A new meta-analysis of previously published studies has found that regular use of aspirin is associated with a 14% reduced risk of breast cancer compared to no use. Laboratory and animal studies suggest that taking aspirin might be associated with reduced risk of breast cancer, but results from these studies have been not been consistent.

To conduct the meta-analysis, the authors searched the MEDLINE database for studies of aspirin use and breast cancer risk that were published, in any language, between January 1, 1966 and July 1, 2011. A total of 33 studies were identified, including 19 population studies, 13 case-control studies, and one randomized controlled trial. The 33 studies included a total of 1,916,448 participants.

Regular aspirin use was found to be associated with a 14% reduced risk of breast cancer in a pooled analysis of all the studies. Results were similar when the population studies and case-control studies were pooled separately. However, the randomized controlled trial did not show any influence of aspirin use on breast cancer risk. The authors conclude that the meta-analysis indicates that regular use of aspirin may be associated with reduced risk of breast cancer. More randomized controlled trials are needed to confirm this association in the future.