PER1 and cancer: In oral cancer, the different PER stand out as components with an impact on many aspects of carcinogenesis as increased downregulation of PER1 correlates with tumor progression [27], diurnal rhythms of PER1 are correlated with carcinogenesis [28], a tumor suppressor role is suggested for PER2 [29] and decreased levels of PER1 are associated with later stages of cancer and lymph node metastasis [30].