ERBB2 and breast cancer: BC is currently divided into 4 subtypes: Luminal A (HER2 −/PR +/ER +), Luminal B (HER2 +/PR +/ER + or HER2 −/PR +/ER +), HER2 overexpression (HER2 +/PR −/ER −), and triple-negative BC (TNBC) (HER2 −/PR −/ER −) [40].