CLOCK and hepatocellular carcinoma: A proper functioning of the biological clock demonstrates tumor suppressing potential, whereas circadian rhythmicity disturbance, like that provoked by shift work in humans and chronic jet lag (CJL) in animal models, is an independent risk factor for HCC: for instance, it worked as tumor promoter in mice exposed to the hepatic carcinogen diethylnitrosamine (DEN) in combination with 8-h advance of light onset every 2 days [29].