ERBB2 and breast cancer: Recognition of the influence of the tumor microenvironment, specifically the immune cell compartment, has gained in importance over the past decade and is now considered a hallmark of tumor progression and resistance to therapy.2,3 Infiltrating lymphocytes have prognostic properties clinically, specifically, lower levels of CD8 T cells in HER2 positive or TNBC, correlate with lower survival rates and response to therapy.4 In addition, macrophages were also shown to be essential for breast cancer progression, both in mouse models and human disease.2,5,6