IDH1 and oligodendroglioma: Although the association between the loss of H3K27me3 immuno-expression and 1p/19q codeletion was confirmed in three independent studies [15, 22, 23], Peckmezci et al. found retained H3K27me3 in 7/28 (25%) oligodendrogliomas, and the co-occurrence of H3K27me3 loss and retained or non-conclusive ATRX staining in 7/74 (10%) IDH-mutant astrocytomas [15].