PATH-19. TERT PROMOTER MUTATION, NOT H3K27M MUTATION IS A PROGNOSTIC FACTOR FOR ADULT THALAMIC GLIOMAS

Abstract

Abstract Purpose Thalamic diffuse glioma is classified as WHO grade 4 as Diffuse midline glioma, H3K27M mutation if H3K27M mutation was found regardless of its histological findings, but the significance of H3K27M mutation is not clear compared with pediatric cases. We aimed to find genetic prognostic factors in adult thalamic diffuse gliomas. METHODS Pathological diagnosis, genetic abnormalities, and clinical course of adult newly diagnosed thalamic gliomas diagnosed and treated at our institution from July 2007 to March 2020 were retrospectively analyzed. RESULTS The number of cases was 41 (24 males, 17 females), median age was 47 years (20-75 years). Tumor localization was 20 cases on the left, 14 cases on the right, and 7 cases on both sides. The pathological diagnosis was GBM 15 cases, DMG 15 cases, AA-IDH WT 7 cases, DA-IDH WT 4 cases, all of which were IDH wild type, and none of them had IDH mutation and 1p/19q co-deletion. H3K27M mutations were found in 15 cases and TERT promoter mutations were found in 12 cases, both of which were completely mutually exclusive. Tumor resection and biopsy was performed in 33 and 8 cases, respectively, and the median removal rate was 95% for those who underwent tumor resection. The median PFS and OS of all cases were 14.3 months and 38 months, respectively, and the median OS by pathological diagnosis was GBM 12.4 months, DMG 47.4 months, AA-IDH WT 37.3 months, DA-IDH WT not reached. The median OS in the H3K27M mutant group (47.4 months) was significantly better (p=0.02) than that in the TERT promoter mutation group (13.5 months). CONCLUSION There was no IDH mutation in adult thalamic gliomas, the H3K27M mutation and the TERT promoter mutation were mutually exclusive. The H3K27M mutation was not a prognostic factor, but the TERT promoter mutation was the strongest prognostic factor.