Per2 mRNA levels did not differ significantly between the irradiated and untreated (control) groups at either ZT0 (t = –1.742, p > 0.1) or ZT8 (t = –0.642, p > 0.5) (Figure 1), when Per2 expression in glioma tissue was high or low, respectively. This evidence concerns the gene PER2 and central nervous system cancer.