Prostate-specific antigen (PSA) response in Black patients with metastatic castration-sensitive prostate cancer (mCSPC) treated with apalutamide (APA) versus abiraterone acetate (ABI): A real-world comparison.

50 Background: Treatment for patients with mCSPC include androgen deprivation therapy (ADT) with the addition of androgen receptor pathway inhibitors (ARPIs). APA and ABI are two ARPIs approved for use with ADT in patients with mCSPC. However, there is limited information on the comparative effectiveness of ARPIs among Black patients. Deep PSA decline ≥90% (PSA90) following initiation of an ARPI is associated with delayed disease progression and improved survival outcomes. This study aimed to compare the proportion of Black patients with mCSPC with PSA90 response by 6 months after APA or ABI initiation. Methods: A retrospective analysis was conducted where Black patients were assigned to exclusive cohorts based on the first APA or ABI dispensation or pharmacy claim on or after 9/17/2019 (index date). Clinical data from US community urology practices (PPS Analytics) were linked with insurance claims data (Komodo; 1/1/2016-12/31/2023). Black patients with ≥12 months of pre-index clinical activity were required to have a diagnosis for metastasis in the absence of castration resistance. Patients were followed from the index date until the earliest of index ARPI discontinuation or switch, radiopharmaceutical initiation, or end of clinical activity/data availability. Pre-index characteristics were balanced between cohorts using inverse-probability of treatment weighting. PSA90 was defined as the earliest ≥90% decline in PSA relative to pre-index PSA. Weighted Kaplan-Meier analysis and a Cox proportional hazards model were used to compare the proportion of patients achieving PSA90 and time-to-PSA90 response. Results: A total of 363 Black patients were identified. The 236 APA and 127 ABI patients’ pre-index characteristics were balanced after weighting (Table). Mean on-treatment follow-up was 11.1 months (APA) and 9.4 months (ABI). The mean number of PSA tests were 4.0 (APA) and 5.3 (ABI). By 6 months post-index, PSA90 response was achieved by a significantly greater proportion of APA patients, as compared to ABI patients (65.4% vs 49.0%; hazard ratio: 1.66 [95% confidence interval: 1.18, 2.35], p=0.004). Median time-to-PSA90 response was 3.3 months for APA and 9.1 months for ABI. Conclusions: This real-world study of patients with mCSPC showed that a higher proportion of Black patients initiating APA, as compared to ABI, attained a PSA90 response within 6 months of treatment initiation, consistent with findings in the overall population. Selection of appropriate ARPIs may reduce health disparities among Black patients with mCSPC. Weighted pre-index characteristics. APA N=236 ABI N=127 Standardized difference (%) Mean age, years 70.1 69.2 9.5 Metastasis type (%) Nodal 59.5 62.6 6.3 Bone 59.2 54.7 9.1 Visceral 14.4 11.6 8.4 Prior use of ADT (%) 88.7 86.6 6.6 Mean PSA level, ng/mL 23.8 24.1 0.6