Aspirin reduces risk of recurrent colorectal adenomas

NEW YORK (Reuters Health) - In patients with a history of colorectal adenomas or cancer, aspirin is effective in reducing the risk of new polyps, according to a meta-analysis by researchers in Europe and the US.

Writing in the Journal of the National Cancer Institute for February 18, Dr. Bernard F. Cole, at the University of Vermont in Burlington, and co-investigators note that "multiple lines of evidence... indicate that aspirin has an antineoplastic effect in the large bowel and reduces the risk of colorectal adenomas."

Their goal was to conduct a meta-analysis of randomized, double-blind, placebo-controlled trials that evaluated aspirin for the secondary prevention of colorectal adenomas, in order to provide more precise estimates of aspirin's effects.

Their literature search turned up four trials conducted in the 1990s, involving 2698 subjects (mean age 58 years, 60% male) treated for at least 1 year who underwent colonoscopic follow-up. Aspirin doses ranged from 81 to 325 mg. Advanced lesions were defined as tubulovillous or villous adenomas, lesion diameter of 1 cm or larger, presence of high-grade dysplasia, or invasive cancer.

The median follow-up interval was 33 months. Adenomas were detected in 37% of 1156 participants randomized to placebo and in 33% of the 1542 assigned to aspirin. Corresponding incidence of advanced lesions was 12% and 9%, respectively.

Aspirin was associated with statistically significant decreases in relative risk of 17% for occurrence of adenoma and 28% for advanced lesions.

"It is advantageous," Dr. Cole and associates note, "that aspirin is effective for preventing advanced lesions because these lesions tend to progress more rapidly to invasive cancer."

The authors note that the effect was evident for subgroups based on age, gender, body mass index, number of lifetime adenomas at baseline, and any history of advanced lesions.

However, their analyses showed that the benefit of aspirin in reducing advanced lesions was substantially greater among subjects with a family history of colorectal cancer than among those without a family history (risk ratio 0.53 vs 0.92, p for interaction = 0.05).

Most of aspirin's benefit appeared during the first year after randomization, with no significant difference between aspirin and placebo beyond 38 months. No dose-response relationship was evident, and there was no significant effect on occurrence of colorectal cancer, which would require longer treatment and follow-up for such an effect to emerge.

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