To date, several anti-HER2 drugs have been approved for the treatment of breast cancer: dual blockade with trastuzumab and pertuzumab, both anti-HER2 humanized monoclonal antibodies (mAb), in combination with chemotherapy is approved as first line treatment for metastatic disease [3]; the antibody–drug conjugate (ADC) trastuzumab emtansine (T-DM1) and the HER2 kinase inhibitor lapatinib are currently approved for further lines of treatment [4,5]. This evidence concerns the gene ERBB2 and breast cancer.