ERBB2 and breast cancer: PKC-δ has been implicated in breast cancer (BC) progressionand therapy response.−, ,  BC is a heterogeneous disease, classified into molecular subtypesbased upon the expression of certain markers, including hormone receptors,and HER2. As such, its molecular subtypesinclude Luminal A, Luminal B, HER2-enriched, and triple-negative BC. Clinically, PKC-δ overexpression in ER+ BC correlates with improved endocrine therapy response, and it was linked to increased tamoxifen resistance.