IDH1 and oligodendroglioma: While the link between the loss of H3K27me3 immunoexpression (Figure 3B) and 1p/19q codeletion seemed to be confirmed in three separate studies [75,76,77], Pekmezci et al. discovered retained H3K27me3 in 7 out of 28 (25%) oligodendrogliomas and observed a co-occurrence of H3K27me3 loss along with retained or non-conclusive ATRX staining in 7 out of 74 (10%) IDH-mutant astrocytomas [78], emphasizing that H3K27me3 status alone cannot be used as an immunohistochemical surrogate for 1p/19q codeletion.