In conclusion, while the mechanism of this subclonal mosaic IDH1 mutation remains uncertain, these data demonstrate that diffuse astrocytomas with subclonal IDH1 mutation may have worse clinical outcomes than their grade-matched clonal IDH1-mutant counterparts, although these patients have later recurrences and survive significantly longer than IDH-wild-type glioblastoma patients. Here, IDH1 is linked to diffuse astrocytoma.