Authors: Megan Ann McNamara, Daniel J. George, Krishnan Ramaswamy, Stanislav Lechpammer, Jack Mardekian, Neil M. Schultz, Li Wang, Onur Baser, Ahong Huang, Stephen J. Freedland

Background: Prostate cancer (PC) is the most common malignancy among US men and the second-leading cause of cancer-related death. African Americans (AAs) have higher mortality from mCRPC than Whites (W). Despite this disparity, a small prior study suggested AAs may have better PSA response to abiraterone acetate (ABAC) than Ws, though radiographic progression did not differ. We evaluated overall survival (OS) in AA vs W chemotherapy-naïve (CN) mCRPC patients (Ps) treated with ABAC or enzalutamide (ENZ).

Methods: This was a retrospective study that used the Veterans Health Administration (VHA) database. Male PC Ps (≥18 years) who had surgical or medical castration were identified from Apr 1, 2013 to Mar 31, 2018. The index date was the first prescription claim date for ABAC or ENZ following castration. Ps had no chemotherapy for 12 months pre-index date and had continuous VA health plan enrollment for ≥12 months pre- and post-index date. Ps were followed until death or disenrollment. Unadjusted and Kaplan-Meier survival analyses adjusted for demographic and clinical characteristics were used to calculate survival time, and multivariate Cox proportional hazards models assessed the relationship between race and OS.

Results: This study included 2,123 W and 787 AA mCRPC Ps with mean ages of 74 and 71 years, respectively. The median follow‐up time was 570 days and 561 days for AA and W, respectively. AA were more prone to comorbid hypertension (77.1% vs 67.1%; p<.0001), type II diabetes (38.1% vs 29.3%; p<.0001), and liver damage or abnormality (8.8% vs 5.2%; p=0.0003) than W . From the unadjusted analysis, the median Kaplan-Meier estimated OS was 910 days for AAs and 784 days for Ws; AAs had better OS than Ws (HR=0.887; 95%CI [0.790-0.996]). From the adjusted analysis, the median Kaplan-Meier estimated OS was 918 days for AAs and 781 days for Ws; AAs still had better OS (HR=0.826; 95%CI [0.732-0.933]).

Conclusions: This large retrospective study provides the first evidence that AA CN mCRPC Ps may have better OS with ABAC or ENZ than W Ps. Trials are needed to validate this finding and explore the mechanisms of racial disparities in outcomes with new hormonal therapies.

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