Nonsteroidal anti-inflammatory drug use and breast cancer risk by stage and hormone receptor status

Background: Epidemiologic studies of the association between nonsteroidal anti-infl ammatory drugs (NSAIDs), such as aspirin and ibuprofen, and breast cancer risk have yielded inconsistent results. We investigated the association of NSAID use with risk of breast cancer in the California Teachers Study cohort, with special attention to risk of specifi c breast cancer subtypes and to type of NSAID used. M ethods: We analyzed data on 114 460 women in the California Teachers Study cohort who were aged 22 to 85 years and free of breast cancer at baseline in 1995 to 1996. Information on frequency and dura-tion of NSAID use was collected through a self- administered questionnaire. A total of 2391 women were diagnosed with breast cancer during the follow-up period from 1995 to 2001. We used Cox proportional hazards regression to estimate relative risks (RR) and 95 % confi dence intervals (CI) of breas