Abstract
Background
Cystic brain metastases (CBM) present significant clinical challenges due to their heterogeneity and the limitations of current diagnostic methods in guiding treatment. Traditional tissue biopsies are invasive and may not capture tumour heterogeneity, while plasma circulating tumour DNA (ctDNA) analysis is impeded by the blood-brain barrier, leading to low sensitivity for detecting intracranial lesions. These limitations create a critical gap in the personalised management of patients with CBM.
Methods
We evaluated the utility of cyst fluid ctDNA as a minimally invasive biomarker for genetic profiling and treatment monitoring in CBM patients. ctDNA was extracted from cyst fluid, tumour tissue, plasma, and cerebrospinal fluid (CSF) samples collected from 18 patients. NGS was performed to analyse genetic mutations. Mutation detection rates and genetic heterogeneity were compared across different sample types. Dynamic changes in ctDNA mutation abundance in cyst fluid were assessed in relation to treatment responses.
Results
Cyst fluid ctDNA demonstrated a higher mutation detection rate and captured more significant genetic heterogeneity than plasma ctDNA and, in some cases, even matched tissue samples. Clinically significant mutations, including actionable driver genes such as EGFR and TP53, were identified in cyst fluid ctDNA but were undetectable in plasma. Moreover, dynamic changes in the abundance of ctDNA mutations in cyst fluid correlated with treatment responses, indicating its potential for real-time therapeutic efficacy monitoring.
Conclusions
Cyst fluid ctDNA provides a sensitive and comprehensive method for capturing the genetic landscape of CBM, effectively overcoming the limitations of tissue biopsies and plasma ctDNA analysis. By establishing a real-time molecular surveillance network, cyst fluid ctDNA analysis redefines precision neuro-oncology paradigms, transitioning CBM management from static histomolecular snapshots to adaptive therapeutic ecosystems.
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Data availability
The datasets generated during and/or analysed during the current study are not publicly available due to being part of an ongoing long-term study but are available from the corresponding author on reasonable request.
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Acknowledgements
We gratefully acknowledge Prof. Xun Jin and Prof. Manqing Cao for their discussions and advice.
Funding
This work was supported by the China Postdoctoral Science Foundation (grant no. 2024M762383) and the National Natural Science Foundation of China (grant no. 82103642, 82073276, 82273100, 82302999, 82272639).
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ZZ, MQC, and JYZ analysed the data; XYJ, PL, WLL, ZFS, CHS, QL, YZP, PW, LWL, YLL, KKY LM and QY provided methodology support and performed data validation; ZZ wrote the manuscript; XGW, XJ, and MQC supervised the study. All authors have read and agreed to the published version of the manuscript.
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All patient samples were collected with informed consent and approved by the Medical Ethical Committee of Tianjin Medical University Cancer Institute and Hospital (bc20250569). Study participants gave informed consent and provided written consent before tissue collection. Separate written informed consent was obtained from all participants whose identifiable images (e.g., radiological images) were included in this study. This consent explicitly permits the publication of the images in print and online formats. All methods were performed in accordance with the relevant guidelines and regulations.
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Zhang, Z., Jin, X., Yin, Q. et al. Cyst fluid ctDNA as a biomarker for genetic profiling and treatment monitoring in cystic brain metastases. Br J Cancer (2025). https://doi.org/10.1038/s41416-025-03047-9
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DOI: https://doi.org/10.1038/s41416-025-03047-9