Risk for stroke and myocardial infarction with abiraterone versus enzalutamide in metastatic prostate cancer patients

Background: Abiraterone and enzalutamide use is associated with significant cardiovascular (CV) morbidity in clinical trials, but the magnitude and clinical relevance of this association in real-world prostate cancer (PC) population remain unknown. Materials and methods: We retrospectively reviewed the MarketScan claims databases (1 January 2013 to 30 September 2018) to identify adults with diagnosis of metastatic PC who received treatment with androgen deprivation therapy (ADT) and novel antiandrogen agents (abiraterone or enzalutamide). The primary CV outcome measure was composite outcome of acute myocardial infarction (MI) or stroke. Secondary outcomes were individual risks of MI or stroke. We used an intention-to-treat approach to analyze the CV outcomes associated with drug exposure among patients with metastatic PC. Cox regression model was used to estimate the independent association of two drugs with CV risk after adjustment for age, baseline atrial fibrillation, and Charlson Comorbidity Index. Results: A total of 6294 patients with metastatic PC who were treated with ADT and either abiraterone or enzalutamide were included in the final analysis. Of these, 4017 (63.8%) patients used abiraterone and 2217 (32.2%) patients used enzalutamide. During the study period, 255 (6.3%) primary endpoint events occurred, resulting in an incidence rate of 4.3 per 100 patient-years. In multivariable analysis, abiraterone use was associated with a 31% increased risk of MI or stroke compared to enzalutamide (hazard ratio 1.31; 95% confidence interval 1.05-1.63; P = 0.01). The incidence rate was similar in patients who switched initial therapy from abiraterone to enzalutamide or vice versa (5.0 versus 5.6 per 100 patient-years, respectively). Conclusions: To our knowledge, this is the first real-world assessment of MI and stroke among metastatic PC patients receiving novel anti-androgens. Our findings of increased MI and stroke risk with abiraterone compared with enzalutamide are consistent with data from clinical trials and suggest that enzalutamide may be preferable for prostate cancer patients at high CV risk.