LAUSR

INTRODUCTION "Diffuse midline glioma H3K27M-mutant" (a mutation genes encoding H3 histone variants) represents a defined pathologic entity since 2016 WHO CNS classifications and include midline structures, namely thalamus, brainstem and spinal cord. H3K27M mutant glioma responds more poorly and is associated with worse clinical outcome. Mutation detection is now diagnostic for 'diffused midline gliomas' We report on a case arising in an atypical non midline localization with an exceedingly adverse course.The present case arises the question of the possible meaning of the H3K27M-mutation also in high grade gliomas (HGG) arising from the cerebral hemispheres, and its implications from a prognostic and therapeutic view. CLINICAL PRESENTATION A 48-year-old woman was admitted with a mass arising from the splenium of the corpus callosum with bilateral hemispheric extension, displaying MRI characteristics typical of a HGG.Needle biopsy confirmed the diagnosis of "diffuse astrocytic neoplasm, WHO grade IV". Immunostaining of the tumor revealed the H3K27M-mutant nuclear expression. The patient was referred to adjuvant therapy and died 3 months after biopsy. CONCLUSIONS This experience highlights the possible negative prognostic impact of H3K27M-m and the possibility that the H3K27M-m could be a reliable prognostic indicator to be considered not only in diffuse midline gliomas but also in gliomas form the cerebral hemispheres. Since the rarity and limited knowledge on this specific mutation this experience, reports should be encouraged.