Background: Despite a preferred endocrine therapy for women with estrogen and progesterone receptor-positive breast cancer, aromatase inhibitors (AIs) have been reported to increase risks of cardiovascular events. Given that breast cancer patients in Asia are younger at diagnosis, it is urgent to investigate this safety concern. Methods: Through the Taiwanese National Cohort, we identified breast cancer patients initiating selective estrogen receptor modulators (SERMs) or AIs from 2010 to 2016. Outcomes includes major adverse cardio-and cerebrovascular events (MACCEs). The average follow-up duration was five years. Results: We identified 16,730 breast cancer patients treated with SERMs and 11,728 receiving AIs. The population was older and had more comorbidities in the AI group than in the SERM group. After adjusting for age, cancer stage, cancer therapies, cardiovascular drugs and comorbidities, despite similar risks of MACCEs between AI and SERM users, the risk of HF was significantly higher in patients treated with SERMs after adjusted mortality as a competing risk. When divided by the age of 50 years, despite a similar MACCEs in the younger population, MACCEs remained significantly higher in the older population who received SERMs. Conclusions: In this Asian cohort, we found that among patients of old age or with advanced cancer stage, the use of SERMs was associated with a higher risk of cardiovascular events than the use of AIs.
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