PER2 and hepatocellular carcinoma: Notably, PLC/PRF/5 PER2 KD and PLC/PRF/5 PER2 KO cells acquired resistance to the antiproliferative effect of EVE and SOR, suggesting that reduced or absent PER2 expression, and its altered cellular localization, as observed in EveR and SorR cells, play a key role in the acquisition of drug resistance in HCC cell model.