Although it has long been known that the circadian rhythm plays crucial roles in physiology, this system had not attracted much attention until recently.1, 2 Common sense, epidemiological evidence, and biomedical studies all indicate that circadian rhythm and its orchestrating circadian clock genes are associated with cancer.3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 24, 25, 26, 27, 28, 29, 30, 31, 34 In this study, we systematically analyzed the dysregulation of circadian clock genes at different molecular levels across 20 types of cancer. This evidence concerns the gene CLOCK and cancer.