Gefitinib is an antineoplastic drug. Gefitinib effectively inhibits all tyrosine phosphorylation sites on EGFR in both the high and low EGFR-expressing cell lines including NR6, NR6M and NR6W cell lines. The phosphorylation sites Tyr1173 and Tyr992 are less sensitive requiring higher concentrations of Gefitinib for inhibition.