ERBB2 and breast cancer: The prognosis of breast cancers is closely related to the surface expression of key molecules, i.e. estrogen and progesterone receptors, and ERBB2 (HER2), defining the classification of breast cancers into three categories: ERBB2 negative (~70% of patients), ERBB2 positive (~15%-20%), and triple-negative (tumours lacking all 3 standard molecular markers; ~15%) (5).