By evaluating a few biomarkers, including the presence of hormone receptors (HRs), excess levels of human epidermal growth factor receptor 2 (HER2) protein, and/or extra copies of the HER2 gene (3, 4), BC is classified into four major molecular subtypes: (i) luminal A (HR+/HER2−); (ii) HER2+; (iii) luminal B (HR+/HER2+); and (iv) triple negative (TNBC; HR−/HER2−; also overlap with the basal-like subtype). This evidence concerns the gene ERBB2 and breast cancer.