Abstract
Metastatic progression in triple-negative breast cancer (TNBC) is strongly influenced by epithelial-mesenchymal plasticity (EMP), which enables transitions between epithelial, hybrid epithelial/mesenchymal (E/M), and mesenchymal cell states. While mesenchymal cells are highly invasive and resistant to therapy, hybrid E/M states confer advantages during metastatic colonization. Both mesenchymal and hybrid states therefore contribute to tumor aggressiveness through distinct mechanisms. However, the molecular regulation governing transitions between mesenchymal and hybrid E/M states remains poorly understood. Here, we identify EPHA4 as a regulator of this transition in TNBC. EPHA4 expression is enriched in mesenchymal TNBC cells, and genetic knockout of EPHA4 in MDA-MB-231 xenograft and 4T1 syngeneic models induces a shift toward hybrid E/M phenotypes. This transition reduces cellular invasion while enhancing metastatic colonization, consistent with the clinical observations of decreased EPHA4 expression in secondary metastases compared to primary tumors. Despite compensatory changes in other Eph/ephrin family members following EPHA4 loss, EPHA4 deficiency is sufficient to drive this phenotypic shift. These findings identify EPHA4 as a regulator of cancer cell plasticity in TNBC and highlight the therapeutic complexity of targeting pathways that govern metastatic state transitions.