Human epidermal growth factor receptor 2 (HER2) is an important prognostic and predicative biomarker in breast cancer (BC) and all patients with newly diagnosed primary or metastatic BCs should be tested for HER2 protein expression by immunohistochemistry (IHC) and/or gene expression by in situ hybridization (ISH) to guide the clinical management [1,2,3]. The gene discussed is ERBB2; the disease is breast cancer.