ERBB2 and breast carcinoma: HER2 is a critical predictive and prognostic indicator in breast cancer, as its overexpression is linked to poorer prognoses (Slamon et al., 1989); ∼15–30% of all breast cancers are HER2+ (Gonzalez-Angulo et al., 2009; Zhang and Yu, 2013; Vu and Claret, 2012).