IDH1 and central nervous system cancer: Unfortunately, surveillance via MR imaging is limited by the frequent presence of pseudoprogression following radiation or immunotherapies and suboptimal sensitivity to early tumor regrowth.7 Peripheral blood D-2-HG has yielded poor sensitivity to IDH-mutant gliomas.8 Additionally, although magnetic resonance spectroscopy for 2-HG has shown pharmacodynamic responses to IDH inhibitors,9 technical challenges have impeded clinical application outside of select centers.