According to the dichotomic classification proposed by the 2018 American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines, about 80% of breast tumors, lacking HER2 protein overexpression, are classified as HER2 negative (HER2-); within them, approximately 45–55% are characterized by HER2 immunohistochemistry (IHC) assay score of 1+ or 2+ with negative in situ hybridization (ISH), referred to as HER2-low BC [9,10]. The gene discussed is ERBB2; the disease is breast cancer.