ERBB2 and breast cancer: Owing to the high degree of heterogeneity at the molecular level, the three distinct subtypes of BC, namely Luminal (positive for ER and/or PR), Her‐2 overexpression (negative for ER and PR, positive for Her‐2), and TNBC (lack of ER, PR, and Her‐2 expression), have different biological, molecular, and clinical characteristics.28, 29