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Year : 2021  |  Volume : 64  |  Issue : 2  |  Page : 351-353
Diffuse midline glioma-H3K27M mutant. A novel entity with a defining and specific IHC marker

Department of Pathology, Dharamshila Narayana Superspeciality Hospital, New Delhi, India

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Date of Submission02-Apr-2020
Date of Decision19-May-2020
Date of Acceptance04-Aug-2020
Date of Web Publication9-Apr-2021


Diffuse Midline Glioma-H3K27M mutant is a specific entity added to the 2016 updated WHO classification of CNS tumours that represents the majority of diffuse intrinsic pontine gliomas, although identical tumours are also found elsewhere in the midline. They are aggressive tumours with a poor prognosis and considered WHO GRADE IV regardless of histological features.[1],[2] Patients with H3K27M–mutant gliomas in unusual anatomical locations have a better prognosis than those with corresponding tumors in the brainstem and this helps in the treatment stratification of diffuse gliomas. Extrapolating from the clinicopathologic features of diffuse pontine gliomas and the poor prognosis seen in pediatric diffuse midline gliomas with H3 K27M mutations, the presence of an H3 K27M mutation in an infiltrating astrocytoma of the midline automatically confers a grade IV status.[2],[3] This case emphasizes the need for Immunohistochemistry using a mutation-specific H3K27M antibody in all cases of midline gliomas.

Keywords: Diffuse midline glioma, grade IV, H3K27M, prognosis

How to cite this article:
Agarwal P, Aiyer HM. Diffuse midline glioma-H3K27M mutant. A novel entity with a defining and specific IHC marker. Indian J Pathol Microbiol 2021;64:351-3

How to cite this URL:
Agarwal P, Aiyer HM. Diffuse midline glioma-H3K27M mutant. A novel entity with a defining and specific IHC marker. Indian J Pathol Microbiol [serial online] 2021 [cited 2021 May 16];64:351-3. Available from: https://www.ijpmonline.org/text.asp?2021/64/2/351/313278

   Introduction Top

The updated 2016 WHO classification of tumours of the CNS defines a novel category Diffuse Midline Glioma with H3K27M mutation. Previously, these tumours were diagnosed as diffuse gliomas and further classified and graded as diffuse astrocytomas, anaplastic astrocytomas and glioblastomas. These diffuse gliomas are found more frequently in children and rarely in adults and seen in midline structures (thalamus, brainstem, and spinal cord). For diffuse midline gliomas in general, the finding of an H3K27M mutation confers a worse prognosis than that of wild type cases. These mutations occur in the histone H3F3A gene (K27M mutations) or less frequently in HIST1H3B and HIST2H3C genes.[2],[4]

These tumors occur often in pediatric patients and show an adverse prognosis with a median survival of 7-11 months.[5]

The optimal adjuvant treatment after maximal surgical resection and radiotherapy is currently unknown.[1],[4]

   Case History Top

We report a case of a Diffuse Midline Glioma, H3K27M mutant in a 10-year 8-month-old male who presented with left upper and lower limb weakness. A brain MRI revealed a heterogenous expansile peripherally enhancing mass in the right thalamus.

After neurosurgical intervention, a stereotactic needle biopsy was sent for histopathological examination composed of four soft tissue bits measuring 0.2–0.4 cm each.

On microscopic examination, the tumour was characterised by atypical glial cells in a fibrillary background without necrosis, microvascular proliferation or mitosis, corresponding histologically to Diffuse Astrocytoma, WHO Grade II [Figure 1]a and [Figure 1]b.
Figure 1: (a) Microphotograph of Atypical Glial Cells in a Fibrillary Background (Haematoxylin And Eosin Stain × 200). (b) Microphotograph of Atypical Glial Cells (Haematoxylin And Eosin ×400)

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In view of the age of the patient and location of the lesion, Immunohistochemistry was advised.

Immunohistochemically, the neoplastic cells were Non-Immunoreactive for IDH-1-R132H (i.e., IDH - wild type) [Figure 2]a with loss of nuclear expression of ATRX [Figure 2]b (signifying ATRX mutation) and were diffusely and strongly Immunoreactive for H3K27M (Clone RM-192) [Figure 2]c and p53 [Figure 2]d.
Figure 2: (a) Non Immuno Reactive In Neoplastic Cells (IHC Stain, IDH ×400). (b) Non Immunoreactive for ATRX In Tumour Cells (IHC Stain, ATRX, ×400). (c) Immunoreactive For H3K27M In Tumour Cells (IHC Stain, H3K27M ×400). (d) Immunoreactive For p53 In Tumour Cells (IHC Stain, p53 ×400)

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After a thorough histopathological and immunohistochemical evaluation, a diagnosis of Diffuse Midline Glioma, H3K27M mutant, corresponding to WHO Grade IV was made.

The patient was put on radiotherapy and is alive after 3 months with some regression of mass but still persistent disease on imaging.

   Discussion Top

Gliomas are the most frequent primary intra-axial neoplasms. Frequent alterations in the genes involved in chromatin remodelling pathways in gliomas, for example, recurrent mutations in the H3 Histone family 3A (H3F3A) and alpha-thalassemia/mental retardation syndrome, X-linked gene (ATRX) have been identified in pediatric gliomas. ATRX loss is also significantly associated with a H3F3A mutation and IDH-1 mutations.[6]

This newly defined entity represents a critical diagnostic challenge for practising surgical pathologists. The importance of recognizing this entity relates to the fact that even if the tumour is conventionally graded as grade II astrocytoma histologically, it behaves like a much more aggressive tumour if H3K27M mutant and is classified as WHO Grade IV irrespective of histology. This case underlines the importance of immunohistochemical evaluation to correctly subtype these gliomas due to its prognostic and clinical significance. Clinically, immunostaining for H3 K27M should be first line for a radiologically suspected midline glioma, particularly when limited tissue is available and/or histopathologic diagnosis is not sufficient for determining malignancy. For these purposes, this study encourages the incorporation of this immunostaining in the evaluation of all midline infiltrating gliomas.[3],[7]

Our findings are corroborated by other studies wherein the histology varied from WHO GRADE II-IV Astrocytoma and also primitive neuroectodermal tumour (PNET) or Pilocytic Astrocytoma (PA)-like histology. Therefore, clinically Classic Diffuse Gliomas represent a diverse histolologic spectrum including multiple cases that fit the WHO criteria of grade II Astrocytoma as in our case but which nevertheless behave clinically as high-grade astrocytomas and harbor the histone K327M mutation.[3],[4],[7]

   Conclusion Top

This wide variation in histologies found to harbor H3K27M mutations makes it imperative to test for this mutation in pediatric and adult gliomas. A mutant-specific antibody that detects K27M mutations in both H3.1 and H3.3 is now widely accepted as a surrogate for molecular testing. Not only is this testing important for proper classification but also prognosis as H3K27M-mutant tumours do worse, emphasizing the need for integration of IHC in the routine evaluation of gliomas including Diffuse Midline Glioma, H3K27M-mutant.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Louis DN, Perry A, Reifenberger G, von Deimling A, Figarella-Branger D, Cavenee WK, et al. The 2016 world health organization classification of tumors of the central nervous system: A summary. Acta Neuropathol 2016;131:803-20.  Back to cited text no. 1
Castel D, Philippe C, Calmon R, Le Dret L, Truffaux N, Boddaert N, et al. Histone H3F3A and HIST1H3B K27M mutations define two subgroups of diffuse intrinsic pontine gliomas with different prognosis and phenotypes. Acta Neuropathol 2015;130:815-27.  Back to cited text no. 2
Wu G, Broniscer A, McEachron TA, Lu C, Paugh BS, Becksfort J, et al. Somatic histone H3 alterations in pediatric diffuse intrinsic pontine gliomas and non-brainstem glioblastomas. Nat Genet 2012;44:251-3.  Back to cited text no. 3
Louis DN, Ohgaki H, Wiestler OD, Cavenee WK, Burger PC, Jouvet A, et al. The 2007 WHO classification of tumours of the central nervous system. Acta Neuropathol 2007;114:97-109.  Back to cited text no. 4
Buczkowicz P, Bartels U, Bouffet E, Becher O, Hawkins C. Histopathological spectrum of paediatric diffuse intrinsic pontine glioma: Diagnostic and therapeutic implications. Acta Neuropathol 2014;128:573-81.  Back to cited text no. 5
Louis DN, Giannini C, Capper D, Paulus W, Branger D, Lopez B, et al. cIMPACT-NOW update 2: Diagnostic clarifications for diffuse midline glioma, H3 K27M-mutant and diffuse astrocytoma/anaplastic astrocytoma, IDH-mutant. Acta Neuropathol 135:639-42.  Back to cited text no. 6
Kleinschmidt-DeMasters BK, Mulcahy Levy JM. H3K27M-mutant gliomas in adults vs. children share similar histological features and adverse prognosis. Clin Neuropathol 2018;37:53-63.  Back to cited text no. 7

Correspondence Address:
Prachi Agarwal
Department of Pathology, Dharamshila Narayana Superspeciality Hospital, New Delhi
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/IJPM.IJPM_287_20

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