Tumor-derived ctDNA was detected in CSF from 42 out of 85 patients (49.4%) and was associated with a disease burden and adverse outcome.The genomic landscape of glioma in the CSF revealed various genetic alterations and resembled the genomes of tumor biopsies.Co-deletion of chromosome arms 1p and 19q (1p/19q codeletion) and mutations in IDH1 or IDH21,2 were shared in all matched ctDNA-positive CSF-tumor pairs.Contrastingly, growth factor receptor signaling pathways showed considerable evolution. The gene discussed is IDH1; the disease is central nervous system cancer.