Miller et al. showed that tumor-derived DNA was detected in CSF from 41 of 85 patients (49.4%) and was associated with disease burden and adverse outcome, co-deletion of chromosome arms 1p and 19q, and mutations in the metabolic genes IDH1 or IDH2 were shared in all matched ctDNA-positive CSF tumor pairs [98]. Here, IDH2 is linked to neoplasm.