According to this system, adult-type diffuse gliomas can be classified into three main entities, which comprise astrocytomas (IDH-mutated gliomas without 1p/19q co-deletion), oligodendrogliomas (IDH-mutated gliomas with 1p/19q co-deletion) and glioblastomas (gliomas without IDH mutation), with an additional group of very rare IDH wildtype tumors not classified as glioblastomas (Figure 3) [24,25,26]. Here, IDH1 is linked to oligodendroglioma.