Moreover, when compared with the control cells transfected with shNC, the cells with down-regulated expression of Id4 (transfected with shId4-1 and shId4-2) formed significantly less number of cell clones in Huh7 (P = 0.023 and 0.029) and PLC/PRF/5 (P = 0.012 and 0.002) cells (Fig. 3f), which suggested that Id4 knockdown inhibited the cell growth ability of HCC cells. Here, ID4 is linked to hepatocellular carcinoma.