Canada, Rabeneck added.

"Patients need to be aware of the physician factors," she said. "I think you need to have your colonoscopy done by someone who is well-trained to do the procedure. By and large, gastroenterologists are those who spend the most time training to do the procedure."

One expert thinks these findings are in line with other data. "It's not surprising," said Dr. Joseph Martz of the division of colon and rectal surgery at Beth Israel Medical Center, in New York City. "Prior studies from others have shown a miss rate with conventional colonoscopy of polyps greater than 10 mm in size, of up to 12 percent," he said.

This study should encourage doctors to refer difficult colonoscopies in patients with prior surgery or diverticulosis for secondary screening by other methods, such as barium enema or virtual colonoscopy, the New York expert said.

Martz feels strongly that, despite miss rates, colonoscopy is still the best method doctors have of screening for colon cancer.

"We must not let such studies dissuade people from obtaining a colonoscopy," he said. "It is our gold standard to compare to for colon and rectal cancer screening, and it is effective screening that is the key to prevention of colon cancer."

The American Cancer Society currently recommends annual stool-based screening for men and women 50 years of age or older and colonoscopy once every 10 years. Other recommended tests include a barium enema or flexible sigmoidoscopy screen, conducted once every 5 years.

More information

The American Cancer Society can tell you more about colon cancer.

SOURCES: Linda Rabeneck, M.D., M.P.H., professor, medicine, and director, division of gastroenterology, University of Toronto; Joseph Martz, M.D., division of colon and rectal surgery, Beth Israel Medical Center, New York City; May 17, 2005, presentation, Digestive Disease Week 2005, Chicago
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