TS overexpression promoted cell proliferation, DNA replication and cell migration in PC9 and HCC827 cells under gefitinib treatment. (A), the TS mRNA level of PC9 and HCC827 cells transfected with overexpressed plasmid of TS (oe‐TS) for 48 h. (B), the TS protein level of PC9 and HCC827 cells transfected with oe‐TS plasmid for 48 h. (C), the IC50 value of gefitinib (GEF) in transfected PC9 and HCC827 cells treated with GEF at gradient concentrations for 48 h. (D, E), colony formation experiments used to estimate the proliferation of PC9 and HCC827 cells transfected with the oe‐TS plasmid with treatment of GEF. (F, G), EdU (green or red) and DAPI (blue) staining assays were conducted to determine the DNA synthesis capacity of the transfected cells under GEF treatment for 48 h. (H, I), wound healing assay used to measure the migration rate of cells transfected with oe‐TS plasmid under GEF treatment for 24 h. J, K, transwell assays used to calculate the number of migrating cells after overexpression of TS under GEF treatment for 24h. All experiments were performed three times. *p < 0.05, **p < 0.01.