Introduction

Sipuleucel-T (sip-T) is an FDA-approved autologous cellular immunotherapy targeting prostatic acid phosphatase in select men with metastatic castration-resistant prostate cancer (mCRPC). Previous retrospective analyses of three sip-T phase 3 trials showed a 30.7-mo overall survival (OS) advantage for African American (AA) patients (pts) vs control pts while in the IMPACT trial, sip-T extended median OS by 4.1 mo vs control (McLeod AUA 2012 #P953). The PROCEED registry provides a prospective opportunity to confirm these observations in a larger group of AA pts.

Methods

PROCEED (NCT01306890) enrolled men with mCRPC. In this analysis, two Caucasian (CAU) pts were matched to each AA pt by baseline prostate-specific antigen (PSA), as PSA correlates with OS in pts receiving sip-T (Schellhammer 2013). OS and time to first anticancer intervention (tACI) post-sip-T were examined; univariate and multivariate analyses evaluated independent factors associated with OS.

Results

420 CAU pts were matched to 210 AA pts; all received ≥1 sip-T infusion. CAU pts had significantly higher baseline median hemoglobin levels (p<0.001; 13.0 g/dL vs 12.1 g/dL for AA pts) and were more likely to receive prior local therapy (p=0.02) or prior chemotherapy (p<0.001). CAU pts had a longer tACI of 9.3 mo vs 7.6 mo for AA pts. However, AA pts had a significantly longer median OS of 39.5 mo vs 28.1 mo for CAU pts (p<0.001; HR 0.665, 95% CI 0.530-0.835). After univariate and multivariate analyses, six baseline characteristics were significantly associated with OS (Table). Younger age, lower PSA or alkaline phosphatase, and higher hemoglobin levels were independently associated with longer OS. No prior chemotherapy and the AA race were also independent predictors of extended OS.

Conclusions

Post-sip-T, median OS for AA pts was significantly extended by nearly 1 year compared with matched CAU pts. In this large prospective analysis, AA race emerged as an independent predictor of longer OS in multivariate analyses, confirming observations of prior retrospective analysis of phase 3 trial data. These results should stimulate additional studies on the biologic basis for AA men's enhanced response to sip-T and potentially other immunotherapies.

Funding

This study was sponsored by Dendreon Pharmaceuticals, Inc