DIFFUSE MIDLINE GLIOMAS, H3K27-ALTERED AS AN INTERDISCIPLINARY CHALLENGE

Abstract INTRODUCTION: Diffuse midline gliomas represent a particular challenge in treatment. DIPG behave like highly malignant glioma with extremely poor prognosis due to location and inoperability. Molecular genetic studies, complementary to classical histopathology, have found an entity for midline gliomas, newly described ten years ago and entered the WHO classification in 2016. This group of childhood tumor with DMG’s, H3K27-altered will be demonstrated in the following with 14 case reports from our clinic. METHODS: Clinical data of four patients with tectum/thalamic gliomas, six with diffuse intrinsic brainstem glioma, two with cerebellar, one with suprasellar, one with spinal glioma were retrospectively studied. MRI data, volume increase, contrast behavior was also analyzed. Tumor tissue was obtained by various surgical procedures and diagnostic workup included histopathology as well as genetics and epigenetics. RESULTS: 14 pediatric patients were treated from 2012 to 2021, median age 7,5 years. Leading symptoms were hydrocephalus, movement disorders, cranial nerve disorders. Four patients (29%) were partially resected, two (14%) received extended biopsy, seven (50%) were (stereo tactically) biopsied, one diagnosed by liquid biopsy (7%). Histological results revealed the presence of GBM in four cases (29 %). Subsequent methylome analyses confirmed that the tumors belonged to the group of diffuse midline gliomas, H3K27-altered. The other ten tumors (71%) were primarily assigned to this H3K27 group. CONCLUSION: The pediatric tumors of the brainstem, the further midline structures, including intraspinal manifestation show different MRI findings, histology, and clinical course. Complementary molecular genetic diagnosis is essential and a meaningful addition to the histological assignment. It is considered proven that the exclusivity of H3K27 – altered tumors of children and adolescents differs from that of IDH mutated gliomas and glioblastomas by their localization of hemispheric processes. Possible therapeutic approaches using targeted therapy require understanding of these oncological mechanisms.