Increasingly, evidence appears to support the use of aspirin for cancer prevention. Aspirin use increases the risk of bleeding, however, and its benefits must be weighed against its harms. Incorporating long-term follow-up from several studies, researchers updated their own earlier analysis of the current research on the effects of aspirin on site-specific cancer incidence and mortality and cardiovascular events in the general population, as well as its potential harmful effects. They analyzed (separately for men and women) the overall benefits and harms associated with taking aspirin for 10 years, starting from ages 50, 55, 60, and 65. United Kingdom cancer incidence and mortality rates were used for baseline rates.

Consistently, evidence showed that long-term use was necessary to prevent cancer; the incidence of cancer was reduced only after three years of aspirin use. A reduction in mortality was seen after five years and persisted for as long as follow-up data were available.

Cancer incidence and mortality were reduced with all daily dosages of aspirin greater than 75 mg, and in those at average risk there was no evidence of a greater reduction with an increasing dose. In randomized controlled trials, the effects of aspirin were similar in men and women and in those younger and older than 60 years at randomization.

Among average-risk people 50 to 60 years old taking aspirin for 10 or more years, there would be a relative reduction in the number of cancer, myocardial infarction, or stroke events of approximately 9% in men and 7% in women over a 15-year period and an overall 4% relative reduction in all deaths over a 20-year period, due mostly to a decrease in cancer deaths. Bleeding is the most important adverse effect, and the risk increases with age.

Further research is needed to determine the optimum dose and duration of aspirin use and to identify individuals at greatest risk for bleeding.-KR

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