Are Aromatase Inhibitors Associated with Higher Myocardial Infarction Risk in Breast Cancer Patients? A Medicare Population-Based Study.

Background Theoretically, the estrogen deprivation induced by aromatase inhibitors (AIs) might cause ischemic heart disease, but empiric studies have shown mixed results. We aimed to compare AIs and tamoxifen with regard to cardiovascular events among older breast cancer patients outside of clinical trials. We hypothesized that AIs increase the risk of myocardial infarction. Methods We identified women age >= 67 years diagnosed with breast cancer from June 30, 2006 to June 1, 2008 in the surveillance, epidemiology, and end results (SEER)-Medicare database, treated with either tamoxifen or an AI, and followed through December 31, 2012. To compare myocardial infarction (MI) risk for the treatment groups of AIs vs tamoxifen, we developed and assigned stabilized probability of treatment weights and used the Fine and Gray model for time to MI with death not related to MI as a competing risk. Results Of the cohort of 5648 women, 4690 were treated with AIs and 958 with tamoxifen; a total of 251 patients developed MI, and 22 patients died of MI during the study period while 476 died of other causes. The hazard for MI was not significantly different between AI vs tamoxifen groups (HR = 1.01, 95% CI 0.72-1.42), after adjusting for the following known MI risk factors at the start of adjuvant therapy: diabetes, ischemic heart disease, congestive heart failure, MI, and peripheral vascular disease. Conclusions In this SEER-Medicare-based population study, there were no significant differences in the risk of MI between AI and tamoxifen users after adjustment for known risk factors.