Characterization of abiraterone responses in African American castrate-resistant prostate cancer.

Abstract

203 Background: African American (AA) men have a higher incidence and mortality from prostate cancer (PCa) compared to other racial groups. Abiraterone acetate (Abi) is approved for treatment of mCRPC. While some AA patients were included in Abi trials, the majority of patients have been Caucasian (CA). To date, there have been no reports of Abi responses exclusively in AA men. This study evaluated Abi responses in AA men with mCRPC. Methods: PSA values during Abi treatment as well as baseline hemoglobin (Hgb), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH) were tabulated. Prior therapy with docetaxel (Doc) or enzalutamide (Enza) was recorded. PSA response, progression and duration were assessed and compared between racial groups. PSA response, duration of response, and progression were defined by PCWG2 criteria. PSA half-life (PSAHL) based on time to nadir was calculated to assess rate of PSA decline. Results: A total of 74 Abi patients with mCRPC (n = 20 AA; n = 54 CA) were assessed from a single institution. Median AA baseline Hgb, ALP, LDH, and PSA were 11.8 (r = 6.4-15.4), 220 (r = 88-713), 209 (r = 157-401), and 48.41 (r = 4.8-1460) respectively. Median CA baseline Hgb, ALP, LDH, and PSA were 12.35 (r = 7.6-15), 165.5 (r = 70-1699), 218 (r = 133-528), and 44.84 (r = 1.71-2890) respectively. There were no significant differences in baseline labs between AA and CA. Prior use of Doc or Enza was 30% and 5% for AA; 31% and 4% for CA. PSA response was not significant for PSA decline of >30% (>30%: AA = 40%; CA = 44%), >50% (>50%: AA = 35%; CA = 30%), or >90% (>90%: AA = 20%; CA = 9%). In addition, no significant differences between the time to nadir (AA median = 209 days; CA median = 218 days), rate of PSA decline (AA PSAHL median = 72.4 days; CA PSAHL median = 80.1 days), or time to progression was observed. The median treatment length was 278 days and median time to progression was 66 days for AA men; 264 days and 88 days for CA men. Conclusions: Abi response rates, duration of response, and time to progression were not statistically different in AA men compared to CA men in patients with mCRPC. Larger studies are needed to fully evaluate this observation.