PER2 and hepatocellular carcinoma: It was found that the mRNA levels of Per1, Per2, Per3 and Cry2 in HCC tissues were markedly decreased in comparison with those in the paired peritumoral tissues, while no significant difference was observed in the mRNA levels of CLOCK, BMAL1, Cry1 and CK1ɛ compared with the peritumoral tissues (Fig. 1).