IDH1 and central nervous system cancer: CSF is increasingly considered the most robust source for glioma liquid biopsies.10 Higher 2-HG has been previously reported in CSF of patients with IDH-mutant, compared to IDH-wild type, gliomas, with one study reporting 84% sensitivity and 90% specificity for IDH-mutant gliomas.1 However, the ability of D-2-HG to serve as a longitudinal monitoring biomarker responsive to therapy remains unknown.