BIOM-35. DIAGNOSTIC POTENTIAL OF SOLUBLE CD163 IN THE CSF FOR GLIOMA GRADING AND IMMUNE PROFILING

Abstract BACKGROUND The tumor microenvironment (TME) is a critical determinant of glioma progression. Macrophages, particularly the anti-inflammatory M2 subtype, are key constituents of the TME. Tumor-associated macrophages (TAMs), predominantly M2 phenotype, express the surface marker CD163. A soluble form of CD163 (sCD163) can be detected in the cerebrospinal fluid (CSF). Although tissue CD163 expression has been linked to glioma grade and prognosis, the relevance of CSF sCD163 levels remains unexplored. METHODS We retrospectively analyzed 105 patients with WHO grade 2 or higher gliomas who underwent biopsy or surgical resection between 2006 and 2023, with archived preoperative CSF samples. CSF sCD163 levels were quantified using ELISA and Bio-Plex Pro Human Inflammation Assays. CD163 expression in tumor tissues was evaluated by immunohistochemistry. We examined associations among CSF sCD163 levels, tissue CD163 expression, WHO grade, and IDH mutation status. RESULTS The cohort included 11 patients with grade 2, 5 with grade 3, and 89 with grade 4 gliomas. IDH mutations were identified in 22 cases (21.0%). CSF sCD163 levels showed a strong positive correlation with CD163 expression in tumor tissue (p < 0.0001). Both CSF sCD163 and tissue CD163 levels were significantly elevated in grade 4 gliomas compared to grades 2/3 (p < 0.0001), and in IDH wild-type tumors compared to IDH-mutant tumors (p < 0.0001). CONCLUSION CSF sCD163 levels reflect M2 macrophage infiltration in gliomas and are associated with tumor grade and IDH mutation status. These findings suggest that sCD163 may serve as a less-invasive biomarker for evaluating the immune microenvironment in gliomas and support its potential utility in glioma classification and prognosis.