RRM2 positivity was significantly higher in WHO grade IV gliomas (mean=9.3%) than in WHO grade III (mean=4.15%; P=0.0134, One-way ANOVA and Tukey’s multiple comparisons test) and grade II (mean=1.1%; P<0.0001, One-way ANOVA and Tukey’s multiple comparisons test), whereas there was no significant difference in mean positivity between WHO grade II and III tumours (Fig. 6e). This evidence concerns the gene RRM2 and central nervous system cancer.