HER3 has been implicated in breast cancer resistance to multiple therapies, including antiestrogen therapies fulvestrant and tamoxifen, EGFR and HER2 small molecule inhibitors such as erlotinib and lapatinib, and HER2 directed antibodies such as Herceptin (trastuzumab) and Pertuzumab [4, 14, 15]. The gene discussed is ERBB2; the disease is breast cancer.