An inhibitor of mutant EGFRs; selective for EGFR mutant cell lines, including H3255 and HCC827 lung adenocarcinoma cells (IC50s = 6.11 and 1.52 nM, respectively) and resistant H1975 NSCLC cells (IC50 = 4.18 nM), over cells expressing wild-type EGFR (IC50 = 160.6 nM for HaCaT keratinocytes); decreases phosphorylation of EGFR in H3255, HCC827, and H1975 cells (EC50s = 5, 1, and 3 nM) and inhibits cell proliferation of H3255, HCC827, and H1975 cells (EC50s = 9, 11, and 25 nM) but does not affect cell proliferation in cell lines containing wild-type EGFR; reduces tumor growth in an HCC827 lung adenocarcinoma mouse xenograft model at doses ranging from 3 to 100 mg/kg per day