More evidence that aspirin lowers cancer risk.

Abstract

Two studies at September’s American Association for Cancer Research meeting build on evidence suggesting that nonsteroidal anti-inflammatory drugs (NSAIDs) reduce the risk of developing several cancers and the risk that cancer will spread. But the evidence isn’t yet strong enough to persuade clinicians to recommend NSAIDs as a preventive. In the first study, Adriana C. Vidal, Ph.D., assistant professor of surgery at Duke University School of Medicine in Durham, N.C., and colleagues studied data from a clinical trial that tested whether taking dutasteride could reduce risk of prostate cancer. The researchers wondered whether men taking NSAIDs concurrently for other conditions were less likely to develop prostate cancer, independent of dutasteride. The trial included 6,390 men, half of whom did not take NSAIDs. Among the other half, 21% took aspirin, 18% took other NSAIDs, and 11% took both. All men had prostate cancer–negative biopsy samples before the trial and received biopsies at 2and 4-year intervals, regardless of prostatespecific antigen level. Compared with participants not taking NSAIDs, men taking aspirin, other NSAIDs, or both cut their risk of prostate cancer by 13%. They also had a 17% reduced risk of high-grade prostate cancer. But researchers found no association between taking NSAIDs and risk of lowgrade prostate cancer. Risk reductions held up regardless of whether patients were in the dutasteride or placebo arm or whether participants were from Europe or North America. People commonly take aspirin to prevent heart attacks. At low doses, it inhibits the enzyme cyclooxygenase 1 (COX-1) in platelets, which then inhibits thromboxane A2. That keeps platelets from aggregating, so blood can’t clot. At high doses, NSAIDs inhibit COX-1 and COX-2 in other cell types. COX-2 regulates expression of prostaglandin E2 (PGE2). How inhibiting COX-2 affects cancer isn’t clear, but researchers think that it interrupts PGE2 in addition to other pathways that promote tumor growth. Many observational and retrospective studies suggest that NSAIDs reduce risk of several cancers. A meta-analysis of eight randomized clinical trials, for example, found that taking daily aspirin for 4 or more years reduced risk of death from cancer by about 20% (Lancet 2011;377:31– 4). But the risk of gastrointestinal bleeding and ulcers makes most clinicians reluctant to add NSAIDs to their box of prevention tools.