ERBB2 and breast cancer: The US Food and Drug Administration’s (FDA) 1998 approval of the anti-HER2 monoclonal antibody trastuzumab [6], and subsequent approvals of other HER2-targeted therapies have redefined the treatment landscape for patients with HER2 + breast cancer, as these therapies offered improved progression-free survival (PFS) and overall survival (OS) compared to chemotherapy alone [7–12].