Use of Bisphosphonates and Risk of Breast Cancer in a French Cohort of Postmenopausal Women

PurposeTo assess whether bisphosphonate (BP) use is associated with decreased breast cancer incidence in a cohort of postmenopausal women.MethodsThe study population included 64,438 postmenopausal women participating in the French E3N (Etude Epidemiologique aupres de femmes de la Mutuelle Generale de l'Education Nationale) prospective cohort, with data self-reported in biennial questionnaires matched with data from a drug reimbursement database. Exposure to BPs and the use of other osteoporosis treatments during follow-up were determined using reimbursement data. Other covariates (breast cancer risk factors, clinical risk factors for osteoporotic fractures, and bone mineral density surveillance) originated from the questionnaires. Hazard ratios (HRs) of breast cancer were estimated using Cox proportional hazards models, considering exposure as a time-varying variable.ResultsOver an average of 7.2 years of follow-up (2004 to 2011), 2,407 first primary breast cancer cases were identified. The HR of breast c...