Evaluating abiraterone responses in African Americans with metastatic CRPC.

Abstract

244 Background: A disparity between African American (AA) and other racial groups is documented in prostate cancer incidence and mortality. For metastatic CRPC, abiraterone (Abi) showed improvement in overall survival and gained FDA approval. However, Phase III trials enrolled mostly Caucasian (CA) patients. Documentation of Abi response rates in AA men is scant. Further characterization of Abi responses in AA men was the objective of this study. Methods: Age at diagnosis, prior enzalutamide (Enza) and/or docetaxel (Doc), and duration of Abi treatment were assessed. Baseline values at Abi initiation for alkaline phosphatase (ALP), hemoglobin (Hgb), and lactate dehydrogenase (LDH) were recorded. PSA values at baseline and throughout treatment were also logged. The velocity of PSA decline was determined by the PSA half-life (PSAHL) based on time to nadir. PCWG2 criteria were used to define PSA response and progression. Results: This was a single institution, retrospective cohort of 103 patients with mCRPC treated with Abi (n = 24 AA; n = 79 CA). Median age at diagnosis was 61.8 years and 62.4 years for AA and CA respectively. Prior Enza/Doc was 4.2%/33.3% for AA and 6.3%/29.1% for CA. Median duration of Abi therapy in AA was 207 days and 253 days for CA; neither median age or duration were statistically distinct. Median AA baseline ALP, Hgb, LDH, and PSA was 136 (range (r) = 59-653), 11.8 (r = 8.9-15.4), 256 (r = 157-401), and 59.9 (r = 4.8-1658) respectively. Median CA baseline ALP, Hgb, LDH, and PSA were 88 (r = 51-1600), 12.4 (r = 8.4-15.0), 204 (r = 100-528), and 40.6 (r = 2.5-2890) respectively. The difference in baseline lab values between AA and CA were insignificant. No statistical difference was seen in median PSAHL (AA = 55 days; CA = 64 days), or PSA decline of > 30% (AA = 50%; CA = 52%), > 50% (AA = 46%; CA = 39%), or > 90% (AA = 21%; CA = 14%). Finally, neither the median time to nadir (AA = 119 days; CA = 137 days) or progression (AA = 157 days; CA = 131 days) were significantly different. Conclusions: Comparison between AA men and CA men in mCRPC patients being treated with Abi showed no statistical difference in response rates, duration of response, or time to progression. Prospective, multi-institutional studies are needed to further assess these findings.