Epertinib hydrochloride (S-22611 hydrochloride) shows potent antitumor activity. Epertinib hydrochloride is a potent, orally active, reversible, and selective tyrosine kinase inhibitor of EGFR, HER2 and HER4, with IC50s of 1.48 nM, 7.15 nM and 2.49 nM, respectively.