SUMMARY Mechanical forces generated by a rigid extracellular matrix (ECM) in the tumor microenvironment play a key role in tumor progression and metastasis. We recently discovered a critical role of EPHA2 non-canonical signaling in promoting epithelial-mesenchymal transition (EMT) and tumor invasion and metastasis in response to increasing ECM stiffness in the tumor microenvironment. Furthermore, we found that activation of EPHA2 canonical signaling by the ephrinA1 ligand potently inhibits stiffness-induced breast cancer cell invasiveness. Based on these results, we hypothesize that EPHA2 functions as a key rheostat that integrates both mechanical and biochemical cues from the tumor microenvironment to regulate mechanosignaling in breast cancer progression and metastasis. We propose to combine biochemical, 2D and 3D cell culture assays, and in vivo xenograft models to elucidate EPHA2 signaling mechanisms in breast cancer malignancy induced by ECM rigidity through three specific aims. (1) Determine how ECM rigidity activates EPHA2 non-canonical signaling to promote EMT and invasion. (2) Determine how EPHA2 canonical signaling blocks EMT and invasion induced by ECM rigidity. (3) Examine the role of EPHA2 non-canonical and canonical signaling in breast cancer invasion and metastasis in vivo. Together, these studies will inform on the potential usefulness of activating EphA2 canonical signaling for inhibition of breast cancer invasiveness and metastasis.