BC is a heterogeneous disease and can be classified according to the tumor immunohistochemical profile, characterized by the presence or absence of hormone-receptor expression (HR-positive [HR +]/HR-negative [HR −] status) and/or human epidermal growth factor receptor 2 (HER2) protein expression and/or HER2gene amplification (HER2 − positive [HER2 +]/HER2 − negative status [HER2 −]) in the tumor cells. This evidence concerns the gene ERBB2 and breast cancer.