MUC1 downregulation increases the apoptosis of NCI-H1650 cells. At 48 h after transfection with MUC1-siRNA or control-siRNA, flow cytometry was conducted to detect the cell apoptosis, and cell apoptosis rate (early apoptosis rate + late apoptosis rate) was calculated. All data are presented as the mean ± standard deviation of three independent experiments. **P<0.01, vs. NC and BL groups. MUC1, mucin 1; siRNA, small interfering RNA; NC, negative control group (transfected with control-siRNA); BL, blank control group (non-transfected); siRNA, MUC1-siRNA group (transfected with MUC1-siRNA).