TP53 mutations in 94% and loss of α-thalassemia/mental-retardation-syndrome-X-linked (ATRX) in 33% of IDH mutant astrocytomas grade II/III and 1p/19q codeletions with IDH mutations classify the diffuse and anaplastic oligodendrogliomas [38–40]. This evidence concerns the gene IDH1 and oligodendroglioma.