IDH1 and neoplasm: In contrast, subtype C3 contained a slightly higher proportion of cases of WHO grade II than did the other subtypes (χ2 test, FDR < 0.0001); meanwhile, the proportion of cases with mutant IDH1 in the tumor was significantly higher in subtype C3 than in subtypes C1 and C2 (χ2 test, FDR < 0.0001, Figures 3A, B).