Following the current guideline, of the 14 oligoastrocytomas initially observed, 5 were reclassified to diffuse astrocytoma, IDH mutant; 5 were diffuse astrocytoma, IDH-wild-type; and 4 were oligodendrogliomas, IDH mutant, 1p19q co-deleted. This evidence concerns the gene IDH1 and oligoastrocytoma.