IDH1 and central nervous system cancer: Finally, the IDH1 inhibitor olutasidenib was evaluated in a phase Ib/II study, in 26 patients with recurrent IDH-1 mutant gliomas of whom 88% had enhancing tumors.144 Fifty-eight percent of the patients had a grade 3 glioma, and 27% had a grade 4 astrocytoma.