e16540 Background: Metastatic castration-resistant prostate cancer (mCRPC) phenotype involves androgen-receptor signalling mechanisms that support the use of enzalutamide (EZ) and abiraterone (Abi). These therapies improve overall survival (OS) and quality-of-life, with a favourable safety profile. There is no validated data defining the best drug or sequence to be used. Methods: A retrospective cohort of mCRPC patients (pts) was analysed at AC Camargo Cancer Center. The primary objective was to compare progression-free survival (PFS) and OS in patients treated with EZ or Abi as first line (docetaxel naïve pts). Kaplan-Meier, Log-Rank Test and Cox Regression were used for survival analysis. To address unbalanced characteristics between the two treatment groups treatment efficacy was compared in a propensity score matched cohort. Results: From May, 2002 to September, 2017, 120 pts were treated with Abi (84%) or EZ (36%). Median follow-up was 21.2 months. Median age at diagnosis was 66 (48-84), the majority were Gleason score 7 (34%) and median baseline PSA was 14. Median PFS was 17.4 months in EZ and 10.6 months in Abi group (HR = 0.65; 95%CI: 0.39-1.10; p = 0.11). Median OS was not reached and 31.6 months for EZ and Abi, respectively (HR = 0.60; 95%CI: 0.27-1.36; p = 0.22). EZ was associated with a better PSA response in the first 4 months of treatment (p < 0.001). Independent prognostic factors for worse OS and PFS were ECOG ≥ 1, treatment toxicity ≥ G1 and lower PSA doubling time before treatment and for better OS and PFS were PSA response in the first 4 months and alkaline phosphatase and lactate dehydrogenase response at any time. In the propensity score matched cohort including 72 patients PFS was better in EZ group (HR = 0.36; 95%CI: 0.20-0.64; p < 0.001) but there was no difference in OS (HR = 0.66; 95%CI: 0.27-1.63; p = 0.37). Conclusions: EZ was associated with prolonged PFS and better PSA response, with no OS improvement when compared with Abi for mCRPC before docetaxel, in a propensity score matched analysis.
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