Then the correlation analysis of DNA methylation level and transcript level of CCNE1 and E2F1 in 370 lung squamous cell carcinoma and 456 lung adenocarcinoma tissues from TCGA cohort was performed to identify the possible mechanism underlying CCNE1 and E2F1 DNA methylation in NSCLC by cBioPorta. Here, CCNE1 is linked to squamous cell lung carcinoma.