In both the TCGA and GEO datasets, the candidate clock genes cryptochrome circadian regulator 1 (CRY1), cryptochrome circadian regulator 2 (CRY2), F-box and leucine rich repeat protein 3 (FBXL3), timeless circadian clock (TIM), and G protein-coupled estrogen receptor 1 (GPER1) were identified based on their consistently lower or higher expression levels in lung adenocarcinoma tissues than in normal tissues (Additional file 1: Fig. S6A-C). Here, CRY2 is linked to lung adenocarcinoma.