Enhancement of apoptosis induction by the combination of EGFR siRNA plus gefitinib or erlotinib. Lung cancer cells were treated with different drugs 24 h before the EGFR siRNA transfection. Forty-eight hours post transfection, the cell cultures were assayed for caspase-3/7 activity. (A: gefitinib; B: erlotinib). *P < 0.05 and **P < 0.01 compared to controls with siRNA transfection alone. "black triangle" P < 0.05 and "double black triangles" P < 0.01 compared to agents plus control siRNA.