Tucatinib, an ATP-competitive, small-molecule tyrosine kinase inhibitor, is a new approach by the US Food and Drug Administration (FDA) to treat advanced breast cancer in a patient who is HER2-positive in combination with trastuzumab (Herceptin) and capecitabine (Xeloda) [8,9,10,11]. The gene discussed is ERBB2; the disease is breast cancer.