Overexpression of the HER2 in breast cancer is classified as “HER2-positive breast cancer” and is considered as one of the most aggressive forms of breast cancer as its status is the marker of poor prognosis, higher mortality in early-stage disease, increased incidence of metastases, and reduced time to relapse comparing with HER2-normal breast cancer (Figure 1). This evidence concerns the gene ERBB2 and breast carcinoma.