The overexpressed human epidermal growth factor receptor 2 positive breast cancer (HER2+ BC) comprises 15–20% of breast cancer cases and displays sensitivity to anti-HER2-targeted medicines, such as transtuzumab (binding specifically to the HER2 receptor and preventing its activation), pertuzumab (blocking the dimerization of HER2 with other growth factor receptors), lapatinib (inhibiting directly the internal kinase activity of HER2 and epidermal growth factor receptor), and T-DM1 (allowing tertuzumab to deliver chemotherapy directly to HER2-overexpressing tumor cells) [3]. The gene discussed is ERBB2; the disease is breast carcinoma.