1044 Liquid Biopsy for Glioblastoma: Utilizing Plasma Extracellular Vesicles for Tumor Diagnosis and Monitoring

INTRODUCTION: Glioblastoma (GBM), the deadliest brain tumor in adults, is traditionally diagnosed and characterized using neuroimaging and brain biopsies. These methods, however, suffer from limited specificity and sensitivity. The surgical risks associated with tumor sampling further complicate the monitoring of GBM's molecular progression. Extracellular vesicles (EVs) secreted by GBM cells, which cross the blood-brain barrier and carry tumor-derived molecules, present a promising avenue for the continuous evaluation of GBM presence and status. METHODS: We isolated EVs using SEC from plasma and characterized them via immunoblotting, flowcytometry, and TEM. The concentration and size of EVs were measured using TRPS. We compared EV levels in 50 GBM patients pre-surgery with those in non-GBM controls, which included 100 healthy individuals and 50 patients with pther brain malignancies. Longitudinal assessments of plasma EVs were performed in 44 GBM patients by comparing pre-operative and post-operative samples taken 72 hours after surgery. We analyzed surface markers using MACSPlex and proteomic analyses RESULTS: We found higher concentrations and sizes of plasma EVs in GBM patients compared to controls, with a noticeable decrease post-operatively. Multiplex flow cytometry indicated universal expression of CD9, CD63, and CD81 across all samples, with significant enrichment of CD63 and CD81 in GBM. The expression profiles of the other 34 markers were similar across all samples, suggesting dilution of tumor-derived EVs among non-tumor EVs. However, T-cell markers CD8 and HLA-DRDPDQ were more prevalent on GBM-derived EVs. Proteomic analysis identified over 2,000 proteins in all samples, with 117 being upregulated in GBM samples. CONCLUSIONS: Our findings suggest that monitoring circulating EV levels provides a reliable, non-invasive method for the differential diagnosis and follow-up of GBM patients. The combined analysis of EV concentration, size, and proteome offers potential as promising biomarkers for longitudinal monitoring of GBM, supporting the implementation of liquid biopsy in GBM care.