IDH1 and oligoastrocytoma: Only very rare reports describe tumours as “true” oligoastrocytomas, consisting of histologically and genetically discrete astrocytic (IDH-mutant, ATRX-mutant, 1p/19q-intact) and oligodendroglial (IDH-mutant, ATRX-wildtype, and 1p/19q-codeleted) mixed populations of tumour cells [36,37].