Abstract PO4-13-05: Spotlight on PSMA as a new theranostic biomarker for breast cancer

Abstract Breast cancer patients are risk-stratified on the basis of the subtype classification. However, this parameter is not completely accurate in discriminating between high- and low-risk disease, creating a need for a reliable marker to determine aggressiveness. Prostate-specific membrane antigen (PSMA) could fulfill this need given that it has been reported to be expressed by breast cancer tumor cells and the endothelial cells of tumor vessels. We analyzed 68 breast cancers (BC) of whom 14 luminal A, 28 Luminal B, 15 HER2 positive and 11 triple negative BC to assess whether PSMA expression by immunohistochemistry was different in the several tumor subtypes and was related to ki67 expression and stromal TILs. PSMA positivity was calculated as the number of positive vessels on 10 fields at 40X magnifications. Kruskal Wallis’s test was used to assess difference in PSMA positivity among BC subgroups and Dunn’s test was performed for post-hoc comparisons; Spearman’s rho coefficient was calculated to analyze the correlation among PSMA, KI67 and TILs. Our results show that median PSMA was higher both considering the number of positive vessels and the staining intensity in TNBC compared to Luminal A and B tumors (p 0.001). Ki67 was higher in TNBC compared to Luminal A tumors (p 0.001). We saw a correlation between PSMA and ki67, especially in HER2+ tumors (p=0.002), while a correlation between PSMA and TILs was observed in TNBC (p=0.014). The analysis of PSMA expression on the lymph nodes showed the same trend observed for the primary tumors given that it was higher in TNBC compared to HER2 positive and luminal cancers. Our results suggest that PSMA could be used as theranostic biomarker in BC considering that it is highly expressed in more aggressive tumors and the possibility to treat PSMA-expressing patients for anti-angiogenesis and/or radionuclide treatment. Citation Format: Sara Bravaccini, Stefania Cortecchia, Flavia Foca, Giovanni Martinelli, Sara Ravaioli, Maria Maddalena Tumedei, Federica Matteucci, Roberta Maltoni, Giovanni Paganelli, Francesca Poli, Maurizio Puccetti. Spotlight on PSMA as a new theranostic biomarker for breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-13-05.