With cancer on track for becoming the leading cause of death in the developed world,1 the search is on for preventive measures. One of the most effective—and least costly—solutions may be no farther away than the pain relief shelf at the corner pharmacy.

Interest in aspirin as a cancer preventative dates back to the 1980s and 1990s, when data from observational studies suggested that regular users of aspirin had lower rates of adenomas and colorectal cancer.2 Later, randomized controlled trials demonstrated that daily aspirin use for a year or more reduced the number and size of adenomas in patients with a previous history of adenomas or a previous history of colon cancer.3-5 The rates of pancreatic, breast, and skin cancer also seemed to be lower in regular users of aspirin.6-8

More recently, a 20-year follow-up study of subjects in cardiovascular risk reduction trials found that 5 years of treatment with ≥75 mg per day of aspirin reduced long-term colorectal cancer incidence and mortality.9 A year ago, analysis of data from eight cardiovascular trials found that daily aspirin therapy reduced the 20-year risk of death from cancer of any type.10 The effect was greatest in gastrointestinal cancers, and most of the benefit occurred after 5 years of treatment.10 In a randomized trial conducted by Burn and colleagues, aspirin was shown to reduce the risk of colorectal cancer in subjects with hereditary colon cancer (Lynch syndrome).11

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Now, a trio of systematic reviews—all published the same day in The Lancet and The Lancet Oncology—has focused attention on the ability of aspirin to reduce the incidence of all cancers and to reduce metastasis and mortality.

Short-term Effects of Aspirin on Cancer Incidence

In the first of the recent studies, a team from the University of Oxford investigated the short-term effects of aspirin therapy on cancer incidence and mortality.12 Earlier studies had not been designed to detect short-term effects of aspirin on cancer mortality or the overall incidence of cancers, provided insufficient data on women, and did not examine the risk-to-benefit ratio of daily aspirin therapy. To address these issues, the investigators combined data from 51 trials of aspirin for the prevention of vascular events, which included a total of >75,000 patients. They found that allocation to aspirin reduced the risk of nonvascular death by 12% and the risk of death from cancer by 15% (odds ratio [OR] 0.85, confidence interval [CI] 0.76-0.96, P=0.008).