Evaluating overall survival with abiraterone acetate compared to enzalutamide in patients with chemotherapy-naïve metastatic castration-resistant prostate cancer: Real-world data from the Flatiron electronic health records database.

e17033 Background: Real-world effectiveness of abiraterone acetate (abi) vs enzalutamide (enza) in chemotherapy-naïve metastatic castration-resistant prostate cancer (mCRPC) has been examined using large databases, generally showing worse overall survival (OS) with abi. Here, we used similar methodology to examine OS with abi vs enza in the Flatiron electronic health records database between 2014 and 2023. Methods: This retrospective analysis of the Flatiron database included chemotherapy- and androgen receptor pathway inhibitor (ARPI)-naïve patients (pts) primarily managed by community medical oncologists, aged ≥18 years diagnosed with mCRPC who initiated first-line (1L) abi or enza (index from September 10, 2014 to June 30, 2020) on, after, or up to 30 days prior to the mCRPC diagnosis date. OS, time to treatment (tx) discontinuation, and time to subsequent tx were evaluated in pts initiating abi or enza from index to May 31, 2023. OS was also evaluated in the subset of pts who only received abi or enza with no subsequent tx. Time-to-event outcomes were evaluated using the Kaplan–Meier method and Cox proportional hazards models. Stabilized inverse probability tx weighting (sIPTW) was used to adjust for potential baseline confounders. Results: Overall, 2733 pts received 1L abi (n=1316) or enza (n=1417); mean age at initiation was 75 years. Median follow-up was 21.8 and 23.2 months (mo) for the abi and enza cohorts, respectively. sIPTW-adjusted median OS (24.6 vs 25.8 mo; hazard ratio [HR] 1.13; 95% confidence interval [CI] 1.03, 1.23; P =0.0092), time to tx discontinuation (7.9 vs 9.5 mo; HR 1.21; 95% CI 1.11, 1.31; P <0.0001), and time to subsequent tx (14.7 vs 17.8 mo; HR 1.20; 95% CI 1.08, 1.32; P =0.0004) were shorter with abi vs enza. Pts who received only 1L abi or enza and no subsequent tx (n=1102; 40%) had a median follow-up of 10.4 and 14.2 mo, respectively. For these pts, sIPTW-adjusted median OS (14.0 vs 17.7 mo; HR 1.32; 95% CI 1.14, 1.53; P =0.0002) and time to tx discontinuation (7.5 vs 10.6 mo; HR 1.30; 95% CI 1.12, 1.50; P =0.0005) were also shorter with abi vs enza. Conclusions: In pts with chemotherapy- and ARPI-naïve mCRPC from the Flatiron database, 1L abi was associated with significantly shorter OS, tx duration, and time to subsequent tx compared with enza, with greater differences in pts who received no subsequent tx. These results add to the growing body of real-world evidence that 1L abi is associated with worse OS compared with 1L enza for pts with mCRPC. Disclosure: A GenAI tool (10/01/24; Pfizer; GPT-4o) developed the first draft; authors assume content responsibility.