The present study assessed plasma
IgG in patients with metastatic recurrent
breast cancer (mrBC) that is reactive to various
T-cell epitope peptides of prostate-related
antigens (PRAs), such as
prostate-specific antigen, prostate-specific membrane
antigen and prostate
acid phosphatase. Patients were treated with personalized
peptide vaccines (PPVs) which were selected and administered from a panel of candidate
peptides based on
human leukocyte antigen-types and prevaccination
IgG levels to each
peptide. The
peptide panel consisted of 27 cytotoxic T-lymphocyte-
epitope peptides derived from
tumor-associated
antigens, not including PRA. PRA
peptides and
peptide panels were retrospectively analyzed in 77 PPV-treated patients. The results revealed that PRA reactive
IgG levels were increased after vaccination in 31 of the 97 patients included in the present study. Although there was no significant association between anti-PRA
peptide levels and progression-free survival (PFS) or overall survival, anti-PRA
peptide levels were significantly associated with PFS (P=0.009) in
estrogen-receptor positive (ER+) patients with
cancer. The results suggested that plasma anti-PRA
IgG levels may be a useful prognostic marker for monitoring PPVs, particularly for ER+ patients with mrBC (trial registration no. from the UMIN Clinical Trials Registry, UMIN000001844).