EGFR and breast cancer: However, it is still unclear whether luminal BCSCs overexpress HER2 or another receptor family such as EGFR, as the hetero-dimerization of HER2 and EGFR is critical for the activation of the downstream pathway of HER2 [11]; if so, HER2-targeted therapy could eradicate luminal breast cancer stem cells in response to therapeutic treatments such as irradiation.