ERBB2 and breast cancer: Based on molecular classification, breast cancer includes the following subtypes: luminal A (ER+ and/or PR+/HER2−); luminal B (ER+ and/or PR+/HER2+); human epidermal growth factor (EGF) receptor 2 (HER2) overexpressing (ER-/HER2+); and basal-like (ER/PR−/HER−), commonly known as triple-negative (TNBC) due to its resistance to available receptor-targeted therapies.