Overexpression of Per1 and Per2 inhibits the growth of cancers cells (Gery et al., 2006; Hua et al., 2006) and increases apoptosis in tumor cells (Fu et al., 2002; Gery et al., 2006; Hua et al., 2006; Sun et al., 2010). The gene discussed is PER2; the disease is cancer.