Low dose aspirin doesn't lower women's cancer risk

Question Is low dose aspirin effective in reducing the risk of cancer among healthy women?

Synopsis Observational trials suggest that aspirin may be effective in preventing cancer. In the women's health study, the investigators randomised (concealed allocation assignment) 39 876 healthy women aged 45 or older to receive either aspirin 100 mg every other day or placebo. Individuals blinded to treatment assignment assessed outcomes. Follow-up occurred for an average of 10.1 years for more than 97% of the subjects. On intention to treat analysis, aspirin did not significantly reduce the incidence of any cancer, including breast, colorectal, and lung. There was no reduction in cancer mortality either overall or by site, except for lung cancer mortality (number needed to treat for 10 years = 800). All cause mortality was also not reduced by aspirin.

Bottom line Low dose aspirin does not reduce the risk of lung, breast, colorectal, or other site cancer in healthy women aged 45 years and older. There may be a protective effect on reducing lung cancer mortality, but overall mortality is not reduced.

Level of evidence 1b (see www.infopoems.com/levels.html). Individual randomised controlled trials (with narrow confidence interval).

Cook NR, Lee IM, Gaziano JM, et al. Low-dose aspirin in the primary prevention of cancer. The women's health study: a randomized controlled trial. JAMA 2005;294: 47-55.

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