Supratentorial Ependymoma Research Articles

STEM-11. MULTIDIMENSIONAL PROFILING OF TUMOR CELL HETEROGENEITY REVEALS CELL-LINEAGE SPECIFIC FUNCTIONS IN SUPRATENTORIAL EPENDYMOMAS

Abstract Supratentorial ependymomas (ST-EPN) are aggressive pediatric brain tumors that are categorized into distinct molecular subgroups. However, the developmental origins, tumor microenvironment, and phenotypic characteristics of tumor subpopulations across these subgroups are still poorly understood. In this study, we explored the human developmental signatures, global spatial organization, and the morphological and migratory tumor cell state behaviors in ST-EPN tumors at unprecedented resolution. We profiled 42 ST-EPN patients encompassing ZFTA-RELA (n = 20), ZFTA-Clusters 1 to 4 (n=20), and ST-YAP1 (n=4) subgroups by single-cell RNA sequencing (scRNA-seq), spatial transcriptomics, and live-cell imaging. We identified recurrent tumor cell states across tumors, that cover both generic cell processes (including cycling and mesenchymal/hypoxia) and human embryonic and fetal brain developmental signatures. ST-EPN subgroups displayed distinct developmental signatures, mapping to two separate temporally restricted progenitors-neuroepithelial-like and embryonic-like cells. Additionally, tumors showed diverging patterns of neuronal or ependymal differentiation, with ZFTA-Cluster 3 tumors as especially distinct from other subgroups in both developmental origin and differentiation. Furthermore, by utilizing 10X Xenium and novel algorithms we discovered that mesenchymal/hypoxia is critical for driving global tissue architecture to become more organized. Notably, recurrent tumors exhibited higher proportion of mesenchymal/hypoxia cells and greater structure than primary tumors. Lastly, by superimposing molecular and functional assays in both in vivo and in vitro models, we found that cell states exhibit distinct morphological and migratory behaviors, with neuronal-like cells being the most invasive. Neuronal-like cells especially exhibited distinct behavioral patterns reminiscent of neuronal migration during development. Moreover, we demonstrated the crucial role of neuronal microenvironment in promoting plasticity of cells toward this neuronal lineage. Taken together, we present a multidimensional framework for investigating cellular states within ST-EPN tumors, offering novel insights into their developmental origins, patterns of spatial organization, and cellular behavioral characteristics.

TMET-36. INCREASED METHIONINE CYCLE DRIVES PYRIMIDINE METABOLISM IN LETHAL PEDIATRIC EPENDYMOMAS

Abstract Supratentorial ependymomas (ST-EPN) are pediatric brain tumors found in the cerebral hemisphere, driven by the oncogenic fusion of ZFTA with RELA. Other than surgery and radiotherapy, these tumors do not have effective therapeutic options. Recurrent ST-EPN tumors are highly aggressive and hard to treat, which makes these tumors lethal. To understand the disease mechanism and potentially identify or develop therapeutic targets, we established patient-derived models and interrogated the genetic and metabolic dependencies using cutting-edge, near-genome-wide genetic screening and metabolomic tools. Our integrative transcriptomics and metabolic analysis identify that the ZFTA-RELA fusion drives methionine metabolic reprogramming in the cancer stem cells to regulate permissive epigenetic status and pyrimidine nucleotide synthesis to fuel tumor growth. Limiting methionine or inhibiting MAT2A, a rate-limiting enzyme of methionine metabolism in ST-EPN cells, results in profound cell cycle arrest and make the cells vulnerable to pyrimidine inhibitors compared to other pediatric brain tumors. Thus, for treatment, along with radiotherapy, blocking the methionine cycle by using the methionine limited diet or in combination with pyrimidine metabolism inhibitors can be a novel therapeutic strategy against the aggressive paediatric ST-EPN tumors.

Case report: Polymorphous low-grade neuroepithelial tumor of the young and supratentorial ependymoma diagnosed in an adult male

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a rare central nervous system (CNS) pathology predominantly observed in the pediatric population. Ependymomas also exhibit a peak incidence in early childhood, with rare presentations after early adulthood. In this report, we describe a rare case of a 41-year-old man diagnosed sequentially with a polymorphous low-grade neuroepithelial tumor of the young, followed by a supratentorial ependymoma within a year. He underwent tumor resection for both tumors, as well as adjuvant radiation therapy for the ependymoma. Despite these interventions, he ultimately succumbed to tumor progression and postoperative complications. Currently, no genetic syndromes are known to link these two primary CNS tumors. Two commonalities at the chromosomal and cellular level include histone gene H3F3A mutations and positive glial fibrillary acidic protein staining on immunohistochemistry. To the best of our knowledge, this unique dual pathology has not been previously described in the literature, making this case an avenue for further investigation and research into connections between these two distinct CNS pathologies.

Supra-tentorial Ependymomas with ZFTA Fusion, YAP1 Fusion, and Astroblastomas, MN1-altered: Characteristic Imaging Features.

Supratentorial (ST) ependymoma subgroups are defined by two different fusions with different prognoses. Astroblastomas, MN1-altered, have ependymal-like histopathologic features and represent adifferential diagnosis in children. We hypothesized that ZFTA-fused ependymoma and YAP1-fused ependymoma on the one hand, and astroblastoma, MN1-altered, on the other hand, show different MRI characteristics. We retrospectively analyzed the preoperative imaging of 45patients with ST ependymoma or astroblastoma between January 2000 and September 2020, blinded to histomolecular grouping. Several characteristics, such as location, tumor volume, calcifications, solid/cystic component, and signal enhancement or diffusion were evaluated. We compared imaging characteristics according to their molecular subtype (ZFTA-fused, YAP1-fused, and astroblastoma, MN1-altered). Thirty-nine patients were classified as having an ependymoma, 35with aZFTA fusion and four with aYAP1 fusion, and six as having an astroblastoma, MN1-altered. YAP1-fused ependymomas were more likely to involve at least 3lobes than ZFTA-fused ependymomas. Astroblastomas were located in the frontal lobe in 100% of the tumors versus 49% of the ependymomas. Cerebral blood flow by arterial spin labeling was higher in astroblastomas than in ependymomas. There were no differences in the other characteristics between the molecular groups. All the tumors showed common features: intra-axial extra-ventricular tumors, very frequent contrast enhancement (39/43, 91%), acystic/necrotic component (41/45, 91%), restricted diffusion (32/36, 89%), calcifications (15/18, 83%), and peri-tumoral edema (38/44, 86%). The distinction between ST ependymoma subtypes and astroblastomas can be guided by several imaging features. These tumors share common imaging features that may help to differentiate ST ependymomas and astroblastomas from other pediatric ST tumors.

Supratentorial ependymoma, ZFTA fusion-positive, with extensive mesenchymal differentiation.

Supratentorial ependymoma, ZFTA fusion-positive, with extensive mesenchymal differentiation.

Clinicopathological profile of ependymomas with special reference to survival data - Experiences of a tertiary care center'.

Ependymomas exhibit heterogeneity across age, location, histology, molecular nature and survival suggestive of an epigenetic component in its pathogenesis. The CNS WHO classification (2021) classifies ependymomas based on DNA methylation profiles. Studies suggest that molecular sub-types remain stable throughout the course of disease. Immunohistochemical expression of L1CAM, has been identified as a surrogate marker for ZFTA/c11orf95-RELA fusion in supratentorial ependymomas. This study aims at realising its utility specially in resource-poor setups. Forty-three histopathologically-proven cases of ependymoma under treatment over the period of three years were selected. Histopathological examination followed by routine IHC staining for GFAP, S-100, EMA and Ki-67 in all cases and L1CAM in the supratentorial ependymomas was done. We have followed-up almost all cases during our study period and was correlated with the IHC expression patterns and clinico-pathological parameters, including survival. In our study the commonest location for ependymomas was spine in adults and posterior fossa in pediatric age group. Majority cases belonged to CNS WHO Grade 2 both in adults and in the paediatric age group. Supratentorial location of ependymomas with positive immuno-reactivity for L1CAM and a higher Ki-67 labelling index were associated with poor survival. Our study revealed that L1CAM is an effective surrogate marker for supratentorial ependymomas possibly carrying the ZFTA Fusion gene product. The L1CAM immuno-reactivity also corresponded with the survival data. However, larger population-based studies are required to validate these results further.

MODL-08. PATIENT-DERIVED ORGANOIDS RECAPITULATE THE MOLECULAR LANDSCAPE OF PEDIATRIC BRAIN TUMORS

Abstract BACKGROUND Pediatric brain tumors (PBT) are the leading cause of non-accidental death in pediatric age. These tumors are rare and lack adequate experimental models capable of accurately capturing their complex molecular landscape. METHODS AND RESULTS Our team has established specific protocols for the generation and expansion of ex-vivo patient-derived organoids (PDO) from fresh surgical material of a variety of PBT, within a clinically relevant timeframe. These include pilocytic astrocytomas, a pleomorphic xanthoastrocytoma, a rosette-forming glioneuronal tumor, a supratentorial ependymoma, diffuse high-grade gliomas, a medulloblastoma, an atypical teratoid rhabdoid tumor, and a meningioma. The PDO cultures were set within 7-15 days, with organoids reaching 200-800 μm in diameter. Immunofluorescence analysis using confocal high-content microscopy imaging revealed that PDO kept the protein markers typically found in the corresponding primary tumors. Likewise, at a genomic level, PDO recapitulated the molecular landscape of corresponding primary tumors, as denoted by the maintenance of NF1, PIK3CA, and FGFR1mutations (rosette-forming glioneuronal tumor), KIAA1549::BRAF fusions (pilocytic astrocytomas), ZFTA::RELA fusion(supratentorial ependymoma) or gene amplifications, such as KRAS, CDK4, MDM2, GLI1, PTPN11 and PI3KCA. Additionally, PDO exhibited minimal genetic drift after over one month in culture. In three PBT cases from a medulloblastoma, an atypical teratoid rhabdoid tumor, and a meningioma, where no molecular alterations were detected using a comprehensive NGS panel, we are running DNA methylation arrays and copy number variations. CONCLUSIONS Our results underscore the potential of PDO as a robust ex-vivo experimental model. The generated PDO cultures can be rapidly established and retain key molecular features of corresponding primary tumors. This preclinical model presents versatile applications, serving as a valuable molecular tool for precision medicine approaches in PBT patients, the study of PBT biology, and the acceleration of drug development processes within the context of PBT.

EPEN-12. EZHIP IMPACTS CELLULAR DIFFERENTIATION IN POSTERIOR FOSSA GROUP A EPENDYMOMA

Abstract BACKGROUND High-risk ependymomas are central nervous system tumors comprising ten molecular groups with posterior fossa group A (PFA) and supratentorial ependymoma with zinc finger translocation associated (ST-ZFTA) fusions being among the most aggressive subgroups in children. Loss of H3K27 trimethylation maintained by Enhancer of Zeste homologs Inhibitory Protein (EZHIP) overexpression in PFA or ZFTA-RELA oncofusions in ST-ZFTA ependymoma are known as important driver events. Additionally, we uncovered that high-risk ependymomas arise from undifferentiated cell populations, while more differentiated ependymal-like signatures (e.g. ciliogenic programs) are enriched in prognostically favourable subtypes. METHODS We investigated presence of “ependymal-like” signatures by analysing mRNA expression of selected genes (RSPH1, DNAAF1, SLC47A2, CAPS, CAPS-L) in ependymoma bulk samples (n=90). Gene expression was correlated to clinicopathological characteristics (EZHIP expression, 1q-gain/6q-loss, DNA methylation subtype). Impact on mRNA levels of ependymal-like markers was investigated upon an inducible EZHIP knockdown using lentiviral vectors in EPD210FH PFA cells. RESULTS Ependymal-like markers were significantly lower expressed in ST-ZFTA as compared to spinal and PFB ependymoma. In PFA ependymoma two distinct groups showing either low or high expression of these ependymal-like genes were present. In detail, “ependymal-like-high” PFA were assigned to the PFA-2 subtype which was also confirmed in an independent cohort. EZHIP was strongly negative prognostic in our cohort and the expression was distinctly induced during PFA progression accompanied by increased ependymal-like signature genes. This suggests an impact of EZHIP on cell differentiation processes particularly during PFA progression. Knock-down of EZHIP in EPD210FH PFA cells increased expression of ependymal signature genes associated with ciliogenesis. Next, we will spatially dissect the correlation between EZHIP and ependymal-like genes in primary and recurrent PFA and investigate DNA methylation, histone marks and EZHIP binding at these gene loci. CONCLUSION Overall, our data indicate that ependymal-like cell differentiation is deregulated by EZHIP particularly in progressive PF-A ependymoma.

METB-11. HOW METHYLATION PROFILING HELPS IN DIAGNOSING AND TREATING PEDIATRIC BRAIN TUMORS IN INDONESIA

Abstract BACKGROUNDS Pediatric brain tumors (PBT) exhibit extensive heterogeneity, impacting treatment outcomes. While traditionally classified based on histopathological features, recent WHO classifications have integrated DNA methylation array profiling amongst other molecular characteristics, which improves diagnostic accuracy and thus treatment decisions. However, access to this technology is limited in low- and middle-income countries (LMICs) like Indonesia. As part of the MNP Outreach Consortium, we aimed to introduce methylation profiling in Indonesia to aid in diagnosing and stratifying PBT patients. METHODS In 2023, we conducted a case series involving seven challenging PBT cases from Cipto Mangunkusumo National General Hospital, re-assessing them with methylation profiling. RESULTS Through collaboration with the Institute of Neuropathology Heidelberg and the DKFZ, our centre adopted a discerning approach to re-evaluate histopathological samples from complex cases. This endeavour yielded notable results, reaffirming four initial diagnoses and altering three others Amongst the findings, one case initially diagnosed as anaplastic ependymoma, CNS WHO grade 3, was reclassified as a supratentorial ependymoma with YAP1 fusion gene, based on methylation class. Noteworthy within this latter group, one case initially categorized as low-grade pilocytic astrocytoma was reclassified as high-grade diffuse midline glioma, H3 K27 altered. Moreover identifying the copy number plot could indicate a KIAA1549::BRAF fusion to reclassify a case from diffuse pediatric glioma WHO grade 2 to pilocytic astrocytoma WHO grade 1. The recurrent pigmented neuroectodermal tumor of infancy (MNTI) was reclassified as Medulloblastoma, non-WNT/non-SHH, group 3 subtype II on methylation profiling, highlighting molecular similarities and potential treatment insights. These findings offer insights into genetic mechanisms and guide treatment strategies. CONCLUSION Accurate diagnosis, facilitated by advanced molecular profiling, enhances prognostication and enables personalized treatment plans, even in LMICs. This underscores the importance of expanding access to advanced diagnostic technologies in resource-limited settings.

EPEN-29. IS THE OUTCOME OF SUPRATENTORIAL EPENDYMOMA WITH ZFTA FUSION REALLY POOR?

Abstract BACKGROUND Survival of children with intracranial ependymoma is known to depend, in part, on the molecular group of the tumor. Previous studies have linked both PFA and ZFTA molecular group ependymomas to poor outcomes. As part of an unplanned analysis from ACNS0831, we explored outcomes for ZFTA supratentorial (ST) and PFA ependymomas. METHODS Patients were stratified by location, grade and extent of resection. Grade 2, ST tumors with no evidence of disease were observed only, N=37. All other patients were randomized to RT versus RT + maintenance chemotherapy or non-randomly assigned to RT + M if residual disease. A planned “as treated” analysis was performed by actual treatment received for randomized patients, excluding those who did not receive RT. Molecular groups were compared using two-sided log-rank tests stratified by study arms for all and randomized patients. Molecular characterization was achieved in 161/166 (97%) ST and 282/283(99.6%) PF. Among ST, 94% were classified ZFTA and 6% YAP1. Homozygous CDKN2A deletion was detected in 16 tumors, all ZFTA and WHO grade 3. Among posterior fossa ependymomas, 88% were classified as PFA and 12% as PFB. RESULTS There was no statistical difference in outcome according to treatment. Across all study arms, 5-year EFS was 69.6%+4.3 for ZFTA vs. 52.9%+3.4 for PFA (p=0.028). For the randomized cohort, 5-year EFS was 72.1+4.8 for ZFTA vs. 60.1+3.9 for PFA (p=0.076). For the randomized cohort with initial GTR/NTR, 5-year EFS was 74.1+5.1 for ZFTA patients vs. 61.0+4.2 for PFA patients (p=0.045). The 5-year EFS was 66.7+12.2 for ZFTA patients with CDKN2A deletion vs. 69.3+4.7 for ZFTA patients without CDKN2A deletion (p=0.232) CONCLUSION Children with ST ZFTA ependymomas have a significantly better outcome than those with PFA tumors. Homozygous deletion of CDKN2A was present in 12% of ST ependymomas but was not an indicator of poor outcome.

EPEN-25. “CONCERNING EPENDYMOMAS, A FURTHER SUBDIVISION IS NEITHER MORPHOLOGICALLY NOR BIOLOGICALLY NECESSARY”: A NARRATIVE REVIEW OF RESEARCH ON EPENDYMOMAS BETWEEN 1865 AND 2024

Abstract BACKGROUND The history of research on ependymomas dates back to the nineteenth century. However, ependymomas have received much less attention than other neuro-oncological diseases. This narrative review investigates the history of ependymoma as a distinct tumour entity. METHODS A comprehensive literature search in German, English and French was carried out for publications from 1850 to 2024 in PubMed, the Internet Archive, and the library of Heidelberg University. Additionally, the evolution of the classification of ependymoma throughout the editions of the WHO classification of CNS tumours was analysed. RESULTS The first major systematic description of ependymal tumours was published in 1865 by Rudolf Virchow, who hypothesized that ependymomas originated from chronic irritations to the ependyma. In 1899, perivascular (pseudo-)rosettes were described for the first time. Subsequently, Percival Bailey and Harvey Cushing’s systematic classification efforts laid the groundwork for new advancements. Debates about the classification of ependymomas can already be found in publications by Percival Bailey or Gustave Roussy in 1924, with a major focus on the definition of ependymoblastoma as an independent entity, which was only resolved in 2016 with the introduction of the new diagnosis ETMR. Klaus Joachim Zülch’s important mid-20th-century work highlighted clinical variations within ependymomas but deemed no further stratification necessary. The WHO’s classifications in 1979, 1993, 2000 and 2007 relied on histopathology, with only minor details being adapted over the years. A new era began in 2016 with the recognition of C11orf95-RELA (ZFTA-RELA) as a defining hallmark of supratentorial ependymomas. The latest WHO classification in 2021 adopted a molecular-anatomical approach, incorporating new subgroups and abandoning histomorphological subtypes due to limited prognostic value. Tumor grading became mostly optional. CONCLUSIONS This review summarises the significant evolution in ependymoma research, particularly in the 2010s. Strikingly, many of the questions that Virchow, Bailey or Roussy investigated, remain unanswered in 2024.

EPEN-22. ZFTA FUSION ONCOPROTEINS DRIVE ONCOGENESIS THROUGH ASSEMBLY OF BIOMOLECULAR CONDENSATES

Abstract BACKGROUND Ependymomas continue to be an aggressive brain tumor entity without targeted therapies. The highly recurrent fusion oncoprotein (FO), ZFTA-RELA, is known to be associated with about 70% of supratentorial ependymomas. While recent studies have highlighted that the fusion protein is involved in aberrant DNA binding and subsequent oncogenic gene expression, the precise mechanisms underlying the transcriptional dysregulation remain elusive. METHODS Using super-resolution and lattice-sheet microscopy, we demonstrate that ZFTA-RELA forms dynamic liquid-like nuclear condensates. ZFTA-RELA condensates recruit co-factors like Med1, and Brd4 and are associated with the transcription of ependymoma oncogenes (Notch1 and Ccnd1). We leveraged machine learning models trained on FOs in other cancers to identify critical intrinsically disordered domains (IDRs) within ZFTA-RELA. A series of mutagenesis experiments were conducted to determine IDRs important for condensate formation, transcription, and tumor initiation. We also performed NMR spectroscopy to unravel the protein structure of ZFTA-RELA zinc finger binding domains. RESULTS We demonstrate that transcriptional condensate formation of ZFTA-RELA is an important cellular phenotype that is tightly linked with oncogenic transcription and tumor initiation. Further, we identify key residues within the zinc finger domain of ZFTA that are required for DNA binding of oncogenic target genes and condensate formation. Deletion of the key IDRs within ZFTA-RELA disrupts condensates and abolishes transcriptional activation and tumorigenesis. We also show that condensate formation is an underlying feature found across all other ZFTA-fusion oncoproteins, providing a model to understand how ZFTA FOs drive cancer. CONCLUSION Our studies provide mechanistic insights into the biophysical and structural basis of ZFTA fusion oncoproteins. These findings provide a framework to develop druggable strategies through targeting ZFTA FO zinc finger domains or disruption of oncogenic condensates.

EPEN-04. OVERWHELMING ZFTA-RELA NUCLEAR LOCALIZATION AS A THERAPEUTIC STRATEGY AGAINST EPENDYMOMA

Abstract BACKGROUND Pediatric ependymoma is a malignant brain tumor without targeted therapies. The 10-year survival is close to 50%, as this relentless tumor often relapses years following initial diagnosis. Over two thirds of supratentorial ependymomas harbor a gene fusion between ZFTA and RELA (ZFTA-RELA). Despite evidence that ZFTA-RELA drives tumorigenicity, mechanistic details remain elusive, hindering efforts to uncover therapeutic vulnerabilities. Since direct targeting of ZFTA-RELA is not currently possible, we hypothesized that ZFTA-RELA fusion binding partners would represent vulnerabilities amenable to therapeutic targeting. METHODS We investigated the biochemical basis of ZFTA-RELA, with the goal of identifying key members of the protein interaction landscape. This was performed in our in utero electroporation mouse model of ZFTA-RELA ependymoma. A series of sucrose gradient and immuno-precipitation experiments were performed, coupled with mass spectrometry. ZFTA-RELA interaction proteins were functionalized using focused CRIPSR-Cas9 library screens in cell cultures. Critically, these revealed novel dependencies and druggable targets, with XPO1 emerging as a lead candidate. In vitro and in vivo studies were conducted to evaluate targeting XPO1 in ZFTA-RELA ependymoma. RESULTS ZFTA-RELA regulates XPO1 gene transcription, and elevated gene expression is associated with poor survival in these patients. While expression of ZFTA-RELA is necessary for oncogenic transcription, extremely elevated nuclear localization is associated with reduced growth. This suggests a ‘goldilocks’ model in which XPO1 titrates precise levels of nuclear ZFTA-RELA protein. We reveal that a potential therapeutic vulnerability emerges through modulation of ZFTA-RELA nuclear localization. Supporting this, chemical inhibition of XPO1 using Selinexor, has a direct effect on ZFTA-RELA cellular localization patterns. Critically, in patient derived orthotopic xenograft models, XPO1 inhibition exerts anti-tumor effects both in vitro and in vivo. CONCLUSION Our findings reveal a novel therapeutic strategy in ependymoma, and provide the mechanistic and pre-clinical data needed to develop a clinical trial for patients with ZFTA-RELA ependymoma.

Disappearance of "Elongated Pony Tail Sign" Following Chemoradiotherapy in a Case of Primary Cerebellopontine Angle Ependymoma With Spinal Drop Metastasis: 18 F-FDG PET/CT Scan Findings.

Ependymomas are rare glial tumors that commonly arise from the lining cells of ventricular system and constitute ~10% of intracranial pediatric malignancies. The incidence of ependymoma in adults is rare. Due to close approximation with the ventricular system, subtentorial ependymomas are more prone to show cerebrospinal fluid metastasis compared with supratentorial ependymomas. We present a case of subtentorial cerebellopontine angle ependymoma with diffuse spinal drop metastases showing "elongated pony tail appearance" in a 69-year-old man with complete metabolic response on 18 F-FDG PET/CT imaging following chemoradiotherapy.

CNS tumors with PLAGL1-fusion: beyond ZFTA and YAP1 in the genetic spectrum of supratentorial ependymomas

A novel methylation class, “neuroepithelial tumor, with PLAGL1 fusion” (NET-PLAGL1), has recently been described, based on epigenetic features, as a supratentorial pediatric brain tumor with recurrent histopathological features suggesting an ependymal differentiation. Because of the recent identification of this neoplastic entity, few histopathological, radiological and clinical data are available. Herein, we present a detailed series of nine cases of PLAGL1-fused supratentorial tumors, reclassified from a series of supratentorial ependymomas, non-ZFTA/non-YAP1 fusion-positive and subependymomas of the young. This study included extensive clinical, radiological, histopathological, ultrastructural, immunohistochemical, genetic and epigenetic (DNA methylation profiling) data for characterization. An important aim of this work was to evaluate the sensitivity and specificity of a novel fluorescent in situ hybridization (FISH) targeting the PLAGL1 gene. Using histopathology, immunohistochemistry and electron microscopy, we confirmed the ependymal differentiation of this new neoplastic entity. Indeed, the cases histopathologically presented as “mixed subependymomas-ependymomas” with well-circumscribed tumors exhibiting a diffuse immunoreactivity for GFAP, without expression of Olig2 or SOX10. Ultrastructurally, they also harbored features reminiscent of ependymal differentiation, such as cilia. Different gene partners were fused with PLAGL1: FOXO1, EWSR1 and for the first time MAML2. The PLAGL1 FISH presented a 100% sensitivity and specificity according to RNA sequencing and DNA methylation profiling results. This cohort of supratentorial PLAGL1-fused tumors highlights: 1/ the ependymal cell origin of this new neoplastic entity; 2/ benefit of looking for a PLAGL1 fusion in supratentorial cases of non-ZFTA/non-YAP1 ependymomas; and 3/ the usefulness of PLAGL1 FISH.

In vitro and in vivo modeling systems of supratentorial ependymomas.

Ependymomas are rare brain tumors that can occur in both children and adults. Subdivided by the tumors' initial location, ependymomas develop in the central nervous system in the supratentorial or infratentorial/posterior fossa region, or the spinal cord. Supratentorial ependymomas (ST-EPNs) are predominantly characterized by common driver gene fusions such as ZFTA and YAP1 fusions. Some variants of ST-EPNs carry a high overall survival rate. In poorly responding ST-EPN variants, high levels of inter- and intratumoral heterogeneity, limited therapeutic strategies, and tumor recurrence are among the reasons for poor patient outcomes with other ST-EPN subtypes. Thus, modeling these molecular profiles is key in further studying tumorigenesis. Due to the scarcity of patient samples, the development of preclinical in vitro and in vivo models that recapitulate patient tumors is imperative when testing therapeutic approaches for this rare cancer. In this review, we will survey ST-EPN modeling systems, addressing the strengths and limitations, application for therapeutic targeting, and current literature findings.

Imaging of supratentorial ependymomas with radio-pathological correlation.

Supratentorial ependymoma (STE) is a rare tumor with distinct genetic alterations, whose imaging features have been scarcely studied. This study aims to review the computed tomography (CT) and magnetic resonance imaging (MRI) features of a cohort of histopathologically proven STE to identify the distinguishing features of STE, and look for specific signs of zinc finger translocation associated (ZFTA) fused STEs. Ethical clearance was obtained from the institutional ethics committee. The magnetic resonance (MR) images, CT images when available, clinical details, and pathological reports of 25 patients from a single institute with histopathologically proven STE were retrospectively reviewed. Imaging features, demographic details, pathological and molecular features, and type of surgical resection were described and tabulated. Relevant associations with imaging features were computed and tabulated. The study showed that STEs are common in the pediatric population with no sex predilection. The periventricular location was the most common. A significant association between periventricular location and the presence of a cystic component (P value = 0.023) and the presence of the periwinkle sign/stellate sign (P value = 0.045) was found. Common features of ZFTA fused STEs included periventricular or intraventricular location, cystic component, necrosis, and the periwinkle sign. A significant association was found between ZFTA fusion and cystic component (P value = 0.048). This study attempts to identify the imaging features of STEs and their associations with molecular pathology and surgical outcome, and the distinguishing features of ZFTA fused STEs.

Overcoming the challenge of a thin skull in a 2-year-old patient undergoing laser interstitial thermal therapy using an individualized stereotactic platform: illustrative case.

Ependymoma is the third most common pediatric brain tumor that can present with headaches, cranial nerve deficits, nausea, vomiting, and ataxia. Current treatment is maximal safe resection followed by radiation therapy. More recently, laser interstitial thermal therapy (LITT) has become an alternative to traditional resection. In this report, the authors describe the utilization of a single-use, patient-specific stereotactic platform for the treatment of supratentorial ependymoma with LITT. A 2-year-old female had a complex history of supratentorial ependymoma after multiple craniotomies for repeated tumor progression and ventriculoperitoneal shunt placement. Imaging demonstrated an enlarging, complex, enhancing mass in the right occipital region. LITT was decided on for treatment. Given the thinness of the patient's skull, which precluded traditional means of stereotaxy, the authors elected to use a personalized stereotactic platform. Immediate postoperative imaging captured complete laser ablation of the tumor, with long-term imaging demonstrating a decreased tumor size. Individualized stereotactic platforms are increasingly used in adult populations, but pediatric use continues to be infrequent. In this report, the authors present the youngest reported case using a personalized stereotactic platform and show the effectiveness of this system for performing LITT in the youngest of populations with very thin skulls.

Abstract B010: Revealing the Influence of the Infantile Immune System on the Developmental Origins of Childhood Ependymoma: An Integrative Multi-Omic Investigation of Supratentorial Ependymoma Tumorigenesis Driven by ZFTA-RELA Fusion

Abstract Despite advances in treatment, the recurrence rate of childhood supratentorial ependymomas remains distressingly high, with approximately 60% of patients experiencing relapse. Moreover, the rigorous treatment regimen poses significant challenges to the quality of life of affected children. Among supratentorial ependymomas, those driven by the ZFTA-RELA fusion represent over 70% of cases. Here, we present the pioneering development of a spontaneous genetically engineered mouse model (GEMM) for ZFTA-RELA fusion-driven ependymoma. By targeting the Nestin-Flx-STOP-Flx-ZFTA-RELA open reading frame with luciferase to the Rosa-26 locus of C57B/L6 mice, and subsequently crossing them with the Nestin-CreERT2 line, we successfully induced recombination in neural progenitor cells. Consequently, resulting in the development of forebrain tumors that could be monitored through non-invasive bioluminescence imaging from postnatal day 20. Recognizing the neonatal origins of ZFTA-RELA ependymoma, our study employed an integrated multi-omic approach to investigate the complete developmental trajectory of this tumor, spanning from embryonic stages to postnatal tumor formation. Notably, we uncovered a reservoir of immature immune populations in the developing brain, which we implicate in the central tolerance of ependymoma tumorigenesis. The coordinated interaction between these immature immune populations in the developing brain and immune cell progenitors in the skull bone marrow niche establishes a unique environment that fosters tumor formation. In light of these findings, we propose that immunotherapeutic strategies aimed at augmenting these immature immune populations hold promise as potential therapeutic interventions. By exploiting the intricate interplay between these populations, we may unlock new avenues for targeted immunotherapies in ZFTA-RELA ependymoma. Our research sheds vital light on the critical role played by the pediatric immune system in the developmental origins of this devastating malignancy, opening up exciting possibilities for improved treatments and outcomes in the future. Citation Format: Elizabeth Cooper, Sigourney Bonner, Amir Jassim, Gunjan Katyal, Alisha Kardian, Stephen C. Mack, Katherine Masih, Jessica T. Taylor, Claire King, Katherine Wickham Rahrmann, Linda Hu, Richard J. Gilbertson. Revealing the Influence of the Infantile Immune System on the Developmental Origins of Childhood Ependymoma: An Integrative Multi-Omic Investigation of Supratentorial Ependymoma Tumorigenesis Driven by ZFTA-RELA Fusion [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2023 Oct 1-4; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2023;11(12 Suppl):Abstract nr B010.

An 89-year-old Filipino female with ruptured middle cerebral artery aneurysm within a supratentorial ependymoma: A case report and literature review

An 89-year-old Filipino female with ruptured middle cerebral artery aneurysm within a supratentorial ependymoma: A case report and literature review