10210-STMO-13 CLINICAL AND GENETIC ANALYSIS OF ADULT THALAMIC GLIOMAS - SIGNIFICANCE OF H3K27M AND TERT MUTATIONS

Abstract

Abstract Adult thalamic glioma (ATG) is a rare but deep lesion that is difficult to remove and often refractory to treatment. The diffuse midline glioma (DMG), H3K27M-mutant, newly introduced in the WHO 2016 classification, constitutes part of ATG, but the significance of H3K27M mutations in adult ATG and the prognosis of thalamic DMG are variable and inconsistent among reports. We retrospectively analyzed clinical, pathological, and molecular characteristics of 45 consecutive ATG cases operated on at our institution from 2007 to 2022, and examined outcomes and prognostic factors. The median age was 45 years (range, 18-74), median preoperative KPS was 70% (range, 40-100), median maximum tumor diameter on MRI was 37 mm (range, 22.6-62.6), Gd contrast was present in 31, and bilateral disease was present in 8 patients. 31 patients underwent resection and 14 underwent biopsy. Differences in the surgical approach did not affect OS. WHO G2: 2, G3: 7, and G4: 36, and all IDH wild-type. The mPFS for all patients was 9.5 months and mOS was 26.0 months; G4 consisted of 19 DMG and 17 GBM with mOS of 30.4 months DMG vs. 12.4 months GBM (P=0.012). Analysis of all cases showed a trend toward better prognosis for H3K27M mutation cases (P=0.118), while TERT was significantly worse for the mutation type with 29.2 months for wild type vs. 9.3 months for the mutation type (P=0.026). In univariate analysis, age and TERT mutation status were prognostic factors for OS, and in multivariate analysis, WHO grade was a prognostic factor for OS in addition to these factors. In the past literature of pediatric cases, H3K27M mutation was often reported as a prognostic factor, but in the present study, TERT mutation was the prognostic factor, suggesting that the significance of H3 mutation in thalamic gliomas in adults and children is different.