Abiraterone acetate followed by enzalutamide in chemotherapy-naïve metastatic castration-resistant prostate cancer (mCRPC) treated in the US Oncology Community Setting.

Abstract

e16061 Background: Both abiraterone acetate (AA) and enzalutamide (enza) are highly effective in men with chemo naïve mCRPC. AA was FDA approved in this setting in 2012, and enza in 2014 and thus many physicians use AA followed by enza. Although there are published data on sequencing of AA followed by enza, most of these reports are in the post-chemo setting. There are limited data on the effectiveness, of AA followed by enza when both agents are given in the chemo-naive setting. This study was conducted to assess this in 22 sites in a community setting. Methods: This retrospective, observational cohort study used the iKnowMed (iKM) electronic medical record and chart review to evaluate mCRPC pts who received AA followed by enza (both in the chemo-naïve setting) from 1/1/2011 to 12/31/2013 and followed through 4/30/14. 168 pts were identified, 136 pts were evaluable, of whom 24 pts initiated enza before termination of AA. Results: Pt characteristics for 136 pts: median age: 77 yrs (range, 50–93), Caucasian 61%, Gleason 8-10 46%, ECOG PS 0-1 79%, bone/nodal/visceral metastases 90%/21%/30%, respectively. Median PSA/LDH/ALK/HGB at start of AA therapy was 53/208/90/12, respectively. The median follow-up is 16.2 months. Median exposure to AA was 7.4 months (range, < 1-31 mos), PSA reductions of ≥ 30% and ≥ 50% while on AA were 70% and 57%, respectively. Most patients discontinued AA due to progressive disease (PD) (79%). The median exposure to enza was 2.8 months ( < 1-14.7), PSA reductions of ≥ 30% and ≥ 50% while on enza were 46% and 33%, respectively, 39% discontinued enza due to PD, 17% due to death, and 25 (18%) pts were still on enza by the end of study period. For 24 pts (18%) who initiated enza before AA stop, median overlapping period was 2.3 months (0.2 – 16.8). Conclusions: This large multicenter study with short follow-up demonstrates the activity of enza post AA in the chemotherapy-naïve setting. Combination use of the 2 drugs occurred in 18% of patients.