Breast cancer and nonsteroidal anti-inflammatory drugs: prospective results from the Women’s Health Initiative

We analyzed data from the prospective Women’s Health Initiative (WHI) Observational Study to examine the effects of regular use of aspirin, ibuprofen, and other nonsteroidal anti-inflammatory drugs (NSAIDs) on breast cancer risk. We studied a population of 80,741 postmenopausal women between 50 and 79 years of age who reported no history of breast cancer or other cancers (excluding nonmelanoma skin cancer), and we completed a personal baseline interview that elicited comprehensive health information including data on breast cancer risk factors and NSAID use. All of the cases were adjudicated by WHI phy-sicians using pathology reports. Our analysis was based on 1392 con-firmed cases of breast cancer. Relative risks (RRs) with 95 % confidence intervals (CIs) were estimated with adjustment for age and other breast cancer risk factors. Regular NSAID use (two or more tablets/week) for 5–9 years produced a 21 % reduction in the incidence of breast cancer (RR