γH2AX foci formation after combination treatment of gefitinib and ionizing radiation (IR). A, NCI-H460 and A549 cells were treated with gefitinib or vehicle for 48 h, exposed to 6 Gy IR, and fixed and stained with anti-γH2AX (green) antibody and DAPI after the indicated time points. B, Average number of γH2AX foci per cell was counted and plotted. At least 50 cells were counted. Error Bars, SE of three independent experiments.