Abstract P3-05-09: Prognostic factors for therapeutic personalized peptide vaccines in patients with metastatic recurrent breast cancer

Background: We have previously reported the prognostic role of humoral antigen spreading response against prostate-related antigen (PRA) for metastatic recurrent breast cancer (mrBC) patients who received personalized peptide vaccine (PPV) therapy (Toh U, SABCS 2015). The prognostic effect was additionally evaluated by the clinical relevant factors including intrinsic subtype, the regimens of combined chemo-hormonal therapies in present study. Methods: We analyzed serum IgG responses to all of the peptide candidates included PRAs (PSA, PAP and PMSA) after PPV therapy by the Luminex systemusing peripheral blood samples from 77 vaccinated mrBC patients. The clinical factors and relevant events were statistically evaluated. Results: After 6 and 12cycles of PPV therapy, the serum IgG of anti-PSA, anti-PAP, and/or anti-PMSA increased significantly in 31 patients (PRA response group), and the median progression free survival (PFS) and median overall survival (OS) were 8.1 and 14.3 months, but were 5.1 and 10.8 months, respectively, in the remaining 46 patients with no anti-PRA IgG response (PRA non-response Group). The anti-PRA IgG level was marginally correlated withPFS (p=0.059) and OS (p=0.082) between these two groups, which was a significant prognostic factor for PFS (Log-rank: 0.009) in estrogen-positive cancer patients (ER+). The statistical analyses showed that the clinical outcome was in favor of > 60 year-old patients, those with longer PPV therapies (>3 months), and those who received combined standard hormonal therapies or bisphosphonate/anti-RANKL therapy. Conclusions: This study indicated a clinical significance between the pre-and post- PPV therapy measurement of serum anti-PRA IgG in patients with mrBC, which may be a useful prognostic marker for monitoring peptide vaccine treatment outcomes, particularly for patients > 60 years with ER+ breast cancer. These results also suggest that the immunotherapeutic peptide vaccine could be efficiently combined with hormonal therapy, anti-HER2 therapy, and bisphosphonate/anti-RANKL therapy in mrBC patients. Citation Format: Toh U, Saku S, Iwakuma N, Takao Y, Okabe M, Akashi M, Yamada A, Shichijo S, Itoh K, Akagi Y. Prognostic factors for therapeutic personalized peptide vaccines in patients with metastatic recurrent breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-05-09.