Aspirin and prostate cancer prevention

Aspirin has been associated to a reduced risk of colorectal, and possibly of other cancers. Data from at least 25 observational studies also suggest a modest reduced risk of prostate cancer in regular aspirin users, with a summary relative risk, RR, of 0.91 (95 % confidence interval, CI, 0.86-0.96) overall, 0.87 (95 % CI 0.74-1.02) from nine case-control studies, and 0.92 (95 % CI 0.87-0.97) from 16 cohort studies. However, risk estimates are heterogeneous and there is no relation with frequency, dose, or duration of aspirin use. Data from randomized controlled trials of aspirin for the prevention of vascular events showed a nonsignificant reduced risk of death from prostate cancer after a latent period of five or more years (RR 0.52, 95 % CI 0.20-1.24) based on 37 deaths from prostate cancer from seven trials. The RR was 0.81 (95 % CI 0.61-1.06) after 20 years of follow-up, based on 210 cases from three trials with long-term follow-up. Thus, data from observational studies and clinical trials are compatible with a modest favorable effect of aspirin on prostate cancer. Inference for causality and public health implications are, however, far from conclusive given the heterogeneity of results and the lack of dose and duration-risk relationships. Data on prostate cancer survival are still limited and inconsistent.