E2F4 and head and neck squamous cell carcinoma: In the unpaired comparison, we found that the mRNA expressions of all E2Fs in HNSCC patients were significantly higher than those of normal tissues (P < 0.05) (Fig. 1A-H) and the differences were more significant in E2F1, E2F3, E2F4, E2F5, E2F6, and E2F7 (P < 0.001).