CDK4 and neoplasm: The p53 signalling pathway and its key elements such as CDK2NA, CHEK2, CDK4, CCNE1, CCNB3, TP53AIP1, IGFBP3, SERPINB5, GTSE1 and TP73 were highly upregulated in LUSC tumours when compared with their matched normal tissue controls (Fig. 3B) but not in LUAD tumours (Fig. 3C).