Based on the 2018 American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guideline update, HER2+ BC is clinically characterized by a complete and intense circumferential membrane staining for the HER2 protein in >10% of tumor cells (3+ score) at immunohistochemistry (IHC) and/or in situ hybridization (ISH)-based techniques with a HER2/chromosome enumeration probe 17 (CEP17) ratio ≥ 2.0 and an average HER2 gene copy number ≥ 4.0 signals/cell [4]. The gene discussed is ERBB2; the disease is breast cancer.