The impact of androgen receptor pathway inhibitors as starting treatment in metastatic castration-sensitive prostate cancer on patient outcomes (OASIS Japan).

We examined the impact of starting treatment on clinical outcomes in men with metastatic castration-sensitive prostate cancer (mCSPC). This retrospective observational cohort study used claims data from the Medical Data Vision (MDV) hospital-based administrative dataset in Japan. All patients with newly diagnosed mCSPC from 1 January 2018 to 31 March 2024 were enrolled and followed up until 30 September 2024. Time-to-event analyses used Kaplan-Meier methods. The risk of death, onset of castration resistance, time to ≥ 50% PSA decline (PSA50), ≥ 90% PSA decline (PSA90), and undetectable PSA level (≤ 0.2 ng/mL) was compared between androgen receptor pathway inhibitors (ARPIs) and combined androgen blockade (CAB) or androgen-deprivation therapy (ADT) alone using a Cox proportional hazard model adjusted for age, body mass index, co-morbidities, visceral metastases, and baseline PSA. 22,559 patients with mCSPC had received relevant treatment of whom 15,797 were included in the analysis: 1167 (5.2%) started on apalutamide (APA) + ADT, 1407 (6.2%) on enzalutamide + ADT, 1262 (5.6%) on abiraterone acetate plus prednisone + ADT, and 11,961 (53.0%) on CAB/ADT alone. The median age was between 74 and 78 years in each group. Bone metastases were present in 60.5% to 72.6% of patients, visceral metastases in 2.8% to 5.7%, and nodal metastases in 19.3% to 29.4%. Overall survival and castration resistance-free survival were significantly longer in patients initially treated with APA + ADT compared to CAB/ADT (p < 0.0001 for both comparisons). In patients with regular PSA assessment, a higher percentage of patients starting with APA + ADT achieved PSA50, PSA90 and undetectable PSA at 3 months compared with CAB/ADT (p < 0.0001, p = 0.0005, p < 0.0001, respectively). Use of APA + ADT as a starting treatment for mCSPC was associated with better clinical outcomes versus traditional CAB or ADT in real-world clinical practice in Japan.