Tucatinib (Irbinitinib, ONT-380, ARRY-380) is an oral, potent, selective, reversible and ATP-competitive small-molecule inhibitor of ErbB-2 (also called HER2) with IC50s of 8 nM and 7 nM for ErbB-2 and p95 HER2, respectively in cell-based assays, showing ~500-fold selective for HER2 vs EGFR. It has potential antineoplastic activity.