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Medulloblastomas are malignant embryonal brain tumours that may harbour mutations in histone-modifying genes, while mutations in histone genes have not been detected to date. We here describe the first SHH medulloblastoma with H3 K27M mutation. This may have diagnostic implications as H3 K27M mutations are the hallmark of diffuse midline gliomas, H3 K27M mutant, WHO grade IV. Medulloblastomas arise in midline structures and thus must not be mistaken for DMG when using an antibody detecting the H3 K27M mutation.

Diffuse intrinsic pontine glioma (DIPG) is a lethal pediatric tumor with no currently available treatment options. More than 60-70% DIPG tumors harbor heterozygous mutations at genes encoding histone H3 proteins that replace lysine 27 with methionine (K27M). In this review, we discuss how K27M mutation reprograms the cancer epigenome to lead to tumorigenesis, and highlight potential drug targets and therapeutic agents for DIPG.

Diffuse midline glioma with H3 K27M mutation is a new tumor entity from 2016 which is highly aggressive and classified as a WHO Grade IV tumor regardless of histopathologic features. We report a case of a 40-year-old male with diffuse midline glioma with pathology confirmation of histone H3 K27M mutation presenting predominately with subacute lower motor neuron syndrome mimicking long segmental myelitis. Our case will remind physicians that diffuse midline gliomas with H3 K27M mutation should be considered for differential diagnosis when there is long segmental spinal cord lesion. Careful evaluation should be done when there is atypical clinical manifestation.

Diffuse intrinsic pontine gliomas (DIPGs) are incurable childhood brainstem tumors with frequent histone H3 K27M mutations and recurrent alterations in PDGFRA and TP53. We generated genetically engineered inducible mice and showed that H3.3 K27M enhanced neural stem cell self-renewal while preserving regional identity. Neonatal induction of H3.3 K27M cooperated with activating PDGFRα mutant and Trp53 loss to accelerate development of diffuse brainstem gliomas that recapitulated human DIPG gene expression signatures and showed global changes in H3K27 post-translational modifications, but relatively restricted gene expression changes. Genes upregulated in H3.3 K27M tumors were enriched for those associated with neural development where H3K27me3 loss released the poised state of apparently bivalent promoters whereas downregulated genes were enriched for those encoding homeodomain transcription factors.

BACKGROUND AND PURPOSE: Diffuse midline gliomas with histone H3 K27M mutation are biologically aggressive tumors with poor prognosis defined as a new diagnostic entity in the 2016 World Health Organization Classification of Tumors of the Central Nervous System. There are no qualitative imaging differences (enhancement, border, or central necrosis) between histone H3 wildtype and H3 K27M-mutant diffuse midline gliomas. Herein, we evaluated the utility of diffusion-weighted imaging to distinguish H3 K27M-mutant from histone H3 wildtype diffuse midline gliomas. MATERIALS AND METHODS: We identified 31 pediatric patients (younger than 21 years of age) with diffuse gliomas centered in midline structures that had undergone assessment for histone H3 K27M mutation. We measured ADC within these tumors using a voxel-based 3D whole-tumor measurement method. RESULTS: Our cohort included 18 infratentorial and 13 supratentorial diffuse gliomas centered in midline structures. Twenty-three (74%) tumors carried H3-K27M mutations. There was no difference in ADC histogram parameters (mean, median, minimum, maximum, percentiles) between mutant and wild-type tumors. Subgroup analysis based on tumor location also did not identify a difference in histogram descriptive statistics. Patients who survived 1 year (1.46 × 10(−3)mm(2)/s; 95% CI, 1.19–1.67; P < .06). Average ADC values for diffuse midline gliomas were 1.28 × 10(−3)mm(2)/s (95% CI, 1.21–1.34) and 0.86 × 10(−3)mm(2)/s (95% CI, 0.69–1.01) for hemispheric glioblastomas with P < .05. CONCLUSIONS: Although no statistically significant difference in diffusion characteristics was found between H3-K27M mutant and H3 wildtype diffuse midline gliomas, lower diffusivity corresponds to a lower survival rate at 1 year after diagnosis. These findings can have an impact on the anticipated clinical course for this patient population and offer providers and families guidance on clinical outcomes.

Diffuse midline glioma (DMG), including diffuse intrinsic pontine glioma (DIPG) constitutes up to 20% of pediatric brain cancer and has a median survival of less than one year. The ongoing development of immunotherapy has shown significant promise in many fields, including that of gliomas. Genetic studies have revealed that greater than 70% of DIPG cases harbor an amino acid substitution from lysine (K) to methionine (M) at position 27 of histone 3 variant 3 (H3.3). We have previously identified novel HLA-A*02:01-restricted neoantigen epitope encompassing the H3.3K27M mutation. Accordingly, we have implemented a clinical trial through the Pacific Pediatric Neuro-Oncology Consortium (PNOC). Newly diagnosed DIPG patients who are HLA-A2+ and H3.3K27M+ underwent radiation therapy, and then received the H3.3K27M peptide vaccine, combined with the tetanus toxoid (TT) peptide, emulsified in Montanide. The TLR3 agonist, Poly-ICLC, was given concurrently to improve therapeutic effects of the vaccine. Our objective is to characterize vaccine-induced H3.3K27M-specific T cells from peripheral blood at several time points of the study through the evaluation of a large number of analytes utilizing a novel H3.3K27M-specific dextramer-based mass cytometry method. The specificity of the H3.3K27M-specific dextramer was validated through significant binding to H3.3K27M TCR-transduced CD8 T cells and lack of non-specific binding. Subsequently, patient-derived PBMC samples were analyzed using this methodology, revealing a time course-dependent, progressive expansion of CD45RA+ effector memory cells with an inverse downregulation of CD45RO+ in H3.3K27M-specific CD8 T cells. Additionally, progressive upregulation of HLA-DR was observed in several myeloid-derived populations through the course of the trial. Future plans include the longitudinal quantification of IFN-γ and TNF-α expression as a response to the H3.3K27M peptide vaccine at each time point. The development of this methodology may greatly aid in the comprehensive evaluation of immunotherapeutic outcomes on the cellular basis.

ID1 regulates transcription by interacting with bHLH transcription factors and previous work has shown that over-expression of the recurrent DIPG H3F3A K27M and ACVR1 mutations in cultured astrocytes lead to an increase in ID1 expression; this has not been validated in human DIPG. DNA (exome)/RNA sequencing of 34 DIPGs and 17 normal samples (SickKids) revealed that ID1 expression was significantly increased in tumor as compared to normal (p=0.001). ID1 expression was significantly higher in H3F3A K27M-mutated tumors as compared to normal (p=0.003), but not in ACVR1-mutated tumors. This was confirmed in an analysis of pediatric high-grade gliomas (PedcBioPortal) where ID1 expression was increased in H3F3A K27M-mutated tumors as compared to H3 wildtype (p=0.0055, n=189), but not in ACVR1-mutated tumors as compared to ACVR1 wildtype (p=0.1178, n=114). In an additional patient with DIPG at autopsy, multi-focal sequencing revealed clonal mutations in HIST1H3B K27M and ACVR1 and ID1 expression correlated with tumor size and cerebellar invasion. We identified several genes whose expression in pediatric HGG correlated with that of ID1 and which have been implicated in invasion and/or metastasis in various solid tumors. ChipSeq revealed reduced K27 me3 and elevated K27 acetylation at the ID1 locus in multiple K27M-mutant DIPG cell lines, pointing to an epigenetic control of this phenotype in H3F3A K27M-mutated DIPGs. Based on these data, we propose that epigenetically controlled upregulation of ID1 promotes DIPG invasion in H3F3A K27M-mutated DIPG and represents an optimal therapeutic target.

Background The novel entity of "diffuse midline glioma, H3 K27M-mutant" has been defined in the 2016 revision of the World Health Organization (WHO) classification of tumors of the central nervous system (CNS). Tumors of this entity arise in CNS midline structures of predominantly pediatric patients and are associated with an overall dismal prognosis. They are defined by K27M mutations in H3F3A or HIST1H3B/C, encoding for histone 3 variants H3.3 and H3.1, respectively, which are considered hallmark events driving gliomagenesis. Methods Here, we characterized 85 centrally reviewed diffuse gliomas on midline locations enrolled in the nationwide pediatric German HIT-HGG registry regarding tumor site, histone 3 mutational status, WHO grade, age, sex, and extent of tumor resection. Results We found 56 H3.3 K27M-mutant tumors (66%), 6 H3.1 K27M-mutant tumors (7%), and 23 H3-wildtype tumors (27%). H3 K27M-mutant gliomas shared an aggressive clinical course independent of their anatomic location. Multivariate regression analysis confirmed the significant impact of the H3 K27M mutation as the only independent parameter predictive of overall survival (P = 0.009). In H3 K27M-mutant tumors, neither anatomic midline location nor histopathological grading nor extent of tumor resection had an influence on survival. Conclusion These results substantiate the clinical significance of considering diffuse midline glioma, H3 K27M-mutant, as a distinct entity corresponding to WHO grade IV, carrying a universally fatal prognosis.

Pediatric diffuse midline glioma is a highly morbid glial neoplasm that may arise in the thalamus or brainstem (also known as diffuse intrinsic pontine glioma or DIPG). Because tumor anatomic location precludes surgical resection, diagnosis and treatment is based on MR imaging and analysis of biopsy specimens. Up to 80% of pediatric diffuse midline gliomas harbor a histone H3 mutation resulting in the replacement of lysine 27 with methionine (K27M) in genes encoding histone H3 variant H3.3 (H3F3A) or H3.1 (HIST1H3B). H3K27M mutant glioma responds more poorly to treatment and is associated with worse clinical outcome than wild-type tumors, so mutation detection is now diagnostic for a new clinical entity, diffuse midline glioma H3K27M mutant, as defined in the most recent WHO classification system. We previously reported patterns of histone H3 trimethylation (H3K27me3) and acetylation (H3K27Ac) associated with H3K27M mutation that impact transcription regulation and contribute to tumorigenesis. Given the clinical implications of the H3K27M mutation and these associated H3 post-translational modifications (PTMs), we set to determine whether they can be characterized via immunohistochemistry (IHC) in a cohort of pediatric glioma (n = 69) and normal brain tissue (n = 4) specimens. We observed 100% concordance between tissue IHC and molecular sequencing for detecting H3K27M mutation. In turn, H3K37M and H3K27me3 results, but not H3K27Ac staining patterns, were predictive of clinical outcomes. Our results demonstrate H3K27M and H3K27me3 staining of pediatric glioma tissue may be useful for diagnosis, stratification to epigenetic targeted therapies, and longitudinal monitoring of treatment response.

Diffuse intrinsic pontine glioma (DIPG) is a high-grade glioma that originates in the pons and is seen exclusively in children. Despite numerous efforts to improve treatment, DIPG remains incurable with 90% of children dying within 2 y of diagnosis, making it one of the leading causes of death in children with brain tumors. With the advent of new genomic tools, the genetic landscape of DIPG is slowly being unraveled. The most common genetic alterations include a K27M mutation in H3.3 or H3.1, which are found in up to 78% of DIPGs, whereas p53 mutations are found in up to 77%. Other recently discovered alterations include amplification of components of the receptor tyrosine kinase/Ras/phosphatidylinositol 3-kinase signaling pathway, particularly platelet-derived growth factor receptor A. Recapitulating such alterations, genetically engineered DIPG preclinical models have been developed, and DIPG xenograft models have also been established. Both models have strengths and weaknesses but can help with the prioritization of novel agents for clinical trials for children with DIPG. As we move forward, it is important that we continue to study the complex and unique biology of DIPG and develop improved preclinical models to increase our understanding of DIPG pathogenesis, allowing translation into successful therapies in the not too distant future.

© 2015 International Society of Neuropathology 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.

Pediatric glioblastomas (GBM) are highly aggressive and lethal tumors. Recent sequencing studies have shown that ~30 % of pediatric GBM and ~80 % of diffuse intrinsic pontine gliomas show K27M mutations in the H3F3A gene, a variant encoding histone H3.3. H3F3A K27M mutations lead to global reduction in H3K27me3. Our goal was to develop biomarkers for the histopathologic detection of these tumors. Therefore, we evaluated the utility of measuring H3K27me3 global reduction as a histopathologic and prognostic biomarker and tested an antibody directed specifically against the H3.3 K27M mutation in 290 samples. The study cohort included 203 pediatric (including 38 pediatric high-grade astrocytomas) and 38 adult brain tumors of various subtypes and grades and 49 non-neoplastic reactive brain tissues. Detection of H3.3 K27M by immunohistochemistry showed 100 % sensitivity and specificity and was superior to global reduction in H3K27me3 as a biomarker in diagnosing H3F3A K27M mutations. Moreover, cases that stained positive for H3.3 K27M showed a significantly poor prognosis compared to corresponding negative tumors. These results suggest that immunohistochemical detection of H3.3 K27M is a sensitive and specific surrogate for the H3F3A K27M mutation and defines a prognostically poor subset of pediatric GBM. Electronic supplementary material The online version of this article (doi:10.1007/s00401-014-1338-3) contains supplementary material, which is available to authorized users.

Pediatric glioblastomas (GBM) are lethal and fatal tumors and ∼30% of GBM and ∼80% of diffuse intrinsic pontine gliomas show K27M mutations in the H3F3A gene, a variant encoding histone H3.3. These mutations lead to global reduction in H3K27me3. Our goal was to develop biomarkers for the histopathologic detection of these tumors. Therefore, we evaluated the utility of measuring H3K27me3 global reduction as a biomarker and tested an antibody directed specifically against the K27M mutation in 290 samples of 203 pediatric (including 38 pediatric high-grade astrocytomas), 38 adult brain tumors of various subtypes and grades and 49 non-neoplastic reactive brain tissues. Detection of K27M by immunohistochemistry showed 100% sensitivity and specificity and was superior to reduction in H3K27me3 as a biomarker. Moreover, cases that stained positive for K27M showed a significantly poor prognosis compared to corresponding negative tumors. These results suggest that immunohistochemical detection of K27M is a sensitive and specific surrogate for K27M mutations and a prognostic marker.

Meeting abstracts Malignant gliomas, such as glioblastoma (GBM) and diffuse intrinsic pontine gliomas (DIPG), are lethal brain tumors in both adults and children. Indeed, brain tumors are the leading cause of cancer-related mortality and morbidity in children. Children with DIPG have one-year