Abstract 1351: Ephrin receptor A4 regulation of the tumor microenvironment in triple-negative breast cancer

Metastasis is the leading cause of mortality for cancer patients and is particularly difficult to manage in Triple-Negative Breast Cancer (TNBC), a subtype of breast cancer with limited targeted therapies and biomarkers. Ephrin Receptor A4 (EPHA4) is a receptor tyrosine kinase activated by cell-cell contact that regulates various developmental pathways, and a cell surface receptor that has the potential to be targeted pharmacologically. In the context of TNBC, EPHA4 has been found to have mixed effects on regulating factors that may influence metastasis: while EPHA4 expression promotes in-vitro cell invasion, EPHA4 activation also enhances T cell-mediated antitumor immunity. Considering EPHA4’s function of mediating cell-cell interaction, it may play an important role in modulating the tumor microenvironment via cancer-immune cell interactions. However, EPHA4’s functions within the tumor microenvironment and how this relates to its regulation of metastasis remain poorly understood. To characterize EPHA4 as a potential target for TNBC metastasis, we conducted single-cell RNA-sequencing of a syngeneic, orthotopic TNBC mouse model to investigate how EPHA4 regulates the tumor microenvironment. Control or EPHA4 knockout 4T1 cells were injected into BALB/C mice and primary tumors were isolated and sequenced. There is no literature consensus on methods of marker-based annotation of tumor cells in the 4T1 syngeneic model, and we instead applied an aneuploidy analysis algorithm to increase the accuracy of tumor cell annotations. EPHA4 was found to increase the proportion of T cells, NK cells and B cells in the tumor microenvironment. EPHA4 also promoted tumor-intrinsic genetic pathways regulating T cell activation and antigen processing and presentation via MHC class II. Overall, EPHA4 modulates the immune landscape in TNBC, serving as a potential mechanism by which it regulates metastasis. Citation Format: Hoi Wan (Karen) Lee, Wenchao Liu, Madeline Henn, Marsha Rosner. Ephrin receptor A4 regulation of the tumor microenvironment in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1351.