P18.42.B TAU AND AMYLOID BETA PATHOLOGY IN IDH-MUTANT GLIOMA

Abstract BACKGROUND With an aging population the incidence of brain tumors and neurodegenerative diseases is increasing. Although biological associations between glioma and Alzheimer’s disease (AD) have been suggested, the frequency of comorbidity is insufficiently defined. We here screen tumor-adjacent cortex of a representative cohort of patients with low grade glioma for AD neuropathological changes (ADNC) specifically for phosphorylated tau (pTau) and amyloid beta (Abeta) deposition, microglial activation, amyloid precursor protein (APP) expression, diffuse axonal injury, and cortical tumor cell infiltration. MATERIAL AND METHODS A total of 85 patients with astrocytoma, IDH mutant, CNS-WHO grade 2-3, (N=37, median age: 39) and oligodendroglioma, IDH mutant and 1p-19q co-deleted, CNS-WHO grades 2-3 (N=48 median age: 50) were included. 2µm sections were immunohistochemically stained for the markers b-A4, t-AT8, NeuN, APP and Iba1. Whole slide quantification was performed using Matlab and QuPath codes. For a subset of 15 patients, longitudinal samples were available for analysis of post-treatment effects. RESULTS The median cell density in the tumor-adjacent cortex was 1355/mm2 for astrocytoma and 1392/mm2 for oligodendroglioma, which was significantly higher than in non-tumor infiltrated cortex (median: 1030 cells/mm², p-value