A recommended test for colon cancer misses more than half of all pre-cancerous polyps in women, suggesting a major gender difference and a need to reassess screening guidelines, researchers report in an analysis that will be released Thursday.
In research funded by the National Cancer Institute, medical experts found that sigmoidoscopy, a test recommended for years to detect pre-cancerous lesions, has double the failure rate in women compared with men. Women fared far better with colonoscopy.
A flexible sigmoidoscope examines the first 25 percent of the colon, while in a colonoscopy the entire colon is inspected. Women, researchers found, tended to develop polyps deeper in the colon, which means advanced, deep-seated polyps can be easily missed with sigmoidoscopy. Results of the analysis, which involved nearly 1,500 women ages 50 to 79, are reported in Thursday's New England Journal of Medicine.
"Previously almost all of the data on screening had been collected in men," said Dr. Philip Schoenfeld, lead investigator. "Medical literature is littered with cases in which studies are conducted in men but results are often extrapolated to women."
As part of the study, doctors first screened women through colonoscopy, a procedure that requires a sedative. They followed it by calculating how many of the growths would have been missed had the patients been screened only through sigmoidoscopy.
"Should this change the standard of care? I sure hope so," said Schoenfeld, an assistant professor of medicine at the University of Michigan. "Current guidelines call for sigmoidoscopy, and some insurers do not cover colonoscopy."
While colonoscopy is underwritten as first-line screening by many plans, others first require a positive fecal occult-blood test or evidence of polyps detected through sigmoidoscopy before a colonoscopy can be covered. Schoenfeld and colleagues found that 65 percent of advanced pre-cancerous polyps would be missed with sigmoidoscopy alone, possibly transforming a treatable condition into a life-threatening one based on ineffective screening.
Dr. Avi Barbasch of the American Cancer Society said that despite the compelling findings it's not yet time to dispense with sigmoidoscopy. "I think it's fair to review this paper and all of the other evidence out there. If the science has changed, then the recommendations should change. We want good recommendations," said Barbasch a clinical professor of medicine at Mt. Sinai Hospital in Manhattan.
Still, sigmoidoscopy was in question even before the new results, because it has been found to miss about one-third of polyps in men of average risk.
From age 50 onward for both genders, recommendations for the early detection of colon cancer call for a fecal occult blood test every year; sigmoidoscopy or a double contrast barium enema every five years and a colonoscopy every 10.
Late in the day the American Cancer Society issued a formal statement on Schoenfeld's report.
"This is an important and somewhat concerning study. It is important to keep in mind that the total number of women who had what the researchers called advanced neoplasia -- polyps that have a cancerous potential -- was very small," said Dr. Durado D. Brooks, the society's director of prostate and colorectal cancer: "It would be good to see corroboration of these findings in other studies."
Wednesday, the American Cancer Society issued a statement recommending that patients talk to their doctors about colorectal cancer screening options.
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