The results showed that the three lung cancer cell lines with wild-type EGFR exons 19–21 (A549, 95D, CALU-1) and the NCI-H1975 cell line with the T790M/L858R double mutation exhibited relative resistance to gefitinib, with IC50 values of 20.80 nM, 13.51 nM, 26.36 nM, and 14.26 nM, respectively. This evidence concerns the gene EGFR and lung carcinoma.