ERBB2 and breast cancer: Human epidermal growth factor receptor 2 (HER2)-positive breast cancers have long been treated with targeted therapy, comprising either monoclonal antibodies, such as trastuzumab or pertuzumab, which bind to the extracellular domain of HER2, or tyrosine kinase inhibitors (TKIs), such as the reversible inhibitors lapatinib and tucatinib and the irreversible inhibitor neratinib[1].