IDH1 and astrocytoma (excluding glioblastoma): Recent genomic studies have provided evidence the large majority of oligodendrogliomas, particularly those with 1p/19q codeletion, exhibit the proneural gene expression signature, and like some glioblastomas originating from low-grade astrocytomas, have IDH1/IDH2 mutations and a G-CIMP phenotype; however, a very important point of divergence between these two types of tumors is the presence of TP53 mutations in G-CIMP+ glioblastomas and 1p/19q codeletion (mediated by a t(1;19) translocation) in oligodendrogliomas.