Revisiting gliomatosis cerebri in adult-type diffuse gliomas: a comprehensive imaging, genomic and clinical analysis.

Although gliomatosis cerebri (GC) has been removed as an independent tumor type from the WHO classification, its extensive infiltrative pattern may harbor a unique biological behavior. However, the clinical implication of GC in the context of the 2021 WHO classification is yet to be unveiled. This study investigated the incidence, clinicopathologic and imaging correlations, and prognostic implications of GC in adult-type diffuse glioma patients. Retrospective chart and imaging review of 1,211 adult-type diffuse glioma patients from a single institution between 2005 and 2021 was performed. Among 1,211 adult-type diffuse glioma patients, there were 99 (8.2%) patients with GC. The proportion of molecular types significantly differed between patients with and without GC (P = 0.017); IDH-wildtype glioblastoma was more common (77.8% vs. 66.5%), while IDH-mutant astrocytoma (16.2% vs. 16.9%) and oligodendroglioma (6.1% vs. 16.5%) were less common in patients with GC than in those without GC. The presence of contrast enhancement, necrosis, cystic change, hemorrhage, and GC type 2 were independent risk factors for predicting IDH mutation status in GC patients. GC remained as an independent prognostic factor (HR = 1.25, P = 0.031) in IDH-wildtype glioblastoma patients on multivariable analysis, along with clinical, molecular, and surgical factors. Overall, our data suggests that although no longer included as a distinct pathological entity in the WHO classification, recognition of GC may be crucial considering its clinical significance. There is a relatively high incidence of GC in adult-type diffuse gliomas, with different proportion according to molecular types between patients with and without GC. Imaging may preoperatively predict the molecular type in GC patients and may assist clinical decision-making. The prognostic role of GC promotes its recognition in clinical settings.

Astroblastoma With a Novel YAP1::BEND2 Fusion: A Case Report.

In the most recent fifth edition of the World Health Organization Classification of Tumors of the Central Nervous System, astroblastoma has been defined by molecular rearrangements involving the MN1 gene, with common partners being BEND2 or CXXC5 . Accordingly, this tumor entity is now known as "astroblastoma, MN1 -altered." However, gliomas with EWSR1::BEND2 fusions, devoid of MN1 fusion alterations, have recently been shown to exhibit astroblastoma-like histomorphologic features and reside in a distinct epigenetic subgroup based on DNA methylation studies similar to high-grade neuroepithelial tumor with MN1 alteration, which includes astroblastoma, MN1 altered tumors. This new epigenetically distinct subtype of astroblastoma containing EWSR1::BEND2 fusions lacks the required MN1 alteration and, thus, does not satisfy the current molecular classification of these lesions. Here, we describe a case of glioma with histologic features and DNA methylation profiling consistent with astroblastoma with a novel YAP1: : BEND2 fusion. This case and others further expand the molecular findings observable in astroblastoma-like tumors outside the constraints of MN1 alteration. Such cases of astroblastoma with EWSR1::BEND2 and YAP1::BEND2 fusions challenge the current molecular classification of astroblastoma based solely on an MN1 alteration.

Exploring a distinct FGFR2::DLG5 rearrangement in a low-grade neuroepithelial tumor: A case report and mini-review of protein fusions in brain tumors.

We report the novel clinical presentation of a primary brain neoplasm in a 30-year-old man with a mass-like area in the anteromedial temporal lobe. Histopathological analysis revealed a low-grade neuroepithelial tumor with cytologically abnormal neurons and atypical glial cells within the cerebral cortex. Molecular analysis showed a previously undescribed FGFR2::DLG5 rearrangement. We discuss the clinical significance and molecular implications of this fusion event, shedding light on its potential impact on tumor development and patient prognosis. Additionally, an extensive review places the finding in this case in the context of protein fusions in brain tumors in general and highlights their diverse manifestations, underlying molecular mechanisms, and therapeutic implications.

Revisiting prognostic factors of gliomatosis cerebri in adult-type diffuse gliomas.

PURPOSE: There is lack of comprehensive analysis evaluating the impact of clinical, molecular, imaging, and surgical data on survival of patients with gliomatosis cerebri (GC). This study aimed to investigate prognostic factors of GC in adult-type diffuse glioma patients. METHODS: Retrospective chart and imaging review was performed in 99 GC patients from adult-type diffuse glioma (among 1,211 patients; 6 oligodendroglioma, 16 IDH-mutant astrocytoma, and 77 IDH-wildtype glioblastoma) from a single institution between 2005 and 2021. Predictors of overall survival (OS) of entire patients and IDH-wildtype glioblastoma patients were determined. RESULTS: The median OS was 16.7 months (95% confidence interval [CI] 14.2-22.2) in entire patients and 14.3 months (95% CI 12.2-61.9) in IDH-wildtype glioblastoma patients. In entire patients, KPS (hazard ratio [HR] = 0.98, P = 0.004), no 1p/19q codeletion (HR = 10.75, P = 0.019), MGMTp methylation (HR = 0.54, P = 0.028), and hemorrhage (HR = 3.45, P = 0.001) were independent prognostic factors on multivariable analysis. In IDH-wildtype glioblastoma patients, KPS (HR = 2.24, P = 0.075) was the only independent prognostic factor on multivariable analysis. In subgroup of IDH-wildtype glioblastoma with CE tumors, total resection of CE tumor did not remain as a significant prognostic factor (HR = 1.13, P = 0.685). CONCLUSIONS: The prognosis of GC patients is determined by its underlying molecular type and patient performance status. Compared with diffuse glioma without GC, aggressive surgery of CE tumor in GC patients does not improve survival.

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY): A case report with surgical and neuropathological differential diagnosis.

BACKGROUND: Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a rare entity of low-grade neuroepithelial tumors that primarily affects children and young adults. This distinct type of tumor presents unique challenges in diagnosis and management. With its relatively recent identification, researchers and clinicians are striving to understand the characteristics, behavior, and optimal treatment strategies. The symptoms are primarily related to seizures. However, PLNTY can be asymptomatic in some cases. MATERIALS AND METHODS: This is a single-center case report study and a literature review paper. We reviewed a case treated and diagnosed at the Ankara University Faculty of Medicine, Department of Neurosurgery. The demographic data, clinical follow-ups, laboratory, and radiological data of the patients were assessed. RESULTS: We present a 32-year-old male patient who has undergone gross total surgical excision with strict clinical follow-up. Clinical course as well as surgical data of the patient were observed and analyzed. CONCLUSION: On imaging, morphologic resembling and indistinctive clinical course can be nonspecific, contributing to diagnostic uncertainties. This case report was written with the notion that rare diagnoses present an opportunity to understand the progression and patho-oncological factors that can pave the way for better treatment.

BCOR::CREBBP fusion in malignant neuroepithelial tumor of CNS expands the spectrum of methylation class CNS tumor with BCOR/BCOR(L1)-fusion.

Methylation class "CNS tumor with BCOR/BCOR(L1)-fusion" was recently defined based on methylation profiling and tSNE analysis of a series of 21 neuroepithelial tumors with predominant presence of a BCOR fusion and/or characteristic CNV breakpoints at chromosome 22q12.31 and chromosome Xp11.4. Clear diagnostic criteria are still missing for this tumor type, specially that BCOR/BCOR(L1)-fusion is not a consistent finding in these tumors despite being frequent and that none of the Heidelberger classifier versions is able to clearly identify these cases, in particular tumors with alternative fusions other than those involving BCOR, BCORL1, EP300 and CREBBP. In this study, we introduce a BCOR::CREBBP fusion in an adult patient with a right temporomediobasal tumor, for the first time in association with methylation class "CNS tumor with BCOR/BCOR(L1)-fusion" in addition to 35 cases of CNS neuroepithelial tumors with molecular and histopathological characteristics compatible with "CNS tumor with BCOR/BCOR(L1)-fusion" based on a comprehensive literature review and data mining in the repository of 23 published studies on neuroepithelial brain Tumors including 7207 samples of 6761 patients. Based on our index case and the 35 cases found in the literature, we suggest the archetypical histological and molecular features of "CNS tumor with BCOR/BCOR(L1)-fusion". We also present four adult diffuse glioma cases including GBM, IDH-Wildtype and Astrocytoma, IDH-Mutant with CREBBP fusions and describe the necessity of complementary molecular analysis in "CNS tumor with BCOR/BCOR(L1)-alterations for securing a final diagnosis.

Spinal astroblastoma, MN1 altered in 3-year-old child: An uncommon tumor at an unusual site.

Astroblastoma is an uncommon circumscribed glial tumor mostly involving the cerebral hemisphere. The characteristic molecular alteration is meningioma (disrupted in balanced translocation) 1 (MN1) rearrangement. No definite World Health Organization grade has been assigned as both low- and high-grade tumors are known to occur. Tumors in the spine are extremely rare; to date only three cases have been reported in the literature. A vigilant microscopy and ancillary testing aid in diagnosis when the tumors present in unusual locations, as in our case. The prompt differentiation of this tumor from its mimickers is a mandate as modalities of management are different and not clearly established.

Expanding the Imaging Spectrum of Polymorphous Low-Grade Neuroepithelial Tumor of the Young in Children.

Polymorphous low-grade neuroepithelial tumors of the young (PLNTY) are rare brain tumors first described in 2017 and recently included in the 2021 5th World Health Organization Classification of Tumors of the Central Nervous System. They typically affect children and young adults. Few pediatric cases have been reported in the literature. The most common imaging features described, include location within the temporal lobe, involvement of the cortical/subcortical region, coarse calcifications, and well-defined margins with solid and cystic morphology, with slight-or-no enhancement. However, there is limited information on imaging features in children. We present the imaging spectrum of neuroimaging features in a series of pediatric patients with a histologically and molecularly proved PLNTY diagnosis. Coarse calcifications are uncommon in children compared with the adult literature, and they may develop with time. The transmantle-like sign can be observed, and adjacent cortical dysplasia may be seen. Seizure recurrence may occur despite gross total resection of the tumor.

Clinicopathological analysis of rosette-forming glioneuronal tumors.

BACKGROUND: This study aimed to investigate the clinicopathological characteristics, diagnostic indicators, and critical factors for the differential diagnosis of rosette-forming glioneuronal tumor (RGNT). PATIENTS AND METHODS: This retrospective study included six surgically treated RGNT cases. We analyzed and summarized their clinical manifestations, radiological features, histological morphology, immunophenotype, and molecular genetic changes, supplemented with a literature review. RESULTS: The patients comprised four males and two females with a mean age of 35 years. The tumors were located in the cerebellum (two cases); the fourth ventricle, quadrigeminal cistern, and third ventricle (one case each); and the fourth ventricle and brainstem (one case). Clinical manifestations included headaches in four cases, left eyelid ptosis in one case, and one asymptomatic case only identified during physical examination. Microscopically, the tumor cells were uniform in size and were marked by rosette-like or pseudorosette-like structures around the neuropil and blood vessels. Immunohistochemistry revealed biphasic patterns. The central neuropil components of the rosette-like structures around the neuropil and the pseudorosette structures of the perivascular regions expressed Syn, while the cells surrounding the rosettes expressed Olig2 and not GFAP. GFAP and S-100 were expressed in the glial components but not in the rosette or pseudorosette regions. The Ki-67 proliferation index was typically low. Molecular genetic analysis showed that the main molecular changes involved FGFR1 mutation accompanied by PIK3R1 mutation. None of the patients received chemoradiotherapy postoperatively. Follow-up durations varied between 4 and 23 months with no recorded recurrence or metastasis. CONCLUSION: RGNT is a comparatively rare mixed glioneuronal tumor that occurs in the midline structures. Its morphology shows certain overlaps with other low-grade neuroepithelial tumors. Identifying the rosettes around the neuropil is critical for morphological diagnosis, and the molecular identification of FGFR1 mutations accompanied by PIK3R1 mutations can facilitate diagnosis.

Bright diffusion sign: A sensitive and specific radiologic biomarker for multinodular and vacuolating neuronal tumor.

BACKGROUND AND PURPOSE: Accurate differentiation between multinodular and vacuolating neuronal tumor (MVNT) and dysembryoplastic neuroepithelial tumor (DNET) is important for treatment decision-making. We aimed to develop an accurate radiologic diagnostic model for differentiating MVNT from DNET using T2WI and diffusion-weighted imaging (DWI). MATERIALS AND METHODS: A total of 56 patients (mean age, 47.48±17.78 years; 31 women) diagnosed with MVNT (n = 37) or DNET (n = 19) who underwent brain MRI, including T2WI and DWI, were included. Two board-certified neuroradiologists performed qualitative (bubble appearance, cortical involvement, bright diffusion sign, and bright apparent diffusion coefficient [ADC] sign) and quantitative (nDWI and nADC) assessments. A diagnostic tree model was developed with significant and reliable imaging findings using an exhaustive chi-squared Automatic Interaction Detector (CHAID) algorithm. RESULTS: In visual assessment, the imaging features that showed high diagnostic accuracy and interobserver reliability were the bright diffusion sign and absence of cortical involvement (bright diffusion sign: accuracy, 94.64 %; sensitivity, 91.89 %; specificity, 100.00 %; interobserver agreement, 1.00; absence of cortical involvement: accuracy, 92.86 %; sensitivity, 89.19 %; specificity, 100.00 %; interobserver agreement, 1.00). In quantitative analysis, nDWI was significantly higher in MVNT than in DENT (1.52 ± 0.34 vs. 0.91 ± 0.27, p < 0.001), but the interobserver agreement was fair (intraclass correlation coefficient = 0.321). The overall diagnostic accuracy of the tree model with visual assessment parameters was 98.21 % (55/56). CONCLUSION: The bright diffusion sign and absence of cortical involvement are accurate and reliable imaging findings for differentiating MVNT from DNET. By using simple, intuitive, and reliable imaging findings, such as the bright diffusion sign, MVNT can be accurately differentiated from DNET.

"Hemispheric pilocytic astrocytoma" revisited: A comprehensive clinicopathological and molecular series emphasizing their overlap with other glioneuronal tumors.

Pilocytic astrocytomas (PA) typically exhibit distinct clinical, radiological, histopathological, and genetic features. DNA-methylation profiling distinguishes PA according to their location (infratentorial, midline, hemispheric, or spinal). In the hemispheric location, distinguishing PA from glioneuronal tumors remains a common diagnostic challenge for neuropathologists. Furthermore, the current version of the DKFZ classifier seems to have difficulty separating them from gangliogliomas. In this study, after central radiological review, we identified a histopathologically defined set of PA (histPA, n = 11) and a cohort of DNA-methylation defined PA (mcPA, n = 11). Nine out of the 11 histPA matched the methylation class of hemispheric PA, whereas 2 cases were classified at the end of the study as dysembryoplastic neuroepithelial tumors. Similarly, the mcPA cohort contained tumors mainly classified as PA (7/11), but 4 cases were classified as glioneuronal. The analysis of the 16 tumors with an integrated diagnosis of PA revealed that they affect mainly children with a wide spectrum of radiological, histopathological (i.e. a predominantly diffuse growth pattern), and genetic characteristics (large range of mitogen-activated protein kinase alterations). Based on these results, we consider hemispheric PA to be different from their counterparts in other locations and to overlap with other glioneuronal tumors, reinforcing the necessity of interpreting all data to obtain an accurate diagnosis.

Transcriptional features of low-grade neuroepithelial tumors with the BRAF V600E mutation associated with epileptogenicity.

Low-grade neuroepithelial tumors are major causes of drug-resistant focal epilepsy. Clinically, these tumors are defined as low-grade epilepsy-associated neuroepithelial tumors (LEATs). The BRAF V600E mutation is frequently observed in LEAT and linked to poor seizure outcomes. However, its molecular role in epileptogenicity remains elusive. To understand the molecular mechanism underlying the epileptogenicity in LEAT with the BRAF V600E genetic mutation (BRAF V600E-LEAT), we conducted RNA sequencing (RNA-seq) analysis using surgical specimens of BRAF V600E-LEAT obtained and stored at a single institute. We obtained 21 BRAF V600E-LEAT specimens and 4 control specimens, including 24 from Japanese patients and 1 from a patient of Central Asian origin, along with comprehensive clinical data. We submitted the transcriptome dataset of 21 BRAF V600E-LEAT plus 4 controls, as well as detailed clinical information, to a public database. Preliminary bioinformatics analysis using this dataset identified 2134 differentially expressed genes between BRAF V600E-LEAT and control. Additionally, gene set enrichment analysis provided novel insights into the association between estrogen response-related pathways and the epileptogenicity of BRAF V600E-LEAT patients. Our datasets and findings will contribute toward the understanding of the pathology of epilepsy caused by LEAT and the identification of new therapeutic targets.

A case of disseminated spinal astroblastoma harboring a MAMLD1::BEND2 fusion.

Astroblastoma, MN1-altered, is a rare neoplasm of the central nervous system (CNS). This malignancy shares similar histopathological features with other CNS tumors, including ependymomas, making it challenging to diagnose. DNA methylation profiling is a new and robust technique that may be used to overcome this diagnostic hurdle. We report the case of a now 25-year-old female diagnosed with what was initially called an ependymoma located in the cervical spine at the age of 2 years old. After initial resection, the tumor recurred multiple times and within 2 years of diagnosis had disseminated disease throughout the brain and spinal cord. She has now undergone over two decades of treatment, including multiple surgical resections, radiation therapy, and administration of numerous chemotherapeutic agents. In 2021, the patient presented to our institution with lumbosacral radicular symptoms due to enlarging lesions within the lumbosacral spine. Reexamination of formalin-fixed, paraffin-embedded material from the patient's tumor using genomic DNA methylation profiling resulted in a diagnostic change from grade III anaplastic ependymoma to astroblastoma, MN1-altered. This work describes another confirmed case of astroblastoma, MN1-altered, to the growing body of literature.

Long-term epilepsy associated-tumors (LEATs): what is new?

Long-term epilepsy-associated tumors (LEATs) include a series of neoplasms that commonly occur in children, adolescents, or young adults, have an astrocytic or glioneuronal lineage, are histologically benign (WHO grade1) with a neocortical localization predominantly situated in the temporal lobes. Clinically, chronic refractory epilepsy is usually the unique symptom. Gangliogliomas (GG) and dysembryoplastic neuroepithelial tumors (DNT) are the most common representative entities besides pilocytic astrocytomas (PA) and angiocentric gliomas (AG). Recent molecular studies have defined new clinicopathological entities, which are recognized by the WHO 2021 classification of brain tumors. Some of them such as diffuse astrocytoma MIB or MYBL1 altered, polymorphous low-grade neuroepithelial tumor of the young (PLNTY), and multilocular and vacuolating neuronal tumor (MVNT) are currently considered LEATs. The relationship between LEATs and epilepsy is still a matter of debate, and there is a general agreement about the beneficial effects of an early neurosurgical intervention on the clinical outcome.

Tumores associados a epilepsia de longa duração constituem uma série de neoplasias asatrocitárias ou glioneuronais que comumente incidem em crianças, adolescentes e jovens adultos e que são histologicamente benignos (OMS grau 1), de localização neocortical e predominantemente situados nos lobos temporais. Clinicamente, a epilepsia crônica refratária é, de modo geral, o único sintoma. Gangliogliomas (GG) e tumores neuroepiteliais disembrioplásticos (DNT) são as entidades mais representativas associadas a astrocitomas pilocíticos (AP) e gliomas angiocêntricos (GA). Estudos moleculares recentes permitiram a definição de novas entidades clínico-patológicas reconhecidas pela classificação de tumores cerebrais da OMS 2021. Algumas delas, como o astrocitoma difuso MIB ou MIBL1 alterados, o tumor neuroepitelial polimorfo do jovem (PLNTY) e o tumor neuronal multilocular e vacuolizado (MVNT) são atualmente considerados tumores associados a epilepsia de longa duração. A relação entre este grupo de tumores e epilepsia é ainda debatida e há um consenso geral sobre o benefício prognóstico de intervenção cirúrgica precoce.

Glioneuronal and Neuronal Tumors of the Central Nervous System.

Glioneuronal and neuronal tumors (GNTs) are rare neoplasms composed of neural and glial elements frequently located in the temporal lobe. Epilepsy is the main symptom and diagnosis mostly occurs before adulthood. The great majority of GNTs are WHO grade I tumors, but anaplastic transformations and forms exist. Their common association with focal cortical dysplasia is well recognized and should be taken into consideration during neurophysiological presurgical and surgical planning since the aim of surgery should be the removal of the tumor and of the entire epileptogenic zone according to anatomo-electrophysiological findings. Surgery still remains the cornerstone of symptomatic GNT, while radiotherapy, chemotherapy, and new target therapies are generally reserved for anaplastic, unresectable, or evolving tumors. Furthermore, since many GNTs show overlapping clinical and neuroradiological features, the definition of specific histopathological, genetic, and molecular characteristics is crucial. Epileptological, oncological, neurosurgical, and pathological issues of these tumors make a multidisciplinary management mandatory.

The anatomy of neuroepithelial tumours.

Many neurological conditions conceal specific anatomical patterns. Their study contributes to the understanding of disease biology and to tailored diagnostics and therapy. Neuroepithelial tumours exhibit distinct anatomical phenotypes and spatiotemporal dynamics that differ from those of other brain tumours. Brain metastases display a preference for the cortico-subcortical boundaries of watershed areas and have a predominantly spherical growth. Primary CNS lymphomas localize to the white matter and generally invade along fibre tracts. In neuroepithelial tumours, topographic probability mapping and unsupervised topological clustering have identified an inherent radial anatomy and adherence to ventriculopial configurations of specific hierarchical orders. Spatiotemporal probability and multivariate survival analyses have identified a temporal and prognostic sequence underlying the anatomical phenotypes of neuroepithelial tumours. Gradual neuroepithelial de-differentiation and declining prognosis follow (i) an expansion into higher order radial units; (ii) a subventricular spread; and (iii) the presence of mesenchymal patterns (expansion along white matter tracts, leptomeningeal or perivascular invasion, CSF spread). While different pathophysiological hypotheses have been proposed, the cellular and molecular mechanisms dictating this anatomical behaviour remain largely unknown. Here we adopt an ontogenetic approach towards the understanding of neuroepithelial tumour anatomy. Contemporary perception of histo- and morphogenetic processes during neurodevelopment permit us to conceptualize the architecture of the brain into hierarchically organized radial units. The anatomical phenotypes in neuroepithelial tumours and their temporal and prognostic sequences share remarkable similarities with the ontogenetic organization of the brain and the anatomical specifications that occur during neurodevelopment. This macroscopic coherence is reinforced by cellular and molecular observations that the initiation of various neuroepithelial tumours, their intratumoural hierarchy and tumour progression are associated with the aberrant reactivation of surprisingly normal ontogenetic programs. Generalizable topological phenotypes could provide the basis for an anatomical refinement of the current classification of neuroepithelial tumours. In addition, we have proposed a staging system for adult-type diffuse gliomas that is based on the prognostically critical steps along the sequence of anatomical tumour progression. Considering the parallels in anatomical behaviour between different neuroepithelial tumours, analogous staging systems may be implemented for other neuroepithelial tumour types and subtypes. Both the anatomical stage of a neuroepithelial tumour and the spatial configuration of its hosting radial unit harbour the potential to stratify treatment decisions at diagnosis and during follow-up. More data on specific neuroepithelial tumour types and subtypes are needed to increase the anatomical granularity in their classification and to determine the clinical impact of stage-adapted and anatomically tailored therapy and surveillance.

An enduring debate on gliomatosis cerebri.

Gliomatosis cerebri (GC) is a unique glial tumor that extensively invades the cerebral white matter and has been recognized as an entity of neuroepithelial tumors since the first edition of the WHO classification of brain tumors in 1979. Thereafter, in the fourth edition of the WHO classification in 2007, it was clearly defined as a specific type of astrocytic tumor. However, in the WHO 2016 classification, which was based on the concept of integrated diagnosis using molecular genetics, GC was deleted as it was considered to be only one growth pattern of diffuse glioma and not a specific pathological entity. Since then, there has been criticism by many neuro-oncologists and the establishment of the GC working group at the NIH, and many activities in the world arguing that GC should not be deleted from the clinical discussion of brain tumors. In Japan, positive activities toward multicenter research on GC pathology should be performed, and molecular pathological evidence that can contribute to the WHO classification in the future should be developed. In this article, the author outlined the pathological characteristics of GC, which has been repeated changing since its conception, and also describes his opinion on GC as a neuro-oncologist.

Glioneuronal tumor with ATRX alteration, kinase fusion and anaplastic features (GTAKA): a molecularly distinct brain tumor type with recurrent NTRK gene fusions.

Glioneuronal tumors are a heterogenous group of CNS neoplasms that can be challenging to accurately diagnose. Molecular methods are highly useful in classifying these tumors-distinguishing precise classes from their histological mimics and identifying previously unrecognized types of tumors. Using an unsupervised visualization approach of DNA methylation data, we identified a novel group of tumors (n = 20) that formed a cluster separate from all established CNS tumor types. Molecular analyses revealed ATRX alterations (in 16/16 cases by DNA sequencing and/or immunohistochemistry) as well as potentially targetable gene fusions involving receptor tyrosine-kinases (RTK; mostly NTRK1-3) in all of these tumors (16/16; 100%). In addition, copy number profiling showed homozygous deletions of CDKN2A/B in 55% of cases. Histological and immunohistochemical investigations revealed glioneuronal tumors with isomorphic, round and often condensed nuclei, perinuclear clearing, high mitotic activity and microvascular proliferation. Tumors were mainly located supratentorially (84%) and occurred in patients with a median age of 19 years. Survival data were limited (n = 18) but point towards a more aggressive biology as compared to other glioneuronal tumors (median progression-free survival 12.5 months). Given their molecular characteristics in addition to anaplastic features, we suggest the term glioneuronal tumor with ATRX alteration, kinase fusion and anaplastic features (GTAKA) to describe these tumors. In summary, our findings highlight a novel type of glioneuronal tumor driven by different RTK fusions accompanied by recurrent alterations in ATRX and homozygous deletions of CDKN2A/B. Targeted approaches such as NTRK inhibition might represent a therapeutic option for patients suffering from these tumors.

High-grade neuroepithelial tumor with EP300::BCOR fusion and negative BCOR immunohistochemical expression: a case report.

In the World Health Organization tumor classification (fifth edition), central nervous system (CNS) tumors with BCOR internal tandem duplications have been recognized as a new tumor type. Some recent studies have reported CNS tumors with EP300::BCOR fusions, predominantly in children and young adults, expanding the spectrum of BCOR-altered CNS tumors. This study reports a new case of high-grade neuroepithelial tumor (HGNET) with an EP300::BCOR fusion in the occipital lobe of a 32-year-old female. The tumor displayed anaplastic ependymoma-like morphologies characterized by a relatively well-circumscribed solid growth with perivascular pseudorosettes and branching capillaries. Immunohistochemically, OLIG2 was focally positive and BCOR was negative. RNA sequencing revealed an EP300::BCOR fusion. The Deutsches Krebsforschungszentrum DNA methylation classifier (v12.5) classified the tumor as CNS tumor with BCOR/BCORL1 fusion. The t-distributed stochastic neighbor embedding analysis plotted the tumor close to the HGNET with BCOR alteration reference samples. BCOR/BCORL1-altered tumors should be included in the differential diagnosis of supratentorial CNS tumors with ependymoma-like histological features, especially when they lack ZFTA fusion or express OLIG2 even in the absence of BCOR expression. Analysis of published CNS tumors with BCOR/BCORL1 fusions revealed partly overlapping but not identical phenotypes. Further studies of additional cases are required to establish their classification.