Efficacy and safety of enzalutamide (ENZA) in patients with metastatic castration-resistant prostate cancer (mCRPC) previously treated with abiraterone acetate (Abi): A multicenter, single-arm, open-label study.

Abstract

165 Background: This phase 4, multicenter, single-arm, open-label study evaluated the efficacy and safety of ENZA in patients (pts) with progressing mCRPC previously treated with Abi. Methods: All pts maintained castration therapy with luteinizing hormone-releasing hormone for the duration of the trial or had a bilateral orchiectomy. Pts were required to have progressive disease at study entry and ≥ 24 weeks of Abi treatment prior to receiving 160 mg/day ENZA. Prior chemotherapy was allowed. The primary end point was radiographic progression-free survival (rPFS). The secondary end points were overall survival (OS), prostate-specific antigen (PSA) response, and time to PSA progression. Safety was also assessed. Results: A total of215 pts were enrolled; 214 were treated with ENZA (median age, 73 years). The analysis was performed on data up to 48 weeks after the last pt started ENZA treatment. Median duration of prior Abi therapy was 54 weeks. The median duration of ENZA treatment was 5.7 months: 12 months in PSA responders and 4.6 months in non-PSA responders. 16% of pts received treatment for ≥ 1 year. The most common reason for treatment discontinuation was disease progression (65%). Median rPFS was 8.1 months (95% CI 6.1, 8.3). Median OS was not reached in the overall population and 75% of pts were alive 1 year after treatment initiation. PSA response (confirmed or unconfirmed) rate was 26.5% (48/181). The median time to PSA progression was 5.7 months (95% CI 5.6, 5.8). The overall objective response rate in pts with measurable disease at study entry was 12%. The most common treatment emergent adverse events (TEAEs) were fatigue (32%), decreased appetite (25%), asthenia (18%), back pain (17%), and arthralgia (16%). ENZA was primarily discontinued due to TEAEs in 8% of pts. No seizures were reported. Conclusions: In this study, ENZA remained active in pts with mCRPC previously treated with Abi. Median rPFS in pts with prior chemotherapy was consistent with previously reported data of ENZA in pts with mCRPC and prior chemotherapy/Abi therapy.Reported TEAEs were consistent with the known safety profile of ENZA. Clinical trial information: NCT02116582.