ERBB2 and breast cancer: Correspondingly, the otherwise rare expression in most breast carcinomas of programmed death ligand-1 (PD-L1) – an archetypal immunosuppressive molecule on cancer cells that engages its receptor PD-1 on T-cells to suppress T-cell-mediated immune surveillance [21–23] – is markedly enriched in basal-like and HER2-positive tumors, thereby implying that PD-L1 confers a survival advantage in the tumor microenvironment (TME) of these specific breast cancer subtypes.