The characterization of the Human Epidermal Growth Factor Receptor-2 (HER2) in breast cancer (BC) has dramatically evolved over the last three decades, from a biomarker of poor prognosis to one of clinical benefit for trastuzumab and other anti-HER2 agents, when overexpressed/amplified in tumor cells [1,2,3,4,5]. The gene discussed is ERBB2; the disease is breast cancer.