E2F4 and squamous cell lung carcinoma: The results indicated that the expression levels of E2F1, E2F2, E2F3, E2F5, E2F6, E2F7, and E2F8 were higher in lung adenocarcinoma and squamous cell lung carcinoma tissues than in lung tissues, whereas and the expression level of E2F4 was lower in the former than in the latter (Figure 2).