Intracranial sarcomas can arise secondarily from primary brain tumors, including gliomas and meningiomas, either spontaneously or following radiotherapy. The current WHO classification recognizes sarcomatous transformation in several tumor entities; however, sarcomas arising from meningiomas remain poorly characterized and are regarded as a possible histological manifestation within the spectrum of anaplastic meningiomas. We analyzed nine matched meningioma–sarcoma pairs using integrated histopathological assessment and molecular profiling, including DNA methylation analysis, next-generation sequencing, copy number profiling, and proteomics. Although recurrent sarcomatous tumors were clonally related to their meningioma precursors—sharing identical NF2 alterations and overlapping chromosomal aberrations—they demonstrated pronounced divergence at the histological, immunophenotypic, and epigenetic levels. Importantly, sarcomatous transformation occurred in four cases without prior radiotherapy. Sarcomatous recurrences exhibited loss of meningothelial markers and acquired expression of cytokeratin and myogenic markers. DNA methylation profiling revealed a shift away from canonical meningioma signatures toward profiles resembling non-meningothelial mesenchymal tumors. Proteomic analysis showed consistent upregulation of SOX2 in sarcomatous tumors compared with their primary counterparts, suggesting acquisition of stem-like features during lineage divergence. Clinically, these tumors were associated with aggressive growth, early recurrence, and extracranial metastases, resembling malignant sarcomas more closely than anaplastic meningiomas. In addition, analysis of an institutional cohort of NF2-mutant intracranial tumors (n = 316) suggests that sarcomas with inactivating NF2 mutations may originate from meningiomas even in the absence of a clinically recognized precursor. Together, these findings suggest that sarcomatous transformation represents a rare evolutionary endpoint in NF2-mutant meningiomas, marked by clonal continuity but pronounced biological divergence. These results highlight limitations of morphology-based classification and emphasize the value of integrated molecular diagnostics in distinguishing these tumors from conventional high-grade meningiomas. Given their sarcoma-like behavior despite a meningioma ancestry, these tumors may not be adequately captured by current meningioma grading schemes.

DNA methylation profiling of CNS tumors supports and refines histological diagnoses. Tumor DNA methylation signatures allow for an alignment with reference methylation classes and copy number profiling required for molecular grading. Overall, and especially in cases with limited tissue like in stereotaxic (STX) biopsies, there is a need for informed triage to most promising analysis techniques. Here, we investigated the diagnostic potential and accuracy of DNA methylation profiling and molecular grading in STX samples. FFPE samples of 237 patients were subjected to DNA methylation analysis including the Heidelberg (v11b4), Bethesda (v2) and EpiDiP brain tumor classifiers, copy number profiling and tumor deconvolution using MethylCIBERSORT. 90.5

Sellar region neurocytoma (SELN) is a rare neoplasm whose relationship to other neurocytomas within the central nervous system (CNS) has remained unclear. Prior reports have variably classified SELN as a variant of extraventricular neurocytoma (EVN), while immunohistochemical and ultrastructural studies have suggested a hypothalamic origin. Here, we performed unsupervised clustering of DNA methylation data across a large pan-cancer reference set and identified SELN (n = 20) as distinct from other neurocytomas and regional mimics, as well as clustering with neuroendocrine tumors from other organ sites. SELN exhibited a CIMP-like phenotype, TTF1 negativity (0/8), and AVP (vasopressin) promoter hypomethylation, implicating a magnocellular hypothalamic cell of origin. In evaluable cases, a neuronal/neuroendocrine immunophenotype was observed (synaptophysin 8/8, chromogranin A 5/5) with absent pituitary transcription factor expression (PIT1 and TPIT negative 0/4). DNA sequencing (n = 5) and RNA-based fusion profiling (n = 4) did not detect recurrent mutations or gene fusions, respectively. Patients often presented with visual disturbances or headaches and spanned pediatric and older age groups (median 42 years, range 12.5–75), with no sex predilection. Despite locally aggressive imaging features in some cases (cavernous sinus invasion, carotid encasement, hydrocephalus), disease-free survival (n = 13) was comparable to central neurocytoma, with no disease-related deaths during the limited follow-up. Together, these findings support SELN as a molecularly distinct hypermethylated neuroendocrine-like epitype and clinicopathologic entity.

Tumor Treating Fields (TTFields) are an adjunctive treatment for glioblastoma, isocitrate dehydrogenase wildtype (IDH wt). TTFields indication is not standardized; patient selection is mostly based on a high KPS. Objective: This study aims to identify molecular biomarkers guiding clinical decisions on TTFields initiation. Patients & methods: A retrospective analysis was conducted on 64 patients with newly diagnosed glioblastoma, IDH wt treated with surgery, radiochemotherapy, followed by TTFields. Clinical data (e.g. extent of resection, survival data) were collected. Tumors underwent TSO500 DNA/RNA sequencing and methylation profiling (EPIC). Alterations were analyzed for association with overall survival using Kaplan-Meier as well as univariate and multivariate Cox models. Methylation class, tumor mutional burden, and signaling pathway activation (e.g. PI3K/AKT/mTOR pathway) were also assessed for associations with overall survival. Two TTFields-naïve glioblastoma, IDH wt cohorts served as controls (combined n=175). Molecular profiling revealed 25 alterations occurring in at least 5 patients (e.g., mutations: PTEN, EGFR, deletions: PTEN, CDKN2A/B; amplifications: EGFR). Univariate analyses showed preoperative KPS and MGMT promoter methylation as protective, while EGFR amplification, CDKN2A/B, and PTEN homozygous deletions were linked to worse survival in the TTFields treated cohort. Multivariate analysis confirmed KPS and MGMT as protective and PTEN homozygous deletion as a significant risk factor for worse outcome (HR: 3.86, 95% CI: 1.51–9.87, p=0.0049). Comparative analysis with TTFields-naïve cohorts showed no link between PTEN homozygous deletion and worse outcomes, with homozygous deletion rates comparable across cohorts (controls: 7%, TTFields: 11%). Alongside established protective outcome factors MGMT and KPS, in our cohort of glioblastoma, IDH wt patients treated with TTFields, PTEN homozygous deletion was significantly associated with worse survival. PTEN deletion status may thus predict reduced benefit from TTFields, warranting testing before treatment initiation.

Aim Achieving maximal and safe tumour resection is a key goal in brain tumour surgery. Confocal laser endomicroscopy (CLE) enables real-time visualisation of the tissue microstructure at a cellular level, potentially helping neurosurgeons distinguish non-neoplastic from neoplastic tissue. The core aim of this study was to determine the baseline diagnostic accuracy that can be achieved with CLE alone, when assessed by neuropathologists without prior CLE training and without any additional clinical or contextual information, and to compare these findings to standard haematoxylin and eosin (H & E)-based histology in a blinded setting.Methods CLE images and corresponding H & E-stained slides from 100 brain tumour patients treated at the University Hospital Bern over a 22-month period were analysed. Five blinded neuropathologists with no prior CLE experience independently evaluated the data sets.Results Based on CLE images, neuropathologists differentiated neoplastic from non-neoplastic tissue in 70.7%. The specific tumour type was correctly identified in 47.5%: gliomas in 59.8%, meningiomas in 43.8%, and metastases in 25.7%. In contrast, H & E slides were correctly classified as neoplastic in 87.6%, with 89.1% tumour-type-level accuracy (gliomas 85.6%, meningiomas 94.6%, metastases 88.2%). Confidence levels for CLE diagnoses were generally low, and no learning curve was observed.Conclusions CLE shows potential to distinguish between neoplastic and non-neoplastic tissue, but diagnostic accuracy remains lower than with H & E-stained slides. Training in CLE image interpretation is recommended to improve diagnostic accuracy. CLE imaging may have the potential to become a valuable tool for delineating brain tumour borders.

BACKGROUND AND OBJECTIVES:Extent of resection (EOR) predicts local freedom from recurrence (LFFR) for meningiomas and is a key clinical trial design parameter. Simpson grade (SG) defines EOR based on intraoperative assessment of tumor removal, but MRI-based methods represent promising alternatives. The aim of this study was to compare the prognostic performance of SG vs MRI-based EOR paradigms for predicting recurrence and survival across histomolecular subgroups. METHODS:International multicenter, retrospective cohort study included 475 meningiomas, resected between 1983 and 2024, which were classified by World Health Organization grade and molecular subgroups (DNA methylation, gene expression, and integrated grade). Area under the curve (AUC) was calculated for LFFR and overall survival (OS) from Cox models with a histomolecular subgroup and an EOR paradigm. Delta AUC (ΔAUC) compared EOR predictive performance within each subgroup, and log-rank comparisons of LFFR and OS were performed. RESULTS:MRI-defined gross total resection was associated with significantly longer LFFR and OS when compared with subtotal resection across most histomolecular subgroups. SG1-3 vs 4 distinguished differences in LFFR across several subgroups, but there were no consistent differences in outcomes when comparing degrees of dural treatment. Multivariable Cox including gene expression groups revealed that volumetric EOR (%) had a significantly higher AUC than SG (ΔAUC 0.07, P = .036) for 5-year OS; otherwise, there were no other differences between MRI-based or SG EOR paradigms for 5-year LFFR or OS. Additional significant differences for predicting 10-year LFFR all favored MRI-based EOR paradigms. CONCLUSION:Although SG and MRI-based EOR paradigms provide similar prognostic performance for predicting LFFR and OS in the era of molecular classification, MRI-based definitions may be preferred for future clinical trial inclusion criteria.

Mucinous ovarian carcinoma (MOC) is an epithelial ovarian cancer subtype that is frequently misclassified as extraovarian mucinous metastasis (EOM) because of overlapping features. To address this diagnostic challenge, we perform genome-wide DNA methylation profiling of 58 MOCs, 38 EOMs, and 18 mucinous borderline ovarian tumors (mBOTs) collected from six institutions. Methylation analysis defines two mBOT groups, one epigenetically similar to normal ovary and one resembling MOC. Unsupervised clustering reveals two distinct MOC methylation subtypes with potential prognostic relevance in the internal cohort. Using these data together with 389 external profiles, we develop and validate a three-step machine-learning classifier that distinguishes MOC from EOM with 95.5% accuracy. External validation of this classifier on 21 MOCs and 24 EOMs yields an accuracy of 91.11% for differentiating MOC from EOM. These findings establish an epigenetic framework for mucinous ovarian tumors and provide a robust clinical classification tool.

BeadChip array-based DNA methylation profiling has been recognized by the World Health Organization (WHO) as a key diagnostic tool for brain tumor classification. While its diagnostic utility has been well established, data on technical reproducibility, interlaboratory comparability, and data interpretation under real-world diagnostic conditions remain limited. Bridging this gap, we here report the results of an international proficiency test using the Infinium MethylationEPIC v2.0 platform and the corresponding Brain Tumor Classifier version 12.8. Tissue slides of eight FFPE brain tumor samples, covering a representative range of CNS tumor entities, were distributed among 24 laboratories in 10 different countries. Participants were asked to report methylation classes and copy number variation (CNV) profiles. Pre-array workflows were left to local procedures and results had to be submitted within 15 working days. Technical data reproducibility was high with a median pairwise beta-value correlation of 0.99 (range 0.93-1.0). In general, participating centers generated high-quality data, reflected by consistently low detection p-values (<0.01). Eighteen of the 24 participating centers (75%) successfully passed the test. Of the six centers that failed the test, two laboratories experienced technical issues that led to misclassification of individual cases and contributed to incorrect CNV reporting. Four additional centers showed substantial discrepancies in the interpretation of diagnostically highly relevant CNVs, whereas methylation classification was not impaired. While accurate DNA quantification proved to be an important pre-array step, the use of the DNA restoration kit had only minor influence on overall results. Taken together, our interlaboratory performance testing on EPIC v2.0 CNS tumor profiling confirms high reproducibility of tumor classification but reveals the need for harmonized CNV reporting.

Abstract:With the advent of multi-omic molecular profiling techniques, central nervous system tumor types previously not recognized by conventional neuropathological assessment have emerged, particularly among tumors formerly termed as "CNS- primitive neuroectodermal tumors." Given the diverse histopathological, molecular, radiological, and clinical characteristics of these tumors, diagnostic approaches and treatment strategies need to be adapted to our increasing knowledge. The small number of patients per year for individual tumor types precludes large cohort studies and mandates international cooperation and harmonization. To this end, the SIOPE Brain Tumor Group together with the European Reference Network for Pediatric Cancers has published the European Standards of Clinical Practice guidelines for rare embryonal and sarcomatous tumors.

Abstract Embryonal tumors with multilayered rosettes (ETMR) are highly aggressive brain tumors predominantly affecting children under three years, with median survival of 10–14 months. Understanding mechanisms driving treatment resistance remains critical for improving outcomes. While the cell populations constituting primary tumors have been characterized in the recent years, the molecular landscape at relapse remains elusive. We performed single-cell transcriptomic analysis of 20 samples from 13 patients with ETMR, with a particular focus on seven patients with matched tissue from primary and recurrent/progressive disease. Tumor populations comprised neural stem cell (NSC)-like cells (SOX2+, SOX3+), neuronal progenitor-like cells (TCF4+, NEUROD1+), and neuron-like cells (TUBB3+, NEUROD4+), consistent with previous reports. However, cellular composition shifted dramatically during progression: neuron-like cells decreased from ∼45% in primary tumors to 25% in progressive disease and 10% at relapse, while NSC-like cells expanded to 57% in recurrent tumors. Differential gene expression analysis revealed that relapse-associated NSC-like cells lost neuronal maturation programs while acquiring mesenchymal, HOX-driven, and stem-like characteristics. Significantly upregulated genes included HOX family members, epithelial-mesenchymal transition mediators (COL1A1, MMP2), and developmental regulators (IRX5, HAND2), while neuronal function genes (OTX3, SPON1) were downregulated. Critically, C19MC-amplified NSC-like cells were enriched at relapse while chromosome 2 gain variants decreased, suggesting C19MC amplification drives stem-like populations that dominate recurrent disease. The microenvironment also transformed substantially: relapsed tumors exhibited 3–5 fold increases in infiltrating immune cells, pericytes, and astrocytes compared to minimal tumor microenvironment in primary samples, suggesting more invasive growth patterns. Spatial transcriptomics (Xenium) at single-cell resolution validated these changes and revealed functionally distinct niches where tumor cells interact differentially with stromal compartments. These findings demonstrate that ETMR progression involves coordinated dedifferentiation toward aggressive stem-like states and highlight potential applicability of immunotherapeutic approaches in the relapse setting.

BACKGROUND:Astroblastomas are rare brain tumors predominantly affecting children and young adults, for which molecular subtypes and clinical management remain undefined. METHODS:We analyzed tumor samples, molecular profiles, and clinical data from 200 patients, classified as "Astroblastoma, MN1-altered" under WHO criteria, using DNA methylation profiling, DNA/RNA profiling/sequencing, and survival analyses. RESULTS:DNA methylation analyses identified 3 groups: Group A (n = 143, characterized by MN1::BEND2 fusions, predominantly supratentorial location, with striking female predominance and favorable survival); Group B (n = 37, epigenetically and transcriptionally closely related to Group A, but characterized by EWSR1::BEND2 fusions, with spinal and infratentorial locations and poor prognosis); and Group C (n = 20, epigenetically and transcriptionally distinct, characterized by MN1::CXXC5 fusions, exclusively supratentorially located, with favorable survival). Progression-free and overall survival were significantly shorter in Group B (5-year PFS 14%; 10-year OS 54%) compared to A (5-year PFS 47%; 10-year OS 89%) and C (5-year PFS 75%; 10-year OS 89%). Radiotherapy improved PFS in Group B (hazard ratio 0.25), while no clear benefit was identified for Groups A and C. CONCLUSIONS:Astroblastoma, MN1-altered, comprises 3 molecularly and clinically distinct groups, characterized by different fusion genes, including those without MN1. These new insights, including the identification of potential predictive biomarkers like 14q/16q loss, provide a framework for the development of risk-stratified therapeutic approaches. Importantly, we identified a molecularly defined high-risk group that benefits from radiation therapy. Our findings redefine Astroblastoma as a molecularly diverse tumor type, propose a refined classification, support the development of risk-adapted therapeutic strategies and provide a rational standard of care.

Tumor treating fields (TTFields) are a treatment for glioblastoma, isocitrate dehydrogenase wildtype (GBM, IDH wt) that improves survival, but no validated biomarkers exist to identify patients likely to benefit. This study aims to identify molecular biomarkers guiding clinical decisions on TTFields initiation. Eighty gliomas treated with surgery, radiochemotherapy, and TTFields were reassessed using DNA methylation profiling and TSO500 DNA/RNA panel sequencing, identifying 64 highly characteristic GBM, IDH wt with comprehensive molecular data. Alterations present in ≥5 cases were analyzed for association with survival using Kaplan-Meier and Cox models. Two TTFields-naïve GBM, IDH wt cohorts (n = 175) served as controls. For 18 cases, post-treatment tissue from a second surgery was profiled. Twenty-four alterations occurred in ≥5 patients. Univariate analyses showed KPS and MGMT promoter methylation as protective, while EGFR amplification, CDKN2A/B loss, and homozygous PTEN deletion were linked to worse survival with TTFields. Multivariate analysis confirmed KPS and MGMT as protective and homozygous PTEN deletion as a risk factor (median OS 368 vs. 603 days; HR 3.86, p = 0.0049). In TTFields-naïve cohorts, homozygous PTEN deletion was not associated with outcome, and frequencies were comparable (controls 7%, TTFields 11%). Post-TTFields GBM, IDH wt did not acquire hypermutation or other recurrent molecular alterations. Alongside the established factors MGMT and KPS, PTEN homozygous deletion was associated with worse survival in GBM, IDH wt patients treated with TTFields. Homozygous PTEN deletion may be associated with reduced benefit from TTFields and should be further investigated as a predictive biomarker for TTFields treatment.

Background: Sinonasal undifferentiated carcinoma (SNUC) is an extremely rare, high-grade, and aggressive tumor of the sinonasal tract. Due to the rarity of this malignancy, current treatment guidelines are based on small and often/mainly single-center retrospective datasets. In the absence of a universally accepted standard of care for SNUC, treatment approaches vary across countries and institutions, reflecting real-world clinical practice. The primary aim of this study was to describe real-world treatment and outcomes for patients with confirmed SNUC. Methods: This was an international, multi-center, retrospective, observational cohort study that pooled patients into the largest SNUC dataset to date. Fifteen centers were enrolled to contribute data, including seven from Europe, four from the United States, three from the United Kingdom, and one from Canada. In the absence of a universally accepted standard of care for SNUC, treatment approaches varied across countries and institutions, reflecting real-world clinical practice. Patients included were those with histologically confirmed SNUC who were treated between 1997 and 2021. Results: This study yielded 485 patients treated for SNUC. The median age at diagnosis was 55.6 years (IQR: 44.5-67.6), and 63.7% were male. Most cases presented at advanced stages, with 70.8% as T4a or T4b. Overall survival (OS) outcomes were available for 412 patients, with a median follow-up of 26.0 months. The 5- and 10-year OS were 47.2% (95% CI: 40.8-53.3%) and 39.6% (95% CI: 32.5-46.6%), respectively. Advanced age, dichotomized T-stage (T4a/b vs. T1-3), M-stage, and orbital involvement were significant poor prognostic factors on univariable analysis (p's < 0.01). On multivariable analysis, orbital involvement (HR: 2.73, 95% CI: 1.42-5.27, p = 0.003) and distance metastasis stage (HR: 3.00, 95% CI: 1.25-7.21, p = 0.014) were both independently associated with worse OS. Conclusions: This observational study presents the largest multi-center cohort analysis of SNUC to date, providing new insights into prognostic factors for a rare cancer treated at global centers of excellence. Orbital involvement and the presence of metastases are candidate independent risk factors associated with poorer OS.

Abstract Glioneuronal tumors (GNTs) are a heterogeneous group of brain tumors that are often clinically indolent but can show variable outcomes, including occasional progression. Although recurrent RAS/MAPK alterations motivate targeted therapies, resistance and relapse suggest that driver-linked tumor programs and the cellular context contribute to heterogeneity. Since many GNT types are rare, previous studies have examined subsets, which limit class-wide comparisons. We comprehensively profiled 67 FFPE GNTs across thirteen entities spanning glial- to neuronal-enriched phenotypes using single-nucleus RNA sequencing. Across the cohort, we identified recurrent astrocyte-like (AC-like) and oligodendrocyte progenitor–like (OPC-like) tumor programs and detected two additional programs less well characterized across GNTs: extracellular matrix–like (ECM-like) and neuronal-like (NEU-like). While most tumors contained mixtures of these states, their relative composition varied by entity and tracked with driver: FGFR1- and NTRK-driven tumors were biased toward NEU-like cells, whereas BRAF-driven tumors favored AC/OPC/ECM-like programs. Beyond state composition, clinically aggressive entities showed the strongest MAPK and VEGF signaling signatures despite differing dominant states, and proliferative programs, including G2M checkpoint, increased with MAPK activity. Immune programs also diverged with clinical behavior: less aggressive tumors showed tumor-intrinsic inflammatory programs alongside inflammatory myeloid activation, whereas aggressive entities more often exhibited reduced myeloid content with residual suppressive programs, although some retained substantial inflammatory microglia. PDGFRA-altered tumors showed especially strong inflammatory myeloid signatures. Together, these data establish a spectrum-spanning single-cell map of GNTs that enables cross-entity comparison and highlights driver-linked tumor states, aggressiveness-associated signaling, and myeloid inflammatory or suppressive phenotypes. Ongoing spatial transcriptomics analyses will localize these programs within tissue architecture and support state–immune colocalization analyses across clinical behavior.

Sinonasal undifferentiated carcinomas are rare, aggressive tumors with limited treatment options. Molecular subgroups defined by IDH2 mutations or SWI/SNF complex deficiencies have recently been recognized, but therapeutic implications remain unclear. We performed single-nucleus RNA sequencing on 12 FFPE tumors (six IDH2 mutated (IDH2mt), six SMARCA4 mutated (SMARCA4mt)), generating 59,612 nuclei. Malignant cells were identified by copy number inference, functionally characterized through gene set enrichment analysis, pathway and transcription factor activity analysis, and explored for druggable targets with spatial validation by immunohistochemistry and RNAscope. We identified 17 cell types and four malignant clusters with distinct programs: neuroendocrine-like (enriched in SMARCA4mt tumors), stress-adaptive with ECM remodeling, and EMT/TGF-β-driven. Target expression analysis revealed KIT overexpression in IDH2mt tumors and MET upregulation in SMARCA4mt tumors. The therapeutic relevance of KIT overexpression alone in absence of activating mutations remains uncertain, though treatment with multi-target kinase inhibitors with anti-KIT activity may warrant further investigation. MET overexpression may indicate potential relevance of MET-directed antibody-drug conjugate strategies. Both groups showed elevated CDK4 and DDR1 expression, nominating multi-target kinase inhibitors as potential options. Spatial expression uncovered collagenolysis-dependent DDR1 activation in tumor niches, highlighting DDR1 as a promising therapeutic vulnerability. Despite overlapping histology, IDH2mt and SMARCA4mt sinonasal carcinomas exhibit distinct transcriptional states and actionable dependencies. Our findings provide a framework for precision oncology in these rare tumors, supporting evaluation of KIT-, MET-, CDK4/6-, and DDR1-directed approaches.

Metastatic cancers of unknown primary (CUP) pose significant diagnostic and therapeutic challenges. We present the case of a 63-year old male patient with a CUP showing neuroendocrine differentiation, metastasized to the iliac bone, bone marrow, supraclavicular and retroperitoneal lymph nodes. Immunohistochemical and molecular profiling revealed strong pan-neurotrophic tyrosine kinase (Trk) expression without NTRK-gene fusion, corroborating the neural cell origin. Following molecular tumor board (MTB) discussion, genome-wide methylation profiling suggested the diagnosis of a neuroblastoma but results were below diagnostic thresholds. Subsequent imaging and laboratory findings confirmed an INRGSS stage M neuroblastoma, a rare finding in older adults. Despite multimodal therapy, including polychemotherapy and immunotherapy according to pediatric GPOH neuroblastoma guidelines, disease progression necessitated an experimental approach. Comprehensive molecular analysis and MTB discussion revealed several potential treatment targets, leading to subsequent treatment including dinutuximab beta, nivolumab, cabozantinib, I-131-mIBG radionuclide therapy and alpelisib, unfortunately, all followed by disease progression. This case demonstrates the potential of comprehensive molecular analysis including methylation profiling for diagnosis and treatment guidance in rare tumors. Additional research is urgently required to improve outcomes in elderly patients with neuroblastoma.

BACKGROUND:The HIT network was established in 2000 to create a population-based structure aiming to improve survival rates and reduce late effects for children with central nervous system (CNS) tumors by conducting comprehensive clinical trials. METHODS:The HIT network currently consists of 10 coordinating trial centers mandated by the German Society for Pediatric Oncology and Hematology (GPOH) to conduct clinical trials and research projects, and to provide counseling to local centers for individual patients. The network is complemented by 11 reference centers (neuropathology, tumor biology, neuroradiology, pediatric neurosurgery, cerebrospinal fluid [CSF], assessments, radiotherapy, genetics), biostatistical support, and currently 72 local treatment sites. RESULTS:Numbers of children and adolescents with newly diagnosed CNS tumors registered to trials and registries increased from approximately 500 to more than 600 per year, corresponding to >95% of affected HIT-eligible children and adolescents in Germany. Clinical counseling and upfront reference assessments ensure homogeneous clinical standards and avoid inadequate treatment of individual patients. Since 2007, the established reference services have been partially re-funded by German health insurances. DISCUSSION:The HIT network provides a unique structure for population-based state-of-the-art diagnostic assessments, treatment recommendations and counseling. It increases the "a priori" accuracy of stratification parameters, and the timely inclusion into clinical trials and tumor-specific registries. Favorable outcomes are achieved within the trials and registry landscape, for example, through consistent reference assessments, reducing the gap to real world data. Resulting data facilitate representative, unbiased high-quality research projects across all CNS tumor entities. Interdisciplinary cooperation and competitive scientific output are enhanced.

Biphenotypic sinonasal sarcoma (BSS) is a rare mesenchymal neoplasm characterized by dual neural and myogenic differentiation, recurrent PAX3 gene rearrangements, and low-grade morphology. High-grade transformation has been described, posing significant diagnostic challenges due to overlap among sinonasal tumors. DNA methylation profiling has emerged as a powerful diagnostic tool for sinonasal neoplasms, although BSS was not included in previous cohorts. In this study, we investigated the DNA methylation profile of BSS and its relationship with fusion type and high-grade transformation. Fourteen BSS samples were retrospectively collected from four academic institutions. All cases underwent genome-wide methylation profiling using the Illumina Infinium MethylationEPIC array, and available clinical, radiological, histopathologic, and immunohistochemical data were reviewed. RNA sequencing was performed when sufficient material was available. Methylation profiles were analyzed using t-distributed stochastic neighbor embedding (t-SNE) and compared with a reference cohort of sinonasal tumors. The median patient age was 52.7 years, with a female predominance (M:F ratio 1:2.25). The most common fusion was PAX3::MAML3 (6/12, 50.0%), followed by PAX3::FOXO1 and other rare rearrangements, including PAX3::NCOA2, PAX3::YAP1, and FUS::POU2AF3, detected in one case each (1/12, 8.3%). Most importantly, all BSS samples formed a cohesive epigenetic group upon dimensionality reduction, clearly separated from other sinonasal tumors. No specific clustering was seen among different fusion types or tumor grade. Our findings support that BSS represents a unique and molecularly distinct sinonasal sarcoma with a characteristic DNA methylation signature, independent of gene fusion partners or histologic progression, providing a valuable tool for the classification of challenging cases.

BACKGROUND:Replication repair deficiency is associated with increased risk of developing malignant gliomas. The aim of this study was to investigate primary mismatch repair deficient gliomas (PMMRDGs), a group of IDH-wildtype and H3-wildtype gliomas that is enriched among patients with CMMRD and Lynch syndrome. METHODS:We investigated how PMMRDGs differ from other gliomas with respect to DNA methylation profile, genomic alterations, histopathology, and clinical outcomes. RESULTS:PMMRDGs occur in pediatric, adolescents and the elderly, falling in two related methylation clusters and are characterized by a high frequency of replication repair deficiency. Histology showed multinucleated giant cells, and immunohistochemistry demonstrated loss of MMR protein expression. Survival analysis revealed long-term survival in patients with high mutational burden (>50 mut/Mb) and an intact chromosome 9p region, which was validated in an independent reference cohort. CONCLUSIONS:Overall, our findings indicate that PMMRDGs represent a distinct type of IDH-wildtype gliomas with potential for long-term survival likely driven by immune activation.