Dacomitinib is a highly effective inhibitor of EGFR activating and EGFR T790M acquired resistant mutations as well as the wild-type HER2, gefitinib-resistant oncogenic HER2 mutation, and HER2 amplification both in vitro and in vivo in a broad range of human cancer cell lines including lung cancer, gastric cancer, biliary tract cancer, breast cancer, head and neck cancer, ovarian carcinoma, and squamous-cell carcinoma (63, 89–93). The gene discussed is ERBB2; the disease is breast cancer.