Isomorphic diffuse glioma is a morphologically and molecularly distinct tumour entity with recurrent gene fusions of MYBL1 or MYB and a benign disease course.

The "isomorphic subtype of diffuse astrocytoma" was identified histologically in 2004 as a supratentorial, highly differentiated glioma with low cellularity, low proliferation and focal diffuse brain infiltration. Patients typically had seizures since childhood and all were operated on as adults. To define the position of these lesions among brain tumours, we histologically, molecularly and clinically analysed 26 histologically prototypical isomorphic diffuse gliomas. Immunohistochemically, they were GFAP-positive, MAP2-, OLIG2- and CD34-negative, nuclear ATRX-expression was retained and proliferation was low. All 24 cases sequenced were IDH-wildtype. In cluster analyses of DNA methylation data, isomorphic diffuse gliomas formed a group clearly distinct from other glial/glio-neuronal brain tumours and normal hemispheric tissue, most closely related to paediatric MYB/MYBL1-altered diffuse astrocytomas and angiocentric gliomas. Half of the isomorphic diffuse gliomas had copy number alterations of MYBL1 or MYB (13/25, 52%). Gene fusions of MYBL1 or MYB with various gene partners were identified in 11/22 (50%) and were associated with an increased RNA-expression of the respective MYB-family gene. Integrating copy number alterations and available RNA sequencing data, 20/26 (77%) of isomorphic diffuse gliomas demonstrated MYBL1 (54%) or MYB (23%) alterations. Clinically, 89% of patients were seizure-free after surgery and all had a good outcome. In summary, we here define a distinct benign tumour class belonging to the family of MYB/MYBL1-altered gliomas. Isomorphic diffuse glioma occurs both in children and adults, has a concise morphology, frequent MYBL1 and MYB alterations and a specific DNA methylation profile. As an exclusively histological diagnosis may be very challenging and as paediatric MYB/MYBL1-altered diffuse astrocytomas may have the same gene fusions, we consider DNA methylation profiling very helpful for their identification.

Citation

Annika K Wefers, Damian Stichel, Daniel Schrimpf, Roland Coras, Mélanie Pages, Arnault Tauziède-Espariat, Pascale Varlet, Daniel Schwarz, Figen Söylemezoglu, Ute Pohl, José Pimentel, Jochen Meyer, Ekkehard Hewer, Anna Japp, Abhijit Joshi, David E Reuss, Annekathrin Reinhardt, Philipp Sievers, M Belén Casalini, Azadeh Ebrahimi, Kristin Huang, Christian Koelsche, Hu Liang Low, Olinda Rebelo, Dina Marnoto, Albert J Becker, Ori Staszewski, Michel Mittelbronn, Martin Hasselblatt, Jens Schittenhelm, Edmund Cheesman, Ricardo Santos de Oliveira, Rosane Gomes P Queiroz, Elvis Terci Valera, Volkmar H Hans, Andrey Korshunov, Adriana Olar, Keith L Ligon, Stefan M Pfister, Zane Jaunmuktane, Sebastian Brandner, Ruth G Tatevossian, David W Ellison, Thomas S Jacques, Mrinalini Honavar, Eleonora Aronica, Maria Thom, Felix Sahm, Andreas von Deimling, David T W Jones, Ingmar Blumcke, David Capper. Isomorphic diffuse glioma is a morphologically and molecularly distinct tumour entity with recurrent gene fusions of MYBL1 or MYB and a benign disease course. Acta neuropathologica. 2020 Jan;139(1):193-209

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PMID: 31563982

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