Gulley JL, et al. -Researchers performed a phase 3 trial of PROSTVAC, a viral vector-based immunotherapy that lengthened median overall survival (OS) by 8.5 months vs placebo in metastatic castration-resistant prostate cancer in a phase 2 study. Stratification was done based on prostate-specific antigen (less than 50 ng/mL v 50 ng/mL or more) and lactate dehydrogenase (less than 200 v 200 U/L or more), and patients randomly received PROSTVAC (Arm V; n = 432), PROSTVAC plus granulocyte-macrophage-colony-stimulating factor (Arm VG; n = 432), or placebo (Arm P; n = 433). In this superiority trial, three interim analyses were planned. Findings demonstrated safety as well as good tolerability with PROSTVAC, but there was no effect on OS or alive without events (AWE; ie radiographic progression, pain progression, chemotherapy initiation, or death) in this study population with metastatic castration-resistant prostate cancer. The most commonly experienced cardiac-related events (1.4% to 3.5%) were arrhythmias. Less than 1% of all patients had serious treatment-related events.