Moreover, oncogene c-Myc was upregulated, while P53 was down regulated in the liver of both Per2m/m [18] and mice on chronic jet lag, with ablated Per2 circadian transcription in liver [21] This could explain the significant increase of DEN-induced liver cancers in mice or rats exposed to constant light or iterative shifts in light-dark cycles [22, 23]. Here, PER2 is linked to liver cancer.