ERBB2 and breast cancer: On the basis of the expression profile, BC is further classified in five subtypes: (1) luminal A (approximately 50–60% of cases); (2) normal-like, which is a subtype of the luminal A group, but with worse prognosis (approximately 10% of the luminal A type); (3) luminal B (approximately 10% of cases); (4) HER2-enriched (approximately 20% of cases); and (5) basal-like triple-negative (TNBC) tumors (approximately 10% of cases).