Liquid biopsy in CNS tumors: Current status & future perspectives

Precise classification of central nervous system (CNS) malignancies is vital for the treatment and prognostication. Identification of noninvasive markers can be of importance to guide treatment decisions and in monitoring treatment response. CNS tumors are classified based on morphology with an essential complement of molecular changes, including mutations, amplifications, and methylation. Neuroimaging is the mainstay for initial diagnosis and monitoring tumor response with obvious limitations of imprecise tumor typing and no information on diagnostic, predictive and prognostic markers. Liquid biopsy has evolved as a diagnostic tool in body fluids and is being investigated as a surrogate for tissue biopsy in managing primary and metastatic brain tumors. Liquid biopsy refers to analyzing biological fluids such as peripheral blood, urine, pleural effusion, ascites, and cerebrospinal fluid (CSF); however, peripheral blood remains the primary source of fluid biopsy. The analytes include cell-free DNA (cfDNA) circulating tumor cells (CTCs), circulating micro RNAs (miRNAs), circulating proteins and extracellular vesicles (EVs). Analysis of these components is actively used for early cancer detection, auxiliary staging, prognosis assessment, detection of minimal residual disease (MRD), and monitoring drug resistance in various solid tumors. In recent years, liquid biopsy has been studied in CNS tumors, and analysis of CTCs and cfDNA have become relevant research topics. In the current review, we have explained the clinical potential of liquid biopsy in CNS tumors to assist in diagnosing and predicting prognosis and response to treatment.