When patients were retested five years after a negative colonoscopy, none had colon or rectal cancer and very few had a worrisome advanced polyp.
Twenty-five hundred people initially had a negative screening colonoscopy — no adenomas or cancers were found, although some had safe hyperplastic polyps. About half (1,256) were rescreened five years later. No cancers were found, although 16 people (1.3 percent) had a more serious polyp (advanced adenoma) that could develop into cancer.
Advanced adenomas were defined as polyps one centimeter or larger or polyps with cells containing precancerous changes (high-grade dysplasia).
People who had a hyperplastic polyp during their first screening weren’t any more likely to have an advanced adenoma than those who had no polyps at all.
Men had about twice the risk of any adenomas than women and more than three times the risk of an advanced adenoma.
Thomas Imperiale, M.D. and his colleagues concluded,
Among persons with no colorectal neoplasia on initialscreening colonoscopy, the 5-year risk of colorectal canceris extremely low. The risk of advanced adenoma is also low,although it is higher among men than among women. Our findings support a rescreening interval of 5 years or longer after a normal colonoscopic examination.
Current screening guidelines, updated this year, call for repeating normal screening colonoscopies every 10 years.
SOURCE: Imperiale et al., New England Journal of Medicine, Volume 359, Number 2, September 18, 2008.