Purpose: We have indicated that IgG and CTL boosting response could be a potential prognostic factor for overall survival (OS) and progression free survival (PFS) in metastatic recurrent breast cancer (mrBC) patients, who had received personalized selected peptide vaccine (PPV) therapy in our previously reported clinical phase II study. The aim of this study is to identify the prognostic role of serum value of IgG antibody against prostate related-antigen (PRA), including prostate-specific antigen (PSA), prostate specific membrane antigen (PSMA) and prostate acid phosphatase (PAP) in mrBC patients

Methods: Peripheral blood samples of 77 patients with mrBC were analyzed for serum anti-PRA IgG levels before and after 6th and 12th PPV therapy prospectively. Most of the peptides using for PPV are derived from cancer associated antigens expressing in various types of advanced cancers, but the peptides derived from PRAs were not used in this study.

Results: After PPV therapy, total serum levels of anti-PRA IgG were significantly increased in 31 mrBC patients (Group 1) whereas in remaining 46 rmBC patients (Group 2). Either serum anti-PSA, anti-PAP and/or anti-PMSA IgGs showed a significant increase in patients of Group 1 after 6th (p=0.045) and 12th PPV treatment (p < 0.001), irrespective of their intrinsic subtypes. The median PFS and median OS of Group 1 patients were 8.1 and 14.3 months, while those of Group 2 patients were 5.1 and 10.8 months, respectively. Anti-PRA IgG levels were significantly associated with PFS (p=0.0073; HR: 0.37) and OS (p=0.025; HR: 0.43) between these two groups, whereas no significant relation was found with age, clinical response rate and recurrent metastatic status.

Conclusions: The Group 1 patients with elevated anti-PRA IgG may have better prognosis compared to Group 2 patients who showed no IgG elevation after PPV treatment for rmBC. These results indicated a clinical significance between pre-and post- treatment measurement of serum anti-PRA IgGs in mrBC patients receiving PPV therapy, and may be a useful prognostic marker for monitoring the outcome to PPV treatment of breast cancer.

Citation Format: Toh U, Okabe M, Iwakuma N, Mishima M, Shichijo S, Yamada A, Noguchi M, Itoh K, Akagi Y. Serum IgG response against prostate-related antigen revealed by personalized peptide vaccination in patients with metastatic recurrent breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-11-04.