Purpose: This post hoc analysis evaluated treatment effects, safety, and pharmacokinetics of enzalutamide in Korean patients in the phase 3, double-blind, placebo-controlled PREVAIL trial. Materials and Methods: Asymptomatic or mildly symptomatic chemotherapy-naïve men with metastatic castration-resistant prostate cancer that progressed on androgen deprivation therapy received 160 mg/d oral enzalutamide or placebo (1:1) until death or discontinuation due to radiographic progression or skeletal-related event and initiation of subsequent therapy. Coprimary end points were centrally assessed radiographic progression-free survival (rPFS) and overall survival (OS). Secondary end points included investigator-assessed rPFS, time to initiation of chemotherapy, time to prostate-specific antigen (PSA) progression, PSA response (≥50% decline), and time to skeletal-related event. Results: Of 1,717 total patients, 78 patients were enrolled in Korea (enzalutamide, n=40; placebo, n=38). Hazard ratios (95% confidence interval) for enzalutamide versus placebo were 0.23 (0.02–2.24) for centrally assessed rPFS, 0.77 (0.28–2.15) for OS, 0.21 (0.08–0.51) for time to chemotherapy, and 0.31 (0.17–0.56) for time to PSA progression. A PSA response was observed in 70.0% of enzalutamide-treated and 10.5% of placebo-treated Korean patients. Adverse events of grade ≥3 occurred in 33% of enzalutamide- treated and 11% of placebo-treated Korean patients, with median treatment durations of 13.0 and 5.1 months, respectively. At 13 weeks, the plasma concentration of enzalutamide plus N-desmethyl enzalutamide was similar in Korean and non-Korean patients (geometric mean ratio, 1.04; 90% confidence interval, 0.97–1.10). Conclusions: In Korean patients, treatment effects and safety of enzalutamide were consistent with those observed in the overall PREVAIL study population.
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