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Background: In ARCHES (NCT02677896), ENZA + ADT reduced risk of radiographic progression and improved secondary outcomes in men with mHSPC over PBO + ADT. Here we report the final OS (after 356 events), a key secondary endpoint in ARCHES and a critical benchmark of clinical efficacy, which was immature at the time of primary analysis. Method(s): Men with de novo or relapsed mHSPC (n=1150) were randomized 1:1 to ENZA (160 mg/day) + ADT or PBO + ADT, stratified by disease volume and prior docetaxel use. At the time of data cut-off and unblinding, 180 (31.3%) patients treated with PBO + ADT crossed over to open-label ENZA + ADT. A stratified log-rank test was performed at a two-sided significance level of 0.04 for OS based on an O'Brien-Fleming boundary. Kaplan-Meier estimates of OS and time to subsequent antineoplastic therapy (TTNAnti) were reported and hazard ratios (HRs) were estimated from a stratified Cox proportional hazards model. Safety was assessed via treatment-emergent adverse events. Result(s): Baseline characteristics were similar between treatment arms. As of the data cut-off of May 28, 2021, 397 (34.5%) patients remained on treatment, with a median follow-up of 44.6 months). Median treatment duration was 40.2 months on ENZA + ADT, 13.8 months on PBO + ADT, and 23.9 months for crossover patients. ENZA + ADT extended survival vs PBO + ADT (HR 0.66; 95% confidence interval 0.53, 0.81; p<0.0001) [Table] with similar results in most prespecified subgroups. ENZA + ADT continued to prolong TTNAnti vs PBO + ADT. The safety profile of ENZA + ADT vs PBO + ADT was consistent with findings from the primary analysis. Conclusion(s): This final analysis demonstrates that ENZA + ADT significantly prolongs survival in men with mHSPC and, together with the acceptable safety profile, supports the clinical benefit of ENZA + ADT in men with mHSPC. [Formula presented] Clinical trial identification: NCT02677896. Editorial acknowledgement: This study was funded by Astellas Pha

Background: The clinical benefit of ENZA + ADT versus PBO + ADT in reducing the risk of radiographic progression-free survival (rPFS) events has been shown in men with mHSPC, regardless of baseline PSA levels (> or <= median value) [ARCHES; NCT02677896]. Here, the aim was to further analyze efficacy outcomes by various baseline PSA categories. Method(s): Patients with mHSPC were randomized 1:1 to ENZA (160 mg/day) + ADT or PBO + ADT. Prior ADT and up to six cycles of prior docetaxel were permitted before baseline assessment of PSA levels and study treatment initiation. Post hoc analyses of the primary endpoint (rPFS) and other secondary endpoints by different baseline PSA categories at time of randomization were conducted to assess the efficacy of ENZA + ADT. Result(s): In the overall population (N=1150), >90% received prior ADT and 18% had prior docetaxel treatment. Median duration (range) of prior ADT was 1.6 months (0.03-55.3) for ENZA + ADT patients versus 1.6 months (0.03-198.8) for PBO + ADT patients. Of the overall population with available baseline PSA values (n=1146), 135 patients had <=0.2 mug/L, 388 patients had >0.2-4 mug/L, and 623 patients had >4 mug/L PSA at baseline (Table). Across these subgroups, the beneficial effect of ENZA + ADT on rPFS was observed, irrespective of baseline PSA (Table); similar results were also observed with other endpoints such as time to PSA progression and time to castration resistance. [Formula presented] Conclusion(s): These post hoc analyses demonstrate the clinical benefit of ENZA + ADT versus PBO + ADT based on rPFS and secondary clinical endpoints in patients with mHSPC, irrespective of patients' baseline PSA values. Clinical trial identification: ARCHES; NCT02677896. Editorial acknowledgement: Medical writing and editorial assistance were provided by Beatrice Vetter-Ceriotti, PhD, and Lauren Smith from Complete HealthVizion, funded by the study sponsors. Legal entity responsible for the study: Astellas Pharma Inc. an

Background: ENZA, a potent androgen receptor inhibitor, provides benefit in men with castration-resistant prostate cancer (CRPC). In post hoc analyses, the role of ENZA + ADT in mHSPC patients (pts) randomized within the multinational, double-blind, PBO-controlled, Phase 3 ARCHES study (NCT02677896) was determined by disease volume and risk group stratification. Method(s): mHSPC pts were randomized 1:1 to ENZA (160 mg/day) + ADT or PBO + ADT. The primary endpoint was radiographic progression-free survival (rPFS). Secondary endpoints included prostate-specific antigen (PSA) progression and radiographic responses, overall survival (OS), and quality of life (QoL). Analyses were completed by CHAARTED-defined disease volume and LATITUDE-defined risk groups. Result(s): 1150 pts were randomized (ENZA + ADT, n = 574; PBO + ADT, n = 576). Median follow-up was 14.4 months. ENZA + ADT significantly improved rPFS (hazard ratio [95% CI] 0.39 [0.30, 0.50]; p < 0.0001). ENZA + ADT pts significantly benefited from prolonged rPFS in all subgroups (Table). Significant treatment benefits were observed with ENZA + ADT in several secondary clinical endpoints in the overall population and in both high and low disease volume and risk groups (Table). High QoL at baseline was maintained over time. OS data are immature. Adverse events (AEs) were reported in 85.1% of ENZA + ADT vs. 85.9% of PBO + ADT pts, with no unexpected AEs. [Table presented] Conclusion(s): ENZA + ADT treatment showed efficacy benefit across all mHSPC pts, irrespective of disease volume and risk group. Similar delays in rPFS, symptomatic skeletal events, PSA progression, castration resistance, and improvements in radiographic responses and PSA declines, with maintenance of high QoL over time, were observed. Preliminary safety analysis appears consistent with the safety profile of ENZA in previous CRPC clinical trials. Clinical trial identification: NCT02677896. Editorial acknowledgement: Beatrice Vetter-Ceriotti and Laure