LIQUID BIOPSY IN GLIOBLASTOMA (GBM)CHARACTERIZATION OF PLASMA EXTRACELLULAR VESICLES CONCENTRATION, SIZE AND CARGO FOR NON-INVASIVE GBM DIAGNOSIS, MONITORING AND IDENTIFICATION OF CIRCULATING BIOMARKERS

Glioblastoma (GBM) is a highly aggressive brain tumor that presents extensive heterogeneity and high recurrence rates. Current diagnostic and monitoring approaches, primarily relying on MRI and tissue biopsies, have limitations. MRI sensitivity is limited, and tissue sampling is invasive and may not accurately reflect tumor heterogeneity. Thus, the need for a non- invasive strategy to complement MRI and tissue profiling is critical to implement GBM management. Liquid biopsy, particularly through the analysis of Extracellular Vesicles (EVs), offers a promising avenue. We isolated EVs from 2 mL of plasma using Size Exclusion Chromatography and assessed their concentration and size with Tunable Resistive Pulse Sensing. We observed increased plasma EV levels in GBM patients compared to healthy controls and patients with other CNS malignancies, with a predominance of medium-sized EVs in GBM plasma. Post-surgery, EV levels decreased, suggesting their potential for monitoring disease progression. EV-associated DNA and total plasma exDNA analysis yielded limited insights into parental GBM mutations. Accordingly, shallow WGS of plasma exDNA revealed limited tumor- derived information. However, fragmentation patterns in total plasma exDNA showed differences between GBM patients and healthy controls. Proteomic analysis of plasma EVs effectively distinguished GBM samples from healthy and matched GBM post-surgery samples, allowing the identification of potential companion biomarkers to implement the specific diagnosis of GBM and its longitudinal monitoring.