Naquotinib (ASP8273) is an orally available, irreversible, mutant-selective, epidermal growth factor receptor (EGFR) inhibitor, with potential antineoplastic activity. Naquotinib was found by mass spectrometry to covalently bind to a mutant EGFR (L858R/ T790M) via cysteine residue 797 in the kinase domain of EGFR with long-lasting inhibition of EGFR phosphorylation for 24 h. In the NSCLC cell lines harboring the above EGFR mutations, Naquotinib had IC50 values of 8-33 nM toward EGFR mutants, more potently than that of WT EGFR (IC50 value of 230 nM). In mouse xenograft models, Naquotinib induced complete regression of the tumors after 14 days of treatment. ASP8273 even showed activity in mutant EGFR cell line which is resistant to other EGFR TKIs. Naquotinib is in phase III clinical trials for the oral treatment of EGFR mutated non-small cell lung cancer (NSCLC).