PER2 and hepatocellular carcinoma: The results from the current study demonstrated that, among the HCC cell lines, cell models derived from metastatic lesions exhibited lower PER2 mRNA expression compared to cell lines derived from primary tumors, thus raising the hypothesis that reduced PER2 expression could have a causal role in the acquisition of metastatic phenotype, characterized by gained mesenchymal features, uncontrolled cellular growth capacity, and drug resistance.