The risk of myocardial infarction with aromatase inhibitors relative to tamoxifen in post-menopausal women with early stage breast cancer

Abstract Background Aromatase inhibitors (AIs) may increase cardiovascular risk relative to tamoxifen in post-menopausal women with breast cancer. This risk has not been well-quantified outside of clinical trials. Methods Observational population-based cohort study of women aged >55 years diagnosed with stage I–III breast cancer between 2005 and 2010. Women treated with AIs or tamoxifen were followed to March 2012. The primary outcome was hospitalisation for myocardial infarction (MI). Cause-specific hazards were compared using tamoxifen as the reference group. Inverse probability of treatment weighting using the propensity score was used to reduce confounding due to measured baseline covariates. Results were confirmed using two cause-specific hazards models. Subgroup analyses included women aged ≥66 years, those with prior ischaemic heart disease, and a ‘lower-risk group’ aged