IDH2 and astrocytoma (excluding glioblastoma): A study of 45 samples from paired low-grade astrocytomas and subsequent secondary high-grade gliomas found no changes in IDH mutation status.8 Another study of 51 lower-grade glioma patients that underwent multiple biopsies established a temporal timeline where IDH mutation precedes TP53 mutation or 1p/19q codeletion based on the proportion of patients that developed these mutations over time.