ERBB2 and breast cancer: It is a heterogeneous disease characterized by mutations in several genes that affect its treatment and prognosis.[2] The prognosis of breast cancer varies depending on whether the expression of hormone receptors and human epidermal growth factor receptor 2 (HER2) is positive or negative, which can be determined by immunohistochemical (IHC) staining.[3] Each subtype of breast cancer distinguished by IHC has a different prognosis, and various mutations are expressed in tumor cells.[4–6]