Diffuse hemispheric glioma with H3 p.K28M (K27M) mutation: Unusual non-midline presentation of diffuse midline glioma, H3 K27M-altered?

Diffuse midline glioma, H3 K27-altered (DMG-H3 K27) is an aggressive group of diffuse gliomas that predominantly occurs in pediatric patients, involves midline structures, and displays loss of H3 p.K28me3 (K27me3) expression by immunohistochemistry and characteristic genetic/epigenetic profile. Rare examples of a diffuse glioma with an H3 p.K28M (K27M) mutation and without involvement of the midline structures, so-called "diffuse hemispheric glioma with H3 p.K28M (K27M) mutation" (DHG-H3 K27), have been reported. Herein, we describe 2 additional cases of radiologically confirmed DHG-H3 K27 and summarize previously reported cases. We performed histological, immunohistochemical, molecular, and DNA methylation analysis and provided clinical follow-up in both cases. Overall, DHG-H3 K27 is an unusual group of diffuse gliomas that shows similar clinical, histopathological, genomic, and epigenetic features to DMG-H3 K27 as well as enrichment for activating alterations in MAPK pathway genes. These findings suggest that DHG-H3 K27 is closely related to DMG-H3 K27 and may represent an unusual presentation of DMG-H3 K27 without apparent midline involvement and with frequent MAPK pathway activation. Detailed reports of additional cases with clinical follow-up will be important to expand our understanding of this unusual group of diffuse gliomas and to better define the clinical outcome and how to classify DHG-H3 K27.

68Ga-DOTATATE and 18F-FDG PET Imaging of a Rare Chordoid Meningioma With Intracranial Recurrence and Extracranial Metastases

ABSTRACT

Chordoid meningiomas, rare meningioma variants, are characterized by their histopathological features and clinical behavior resembling that of other chondroid/myxoid neoplasms. We present a case of pathology-proven chordoid meningioma imaged with both 68Ga-DOTATATE and 18F-FDG PET images during a complicated postoperative course with multiple episodes of local recurrence and, ultimately, extracranial metastasis. This case underscores the aggressive behavior of chordoid meningiomas while highlighting how molecular imaging plays an important role in clinical monitoring and guidance of management.

Quantifying intra-tumoral genetic heterogeneity of glioblastoma toward precision medicine using MRI and a data-inclusive machine learning algorithm

BACKGROUND AND OBJECTIVE

Glioblastoma (GBM) is one of the most aggressive and lethal human cancers. Intra-tumoral genetic heterogeneity poses a significant challenge for treatment. Biopsy is invasive, which motivates the development of non-invasive, MRI-based machine learning (ML) models to quantify intra-tumoral genetic heterogeneity for each patient. This capability holds great promise for enabling better therapeutic selection to improve patient outcome.

METHODS

We proposed a novel Weakly Supervised Ordinal Support Vector Machine (WSO-SVM) to predict regional genetic alteration status within each GBM tumor using MRI. WSO-SVM was applied to a unique dataset of 318 image-localized biopsies with spatially matched multiparametric MRI from 74 GBM patients. The model was trained to predict the regional genetic alteration of three GBM driver genes (EGFR, PDGFRA and PTEN) based on features extracted from the corresponding region of five MRI contrast images. For comparison, a variety of existing ML algorithms were also applied. Classification accuracy of each gene were compared between the different algorithms. The SHapley Additive exPlanations (SHAP) method was further applied to compute contribution scores of different contrast images. Finally, the trained WSO-SVM was used to generate prediction maps within the tumoral area of each patient to help visualize the intra-tumoral genetic heterogeneity.

RESULTS

WSO-SVM achieved 0.80 accuracy, 0.79 sensitivity, and 0.81 specificity for classifying EGFR; 0.71 accuracy, 0.70 sensitivity, and 0.72 specificity for classifying PDGFRA; 0.80 accuracy, 0.78 sensitivity, and 0.83 specificity for classifying PTEN; these results significantly outperformed the existing ML algorithms. Using SHAP, we found that the relative contributions of the five contrast images differ between genes, which are consistent with findings in the literature. The prediction maps revealed extensive intra-tumoral region-to-region heterogeneity within each individual tumor in terms of the alteration status of the three genes.

CONCLUSIONS

This study demonstrated the feasibility of using MRI and WSO-SVM to enable non-invasive prediction of intra-tumoral regional genetic alteration for each GBM patient, which can inform future adaptive therapies for individualized oncology.

Image-localized biopsy mapping of brain tumor heterogeneity: A single-center study protocol

Brain cancers pose a novel set of difficulties due to the limited accessibility of human brain tumor tissue. For this reason, clinical decision-making relies heavily on MR imaging interpretation, yet the mapping between MRI features and underlying biology remains ambiguous. Standard (clinical) tissue sampling fails to capture the full heterogeneity of the disease. Biopsies are required to obtain a pathological diagnosis and are predominantly taken from the tumor core, which often has different traits to the surrounding invasive tumor that typically leads to recurrent disease. One approach to solving this issue is to characterize the spatial heterogeneity of molecular, genetic, and cellular features of glioma through the intraoperative collection of multiple image-localized biopsy samples paired with multi-parametric MRIs. We have adopted this approach and are currently actively enrolling patients for our 'Image-Based Mapping of Brain Tumors' study. Patients are eligible for this research study (IRB #16-002424) if they are 18 years or older and undergoing surgical intervention for a brain lesion. Once identified, candidate patients receive dynamic susceptibility contrast (DSC) perfusion MRI and diffusion tensor imaging (DTI), in addition to standard sequences (T1, T1Gd, T2, T2-FLAIR) at their presurgical scan. During surgery, sample anatomical locations are tracked using neuronavigation. The collected specimens from this research study are used to capture the intra-tumoral heterogeneity across brain tumors including quantification of genetic aberrations through whole-exome and RNA sequencing as well as other tissue analysis techniques. To date, these data (made available through a public portal) have been used to generate, test, and validate predictive regional maps of the spatial distribution of tumor cell density and/or treatment-related key genetic marker status to identify biopsy and/or treatment targets based on insight from the entire tumor makeup. This type of methodology, when delivered within clinically feasible time frames, has the potential to further inform medical decision-making by improving surgical intervention, radiation, and targeted drug therapy for patients with glioma.

Integrated molecular and multiparametric MRI mapping of high-grade glioma identifies regional biologic signatures

Sampling restrictions have hindered the comprehensive study of invasive non-enhancing (NE) high-grade glioma (HGG) cell populations driving tumor progression. Here, we present an integrated multi-omic analysis of spatially matched molecular and multi-parametric magnetic resonance imaging (MRI) profiling across 313 multi-regional tumor biopsies, including 111 from the NE, across 68 HGG patients. Whole exome and RNA sequencing uncover unique genomic alterations to unresectable invasive NE tumor, including subclonal events, which inform genomic models predictive of geographic evolution. Infiltrative NE tumor is alternatively enriched with tumor cells exhibiting neuronal or glycolytic/plurimetabolic cellular states, two principal transcriptomic pathway-based glioma subtypes, which respectively demonstrate abundant private mutations or enrichment in immune cell signatures. These NE phenotypes are non-invasively identified through normalized K2 imaging signatures, which discern cell size heterogeneity on dynamic susceptibility contrast (DSC)-MRI. NE tumor populations predicted to display increased cellular proliferation by mean diffusivity (MD) MRI metrics are uniquely associated with EGFR amplification and CDKN2A homozygous deletion. The biophysical mapping of infiltrative HGG potentially enables the clinical recognition of tumor subpopulations with aggressive molecular signatures driving tumor progression, thereby informing precision medicine targeting.

TMIC-58. PATTERNS OF CELLULAR SUBPOPULATION COHABITATION DEFINE GLIOBLASTOMA STATES

Characterizing intra- and inter-tumoral heterogeneity of glioblastoma has historically relied on discrete classifications of malignant cell populations leaving immune and other cell populations, known to exist admixed with the malignant tumor cells, relatively neglected. Manifold learning algorithms can manage deconvolving multiple cell populations and are often used to track cell state transitions in single cell transcriptomics. We applied a manifold learning approach to TCGA microarray data (Nf525) and bulk transcriptomics of 134 image localized biopsies across 30 patients with primary and 9 with recurrent glioblastoma to further elucidate how to organize biopsies across a spectrum of possible tissue states. The algorithm revealed a low-dimensional manifold graph for which each biopsy lives across 3 polarizing tissue states - one that is associated with diffusely invaded brain, one that is enriched in mesenchymal genes, and one that is enriched in classical proliferative tumor signatures. We deconvolved the bulk transcriptomics of the image-localized biopsies to reveal the relative abundance of 18 malignant, immune, and other cell subpopulations in each biopsy. Overlaying the cellular decomposition onto the manifold graph visualizing the tissue state distributions revealed that transitions between states correlate with changes in cellular cohabitation composition. The tumor cellular cohabitation ecologies have the lowest diversity, as inferred by ecological measures such as Shannon entropy and evenness, at the distal poles of the graph when compared to the transitional arms. Further, we found that the relationship between imaging appearance of contrast enhancement on T1-weighted MRI and the biopsy cellular composition varies with sex and primary vs recurrent biopsy status. The limited spectrum of possible tissue states revealed by the manifold learning is suggestive of a limited continuum along which tumor and non-tumoral cell populations can cohabitate. Such a limited low-dimensional biological space may constrain the dynamics of tumor biology in a predictable manner.

PATH-12. DIFFUSE HEMISPHERIC GLIOMA, H3 G34-MUTANT: A COMPREHENSIVE SEQUENCING AND HIGH-RESOLUTION GENOME-WIDE COPY NUMBER ANALYSIS

Diffuse hemispheric glioma, H3 G34-mutant (DHG_H3G34) is a novel tumor type in the 2021 WHO CNS classification. We describe a comprehensive sequencing and high-resolution genome-wide copy number analysis of a series of cases clinically tested by a single laboratory (2018-2022). Cases included tumors from 47 unique patients (1 reportedly recurrent) that had an H3-3A G34 mutation detected using an 187-gene mutation and fusion targeted neuro-oncology NGS panel (n=47). A subset (n=18) of cases was also tested Oncoscan chromosomal microarray. Median age at testing was 20 years (range, 12-50). H3-3A G34 mutations included G34R (n=44; 94%), G34V (n=2) and a novel G34E variant considered to be likely clinically relevant (n=1). All DHG_H3G34 were hemispheric tumors, and one tumor was multifocal with midline involvement. Concurrent mutations recurrently involved ATRX (n=38), TERT promoter (n=3; mutually exclusive with ATRX mutations), TP53 (n=43), PDGFRA (n=26), PTEN (n=5), NF1 (n=4, all patients over 20 years), PIK3CA (n=4) and CDKN2A (n=3). The single recurrent tumor also had an MSH6 mutation, and in addition to 3 other cases, had increased number of sequence variants suggestive of a high tumor mutational burden. A single case also showed an FGFR3::FAM184B (exon 17::exon 2) fusion. All cases with available chromosomal microarray data had unbalanced genomes with multiple chromosomal gains/losses, and regions of copy-neutral loss of heterozygosity. The most frequent recurrent (at least 50% of cases) abnormalities were losses involving 3q, 4q, 10q, 13q and 18q, and 17p copy-neutral loss of heterozygosity encompassing TP53 (all but one case had concomitant TP53 mutation), a pattern reminiscent of IDH-mutant astrocytomas. Oncogene amplifications (PDGFRA and PIK3CA) were detected in 3 (of 18) cases. CDKN2A/B deletion was observed in 8 cases (2 homozygous). In conclusion, we describe additional sequence and copy-number abnormalities in DHG_H3G34, expanding the spectrum of genetic changes associated with this novel tumor type.

PATH-25. H3 K27M-MUTANT DIFFUSE NON-MIDLINE GLIOMA: REPORT OF A CASE WITH EXTENDED FOLLOW-UP

H3 K27M-mutant diffuse gliomas without midline involvement are extremely rare and their clinical behavior remains elusive due to limited reported follow-up data. We describe an H3 K27M-mutant diffuse non-midline glioma patient with extended follow-up. A 34-year-old woman presented with headache, memory loss, periods of changes in taste and smell, and confusion. Imaging studies revealed an 2.3 cm expansile T2/flair hyperintensity with patchy postcontrast enhancement centered in the left amygdala without associated restricted diffusion and no involvement of the midline structures. The tumor was debulked and consisted of a mitotically active infiltrating astrocytic glioma without tumor necrosis or microvascular proliferation, consistent with anaplastic astrocytoma. Targeted 187-gene neuro-oncology NGS testing detected an H3F3A K27M mutation along with a PTPN11 and a PPM1D mutation. FISH 1p/19q-codeletion testing was negative. MGMT promoter was unmethylated. The patient was treated with chemoradiation with temozolomide for 6 weeks followed by 12 cycles of temozolomide. Four years after initial resection, an area of increased post-contrast enhancement indicating tumor recurrence/progression was noted. Partial resection of the recurrent tumor revealed a mitotically active infiltrating astrocytic glioma with tumor necrosis consistent with glioblastoma. Molecular profiling of the recurrent tumor by the neuro-oncology NGS panel detected similar mutational profile (identical H3F3A K27M and PTPN11 mutation; different PPM1D mutation) with an additional SOS1 mutation. The patient completed 4 cycles of Lomustine and although clinically stable, imaging studies showed slight increase in residual tumor size concerning for tumor progression. Lomustine was discontinued, Bevacizumab therapy was initiated and patient was enrolled in clinical trial (NCT02525692). Despite tumor progression, this patient has had a relatively long disease course (5 years) suggesting that H3 K27M-mutant non-midline diffuse gliomas although molecularly similar, may follow a more favorable clinical course than their midline counterparts possibly due to the hemispheric location, which is more amenable for surgical resection.

Spinal intramedullary hemangioblastoma and schwannoma collision tumor: illustrative case

BACKGROUND

Intramedullary spinal cord tumors represent a minority of intradural tumors. Among intramedullary spinal cord tumors, hemangioblastomas are uncommon, and schwannomas are extremely rare. Collision tumors are histologically distinct tumors that are intermingled and growing together.

OBSERVATIONS

In this report, the authors describe a patient with a cervical intramedullary collision tumor involving a hemangioblastoma and schwannoma. To the authors’ knowledge, no prior spinal intramedullary collision tumor involving multiple neoplasms has been described. The patient’s presentation and management are described.

LESSONS

Clinicians should consider the possibility of collision tumors when evaluating intramedullary spinal cord tumors, especially when patient presentation and radiographic findings are atypical. When tumors with similar radiographic characteristics form collision tumors, distinction using preoperative imaging can be extremely challenging. In addition, surgical management of intramedullary collision tumors, like that for all intramedullary spinal cord tumors, should involve meticulous perioperative care and a methodical surgical technique. Maximal safe resection will depend upon histopathological diagnosis, anatomical location of the tumor, presence of distinct dissection planes, and stability of neuromonitoring. Finally, ongoing research on the genetics of intramedullary spinal cord tumors may identify underlying genetic links for intramedullary hemangioblastomas and schwannomas.

Clinicopathologic Features of Diencephalic Neuronal and Glioneuronal Tumors

Neuronal/mixed glioneuronal tumors are central nervous system neoplasms composed of neoplastic neuronal cell components or a mixture of glial and neuronal elements. They occur in cerebral hemispheres, posterior fossa, and spinal cord. Compared with other tumors at these locations, diencephalic neuronal/glioneuronal tumors are very rare and therefore not well characterized. We hereby performed clinicopathologic evaluation on 10 neuronal/glioneuronal tumors arising from the diencephalic region. Morphologically, these tumors resemble their histologic counterparts in other locations, except that lymphocytic infiltrates and microcalcifications are more common than Rosenthal fibers or eosinophilic granular bodies. The BRAFV600 mutation rate is 75%. Given the high percentage of samples being small biopsy specimens, the subtle histologic features and molecular findings greatly aided in establishing the pathologic diagnosis in several cases. At a median follow-up of 42 months, 71% of the tumors demonstrated radiological recurrence or progression, with median progression-free survival of 18 months. Recurrence/progression is observed in tumors across different histologic subtypes, necessitating additional therapies in 56% of the cases. Despite their bland histology, diencephalic neuronal/glioneuronal tumors are not clinically indolent. Their frequent recurrences warrant a close follow-up, and the prevalent BRAF mutation makes MAPK pathway inhibition a plausible treatment option when conventional therapies fail.

A rare case of giant cell tumor involving the clivus resected through Le Fort I Osteotomy and median maxillotomy

Background:

Giant cell tumors (GCTs) are bone tumors that seldom involve the skull. Skull GCTs preferentially occur in the sphenoid and temporal bones with few reported cases involving the clivus. Due to the rarity and complex location, surgical management is not well established for clival GCTs.

Case Description:

A 49-year-old male presented with headaches and blurred vision in the right eye for 2 weeks. Computed tomography (CT) with contrast revealed a sellar mass eroding through the sphenoid sinuses with compression of optic chiasm. Biopsy was consistent with GCT. Patient underwent tumor resection by Le Fort I Osteotomy and median maxillotomy for an extended transsphenoidal approach. Upon discharge, patient showed no neurological deficits and intact cranial nerves.

Conclusion:

This case contributes to the limited amount of skull-based GCT cases worldwide. Additionally, the extended transoral approach can be performed safely in the context of a GCT within the clivus with acceptable morbidity and cosmesis.

Expression of diagnostic neuronal markers and outcome in glioblastoma

BACKGROUND

High-grade gliomas featuring giant cells, often demonstrate immunoreactivity for neuronal markers, a finding prognostically significant according to some studies. We investigated this event in glioblastomas (GBM).

METHODS

Immunoexpression for synaptophysin, neurofilament protein, neuronal nuclear antigen, chromogranin and glial fibrillary acidic protein was analysed in 82 GBM including 11 fibrillary, 8 gemistocytic, 40 giant cell and 23 small cell examples. Survival was compared between tumours exhibiting (GBMpos) or lacking (GBMneg) neuronal markers and also between tumours expressing only one vs. two or more neuronal markers.

RESULTS

Forty-five of the 82 tumours (54.8%) including 5 fibrillary, 5 gemistocytic, 30 giant cell and 5 small cell GBMs expressed at least one neuronal marker, synaptophysin being the most frequent (96%). There was no statistically significant difference in survival between GBMpos and GBMneg tumours, all cytologic subtypes combined (P = 0.22). The same was true when cytologic categories were compared. When only GBMpos tumours were analysed, there was a marginally significant difference in outcome between tumours positive for one vs. multiple markers (P = 0.05). This difference was influenced primarily by giant cell GBMs among which the survival time was significantly shorter in the multiple vs. single marker category (median 123 vs. 295 days, P = 0.014). This difference was not observed in the other GBM cell types. Ultrastructurally, rare neurosecretory granules in glial filament-rich cells were identified in one of four tumours studied.

CONCLUSIONS

Neuronal marker expression is a frequent feature of GBM. Its prognostic significance is limited to the giant cell GBMs expressing two or more neuronal markers, these being associated with shorter survival.

Pseudoneoplasms of the Nervous System

Context.—Pseudoneoplasms of the nervous system vary greatly in nature. Ranging from inflammatory to autoimmune, infectious, malformative, reactive, degenerative, and radiation induced, they all mimic true tumors. Thus, they have the potential to mislead clinicians, radiologists, and pathologists alike. Their clinical and/or neuroimaging and histologic features are readily misinterpreted as tumor. Knowledge of the pitfalls is essential to avoid mismanagement, specifically overtreatment. In such instances, pathologists must take the entire clinical picture into consideration, acquainting themselves with presenting symptoms, physical findings, and neuroimaging.

Objective.—To present 10 examples of pseudoneoplasms of the nervous system, analyze the basis for their mimicry, and discuss their differential diagnosis.

Data Sources.—Review of the pertinent literature related to pseudoneoplasms of the nervous system and review of the consultation files of one of the authors (B.W.S.).

Conclusions.—The identification of tumor mimics may be difficult under the best of circumstances, and maintaining a broad differential diagnosis as well as application of a variety of immunocytochemical and occasionally ultrastructural and/or molecular genetic methods is essential to arrive at a correct diagnosis.