Survival outcomes for African-American (AA) vs matched Caucasian (CAU) patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) treated with sipuleucel-T (sip-T).

Abstract

192 Background: Prostate cancer risk and mortality is higher in AA vs CAU men. In an analysis of three phase 3 mCRPC trials, AA pts appear to derive greater survival benefit with sip-T, an autologous cellular immunotherapy for asymptomatic/minimally symptomatic mCRPC. AA pts on sip-T had a 30.7-month (mo) median overall survival (OS) benefit vs control (AUA 2012 P953), in contrast to a 4.1-mo OS benefit with sip-T vs control for all pts in IMPACT (NEJM 2010;363:411). As the prior analysis did not adjust for baseline differences between races, we matched AA to CAU pts on sip-T to better assess racial differences in sip-T benefit and cumulative antigen presenting cell (APC) activation, which correlates with OS (CII 2013;62:137). Methods: Data were from phase 3 mCRPC trials that randomized pts 2:1 to sip-T or control (D9901 [NCT00005947]; D9902A [NCT01133704]; IMPACT [NCT00065442]). Thirty-three AA sip-T pts were matched with 66 CAU sip-T pts based on predicted Halabi survival. Data were evaluated by the Kaplan-Meier method (event rates) and ANOVA (APC activation). Results: Median follow-up was 23.2 mos. AA pts on sip-T had a 20.6-mo longer median OS (45.3 mos; 95% CI 23.4–NE) vs CAU pts (24.7 mos; 95% CI 18.1–29.4) (HR = 0.49; 95% CI 0.26–0.91; p = 0.02). Median event-free survival (time to death or anticancer intervention [ACI]) was 10.7 mos for AA pts (95% CI 8.5–21.5) vs 8.7 mos for CAU pts (95% CI 6.6–11.5) (HR = 0.74; 95% CI 0.47–1.18; p = 0.20). Median time to next ACI was 23.5 mos in AA pts (95% CI 9.4–NE) vs 16.3 mos in CAU pts (95% CI 9.7–25.6) (HR = 0.78; 95% CI 0.42–1.43; p = 0.42). In AA pts, median APC activation was higher with sip-T infusion 1 vs CAU pts (7.0 vs 5.5, p = 0.004). Median cumulative APC activation over the three infusions was 27.7 (22.6–42.4, AA) vs 25.7 (21.5–33.9, CAU) (p = 0.083). Conclusions: Prior studies found sip-T provides OS benefit to both AA and CAU mCRPC pts. Herein, for men treated with sip-T, AA had longer survival, suggesting sip-T may provide greater OS benefit in AA. The basis for this may be biologic (greater APC activation). Further studies with larger sample sizes are needed to confirm if AA pts derive greater OS benefit from sip-T. Clinical trial information: NCT00005947; NCT01133704; NCT00065442.