IDH1 and oligodendroglioma: As in non-enhancing tumors, there was no GBM in patients younger than 50 years, a subgroup of 10 male and 6 female patients that comprised five glioneuronal/neuronal grade 1 tumors (four gangliogliomas and one angiocentric glioma) and 11 diffuse gliomas of lower grade (two oligodendrogliomas, IDH mutated and 1p/19q co-deleted, grade 2; one astrocytoma, IDH mutated, grade 2; five astrocytomas, NOS, grade 2, and three anaplastic astrocytomas, NOS, grade 3).