Androgen Receptor Signaling Inhibitors in Non‐Metastatic Castration‐Resistant Prostate Cancer in Japan: The ARASHI Study

ABSTRACT Objectives To describe clinical use and outcomes of androgen receptor signaling inhibitors (ARSIs) darolutamide, enzalutamide, and apalutamide in patients with non‐metastatic castration‐resistant prostate cancer (nmCRPC) in Japan. Methods This retrospective, observational study examined health claims data from acute care hospitals (Medical Data Vision Co. Ltd. database) in Japan, for patients with nmCRPC initiating an ARSI between February 2020 and April 2023. Key outcomes were time to initial ARSI discontinuation and time to progression to metastatic castration‐resistant prostate cancer (mCRPC). Results Of 2746 eligible patients, 418 (15%) received darolutamide, 1898 (69%) enzalutamide, and 430 (16%) apalutamide. Median follow‐up was 18.1 months for darolutamide, 20.9 months for enzalutamide, and 24.6 months for apalutamide. The proportion of patients initiating treatment at label dose was 78% (darolutamide), 58% (enzalutamide), and 62% (apalutamide). Median times (95% CI) to discontinuation (unadjusted Kaplan–Meier KM) were 16.1 months (13.3–21.0) for darolutamide, 12.3 months (11.3–13.3) for enzalutamide, and 7.1 months (5.3–9.7) for apalutamide. The KM‐estimated proportions of patients progressing to mCRPC by 24 months (95% CI) were 27% (23–33) for darolutamide, 37% (34–39) for enzalutamide, and 40% (35–45) for apalutamide. The results were consistent across inverse probability of treatment weighting sensitivity analyses. Conclusions We observed that a higher proportion of patients receiving darolutamide were likely to stay on treatment longer than patients receiving enzalutamide or apalutamide, and progression to mCRPC appeared to be delayed in these patients.