Overall survival (OS) benefit with sipuleucel-T by baseline PSA: An exploratory analysis from the phase III IMPACT trial.

4648 Background: Sipuleucel-T is an autologous cellular immunotherapy approved for asymptomatic or minimally symptomatic metastatic castrate-resistant prostate cancer. In the IMPACT trial, sipuleucel-T showed a 22.5% reduction in risk of death vs the control group (hazard ratio [HR]=0.775 [95% CI 0.614, 0.979]; P=0.032). A pre-specified subgroup analysis for baseline prognostic variables showed homogeneous treatment effects consistently favoring sipuleucel-T. In patients (pts) with baseline PSA below vs above the median, there was a trend toward greater treatment effect (HR=0.685 vs. 0.865). In this exploratory analysis, we further sub-divide baseline PSA into quartiles to evaluate potential treatment effect patterns. Methods: The analysis included all randomized pts from IMPACT (n=512). Pts were categorized by baseline PSA quartile (Table), ECOG PS and by median for other baseline prognostic variables (i.e., LDH, PAP, ALP in bone-only disease, and Hgb). Median OS and HR were estimated using Kaplan-Meier ...