In breast cancer cells PKCδ activity can be stimulated by E2 through activation of matrix metalloproteinases (MMPs) followed by the release of membrane‐bound heparin‐binding epidermal growth factor (HB‐EGF) and trans‐activation of the epidermal grow factor receptor (EGFR) (Filardo et al. 2000). Here, EGFR is linked to breast cancer.