3031 Background: Personalized selection of the right peptides for each patient could be a novel peptide-based immunotherapy for boosting anticancer immunity in many patients (pts). Here we describe immunologic and clinical effects of a personalized peptide vaccine for HLA-A2 positive advanced cancer pts who mostly failed the standard therapy. Methods: To evaluate safety and immune responses of vaccination, 74 HLA-A2 positive advanced cancer pts, including 27 hormone refractory prostate cancer (HRPC), 13 colon cancer (CC), 8 pancreatic cancer (PC), 6 gastric cancer (GC), 4 brain tumor (BT), and 16 other types of cancer (Others) pts were enrolled in a phase I/II clinical trial. Pre-vaccination peripheral blood mononuclear cells and/or plasma were measured for their CTL or IgG levels for each of the 14–20 candidate peptides which can induce HLA-A2-restricted CTL activity against cancer cells followed by weekly or bi-weekly subcutaneous administration of the top four peptides (3mg each) showing the strongest immune responses. The protocol was approved by each ethics committee. Results: Vaccination-related adverse events were mainly grade 1 or 2 skin reactions at the injection sites, and there were no severe adverse events except for rectal bleeding in a cervical cancer pt. In the post (6–8th)-vaccination samples, CTL responses were boosted in 46 of 70 pts tested, while IgG responses were boosted in 55 of 73 pts tested, respectively. Best clinical responses were 1 CR, 11 PR, 31 SD, and 31 PD. Objective responses were obtained in urologic and gynecologic cancers or brain tumors by vaccination in the thigh or upper back regions, respectively, suggesting that location of sentinel lymph node near to tumor site is a pivotal factor for tumor regression. Median survival times in all pts are 14.3 months: 25 months in HRPC, 9.7 in BT, 8 in GC, 7 in PC, 6 in CC, and 17 in Others, respectively. Conclusions: This personalized peptide vaccine could be recommended for further stages of clinical trials because of safety, boosting of immune responses, and potential clinical benefits. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration GreenPeptide GreenPeptide GreenPeptide GreenPeptide