LAUSR

5033 Background: To develop a new treatment modality, we conducted a phase III randomized trial of personalized peptide vaccination (PPV) for human leukocyte antigen (HLA) -A24 positive patients with castration-resistant prostate cancer (CRPC) who failed docetaxel chemotherapy. Methods: Patients were randomly assigned in a 2:1 ratio to receive PPV or placebo. Four of 12 warehouse peptides selected based on preexisting peptide-specific immunoglobulin G levels or the corresponding placebo were subcutaneously injected 6 doses weekly followed the maximum of 30 doses bi-weekly until disease progression. The primary end point was overall survival (OS), and secondary end points were progression-free survival (PFS) and immune responses. Results: From August 2013 to April 2016, 310 patients were randomly assigned (207 to PPV and 103 to placebo), and 306 patients were analyzed by the full analysis set (204 to PPV and 102 to placebo). Baseline characteristics were balanced between groups. Estimated median OS was 16.1 months (95% CI, 13 to 18.2) with PPV and 16.9 months (95% CI, 13.1 to 20.4) with placebo (HR, 1.04; 95%CI, 0.79 to 1.37; P = 0.77). Median PFS was also not significantly different among them. Median Grade ≥ 3 adverse events were observed in 41% in both groups. The analysis of treatment arm effects among various subgroups revealed a lower HR for OS in favor of the PPV arm in patients with a < 64% neutrophil proportion (HR, 0.55; 95%CI, 0.33 to 0.93), with a significant interaction test ( P = 0.003). Conclusions: PPV did not prolong either OS or PFS in HLA-A24 positive patients with CRPC progressing after docetaxel chemotherapy. Clinical trial information: 0000113088.