BIOM-30. LONGITUDINAL CEREBROSPINAL FLUID D-2-HYDROXYGLUTARATE FOR DISEASE MONITORING IN PATIENTS WITH IDH-MUTANT GLIOMAS

Abstract Imaging-based monitoring of gliomas is hampered by treatment-related changes, as well as the insidious growth of gliomas harboring the isocitrate dehydrogenase (IDH) mutation. The IDH mutation results in elevated D-2-hydroxyglutarate (D-2-HG), which is detectable in cerebrospinal fluid (CSF) that can be accessed longitudinally from multiple compartments, including cranially via CSF access devices. As such, we evaluated the early utility of CSF D-2-HG as a serially accessible biomarker for IDH-mutant gliomas. A CLIA-approved gas chromatography mass spectrometry assay was developed for CSF D- and L-2-HG. Lumbar and cranial CSF samples were collected from patients with IDH-mutant gliomas or IDH-wild-type brain tumors and non-tumor pathologies via surgical field collection, lumbar punctures, Ommaya reservoirs, and ventriculoperitoneal shunts. First, to confirm the ability of CSF D-2-HG to detect IDH-mutant gliomas, concentrations were compared between IDH-mutant gliomas and wild-type lesions. Cranial, but not lumbar, CSF D-2-HG distinguished primary IDH-mutant gliomas from IDH-wild type lesions (cranial AUC= 0.89, 95% confidence interval (CI)= 0.80-0.97); lumbar AUC= 0.52, 95% CI=0.28-0.76). Indeed, CSF D-2-HG was significantly higher in cranial than lumbar samples from IDH-mutant glioma patients (median lumbar=0.20 μM, cranial = 1.72 μM; p<0.0001), confirming a significantly elevated abundance of CSF D-2-HG only in cranial CSF from IDH-mutant gliomas. Then, response to cytoreduction was evaluated, demonstrating that cranial CSF D-2-HG levels decreased to 0.54x of baseline with resection in seventeen patients (p=0.0129). Changes in tumor-to-CSF contact impacted the serial evaluation of CSF D-2-HG prior to versus after chemoradiation in some patients. Nevertheless, in patients with grade 4 IDH-mutant astrocytomas, serial cranial CSF D-2-HG increased with disease progression and differentiated stability from pseudoprogression when tumor-CSF contact was sufficient. In conclusion, serial cranial CSF D-2-HG shows promise as a monitoring biomarker in patients with IDH-mutant gliomas, although anatomic variables must be considered in parallel to CSF D-2-HG evaluation.