Insights from a Multicenter Study on Adult H3 K27M-Mutated Glioma: Surgical Resection's Limited Influence on Overall Survival, ATRX as Molecular Prognosticator

BACKGROUND

H3 K27M-mutated gliomas were first described as a new grade 4 entity in the 2016 WHO classification. Current studies have focused on its typical appearance in children and young adults, increasing the need to better understand the prognostic factors and impact of surgery on adults. Here, we report a multicentric study of this entity in adults.

METHODS

We included molecularly confirmed H3 K27M-mutated glioma cases in patients >18 years diagnosed between 2016 and 2022. Clinical, radiological, and surgical features were analyzed. Univariate and multivariate analyses were performed to identify prognostic factors.

RESULTS

Among 70 patients with a mean age of 36.1 years, the median overall survival (OS) was 13.6 + 14 months. Gross-total resection was achieved in 14.3% of patients, whereas 30% had a subtotal resection and 54.3% a biopsy.Tumors located in telencephalon/diencephalon/myelencephalon were associated with a poorer OS, while a location in the mesencephalon/metencephalon showed a significantly longer OS (8.7 vs. 25.0 months, p=0.007). Preoperative Karnofsky Performance Score (KPS) < 80 showed a reduced OS (4.2 vs. 18 months, p=0.02). Furthermore, ATRX loss, found in 25.7%, was independently associated with an increased OS (31 vs. 8.3 months, p=0.0029). Notably, patients undergoing resection showed no survival benefit over biopsy (12 vs. 11 months, p=0.4006).

CONCLUSION

The present study describes surgical features of H3 K27M-mutated glioma in adulthood in a large multicentric study. Our data reveal that ATRX status, location and KPS significantly impact OS in H3 K27M-mutated glioma. Importantly, our dataset indicates that resection does not offer a survival advantage over biopsy.

H3K27M-mutant diffuse midline gliomas should be further molecularly stratified: an integrated analysis of 669 patients

INTRODUCTION

H3K27M-mutated diffuse midline gliomas (H3-DMGs) are aggressive tumors with a fatal outcome. This study integrating individual patient data (IPD) from published studies aimed to investigate the prognostic impact of different genetic alterations on survival of these patients.

METHODS

We accessed PubMed and Web of Science to search for relevant articles. Studies were included if they have available data of follow-up and additional molecular investigation of H3-DMGs. For survival analysis, Kaplan-Meier analysis and Cox regression models were utilized, and corresponding hazard ratios (HR) and 95% confidence intervals (CI) were computed to analyze the impact of genetic events on overall survival (OS).

RESULT

We included 30 studies with 669 H3-DMGs. TP53 mutations were the most common second alteration among these neoplasms. In univariate Cox regression model, TP53 mutation was an indicator of shortened survival (HR 1.446; 95% CI 1.143-1.829) whereas ACVR1 (HR 0.712; 95% CI 0.518-0.976) and FGFR1 mutations (HR 0.408; 95% CI 0.208-0.799) conferred prolonged survival. In addition, ATRX loss was also associated with a better OS (HR 0.620; 95% CI 0.386-0.996). Adjusted for age, gender, and tumor location, the presence of TP53 mutations, the absence of ACVR1 or FGFR1 mutations remained significantly poor prognostic factors.

CONCLUSIONS

We outlined the prognostic importance of additional genetic alterations in H3-DMGs and recommended that these neoplasms should be further molecularly segregated. This may aid neuro-oncologists in appropriate risk stratification.

Low-Grade Gemistocytic Morphology in H3 G34R-Mutant Gliomas and Concurrent K27M Mutation: Clinicopathologic Findings

Mutations in histone H3 are key molecular drivers of pediatric and young adult high-grade gliomas. Histone H3 G34R mutations occur in hemispheric high-grade gliomas and H3 K27M mutations occur in aggressive, though histologically diverse, midline gliomas. Here, we report 2 rare cases of histologically low-grade gliomas with gemistocytic morphology and sequencing-confirmed histone H3 G34R mutations. One case is a histologically low-grade gemistocytic astrocytoma with a G34R-mutation in H3F3A. The second case is a histologically low-grade gemistocytic astrocytoma with co-occurring K27M and G34R mutations in HIST1H3B. Review of prior histone H3-mutant gliomas sequenced at our institution shows a divergent clinical and immunohistochemical pattern in the 2 cases. The first case is similar to prior histone H3 G34R-mutant tumors, while the second case most closely resembles prior histone H3 K27M-mutant gliomas. These represent novel cases of sequencing-confirmed histone H3 G34R-mutant gliomas with low-grade histology and add to the known rare cases of G34R-mutant tumors with gemistocytic morphology. Although K27M and G34R mutations are thought to be mutually exclusive, we document combined K27M and G34R mutations in HIST1H3B and present evidence suggesting the K27M-mutation drove tumor phenotype in this dual mutant glioma.

Retrospective analysis on the consistency of MRI features with histological and molecular markers in diffuse intrinsic pontine glioma (DIPG)

PURPOSE

The diagnosis of diffuse intrinsic pontine glioma (DIPG) is based largely on a combination of clinical and radiological findings due to the difficulty of obtaining a biopsy. An accurate evaluation of magnetic resonance imaging (MRI) scans is consequently essential. Recent analyses on the genomic landscape of DIPG revealed recurrent mutations in the H3F3A and HIST1H3B histone genes. We reviewed cases with available tumor tissue from institutional DIPG series to ascertain the consistency between their histo-molecular findings and clinical-radiological features.

METHODS

We conducted a radiological and pathological central review of 22 cases enrolled in institutional DIPG trials. We performed immunohistochemical analyses to detect H3F3A/HIST1H3B K27M mutations, histone trimethylation, and EZH2 expression. Mutational analysis was performed for ACVR1, H3F3A, and HIST1H3B genes.

RESULTS

Patients' median age at diagnosis was 8 years, and their median overall survival was 11 months. Nineteen/22 cases (86%) showed evidence of K27M mutation on immunohistochemistry and/or mutation analysis. Histone trimethylation expression was low or lacking in these mutated cases. Sequence analysis revealed 13 cases with H3F3A and 1 case with HIST1H3B K27M mutation. There was no significant difference in EZH2 expression between the K27M mutant and wild-type DIPGs. Upon external, blinded MRI re-evaluation one lesion not consistent with DIPG showed no evidence of K27M mutation and retained histone trimethylation expression.

CONCLUSION

In conclusion, our study demonstrates a high frequency of histone K27M mutations in DIPG when MRI features are carefully assessed, thus confirming the consistency of imaging with biological markers in our institutional series of DIPG.

Mutant ACVR1 Arrests Glial Cell Differentiation to Drive Tumorigenesis in Pediatric Gliomas

Diffuse intrinsic pontine gliomas (DIPGs) are aggressive pediatric brain tumors for which there is currently no effective treatment. Some of these tumors combine gain-of-function mutations in ACVR1, PIK3CA, and histone H3-encoding genes. The oncogenic mechanisms of action of ACVR1 mutations are currently unknown. Using mouse models, we demonstrate that Acvr1G328V arrests the differentiation of oligodendroglial lineage cells, and cooperates with Hist1h3bK27M and Pik3caH1047R to generate high-grade diffuse gliomas. Mechanistically, Acvr1G328V upregulates transcription factors which control differentiation and DIPG cell fitness. Furthermore, we characterize E6201 as a dual inhibitor of ACVR1 and MEK1/2, and demonstrate its efficacy toward tumor cells in vivo. Collectively, our results describe an oncogenic mechanism of action for ACVR1 mutations, and suggest therapeutic strategies for DIPGs.

A case report of adult cerebellar high-grade glioma with H3.1 K27M mutation: a rare example of an H3 K27M mutant cerebellar tumor

Diffuse midline glioma, H3 K27M mutant, is newly recognized as a distinct category, which usually arises in the brain stem, thalamus or spinal cord of children, and young adults. The oncogenic H3 K27M mutation involves H3.3 (encoded by H3F3A) or H3.1 (encoded by HIST1H3B/HIST1H3C), and the incidence of each mutation differs among the primary sites. Recently, several papers have reported that cerebellar high-grade gliomas in both children and adults also harbor H3 K27 mutation. With the exception of one pediatric case, all of the cases carried the mutation in H3.3. We herein present the case of an adult cerebellar high-grade astrocytic tumor with H3.1 K27M mutation in a 45-year-old man, which also involvedTP53 mutation and was immunonegative for ATRX. Some groups have reported that H3.3 and H3.1 K27M mutations define subgroups of diffuse intrinsic pontine gliomas (DIPGs) with different phenotypes as well as genetic alterations. On comparing the findings of the present case, particularly TP53 mutation status and ATRX expression, to the findings of the previous studies on DIPGs, our case seems unusual among the H3.1 K27M mutant subgroup. Further studies are needed to clarify the exact frequency, clinicopathological characteristics, and genomic alterations of cerebellar gliomas harboring H3 K27M mutation.

Histone H3 K27M mutations in adult cerebellar high-grade gliomas

Adult cerebellar high-grade gliomas (HGG) are rare and their molecular basis has not been fully elucidated. Although a diffuse midline glioma H3 K27M-mutant, a recently characterized variant of HGG, was reported to occasionally occur in the cerebellum, adult cases were rarely tested for this mutation; only five mutant cases have been reported to date. It currently remains unknown whether H3 K27M-mutant cerebellar gliomas share common histological features or have a uniformly dismal prognosis. In the present study, we assessed the prevalence of histone H3 K27M mutations in ten adult cerebellar HGG, identifying two H3F3A-mutant cases. One case was a 70-year-old female with a cystic lesion. Histologically, the tumor was considered to be glioblastoma; however, a part of the tumor exhibiting low proliferative activity appeared to be consistent with long-standing H3 K27M-mutant tumors in the literature. Another case was a 69-year-old male. The tumor showed a distinct circumscribed histology with minimal astrocytic differentiation, suggesting a nosological issue in the diagnosis of diffuse midline glioma. More cerebellar tumors need to be tested for H3 K27M mutations to clarify the clinical and histopathological spectra of this tumor.

Targeting Epigenetic Pathways in the Treatment of Pediatric Diffuse (High Grade) Gliomas

Progress in the treatment of adult high-grade gliomas (HGG), including chemoradiation with concurrent and adjuvant temozolomide for glioblastoma, has not translated into significant therapeutic advances for pediatric HGG, where overall survival has plateaued at 15% to 20%, especially when considering specialized pediatric treatment in tertiary care centers, maximal safe neurosurgical resection, optimized delivery of involved field radiation, and improvements in supportive care. However, recent advances in our understanding of pediatric HGG, including the application of next-generation sequencing and DNA methylation profiling, have identified mutations in the histone variant H3.3 and canonical H3.1 genes, respectively. These mutations are relatively specific to neuroanatomic compartments (cortex, midline structures, thalamus, brainstem) and are often associated with other mutations, especially in specific growth factor receptor tyrosine kinases. Targeting epigenetic pathways affected by these histone mutations, alone or in combination with small molecule inhibitors of growth factor receptor signaling pathways, will inform new treatment strategies for pediatric HGG and should be incorporated into novel cooperative group clinical trial designs.

The role of histone modifications and telomere alterations in the pathogenesis of diffuse gliomas in adults and children

Genetic profiling is an increasingly useful tool for sub-classification of gliomas in adults and children. Specific gene mutations, structural rearrangements, DNA methylation patterns, and gene expression profiles are now recognized to define molecular subgroups of gliomas that arise in distinct anatomic locations and patient age groups, and also provide a better prediction of clinical outcomes for glioma patients compared to histologic assessment alone. Understanding the role of these distinctive genetic alterations in gliomagenesis is also important for the development of potential targeted therapeutic interventions. Mutations including K27M and G34R/V that affect critical amino acids within the N-terminal tail of the histone H3 variants, H3.3 and H3.1 (encoded by H3F3A and HIST1H3B genes), are prime examples of mutations in diffuse gliomas with characteristic clinical associations that can help diagnostic classification and guide effective patient management. These histone H3 mutations frequently co-occur with inactivating mutations in ATRX in association with alternative lengthening of telomeres. Telomere length can also be maintained through upregulation of telomerase reverse transcriptase (TERT) expression driven by mutation within the TERT gene promoter region, an alteration most commonly found in oligodendrogliomas and primary glioblastomas arising in adults. Interestingly, the genetic alterations perturbing histone and telomere function in pediatric gliomas tend to be different from those present in adult tumors. We present a review of these mutations affecting the histone code and telomere length, highlighting their importance in prognosis and as targets for novel therapeutics in the treatment of diffuse gliomas.

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

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.