In LGGs, 94% (15/16) of tumors with malignant transformation upon recurrence harbored IDH1 mutation, whereas 77% (10/13) of tumors recurring without malignant transformationharbored IDH1 mutation(p = 0.299).One case of oligoastrocytoma (WHO grade II) harbored IDH2 mutation and recurred as anaplastic oligoastrocytoma (WHO grade III). Here, IDH1 is linked to anaplastic oligoastrocytoma.