IDH1 and central nervous system neoplasm: According to the guidelines of the 2016 WHO classification of CNS tumors, patients in the TCGA LGG cohort (n = 520) were classified into three groups for further analyses, including IDH1 wild-type, IDH1 mutations with 1p19q codeletion, and IDH1 mutations without 1p19q codeletion (Figure 2A).