PER2 and central nervous system cancer: A decreased expression of Per1 and or Per2 has been reported in numerous cancers: breast cancer (Winter et al., 2007), prostate cancer (Cao et al., 2009), pancreatic cancer (Suzuki et al., 2008), colorectal cancer (Mostafaie et al., 2009), chronic myeloid leukemia (Yang et al., 2011), gliomas (Fujioka et al., 2006; Xia et al., 2010), and intestinal epithelial neoplastic transformation (Yang et al., 2009).