IDH1 and oligodendroglioma: Among the 42 patients with IDH-mutant tumors (hereafter referred to as IDH+) there were 29(69%) grade 2 gliomas (13 oligodendrogliomas; 16 astrocytomas) and 13(31%) grade 3 gliomas (3 oligodendrogliomas; 10 astrocytomas).