Sipuleucel-T in African Americans: A subgroup analysis of three phase III sipuleucel-T trials in advanced prostate cancer.

Abstract

e15148 Background: African American men are disproportionately affected by prostate cancer with an incidence of 231.9 for African Americans and 146.3 for Caucasians (per 100,000). Sipuleucel-T is an autologous cellular immunotherapy indicated for the treatment of men with asymptomatic or minimally symptomatic metastatic castrate resistant (hormone refractory) prostate cancer (mCRPC). Methods: Integrated results from three Phase 3 studies included 737 men who were randomized 2:1 to receive sipuleucel-T or control (non activated autologous peripheral blood mononuclear cells), including 43 (5.8%) patients who were African American. Cox proportional hazards regression analysis, stratified by study and adjusted for baseline prostate specific antigen and lactate dehydrogenase, was used to assess the treatment effect on overall survival in all randomized subjects and the African American subpopulation. Results: Results for the intent to treat population for the 3 studies demonstrated a positive treatment effect (HR=0.735 [95% CI: 0.613, 0.882]; P <0.001). The median survival difference was 3.9 months (25.4 months in the sipuleucel-T arm; 21.5 months in the control arm). Although there were baseline differences favoring the control arm, results were consistent in the African American subgroup (HR=0.288 [95% CI: 0.125, 0.662]; P = 0.003). The median survival difference was 30.7 months (45.3 months in the sipuleucel-T arm; 14.6 months in the control arm). Baseline factors for the African-American population relative to the overall study population included more exposure to prior chemotherapy, and lower age, baseline hemoglobin, ECOG status and bisphosphonate use. Adverse events for the African American subgroup were comparable to the overall study population. Conclusions: African Americans reported a similar adverse event profile to that of the general population studied. While no definitive conclusions can be drawn given the limited sample size, data from the three integrated Phase 3 studies suggest that African American patients benefit from treatment with sipuleucel-T, with the upper bound of the 95% CI of the HR well below one.