Real-world Overall Survival with Abiraterone Acetate Versus Enzalutamide in Chemotherapy-naïve Patients with Metastatic Castration-resistant Prostate Cancer

Background: There are no large head-to-head phase 3 clinical trials comparing overall survival (OS) for abiraterone and enzalutamide. This study used Medicare claims data to compare OS in patients with chemotherapy-naïve metastatic castration-resistant prostate cancer (mCRPC) who initiated abiraterone or enzalutamide.

Methods: This retrospective analysis of the Medicare database (2009-2020) included adult men with ≥1 claim for prostate cancer, metastatic diagnosis, and no prior chemotherapy or novel hormone therapy who initiated first-line (1L) abiraterone or enzalutamide in the index period (September 10, 2014 to May 31, 2017). Cox proportional-hazards models with inverse probability treatment-weighting (IPTW) were used to compare OS between abiraterone- and enzalutamide-treated patients, adjusting for baseline characteristics. Subgroup analyses by baseline characteristics were also conducted.

Results: Overall, 5506 patients who received 1L abiraterone (n = 2911) or enzalutamide (n = 2595) were included. Median follow-up was comparable in both cohorts (abiraterone, 19.1 months; enzalutamide, 20.3 months). IPTW-adjusted median OS (95% CI) was 20.6 months (19.7‒21.4) for abiraterone and 22.5 months (21.2‒23.8) for enzalutamide, with an IPTW-adjusted hazard ratio (95% CI) of 1.10 (1.04-1.16). Median OS was significantly shorter for abiraterone versus enzalutamide in patients ≥75 years old; White patients; patients with baseline diabetes, cardiovascular disease, both diabetes and cardiovascular disease, and renal disease; and across all socioeconomic strata.

Conclusions: In the Medicare chemotherapy-naïve mCRPC population, 1L abiraterone was associated with worse OS versus enzalutamide in the overall population and among subgroups with older age and comorbidities, supporting findings from previous real-world studies and demonstrating a disparity in outcomes.