Results of PROSPECT: A randomized phase 3 trial of PROSTVAC-V/F (PRO) in men with asymptomatic or minimally symptomatic metastatic, castration-resistant prostate cancer.

5006Background: PRO is a PSA-targeted, poxvirus-based cancer vaccine using a heterologous prime-boost regimen comprising a recombinant vaccinia vector prime followed by 6 booster doses with the recombinant fowlpox vector. PROSPECT was designed as a confirmatory trial of a prior randomized phase 2 trial (RandPh2) that showed 8.5 months prolongation of median OS (25.1 m PRO vs 16.6 m Placebo (Pbo)) (Kantoff, JCO 2010; 28:1099) Methods: Double-blind randomization to one of the following 3 arms: PRO+Pbo (V), PRO+GM-CSF (VG), or Pbo+Pbo (P). Stratified per PSA < or ≥ 50 ng/mL and LDH < or ≥ 200 U/L. Primary Endpoint: OS. Secondary endpoints: Alive without event at 6 months (AWE-6) and Safety. Results: Between Dec 2011 and Jan 2015, 1297 pts were randomized in 15 countries. Demographics: mean age: 71 (SD: 8.25), ECOG PS0/1-2: 74%/26%, mean PSA: 74.5 (SD:209). Site of metastasis: bone 74.7, lymph node 15.7, visceral 8.4%. The 3rd interim analysis was held in Sep 2017, after reaching 80% of the expected deaths, a...