ERBB2 and breast cancer: Because the number of MDSCs modulates the activity of immune checkpoint inhibitors,29 evaluating the function of neutrophils in the response to trastuzumab could guide the development of new combinations of trastuzumab and anti-PD-L1 drugs, a promising approach for HER2+ tumours that has been demonstrated in preclinical models30 and in a trial of HER2+ BC patients.31