NEW YORK (Reuters Health) - For people with a history of colorectal polyps or cancer, taking aspirin is an effective way to reduce the chances of new polyps appearing, according to researchers in Europe and the US.

Polyps in the colon can sometimes be a precursor to the development of cancer.

Writing in the Journal of the National Cancer Institute, Dr. Bernard F. Cole, at the University of Vermont in Burlington, and his associates note that "multiple lines of evidence" suggest that aspirin has anti-cancer effects in the large bowel.

Their goal was to pool data from trials that evaluated aspirin for preventing the recurrence of colorectal polyps, in order to provide more precise estimates of aspirin's effects.

Their analysis included four trials conducted in the 1990s, involving 2698 subjects who took aspirin or an inactive "placebo" for at least a year and who underwent periodic examination by colonoscopy.

During follow-up, polyps were detected in 37 percent of 1156 participants given placebo and in 33 percent of the 1542 assigned to aspirin. Rates of advanced growths were 12 percent and 9 percent in the two groups.

While the differences might not seem large, aspirin was associated with a 17 percent lower risk for occurrence of any polyp, and 28 percent reduction in risk for advanced lesions.

"It is advantageous that aspirin is effective for preventing advanced lesions, because these lesions tend to progress more rapidly to invasive cancer," Cole's team points out.

There was no significant effect seen on the occurrence of colorectal cancer, the researchers note, because longer treatment and follow-up would be needed for such an effect to show up.

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