P05.10.B LIQUID BIOPSY VS. STEREOTACTIC BIOPSY IN NON-RESECTABLE GLIOMAS: A MINIMALLY INVASIVE ALTERNATIVE WITH CLINICAL IMPACT?

Abstract BACKGROUND Stereotactic biopsies (STX) are essential for brain tumor diagnosis but carry significant risks, including permanent morbidity (3.1-6.4%) and mortality (0-1.7%)¹ with even higher complication rates for tumors in brainstem, thalamus or spinal cord. Liquid biopsy (LB) from cerebrospinal fluid (CSF) represents a minimally invasive alternative with low complications and the potential for repeated sampling. This study evaluates the diagnostic accuracy, clinical utility, complication rates, cost, and time to diagnosis of LB compared to STX in non-resectable gliomas. MATERIAL AND METHODS We included 45 patients with suspected brain tumors: 25 glioblastomas, 5 astrocytomas, 4 diffuse midline gliomas, 3 oligodendrogliomas, and 6 other gliomas. Tumor locations were supratentorial in 64.4% (n=29), infratentorial in 28.9% (n=13), and spinal in 6.7% (n=3). LB samples underwent standard CSF diagnostics, cytology, and targeted next-generation sequencing (NGS) using a 202-gene brain tumor panel STX samples were examined via histology, immunohistochemistry, and molecular diagnostics (e.g., 850K methylation profiling, NGS). LB results were categorized as: A (definitive tumor diagnosis), B (tumor detected but unclassified), or 0 (no tumor detected). STX diagnoses followed current WHO classification criteria. RESULTS Tumors were detected in all STX samples. LB identified tumors in 86.7% (n=38) of cases, while 13.3% (n=7) were false negatives. Among ctDNA-positive LBs, 51.1% (n=23) received an A-diagnosis and 31.2% (n=14) a B-diagnosis. Notably, 6.7% (n=3) of B-diagnoses remained inconclusive even after STX. Severe complications of STX occurred in 31.1% (n=13) of biopsies, with persistent morbidity at 3 months in 15.6% (n=7). Complication rates varied by location: 13.8% in supratentorial (4/29), 46.2% in infratentorial (6/13), and 100.0% in spinal tumors (3/3). No complications were attributed to LB. Based on LB findings, treatment decisions aligned with current guidelines were feasible in 31.6% (n=12) of ctDNA-positive cases (A and B diagnoses). Direct costs were lower for LB compared to STX. CONCLUSION LB is a promising, less invasive alternative to STX, especially in deep-seated, non-resectable gliomas. While STX remains the diagnostic gold standard, LB may accelerate diagnostic workflows and significantly reduce complication rates, particularly for infratentorial and spinal tumors. Further studies are warranted to refine its diagnostic yield and clinical integration in neuro-oncology.