PER2 and cancer: For example, low Per1, Per2 and Per3 expressions in different cancers were found to correlate with worse histological grade and poor prognosis [3, 5, 11–22]; Cry2 was reported downregulated in breast and pancreatic cancer and its low expression was associated with higher tumor grade and shorter survival time [23, 24]; reduced Bmal1 and CLOCK expressions were confirmed to result in poor outcome of colon, pancreatic, kidney, head and neck cancers [15, 25, 26]; low Npas2 expression was also found to be related with worse overall survival (OS) in colorectal and breast cancers [9, 27].