ERBB2 and cancer: To date, the few studies exploring the dynamics of the tumor microenvironment of HER2+ BC upon trastuzumab treatment have shown that application of this anti-HER2 antibody can impact the immunosuppressive features of the TME, namely by modulating expression of checkpoint ligand PD-L1 both in cancer and immune cells (28, 29, 32, 91, 95).