P05.15.A LIQUID BIOPSY FOR GLIOBLASTOMA: PLASMA EXTRACELLULAR VESICLES FOR TUMOR DIAGNOSIS, MONITORING, AND PATIENT STRATIFICATION

Abstract BACKGROUND The current therapeutic arsenal for glioblastoma (GBM)—including MRI, CT, surgery, chemotherapy, and radiotherapy—remains insufficient for curing this disease. Precision medicine represents the only viable path toward effective treatment, relying on robust biomarkers capable of diagnosing, characterizing, and monitoring the disease while enabling patient stratification. However, a truly effective liquid biopsy for GBM is still lacking. MATERIAL AND METHODS We isolated extracellular vesicles (EVs) from plasma using size-exclusion chromatography (SEC) and characterized them according to established guidelines. EV concentration and size were measured via tunable resistive pulse sensing (TRPS). We compared EV levels in 62 GBM patients before surgery with non-GBM controls, including 79 healthy individuals and 50 patients with brain malignancies that mimic GBM on neuroimaging. Longitudinal plasma EV assessments were performed in 44 GBM patients. EV surface markers and proteomic profiles were analyzed using mass spectrometry in plasma samples from 27 GBM patients and 38 healthy individuals. RESULTS Plasma EV concentration and mean size significantly differ between GBM patients and controls. Following surgery, both parameters become comparable to healthy controls but increase again upon tumor recurrence. EV size and concentration effectively distinguish GBM from control groups (C1 and C2), achieving near-perfect AUC (Area Under the Curve) values, indicative of high sensitivity and specificity. The AUC for EV concentration in GBM vs. other brain tumors is affected by the heterogeneity introduced by brain metastases. EV size is a predictive biomarker for response to radio- and chemotherapy. Longitudinal monitoring of EV concentration reflects GBM progression, even preceding radiological evidence on MRI. Proteomic analysis identified over 2,000 proteins across all samples, with 117 upregulated in GBM patients and enriched in complement cascade pathways. CONCLUSION Our findings demonstrate that tracking circulating EV parameters is a highly sensitive and specific, non-invasive approach for GBM differential diagnosis, patient stratification, and follow-up. The combined analysis of EV concentration, size, and proteome offers promising biomarkers for longitudinal GBM monitoring, supporting the advancement of liquid biopsy in GBM clinical management.