PER2 and cancer: For instance, the expression of Bmal1 is elevated in hepatoma6; altered expression of PER2 due to abnormal methylation is observed in glioma7; mutations of Ck1δ and Ck1ε are associated with an increased incidence of many cancer types.8, 9, 10, 11, 12, 13, 14Thirdly, it has been demonstrated that the expression change in certain rhythm genes regulates cancer progression.