Through specific biomarkers, including hormone receptor (HR) status and levels of the human epidermal growth factor receptor 2 (HER2), BC can be categorized into four subtypes: luminal A (HR+/HER2−), HER2+ (HR-/HER2+), luminal B (HR+/HER2+) and triple-negative (TNBC; HR−/HER2−). This evidence concerns the gene ERBB2 and breast cancer.