Diffuse Midline Gliomas with Histone H3-K27M Mutation: A Series of 47 Cases Assessing the Spectrum of Morphologic Variation and Associated Genetic Alterations

Abstract

Somatic mutations of the H3F3A and HIST1H3B genes encoding the histone H3 variants, H3.3 and H3.1, were recently identified in high-grade gliomas arising in the thalamus, pons and spinal cord of children and young adults. However, the complete range of patients and locations in which these tumors arise, as well as the morphologic spectrum and associated genetic alterations remain undefined. Here, we describe a series of 47 diffuse midline gliomas with histone H3-K27M mutation. The 25 male and 22 female patients ranged in age from 2 to 65 years (median = 14). Tumors were centered not only in the pons, thalamus, and spinal cord, but also in the third ventricle, hypothalamus, pineal region and cerebellum. Patients with pontine tumors were younger (median = 7 years) than those with thalamic (median = 24 years) or spinal (median = 25 years) tumors. A wide morphologic spectrum was encountered including gliomas with giant cells, epithelioid and rhabdoid cells, primitive neuroectodermal tumor (PNET)-like foci, neuropil-like islands, pilomyxoid features, ependymal-like areas, sarcomatous transformation, ganglionic differentiation and pleomorphic xanthoastrocytoma (PXA)-like areas. In this series, histone H3-K27M mutation was mutually exclusive with IDH1 mutation and EGFR amplification, rarely co-occurred with BRAF-V600E mutation, and was commonly associated with p53 overexpression, ATRX loss (except in pontine gliomas), and monosomy 10.

Keywords: DIPG; H3F3A; HIST1H3B; K27M mutation; astrocytoma; diffuse intrinsic pontine glioma; diffuse midline glioma; glioblastoma; histone H3.1; histone H3.3.

Figure 1

Age distribution of the 47 patients with diffuse midline gliomas with histone H3‐K27M mutation at time of initial diagnosis plotted by tumor site. Pons, 17 cases; thalamus, 15 cases; spinal cord, nine cases; other midline sites, six cases.

Figure 2

Example of a diffuse midline glioma negative for histone H3‐K27M mutation. A. H&E stained section of a glioblastoma arising in the medulla of a 46‐year‐old man. B. Immunohistochemistry for histone H3‐K27M mutant protein showed nonspecific cytoplasmic staining in admixed microglia and macrophages with no staining of tumor nuclei.

Figure 3

Pathologic features of a diffuse midline glioma with histone H3‐K27M mutation arising in the pons in an 8‐year‐old boy from the initial biopsy and at autopsy following palliative radiation and chemotherapy. A. Mid‐sagittal T2 FLAIR image at time of presentation demonstrating a nonenhancing, T2‐hyperintense mass expanding the pons with probable infiltration into the adjacent cerebellum. B. H&E stained section from a diagnostic biopsy performed at the time of presentation showing a highly cellular infiltrative astrocytoma with scattered mitotic figures. C. Immunohistochemical stain for histone H3‐K27M mutant protein showing strong nuclear positivity in tumor cells. D,E. Gross photographs of an axial section through the pons (D) and coronal section through the cerebellum (E) from the autopsy performed 12 months after the initial diagnostic biopsy following palliative radiation and chemotherapy with bevacizumab. The pons and cerebellum are markedly expanded and distorted by the tumor and show multiple foci of radiation‐induced necrosis. F,G. H&E stained section from the left cerebellar cortex and corresponding immunohistochemical stain for histone H3‐K27M mutant protein showing massive infiltration by neoplastic astrocytes with prominent subpial accumulation. H. Immunohistochemical stain for histone H3‐K27M from the midbrain highlights cranial nerve infiltration by the tumor cells. I. H&E stained cross‐section of a cranial nerve showing numerous neoplastic astrocytes within the endoneurium.

Figure 4

Examples of diffuse midline gliomas with histone H3‐K27M mutation arising in midline sites other than the thalamus, pons, or spinal cord. A–C. Glioblastoma arising in the cerebellum of a 9‐year‐old boy. (A) Preoperative axial T1 postcontrast MR image demonstrating a peripherally enhancing mass within the left cerebellar white matter and cerebellar peduncle. H&E stained section showing a highly pleomorphic infiltrating astrocytoma with microvascular proliferation (B), and immunohistochemical stain for histone H3‐K27M mutant protein showing strong nuclear positivity in tumor cells (C). D–F. Anaplastic astrocytoma centered in the pineal region of a 65‐year‐old man. (D) Preoperative axial postcontrast CT image demonstrating a faintly enhancing mass in the pineal region. H&E stained section showing an infiltrative astrocytoma with scattered mitotic figures (E), and immunohistochemical stain for histone H3‐K27M mutant protein showing strong nuclear positivity in tumor cells (F). G–I. Glioblastoma arising in the third ventricle in a 19‐year‐old woman. (G) Coronal T1 postcontrast MR image taken following stereotactic biopsy showing a peripherally enhancing mass centered in the third ventricle near the foramen of Monro. H&E stained section showing an infiltrative astrocytoma with clear cytoplasm and well‐developed microvascular proliferation (H), and immunohistochemical stain for histone H3‐K27M mutant protein showing strong nuclear positivity in tumor cells.

Figure 5

Examples of morphologic variation encountered in diffuse midline gliomas with histone H3‐K27M mutation. A,B. Glioblastoma with frequent giant cells arising in the thalamus of a 12‐year‐old girl. C,D Glioblastoma with pilomyxoid features arising in the cervical spinal cord of a 15‐year‐old boy which demonstrates monomorphic piloid astrocytes radially arranged vessels in a prominent myxoid stroma. Other areas of the tumor demonstrated increased cellularity and pleomorphism with brisk mitotic activity and microvascular proliferation (not shown). E–H. Epithelioid glioblastoma with PNET‐like foci arising in the thalamus of a 27‐year‐old woman. The majority of the tumor was composed of epithelioid astrocytes with abundant eosinophilic cytoplasm and distinct cell borders (E), with a smaller component of PNET‐like foci composed of more primitive appearing cells with scant cytoplasm, nuclear molding, and brisk mitotic activity (G). H&E stained sections are shown in A, C, E and G, and corresponding immunohistochemical stained sections for histone H3‐K27M mutant protein are shown in B, D, F and H.

Figure 6

Additional examples of morphologic variation encountered in diffuse midline gliomas with histone H3‐K27M mutation. A–C. Glioblastoma with neuropil‐like islands arising in the thoracic spinal cord of a 25‐year‐old woman. The tumor contained frequent neuropil‐like islands, highlighted by synaptophysin immunohistochemistry (B), circumferentially surrounded by neoplastic astrocytes. Other areas of the tumor contained necrosis and microvascular proliferation (not shown). D–I. Gliosarcoma with ependymal‐like areas arising in the thalamus of an 11‐year‐old girl. Areas within the tumor showed solid growth with uniform ovoid nuclei, no mitotic activity, and perivascular arrangement resembling the pseudorosettes seen in ependymomas (D). Immunohistochemical staining for EMA in these areas of the tumor demonstrated dot‐like cytoplasmic positivity (E). Other areas showed a more anaplastic sarcoma‐like component with fascicles of spindled cells and brisk mitotic activity (G) that demonstrated increased intercellular reticulin deposition (not shown) and loss of markers of glial differentiation, including OLIG2 (H). Strong nuclear staining for histone H3‐K27M mutant protein was seen diffusely throughout the tumor including both the ependymal‐like (F) and sarcomatous components (I). J–O. Malignant glioma with epithelioid/rhabdoid features and ganglionic differentiation arising in the thoracic spinal cord of a 26‐year‐old man. The majority of the tumor was composed of loosely cohesive cells with eccentric nuclei and abundant eosinophilic cytoplasm, many of which contain spherical intracytoplasmic inclusions (J). Immunohistochemistry for MAP2 showed cytoplasmic staining in the majority of cells with absence of staining in these paranuclear inclusions (K). One area of the tumor demonstrated numerous large atypical ganglion‐like cells (M), which demonstrated strong cytoplasmic positivity on MAP2 immunostaining (N), as well as immunoreactivity for neurofilament and synaptophysin (not shown). Strong nuclear staining for histone H3‐K27M mutant protein was seen diffusely throughout the tumor including both the epithelioid/rhabdoid cells (L) and the ganglion‐like tumor cells (O).

Figure 7

Diffuse midline glioma with focal PXA‐like features and both histone H3‐K27M and BRAF‐V600E mutation arising in the thalamus of a 5‐year‐old girl. A. Preoperative coronal T1 postcontrast MR image demonstrating a complex, enhancing multinodular mass centered in the right thalamus with infiltration into the surrounding brain parenchyma. B,D. A large component of the tumor demonstrated histologic features of PXA with pleomorphic astrocytes, fascicular to storiform architecture, solid growth pattern, numerous eosinophilic granular bodies, and occasional xanthomatous cells. These PXA‐like areas were in apposition to a diffusely infiltrative astrocytoma with scattered mitotic figures and infarct‐like necrosis not associated with palisading or microvascular proliferation C. The diffusely infiltrative component of the tumor lacked significant reticulin deposition (E) and had CD34 immunostaining limited to endothelial cells (G), while the PXA‐like areas had a dense intercellular reticulin network (F) and interspersed stellate cells with CD34 staining H. Staining for both BRAF‐V600E and histone H3‐K27M mutant proteins was seen diffusely throughout the tumor including both the infiltrative component (I,K) and the PXA‐like component (J,L).