IDH1 and astrocytoma (excluding glioblastoma): The highest percent decrease was observed in a patient with a largely intraventricular grade 4 IDH-mutant astrocytoma (D-2-HG: 99.1%; D/L ratio: 99.3% by POD2), consistent with the impact of ventricular contact on baseline CSF D-2-HG levels (Figure 1B).