DIPG-17. BIOPSY-PROVEN DIFFUSE MIDLINE GLIOMA IN ADOLESCENTS AND YOUNG ADULTS

INTRODUCTION Diffuse midline glioma (DMG) mostly affects young children. The newly-introduced disease entity DMG, H3K27M-mutant uniformly portends poor prognosis, and therefore that in the pons is usually treated based upon radiological diagnosis without histological confirmation. DMG is rarer in adolescents and young adults (AYA), and remains poorly characterized. In this study, we sought to investigate the clinical, pathological, and molecular profiles of DMG in AYA generation. METHODS Patients of age between 16 and 39 undergoing biopsy at the University of Tokyo Hospital between 2003 and 2019 were included in the study. Clinical data and images were retrospectively reviewed. Genetic analyses were performed in cases with abundant tissues. RESULTS Ten patients included 8 brainstem and 2 thalamic DMG. The median age was 25 years (range, 19–38). Pathological diagnosis was DMG, H3K27M-mutant in 3 patients, glioblastoma, IDH-mutant in 1, anaplastic astrocytoma, IDH-wildtype in 4, diffuse astrocytoma, IDH-mutant in 1, and diffuse astrocytoma, IDH-wildtype in 1. Genetic analyses detected H3F3A-K27M mutation in 2, HIST1H3B-K27M mutation in 1, IDH1-R132H mutation in 1, and IDH1-R132S mutation in 1. With a median follow-up of 23 months (range, 2–61), only 3 patients died 29–61 months after diagnosis, and the remaining 7 patients survived for 2–59 months. Neither IDH1 mutation nor H3K27M mutation was associated with survival in this series. CONCLUSION Survival of AYA patients with DMG was seemingly variable with some long survivors. H3K27M mutation was present in a subset of patients. A further study is warranted to correlate molecular profile with clinical pictures including patient survival.