Topographic correlates of driver mutations and endogenous gene expression in pediatric diffuse midline gliomas and hemispheric high-grade gliomas

We evaluate the topographic distribution of diffuse midline gliomas and hemispheric high-grade gliomas in children with respect to their normal gene expression patterns and pathologic driver mutation patterns. We identified 19 pediatric patients with diffuse midline or high-grade glioma with preoperative MRI from tumor board review. 7 of these had 500 gene panel mutation testing, 11 patients had 50 gene panel mutation testing and one 343 gene panel testing from a separate institution were included as validation set. Tumor imaging features and gene expression patterns were analyzed using Allen Brain Atlas. Twelve patients had diffuse midline gliomas and seven had hemispheric high-grade gliomas. Three diffuse midline gliomas had the K27M mutation in the tail of histone H3 protein. All patients undergoing 500 gene panel testing had additional mutations, the most common being in ACVR1, PPM1D, and p53. Hemispheric high-grade gliomas had either TP53 or IDH1 mutation and diffuse midline gliomas had H3 K27M-mutation. Gene expression analysis in normal brains demonstrated that genes mutated in diffuse midline gliomas had higher expression along midline structures as compared to the cerebral hemispheres. Our study suggests that topographic location of pediatric diffuse midline gliomas and hemispheric high-grade gliomas correlates with driver mutations of tumor to the endogenous gene expression in that location. This correlation suggests that cellular state that is required for increased gene expression predisposes that location to mutations and defines the driver mutations within tumors that arise from that region.

Inhibition of microglial EZH2 leads to anti-tumoral effects in pediatric diffuse midline gliomas

Background Diffuse intrinsic pontine gliomas (DIPG), within diffuse midline gliomas are aggressive pediatric brain tumors characterized by histone H3-K27M mutation. Small-molecule inhibitors for the EZH2-H3K27 histone methyltransferase have shown promise in preclinical animal models of DIPG, despite having little effect on DIPG cells in vitro. Therefore, we hypothesized that the effect of EZH2 inhibition, could be mediated through targeting of this histone modifying enzyme in tumor-associated-microglia. Methods Primary DIPG tissues, and cocultures between microglia and patient-derived DIPG or -pediatric high-grade glioma (pHGG) cell lines, were used to establish the H3-K27M status of each cell type. Antisense RNA strategies were used to target EZH2 gene expression in both microglia and glioma cells. Microglia anti-tumoral properties were assessed by gene expression profile, tumor cell invasion capacity, microglial phagocytic activity, and associated tumor cell death. Results In primary DIPG tissues, microglia do not carry the H3-K27M mutation, otherwise characteristic of the cancer cells. Activation of a microglial tumor-supportive phenotype by pHGG, independently of their H3-K27M status, is associated with a transient H3K27me3 downregulation. Repression of EZH2 in DIPG cells has no impact on tumor cell survival or their ability to activate microglia. However, repression of EZH2 in microglia induces an anti-tumor phenotype resulting in decreased cancer cell invasion capability, increased microglial phagocytosis, and tumor related cell death. Conclusion These results indicate that microglia, beyond the tumor cells, contribute to the observed response of DIPG to EZH2 inhibition. Results highlight the potential importance of microglia as a new therapeutic avenue in DIPG.

Spinal Cord Diffuse Midline Glioma With Histone H3 K27M Mutation in a Pediatric Patient

Background: Diffuse midline glioma (DMG) with histone H3 K27M mutation is a recently identified entity documented in the 2016 World Health Organization (WHO) Classification of Tumors of the Central Nervous System. Spinal cord DMGs with H3 K27M-mutant are commonly reported in adults. Herein, we reported a pediatric patient with spinal cord H3 K27M-mutant DMG.Case Report: A 7-year-old girl with 1-month history of neck pain and 3-week history of progressive weakness in the right hand was presented. Spinal magnetic resonance imaging showed an intramedullary lesion with slight enhancement at the C2-7 levels. With intraoperative neuroelectrophysiological monitoring, the lesion was subtotally resected. Histopathological examination revealed a DMG with histone H3 K27M mutation corresponding to WHO grade IV. Postoperatively, the neck pain was relieved, and the upper-extremity weakness remained unchanged. Oral temozolomide was administrated for 7 months, and radiotherapy was performed for 22 courses. After an 18-month follow-up, no tumor recurrence was noted.Conclusion: Spinal cord H3 K27M-mutant DMGs are extremely rare in pediatric patients. Preoperative differential diagnosis is challenging, and surgical resection with postoperative chemoradiotherapy may be an effective treatment.

Diffuse Midline Glioma with H3-K27M Mutation: A Rare Case with GFAP-positive Anucleate Whorled Patterns

Background: Diffuse midline glioma with H3-K27M mutation is a new tumor type in the 2016 WHO classification of tumors of the central nervous system, with predominantly astrocytic differentiation and is characterized by K27M mutation in either H3F3A/-HIST1H3B/C. It occurs at the midline of the CNS. It is mainly found in children, and adult cases are relatively rare . Although its histopathological features have been widely described, GFAP-positive anucleate whorled patterns have not been reported to the best of our knowledge. Hence, we have reported this unusual case.Case presentation：A woman presented with complaints of walking instability. MRI showed a mass shadow of isometric T1 and slightly longer T2 with mild mixed signals in the third ventricle of the suprasellar region, about 3.4 x 2.5 x 3.4 cm in size. The enhanced scan showed that the lesion was irregular and annular, with a clear edge. The lesion had spread to the right lateral ventricle, which dilated the ventricular system, especially the right lateral ventricle. Furthermore, the lamellar long T2 signal was seen in bilateral paraventricular white matter, the midline structure had shifted to the left, and the corpus callosum was thinner. Radiological findings suggested ependymoma. Subtotal resection craniotomy was performed. After surgery, the patient was routinely treated with temozolomide for chemotherapy and synchronous radiotherapy (Dt=60 Gy/30f). It has been 11 months now, and the patient is living well.Result: We described an extremely rare case of diffuse midline glioma, H3-K27M mutation with GFAP-positive anucleate whorled patterns. Conclusions: This case report provides information on the microscopic morphological features of diffuse midline glioma with H3K27M mutation, which can help pathologists to make a definitive diagnosis of this tumor.

Exploring MRI Characteristics of Brain Diffuse Midline Gliomas With the H3 K27M Mutation Using Radiomics

ObjectivesTo explore the magnetic resonance imaging (MRI) characteristics of brain diffuse midline gliomas with the H3 K27M mutation (DMG-M) using radiomics.Materials and MethodsThirty patients with diffuse midline gliomas, including 16 with the H3 K27M mutant and 14 with wild type tumors, were retrospectively included in this study. A total of 272 radiomic features were initially extracted from MR images of each tumor. Principal component analysis, univariate analysis, and three other feature selection methods, including variance thresholding, recursive feature elimination, and the elastic net, were used to analyze the radiomic features. Based on the results, related visually accessible features of the tumors were further evaluated.ResultsPatients with DMG-M were younger than those with diffuse midline gliomas with H3 K27M wild (DMG-W) (median, 25.5 and 48 years old, respectively; p=0.005). Principal component analysis showed that there were obvious overlaps in the first two principal components for both DMG-M and DMG-W tumors. The feature selection results showed that few features from T2-weighted images (T2WI) were useful for differentiating DMG-M and DMG-W tumors. Thereafter, four visually accessible features related to T2WI were further extracted and analyzed. Among these features, only cystic formation showed a significant difference between the two types of tumors (OR=7.800, 95% CI 1.476–41.214, p=0.024).ConclusionsDMGs with and without the H3 K27M mutation shared similar MRI characteristics. T2W sequences may be valuable, and cystic formation a useful MRI biomarker, for diagnosing brain DMG-M.

Molecular characteristics of H3 K27M mutation gliomas in Chinese adults.

e14018 Background: Diffuse midline glioma H3 K27M–mutant is a specific entity added to the 2016 update of the WHO classification of CNS tumors. H3K27M-mutant gliomas are diagnosed primarily in children and adolescents with TP53 and/or ATRX mutations. However, the characteristics of H3 K27M-mutant gliomas in adults have not been explicitly described. Methods: We performed the 131-gene panel targeted sequencing on tumor samples from 33 adults H3 K27M-mutant gliomas( > 18 years) and 13 children and adolescents H3 K27M-mutant gliomas(≤18 years) in a CAP certified laboratory. Somatic mutations, copy number variations, and fusion genes were detected following the standard operating procedure (SOP). The MS-based assay measured MGMT promoter methylation. We calculated the tumor location and the median age in different cohorts. Results: In our adult cohort, 22/33（66.7%）had a midline location（spinal cord n = 2, thalamus n = 7, brainstem n = 6, cerebellum n = 3, pineal region n = 1, Basal ganglia region n = 3）, 6/33（18.1%）had a non-midline location (Lateral ventricle n = 2, Cerebral hemispheres n = 4). In the children and adolescents cohort, 11/13（84.6%）occurred in midline location, 1/13(7.7%) occurred in the Lateral ventricle. MGMT promoter methylation did not differ in adult and pediatric H3 K27M-mutant gliomas (12.1% vs. 0). H3 K27M-mutant adult gliomas significantly co-occurred with the NF1 mutation(P = 0.008937). The median age of H3 K27M-mutant adult gliomas with NF1 modification (13/33, 39.4%) is higher than the NF1 wild type (49 years vs. 38 years, P = 0.107), although the difference has no statistical significance. Conclusions: In Chinese adults, as in children, H3 K27M mutation gliomas are characterized by a constant midline location, low rate of MGMT promoter methylation. Inconsistently, H3 K27M mutant adult gliomas are featured by a higher rate of NF1 mutations. Our molecular profiling analysis revealed the H3 K27M mutation in adult gliomas. Our research suggests potential molecular pathogenesis of H3K27M mutant adult gliomas and identifies more therapeutic targets for precision medicine.