Associations of aspirin and other anti-inflammatory medications with mammographic breast density and breast cancer risk

PURPOSE: We investigated the associations of aspirin and other non-steroid anti-inflammatory drugs (NSAIDs) with mammographic breast density (MBD) and their interactions in relation to breast cancer risk. METHODS: This study included 3,675 cancer-free women within the Nurses’ Health Study (NHS) and Nurses’ Health Study II (NHSII) cohorts. Percent breast density (PD), absolute dense area (DA), and non-dense area (NDA) were measured from digitized film mammograms using a computer-assisted thresholding technique; all measures were square root-transformed. Information on medication use was collected in 1980 (NHS) and 1989 (NHSII) and updated biennially. Medication use was defined as none, past or current; average cumulative dose and frequency were calculated for all past or current users from all bi-annual questionnaires preceding the mammogram date. We used generalized linear regression to quantify associations of medications with MBD. Two-way interactions were examined in logistic regression models. RESULTS: In multivariate analysis, none of the anti-inflammatory medications were associated with PD, DA and NDA. We found no interactions of any of the medications with PD with respect to breast cancer risk (all p-interactions>0.05). However, some of the aspirin variables appeared to have positive associations with breast cancer risk limited only to women with PD 10–24% (past aspirin OR=1.56, 95% CI 1.03–2.35; current aspirin with