Objective: Previous epidemiological studies have suggested that use of aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs) may be associated with reduced risk of breast cancer, but some studies have been limited in their ability to separate the effects of aspirin from other NSAIDs or to account for breast cancer risk factors.
Methods: We examined the incidence of breast cancer in association with self-reported aspirin, as well as other nonaspirin NSAID use in a large prospective cohort of postmenopausal women (n = 27,616). Over 6 years of follow-up, 938 incident breast cancers were identified.
Results: After adjustment for other breast cancer risk factors, any current use of aspirin or other NSAIDs compared with no use was associated with a reduction in risk of breast cancer [relative risk (RR) = 0.80, 95% confidence interval (CI) 0.67-0.95]. There was a trend of decreasing risk of incident breast cancer with increasing frequency of aspirin use (P(trend) = 0.0011). The multivariate-adjusted RR of breast cancer was 0.71 (95% CI 0.58-0.87) for women who reported using aspirin six or more times per week compared with women who reported no use. These results did not depend on whether women had early or late stage breast cancer. No association was found between nonaspirin NSAID use and incident breast cancer. The adjusted RR of using other NSAIDs six or more times per week compared with no use was 1.01 (95% CI 0.83-1.25).
Conclusion: This prospective study corroborates other reports that use of aspirin might reduce risk of breast cancer.