ERBB2 and breast cancer: As a complex disease with genetic and clinical heterogeneity, breast cancer is generally categorized into 4 molecular subtypes, including Luminal A (ER+/PR+, HER2-, low proliferation), Luminal B (ER+/PR+, HER2-, high proliferation), HER2 enriched (HER2+, ER−, PR−; HER2+, ER+/PR+), Basal-like (HER2−, ER−, PR−) subtype3–5.