Liquid biopsy for neuro-oncology: a non-invasive window into tumor biology

A liquid biopsy is a noninvasive method that analyzes blood and other bodily fluids, such as spinal fluid, urine, and saliva, to detect cancer, classify tumors, identify driver mutations, and monitor treatment responses. This technique involves the qualitative and quantitative analysis of biomarkers including but not limited to circulating tumor cells, cell-free DNA, circulating tumor DNA, microRNA, extracellular vesicles, and proteins. Its noninvasive nature makes it a promising tool for cancer diagnosis and treatment, especially for central nervous system (CNS) tumors, where obtaining a tissue biopsy carries significant surgical risks. Analysis can be conducted in both blood and spinal fluid, with the latter offering advantages for assessing CNS malignancies, such as gliomas and leptomeningeal disease, due to the blood-brain barrier's limitation on the release of tumor cells into the serum. However, challenges such as small sample sizes, variable sensitivity and specificity results, and the lack of standardized, cost-effective methods for biomarker enrichment and detection hinder its uniform adoption in clinical practice. This chapter explores the potential of liquid biopsy in oncology and highlights its advantages and limitations in managing brain tumor patients.