Above all, it is universally accepted that decreased PER1 expression in cancer closely correlates with tumor occurrence and progression by regulating downstream cell cycle genes and cancer-related genes, including Cyclin B1, Cyclin D, Cyclin E, WEE-1, C-MYC, KI-67, MDM2, and p53 [12, 18, 24]. This evidence concerns the gene CCNE1 and cancer.