In this context, recently, two new drugs targeting HER2 were introduced in the clinical treatment of HER2-positive breast cancers: (i) trastuzumab emtansine, an antibody-drug conjugate of trastuzumab with the cytotoxic agent emtansine, a microtubule inhibitor; (ii) pyrotinib, an irreversible pan-ERB receptor tyrosine kinase inhibitor targeting HER1, HER2, and HER4. This evidence concerns the gene ERBB2 and breast cancer.