An orally available covalent inhibitor of human epidermal growth factor receptor 2 (HER2; ERBB2), with potential antineoplastic activity. Upon oral administration, HER2 inhibitor TAS0728 specifically and irreversibly binds to and inhibits the activity of HER2. This prevents HER2-mediated signaling and leads to cell death in HER2- and HER3 (ErbB3)-expressing tumor cells. HER2, a receptor tyrosine kinase mutated or overexpressed in many tumor cell types, play key roles in tumor cell proliferation and tumor vascularization. HER3 has no active kinase domain but is activated through heterodimerization with other members of the EGFR receptor family, such as HER2.