E2F1 and retinoblastoma: Previous study demonstrated that E2F-1 overexpression in lung tumors and nonfamilial retinoblastoma were significantly associated with a high Ki67 index [44, 45], a well-known proliferation marker for the evaluation of cell proliferation [46], suggesting that E2F-1 may block the DDP-resistant NPC cell cycle in G1 phase to reduce the proliferation of cells and enhance the sensitivity to DDP.