# Read the spinal fluid to track brain tumours without opening the skull

Source: https://onco.cc/ideas/idea-bio2-csf-ctdna-monitoring/  
OnCo record `idea-bio2-csf-ctdna-monitoring` (Idea). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Fluid taken from the lower back contains DNA from brain tumours. Testing it can diagnose, monitor and detect resistance without brain surgery.

## Summary

Cerebrospinal fluid ctDNA outperforms plasma for central nervous system tumours and detects leptomeningeal disease earlier than cytology or MRI in several studies, including paediatric brain tumours and lymphoma. Standardisation, assay validation and demonstrating that acting on the result improves outcomes are the missing pieces.

## Fields

- Kind: Idea
- Last checked: 2026-09-08
- Hypothesis: Serial cerebrospinal fluid ctDNA detects central nervous system progression a median of two months before MRI and identifies resistance mutations that change treatment in at least a quarter of patients.
- Rationale: Cerebrospinal fluid is a low-background compartment adjacent to the tumour, giving far higher tumour fraction than plasma. Lumbar puncture is routine, repeatable and cheap compared with any brain imaging or biopsy.
- Proposed test: A prospective monitoring cohort in glioma and in HER2-positive or ALK-positive brain metastasis with paired MRI, reporting lead time and the proportion of patients whose management changes.
- Maturity: early-clinical
- Actor: clinic

## Sources

- Bottleneck evidence (The brain: barrier and sanctuary): Stupp et al., Radiotherapy plus concomitant and adjuvant temozolomide for glioblastoma (NEJM 2005): https://doi.org/10.1056/NEJMoa043330

## Connected records

- cancers: [Diffuse large B-cell lymphoma](https://onco.cc/cancers/dlbcl/), [Glioma & glioblastoma](https://onco.cc/cancers/glioblastoma/), [HER2-positive breast cancer](https://onco.cc/cancers/breast-her2-positive/)
- technologies: [Liquid biopsy (ctDNA)](https://onco.cc/technologies/liquid-biopsy/), [MRD / molecular residual disease testing](https://onco.cc/technologies/mrd-testing/), [MRI](https://onco.cc/technologies/mri/)
- terms: [Circulating tumour DNA (ctDNA)](https://onco.cc/terms/ctdna/), [H3 K27M (diffuse midline glioma)](https://onco.cc/terms/h3k27m/), [Minimal / molecular residual disease (MRD)](https://onco.cc/terms/mrd/)
- bottlenecks: [Biomarkers are not validated or standardised](https://onco.cc/bottlenecks/b-biomarker-validation/), [Dormant cells and minimal residual disease](https://onco.cc/bottlenecks/b-dormancy-mrd/), [The brain: barrier and sanctuary](https://onco.cc/bottlenecks/b-brain-delivery/)

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