Cerebrospinal Fluid in Pediatric Neuro-Oncology: Molecular Diagnosis, Disease Monitoring, and Clinical Translation

Pediatric brain and other central nervous system (CNS) tumors remain a leading cause of cancer-related death in children, while contemporary management increasingly depends on molecular classification, risk stratification, and longitudinal disease assessment. Yet tissue-based profiling has major limitations in pediatric neuro-oncology, particularly for deep-seated, eloquent, or surgically hazardous tumors and when repeat sampling is impractical. For primary CNS tumors, cerebrospinal fluid is generally more informative than plasma because it is anatomically closer to the tumor and more enriched for tumor-derived material. This narrative review summarizes current and emerging applications of cerebrospinal fluid in pediatric neuro-oncology, from conventional staging to molecular diagnosis, methylation-based classification, measurable residual disease detection, pharmacodynamic monitoring, and relapse surveillance. We discuss the biological rationale for cerebrospinal fluid analysis, major pre-analytical and technical determinants of assay performance, and the strengths and limitations of key analyte classes, including cytology, circulating tumor cells, cell-free DNA, RNA, extracellular vesicles, proteins, and metabolites. We also summarize how these approaches are being applied across major pediatric central nervous system tumor entities. Cerebrospinal fluid liquid biopsy is unlikely to replace tissue or imaging, but is increasingly positioned to complement both in precision pediatric neuro-oncology.