PER2 and colorectal cancer: Downregulation of PER2 expression is related to poor outcomes in several tumors, including chronic lymphocytic leukemia, renal cancer, head, and neck squamous cell carcinoma, colorectal cancer, and others (Momma et al., 2017; Xiong et al., 2018; Qiu et al., 2019; Wang et al., 2020).