For example, low Per1 expression in lung cancer was not related to prognosis [28]; downregulated Per2 and Per3 expression were not correlated with gastric and colorectal cancer (CRC) prognosis [29, 30]; low Cry1 expression was not an independent prognostic factor for ovarian cancer [31];reduced expression of Bmal1 and CLOCK were not associated with lung cancer survival and CRC outcomes[28, 30]; Moreover, some studies even implied that overexpression of some of these genes was associated with unfavorable prognosis in patients with cancers. Here, PER2 is linked to cancer.