A major milestone on the way to this goal is the definition of five biologically and clinically meaningful breast cancer subtypes based on genome‐wide expression analyses: Luminal‐A, Luminal‐B, HER‐2, Normal‐like and Basal‐like (Sorlie et al., 2003; Perou and Børresen‐Dale, 2011). Here, ERBB2 is linked to breast cancer.