Enzalutamide after abiraterone in patients with metastatic castrate-resistant prostate cancer (mCRPC).

Abstract

240 Background: Abiraterone is a 17a hydroxylase and C17,20-lyase inhibitor that blocks androgen biosynthesis and is approved for treatment in patients with mCRPC. Enzalutamide, a second-generation androgen receptor signaling inhibitor was recently approved for use in patients with mCRPC post-docetaxel. There is paucity of information regarding sequential use of enzalutamide after abiraterone. Methods: This is a single-center, retrospective analysis of 23 patients with mCRPC who received enzalutamide after progression on abiraterone. Post-treatment prostate specific antigen(PSA) response and time to PSA progression were used to determine enzalutamide efficacy. Patients were followed for 6 months post initiation of enzalutamide. Results: At the time of enzalutamide initiation, median age was 70 years, with average Gleason score of 7 at the time of diagnosis. All patients were on ongoing androgen deprivation therapy, and 15 patients had received prior docetaxel chemotherapy. Median duration of abiraterone and enzalutamide treatment was 7 and 4.5 months respectively. 12 patients had at least one declining PSA value post enzalutamide treatment, with 5 patients showing >25% decline in PSA and 4 patients > 50%. Median time to PSA progression in patients receiving enzalutamide following abiraterone was 2.3 months. Conclusions: Sequential enzalutamide in patients with CRPC post-abiraterone showed only modest activity, indicating that the clinical benefit of sequential use of highly potent androgen pathway inhibitors cannot be assumed, and should be measured in prospective studies.