Gefitinib impurity 5 is an impurity of Gefitinib. Gefitinib is an effective selective EGFR tyrosine kinase inhibitor with oral activity, with an IC50 of 33 nM. Gefitinib selectively inhibits the growth of EGF-stimulated tumor cells (IC50 is 54 nM), and blocks EGFR autophosphorylation in EGF-stimulated tumor cells. Gefitinib can also induce autophagy. Gefitinib has anti-tumor activity.