Use and clinical outcomes of androgen receptor inhibitors (ARIs) for non-metastatic castration resistant prostate cancer (nmCRPC) at labeled doses in Japan.

170 Background: The androgen receptor inhibitors (ARIs) darolutamide (DAR), enzalutamide (ENZ), and apalutamide (APA) are recommended for treatment of nmCRPC in Japan. However, not all patients (pts) start ARI treatment at the label dose. This study provides real-world variations in nmCRPC treatment dosing in Japan and their impact on pt outcomes. Methods: Retrospective observational cohort study using administrative health claims data from >480 acute care hospitals in Japan’s Medical Data Vision (MDV) database. Pts who started an ARI for the first time from 2/2020–4/2023 were classified into 3 cohorts based on the ARI (DAR, ENZ, or APA) prescribed for nmCRPC. This study describes the starting dose, treatment discontinuation and duration, and time to progression to metastatic castration-resistant prostate cancer (mCRPC) among pts who initiated treatment with ARIs at the label dose or lower (<100% label dose). Results: A total of 2746 pts with nmCRPC were treated with ARIs (DAR n=418; ENZ n=1898; APA n=430). Of these, the proportion of pts initiating treatment at the label dose was DAR 78%, ENZ 58%, and APA 62%. Of the pts who continued treatment at 6 months, the proportions receiving the label dose were DAR 76%, ENZ 57%, and APA 45%. Pts who initiated an ARI at the label dose tended to be younger and treated at cancer-specialist hospitals (Table). Among pts who initiated an ARI at the label dose, the DAR cohort had numerically lower discontinuation rates (49% vs ENZ [63%] and APA [74%]), and the probability of progression was lower for the DAR cohort vs ENZ and APA (Table). Among pts who initiated an ARI at a low dose, all 3 cohorts had similar discontinuation and progression rates. Conclusions: A higher proportion of Japanese pts receiving DAR were treated at the label dose during the study period and were more likely to stay on treatment. Within each dose subgroup, pts receiving DAR progressed more slowly to mCRPC than those receiving ENZ or APA. Clinical trial information: N/A. Label dose Low dose (<100% label dose) DAR (n=324) ENZ (n=1097) APA (n=266) DAR (n=94) ENZ (n=796) APA (n=164) Age, median (Q1, Q3), years 80 (75–85) 79 (73–84) 78 (72–83) 84 (78–88) 84 (79–88) 79 (74–84) Charlson Comorbidity Index score ≥1, n (%) 124 (38) 471 (43) 111 (42) 33 (35) 397 (50) 95 (58) Designated cancer hospitals, n (%) 262 (81) 789 (72) 206 (77) 76 (81) 529 (67) 116 (71) Follow-up, arithmetic median (Q1, Q3), months 19 (11–25) 21 (13–31) 27 (17–34) 17 (10–26) 21 (12–31) 21 (12–30) Median (95% CI) time to discontinuation, months 17.6 (13.3−24.8) 11.6 (10.4−13.4) 5.0 (3.9−7.1) 12.8 (7.2−20.2) 12.9 (11.8−14.3) 10.8 (7.6−14.0) KM probability of mCRPC progression at 12 months (95% CI)* 0.16 (0.12−0.21) 0.27 (0.24−0.29) 0.29 (0.24−0.35) 0.18 (0.11−0.28) 0.22 (0.19−0.25) 0.24 (0.18−0.32) *Median time to mCRPC progression was not reached during the study period.