Efficacy and safety of apalutamide in Japanese patients with non-metastatic castration-resistant prostate cancer: A subgroup analysis of a randomized, double-blind, placebo-controlled, phase 3 study

Abstract Background In the global phase-3 SPARTAN (Selective Prostate Androgen Receptor Targeting with ARN-509) study, apalutamide plus ongoing androgen deprivation therapy (ADT) significantly increased metastasis-free survival (MFS) and improved other clinical outcomes in men with non-metastatic castration-resistant prostate cancer (nm-CRPC) who were at high-risk of developing metastases. In this subpopulation analysis of SPARTAN study, the efficacy and safety of apalutamide plus ADT were evaluated in Japanese patients with nm-CRPC. Methods The primary efficacy endpoint was MFS. Secondary efficacy endpoints were time to metastasis, progression-free survival, symptomatic progression, initiation of cytotoxic chemotherapy and overall survival. Safety and pharmacokinetic parameters were also assessed. Results Fifty-five Japanese patients with ongoing ADT were randomized (apalutamide: n=34, placebo: n=21). Median treatment duration was 5.7 months in the apalutamide group and 11.0 months in the placebo group. Median MFS was not reached in the apalutamide group (95% CI: 10.97, not estimable) and was 18.23 months (95% CI: 11.04, 18.50) in the placebo group. Secondary endpoints were improved in the apalutamide group. The safety profile of apalutamide with ADT was comparable with the global population and no new safety signals were identified in this Japanese subpopulation. Although, apalutamide exposure tended to be higher in the Japanese subpopulation compared with the non-Japanese population, this was likely to be explained by body weight and considered not clinically meaningful. Conclusion In the Japanese subpopulation, treatment with apalutamide with ADT resulted in favorable efficacy outcomes with comparable benefit-risk profile to the global population with nm-CRPC who are at high-risk of developing metastases.