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BackgroundAccurate identification of brain tumour molecular subgroups is increasingly important. We aimed to establish the most accurate and reproducible ependymoma subgroup biomarker detection techniques, across 147 cases from International Society of Pediatric Oncology (SIOP) Ependymoma II trial participants, enrolled in the pan-European “Biomarkers of Ependymoma in Children and Adolescents (BIOMECA)” study.MethodsAcross six European BIOMECA laboratories we evaluated epigenetic profiling (DNA methylation array); immunohistochemistry (IHC) for nuclear p65-RELA, H3K27me3, and Tenascin-C; copy number analysis via FISH and MLPA (1q,CDKN2A), and MIP and DNA methylation array (genome-wide copy number evaluation); analysis ofZFTA-andYAP1-fusions by RT-PCR and sequencing, Nanostring and break-apart FISH.ResultsDNA Methylation profiling classified 65.3% (n=96/147) of cases as EPN-PFA and 15% (n=22/147) as ST-ZFTA fusion-positive. Immunohistochemical loss of H3K27me3 was a reproducible and accurate surrogate marker for EPN-PFA (sensitivity 99-100% across three centres). IHC for p65-RELA, FISH, and RNA-based analyses effectively identifiedZFTA-andYAP1-fused supratentorial ependymomas. Detection of 1q gain using FISH exhibited only 57% inter-centre concordance and low sensitivity and specificity whilst MIP, MLPA and DNA methylation-based approaches demonstrated greater accuracy.ConclusionsWe confirm, in a prospective trial cohort, that H3K27me3 immunohistochemistry is a robust EPN-PFA biomarker. Tenascin-C should be abandoned as a PFA marker. DNA methylation and MIP arrays are effective tools for copy number analysis of 1q gain, 6q andCDKN2Aloss whilst FISH is inadequate. Fusion detection was successful, but rare novel fusions need more extensive technologies. Finally, we propose test sets to guide future diagnostic approaches.Key pointsWe evaluated and cross-validated ependymoma biomarkers in a large prospective clinical trial cohort.Accurate biomarker evaluation is critical to the success of clinical trials and patient care.We propose core and core+biomarker test sets for future molecular stratification.Importance of the StudyHigh-risk paediatric ependymoma has a poor prognosis and is devastating at relapse. Molecularly defined ependymoma types need to be accurately and reliably linked to biomarkers to predict clinical outcomes and design clinical trials. Here, we evaluated and cross-validated ependymoma biomarkers in a large prospective clinical trial cohort highlighting the importance of systematic evaluation of different methods. We provide evidence to guide test selection to support the molecular stratification of paediatric ependymoma and deliver insights into the rationalisation of biomarkers for use in resource-limited settings.

Subependymal giant cell astrocytomas (SEGAs) are circumscribed gliomas strongly associated with tuberous sclerosis (TS). TS, a rare genetic disorder caused by inactivating mutations in either of the TSC genes (TSC1/2), leads to upregulation of the mTOR pathway and consecutive cell growth. CNS manifestations other than SEGAs include cortical tubers, white matter glioneuronal hamartomas and subependymal nodules (SENs), which, although regarded as distinct morphological phenotypes, share certain histological characteristics including ballooned astrocytes and giant ganglion-like cells. SEGAs, thought to develop from the median ganglionic eminence (MGE), are most commonly located periventricularly. However, rare cases of extraventricular SEGAs have been reported. We report a case of a cortico-subcortically located SEGA in a TS patient. A two-month-old female TS patient with multiple cortical tubers presented with treatment-resistant epilepsy. A 4cm sized tuber located in the right temporal lobe, showing a transmantle sign on MRI but no typical imaging appearance of SEGA, was surgically resected. Histological evaluation revealed typical morphological characteristics of a tuber with dysmorphic neurons, balloon cells and calcifications in the cortex and adjacent white matter. Focally, a cortico-subcortically located, well delineated area with increased cellularity and morphological features of a SEGA was found. Single mitotic figures were detectable. Immunhistochemically, these cells were strongly positive for GFAP, vimentin, and nestin. Scattered S100-, NeuN-, MAP2- and SMI32-positive cells were present. No expression of class-III-b-tubulin and TTF1a was found. pS6 was expressed in a small fraction of cells. CD34 showed a dense capillary network within the lesion. This case is consistent with prior case reports of SEGA-tissue in tubers of TS patients. However, the SEGA tissue of this case did not display TTF1a-expression, characteristic for SEGAs and considered as a marker for cells originating from the MGE, thus implying a different cellular lineage.

Pediatric high-grade glioma (pHGG) is an incurable disease with a median survival of less than 6 months post-progression and no effective targeted therapy. PDGFRA is commonly altered in pHGG, but targeting PDGFRA in this disease has been unsuccessful, likely due to poor central nervous system (CNS) penetrance. Avapritinib is a novel and CNS-penetrant PDGFRA/KIT inhibitor that is FDA-approved for adults with unresectable or metastatic PDGFRA exon 18-mutant gastrointestinal stromal tumor (GIST) and is being studied in CNS tumors. We performed a pre-clinical and clinical assessment to determine the potential suitability of avapritinib therapy in PDGFRA-driven glioma. A multi-institutional cohort genetic analysis revealed PDGFRA amplification and mutation in 10.2% and 6.1% of pHGG, respectively. Additionally, PDGFRA expression in the absence of genetic events was significantly increased in H3K27-altered diffuse midline glioma (DMG) compared to H3-wildtype pHGG. Avapritinib performed well in: (i) mutant PDGFRA enzyme inhibition and wildtype inhibition at high dose, (ii) minimal off-target kinase inhibition, (iii) brain penetration (peak 10 µM), and (iv) proliferation/pPDGFRA reduction in PDGFRA-amplified and mutant pHGG cell lines. Avapritinib treatment in an aggressive PDX model of pHGG resulted in significant survival benefit. We pursued treatment of eight pediatric and young adult HGG patients with avapritinib across seven institutions. Patients were a mixture of local (N = 4) and metastatic disease (N = 4); all patients were post-initial radiation, with 7/8 having progressed on prior treatment. 7/8 patients had PDGFRA amplifications or mutations, and 7/8 had H3K27M mutations. Therapy was generally well-tolerated. 4/8 patients showed radiographic response to avapritinib, with one patient demonstrating complete response of target lesion and remains on therapy. Avapritinib levels in patients’ CSF and brain tumor tissue reached micromolar levels. These results demonstrate that avapritinib is a potent, selective, and CNS-penetrant PDGFRA/KIT inhibitor that is promising for further study in pHGG with relevant alterations.

Histone 3 lysine27-to-methionine mutant diffuse midline gliomas (H3-K27M DMGs) are among the most lethal brain tumors. Their putative cellular hierarchy has been shown to be driven by self-renewing stem-like cells arrested in an oligodendrocyte precursor-like (OPC-like) state, of which few cells are able to differentiate towards more mature astrocyte (AC)-like and oligodendrocyte (OC)-like cells. However, the spatial organization underlying this tumor cell architecture and its microenvironmental interactions in intact H3-K27M DMG tissues remain unknown. Here, we profiled the single cell transcriptomes of 45 patient H3-K27M DMGs and derived cell population-specific marker gene combinations to characterize the single cell spatial organization of 16 tumors using targeted in situ sequencing. We thereby resolved different malignant and non-malignant cell populations including cycling, OPC-like, AC-like, OC-like, mesenchymal tumor cells, and non-malignant oligodendrocytes, astrocytes, neurons, myeloid cells, T cells, and vascular cells directly in situ. Global neighborhood analyses indicate a higher tendency of cycling OPC-like cells, vascular cells, and neurons to localize within a more restricted homogeneous compartment, whereas AC-like cells, non-malignant astrocytes and myeloid cells tend to intermingle with different cell populations in a more diffuse manner. Among malignant cells, we observed cycling OPC-like and OC-like cells to co-localize within a niche-like structure that is surrounded by more differentiated AC-like cells. We further validated this stem-like niche at the protein level using multiplexed immunofluorescence via the CODEX system. Finally, we characterized relationships between malignant and non-malignant cells, consistently identifying preferred neighborhoods of mesenchymal tumor cells with vascular and myeloid cells. Together, this study resolves the spatial architecture of H3-K27M DMG malignant and non-malignant cells at single cell resolution and identifies a local niche of the oligodendroglial lineage containing the OPC-like cancer stem-like cells, thus providing novel insights into the cancer stem-like compartment in H3-K27M DMGs and suggesting potential avenues for its perturbation.

Central nervous system (CNS) tumors with BCOR internal tandem duplications (CNS-BCOR ITD) are aggressive malignancies recently included in the 2021 WHO Classification of CNS tumors. This entity is characterized by ITDs within the PUFD domain of BCOR, potentially interfering with protein-protein interactions and preventing non-canonical polycomb repressive complex 1.1 (ncPRC1.1) complex formation. Additionally, other BCOR alterations like frame shift mutations and gene fusions have been described. However, the underlying molecular mechanisms promoting tumor aggressiveness remain unknown. We established cell models from one patient harboring a BCOR frameshift mutation and another one with a concomitant BCORL1-fusion. Two additional models were derived from a patient with a CNS-BCOR ITD tumor. Multidrug screening uncovered high sensitivity against defined receptor tyrosine kinase (RTK) inhibitors (TKIs). In detail, ponatinib, nintedanib, and dovitinib reduced cell viability at half maximal inhibitory concentrations (IC50) in the low micro-molar range (

The identification and validation of prognostic and diagnostic biomarkers is a key element of The SIOP Ependymoma II trial, realised through the Biomarkers of Ependymoma in Children and Adolescents study (BIOMECA). BIOMECA aims to identify and validate biomarkers for prediction of outcome whilst enhancing stratification for the next generation of ependymoma trials. We outline our findings from the first 147 consecutive BIOMECA cases (posterior fossa, PF=111; supratentorial, ST=32; spinal, SP=4). We compared various methods for biomarker assessment, across six European laboratories to determine key analysis methods. Methods included: methylation-based classification (EPIC 850K DNA methylation array) (n=141); immunohistochemistry (IHC) for nuclear p65-RELA (n=32), H3K27me3 (n=115), and Tenascin-C (TNC) (n=147); copy number (CN) analysis by FISH, MLPA (1q, CDKN2A) (n=147), and MIP (molecular inversion probe) and DNA methylation array (1q, CDKN2A, 6q, 11q, 13q, 22q) (n=141); analysis of ZFTA- and YAP1-fusions by RT-PCR, sequencing, Nanostring assays and break-apart FISH (n=32). Using DNA methylation-based classification, 91% (n=101/111) of PF cases classified as PF ependymoma group A (PFA) and 69% (n=22/32) of ST cases as ST ependymoma, ZFTA fusion-positive (ZFTA). Most PFAs demonstrated inter-centre agreement for loss of H3K27me3, and were TNC positive, representing surrogate markers for PFA identification. Combinations of p65-RELA IHC, FISH analysis, and RNA-based methods were suitable to identify ZFTA- and YAP1- fused ST ependymomas. Predictive CN alterations were identified by high-resolution, quantitative MIP technology.The integration of histopathology assessment and molecular typing is now critical as the updated 2021 WHO CNS5 classification of ependymomas lists seven molecularly distinct entities. This study highlights the importance of evaluating different methods in a prospective trial cohort. Here, advanced molecular techniques represent powerful tools for the classification of ependymoma entities (DNA methylation array) and for the detection of CN alterations (MIP) and specific fusions, enabling the correct classification and identification of prognostic markers.

H3K27M-mutated diffuse midline glioma (H3K27M DMG) are an almost universally fatal disease with a median survival of less than 6 months post progression and no effective therapy. PDGFRA-signaling has shown to promote and sustain a subset of oligodendrocyte precursor-like tumor cells that are responsible for tumor propagating potential and high proliferation rates. However, first attempts to target PDGFRA in adult glioblastoma with dasatinib/imatinib or pediatric refractory brain tumors with sunitinib were not successful. We report on the first experience in two patients receiving avapritinib, a highly potent, selective, brain penetrant PDGFRA/KIT inhibitor under a compassionate use program. Our first patient with spinal H3K27M DMG developed supratentorial metastases ten months after initial diagnosis. Molecular profiling revealed de novo PDGFRA and KIT amplifications and treatment with dasatinib was initiated. Due to disease progression and novel metastases, therapy was switched to avapritinib showing near complete resolution of the previously unirradiated frontal lesion with additional disease stabilization of other metastatic sites. Following re-resection and irradiation of progressing cerebellar lesions, the patient remains clinically stable on avapritinib therapy over 12 months. The second patient with diffuse intrinsic pontine glioma showed disease progression nine months after diagnosis and was treated with focal re-irradiation (30Gy). As the tumor harbored a PDGFRA R841del alteration, avapritinib was initiated seven weeks after radiation upon further tumor progression resulting in partial response. Pharmacokinetic sampling of cerebrospinal fluid (CSF) detected an increasing CSF/plasma ratio over time and up to 4 µM avapritinib in tumor tissue. Avapritinib CSF levels in both patients were distinctly higher than dasatinib levels. Avapritinib was generally well tolerated besides lower limb edema, elevated LDH and liver enzymes. Hence, effective CNS penetration of avapritinib at pharmacologically relevant brain tumor concentrations resulted in clinical response in two patients with rapidly progressive H3K27M DMG.

Central nervous system (CNS) tumor with BCOR internal tandem duplication (BCOR-ITD) have recently been introduced in the 5th edition of the WHO classification of CNS tumors, however, their molecular makeup and clinical characteristics remain widely enigmatic. This is further complicated by the recent discovery of tumors characterized by gene fusions involving BCOR or its homologue BCORL1. We identified a cohort of 206 BCOR altered CNS tumors via DNA methylation profiling and conducted in-depth molecular and clinical characterization in an international effort. By performing t-SNE clustering analysis we found that BCOR-fusion tumors form a distinct cluster (n=61), adjacent to BCOR-ITD cases (n=145). The identified fusion partners of BCOR(L1) included EP300 (n=20), CREBBP (n=5), and NUTM2HP (n=1). Notably, three cases within the BCOR-ITD cluster harbored a c-terminal intragenic deletion within BCOR. With respect to clinical characteristics gender ratio was balanced in BCOR-fusion cases (m/f, 1.1), whereas predominance of male patients was observed in the BCOR-ITD group (m/f, 1.5). Moreover, age at diagnosis of BCOR-fusion patients was higher as compared to BCOR-ITD cases (15 vs 4.5 years). Interestingly, BCOR-fusion tumors were exclusively found in the supratentorial region being originally diagnosed as ependymomas or gliomas whereas BCOR-ITD emerged across the entire CNS with diverse original diagnoses. 8% of BCOR-ITD and none of BCOR-fusion cases were disseminated at diagnosis. In line with this observation, 40% of first relapses within the BCOR-ITD group were metastatic which was less frequent in BCOR-fusion tumors. Survival estimates demonstrated no differences, generally showing short median PFS (BCOR-fusion, 2 years, n=15; BCOR-ITD, 1.8 years, n=55) and intermediate OS rates (BCOR-fusion, 6.8 years, n=18; BCOR-ITD 6.3 years, n=60). Further molecular and clinical characterization is ongoing potentially revealing first therapeutic leads for these highly aggressive CNS tumor types.

BACKGROUND: Medulloblastoma (MB) are the most common malignant brain tumor in childhood. Developmental gene expression data supported by neuroradiological studies suggest that Wingless (WNT)-MB originate from the lower rhombic lip (LRL), Sonic-Hedgehog (SHH)-MB from the cerebellar hemispheres, and Group 3 and Group 4 MB from the cerebellar vermis. However, there is still insufficient evidence from a neurosurgical perspective supporting this proposed concept. METHODS: Clinical and molecular data from patients aged under 18 years at time of diagnosis who were operated on a histologically confirmed MB at the Department of Neurosurgery of the Medical University of Vienna between 1990 and 2020 were retrospectively analyzed. The location of the tumor origin was defined based on operative reports, surgical videos and preoperative imaging data by an experienced neurosurgeon blinded to the subgroup information. RESULTS: Sufficient data were available in 53 patients. In 28.6% (2 / 7) WNT-MB, 66.7% (6 / 9) SHH-MB and 70.3% (26 / 37) Group 3 and Group 4 MB, the intraoperatively defined site of origin corresponded well with the cellular origin suspected from the molecular subgroup. Within the WNT-subgroup, 57.1% (4 / 7) originated from the vermis, 28.6% (2 / 7) from the LRL and 14.3% (1 / 7) from the cerebellar hemisphere. The origin of SHH-MB was predominantly located in cerebellar hemispheres (66.7% (6 / 9)), while 33.3% (3 / 9) originated from the vermis. Of Group 3 and Group 4 MB, 70.3% (26 / 37) had their origin in the vermis and 29.7% (11 / 37) in the LRL.CONCLUSION: Our results indicate that there is a considerable level of inconsistency between the intraoperatively observed site of origin and the expected cellular origin based on the molecular subgroup, especially in WNT-MB. This discrepancy needs to be discussed when it comes to surgical decision-making accounting for risk stratification.

BACKGROUND High-grade gliomas are among the most aggressive brain tumors across all age groups. BRAF is within the most frequently altered genes in pediatric glioma, sometimes connected with telomerase reverse transcriptase (TERT) promoter mutations, predicting a particularly aggressive course of disease. Precision medicine approaches targeting the MAPK pathway have shown promising results in patients with BRAF-mutated glioma. Although acquired insensitivity to BRAF inhibitors appears as major issue for therapy failure, underlying molecular mechanisms are still poorly understood. METHODS Cell models from an anaplastic pleomorphic xanthoastrocytoma with BRAF V600E and TERT promoter mutations and the recurrent tumor, operated following MAPK pathway-targeting therapy, were established. Furthermore, a dabrafenib-resistant subline of the recurrent tumor was generated. The patient-derived cell models were genetically characterized using array-based genomic hybridization (aCGH). Sensitivity of the cells towards different MAPK pathway inhibitors was tested. Basal expression and activation of MAPK pathway and downstream signals were analyzed by qRT-PCR and Western blots. RESULTS Screening a panel of both primary and immortalized glioma cell models with different BRAF and TERT promoter status revealed significantly induced MAPK pathway activation and enhanced TERT levels in BRAF V600E and TERT promoter double-mutant gliomas. Furthermore, cells with both mutations were hyper-sensitive towards BRAF-targeting agents and BRAF inhibition resulted in reduced TERT levels. ETS1 expression was strongly increased in the recurrent tumor and identified as important player in telomerase re-activation. aCGH revealed gains of chromosomal regions encoding for different ETS-factors in the dabrafenib-resistant subline. Western blot analyses suggested a BRAF/ERK-independent survival mechanism in the dabrafenib-resistant subline. Accordingly, dabrafenib insensitivity triggered cross-resistance towards the MEK inhibitor trametinib. Uncoupled from the MAPK pathway, ETS1 expression was further upregulated in the dabrafenib-resistant subline. CONSLUSION: Taken together, our data demonstrate that MAPK-independent ETS transcription factor upregulation is a central mechanism of BRAF inhibitor therapy failure in BRAF-mutated pediatric glioma patients.

A low dispersion laser ablation setup in combination with inductively coupled plasma-time-of-flight mass spectrometry (LA-ICP-TOFMS) was applied to clinical samples of patients undergoing platinum-based chemotherapy. The platinum accumulation together with the distribution of elements with biological key functions (Mg, P, S, Ca, Fe, Cu and Zn) was studied in central nervous system germ cell tumor (CNS GCT) tissue, which is an aggressive tumor type located in the brain. Heterogeneous elemental distribution patterns were obtained with a pixel size of 10 μm and were correlated to histological analysis of serial sections using hematoxylin eosin staining. Highest platinum accumulation correlated with areas of necrosis, which exhibited high levels of magnesium, sulphur and calcium. Small traces of gadolinium were found in the tumor sections, which is a result of prior magnetic resonance imaging. Iron accumulated in regions, which were dense in blood vessels, whereas areas with fibrosis scar showed the lowest levels of all detected elements. This LA-ICP-TOFMS study demonstrates that the chemotherapeutic drug cisplatin accumulated in the germ cell tumor located in the brain, which is also reflected by the therapy response of the patients.

H3K27M-mutated diffuse midline glioma (H3K27M-DMG) may arise in the pons, thalamus and spinal cord generally having a dismal prognosis. Notably, H3K27M-DMG are driven by oligodendrocyte precursor-like cells which are partly sustained by PDGFRA signaling. Co-mutations including TP53, ACVR1, PDGFRA, KIT and PI3K pathway alterations are present in a subset of cases, and molecular profiling may allow detection of additional targetable alterations. However, small-molecule inhibitors often have limited efficacy associated with low blood-brain-barrier (BBB) penetration. Here, we report on a patient with spinal, leptomeningeal disseminated H3K27M-DMG treated with avapritinib, an orally administered, BBB-penetrant and highly selective KIT and PDGFR inhibitor, provided through a compassionate-use program. Initial therapy consisted of subtotal resection, focal radiotherapy and temozolomide (TMZ) resulting in disease stabilization. Ten months after diagnosis, leptomeningeal metastases were detected, biopsied and treated with local irradiation and TMZ. The patient subsequently received systemic and intrathecal chemotherapy augmented with dasatinib. Molecular analyses of the biopsy revealed the H3F3A and TP53 mutations present in the primary tumor, as well as de novo PDGFRA and KIT amplifications with gene copy numbers of 25 and 21, respectively. Upon further disease progression, therapy with avapritinib was initiated. Assessment of treatment response according to RANO criteria after four months revealed stable disease of the target lesion in the cerebellum and partial response of all non-target lesions. Avapritinib was generally well tolerated with lower limb edema (Grade 2), small intratumoral bleeding (Grade 1) and unrelated hydrocephalus (Grade 3) as reported adverse events. As precaution, treatment was interrupted and re-initiated after one week as the bleeding was stable. A ventriculoperitoneal shunt was implanted resolving the hydrocephalus. Pharmacokinetic analyses revealed up to 65% avapritinib plasma exposure and clinically relevant levels in cerebrospinal fluid. In summary, we report on first effective therapy of treatment-resistant H3K27M-DMG with avapritinib as clinical proof of concept.

BACKGROUND Embryonal tumours with multilayered rosettes (ETMR) are highly aggressive tumors, mostly occurring in infants. Published clinical data refer to retrospective cohorts of inhomogeneously treated patients. Here, we describe the outcome of patients, who were prospectively treated within the P-HIT2000-trial, the subsequent HIT2000-interim-registry and earlier HIT-trials. PATIENTS AND METHODS Nineteen patients from the P-HIT2000-trial (2001–2011), 12 patients from the subsequent HIT2000-interim-registry (2012–2014) and 4 patients from earlier HIT-trials with centrally reviewed neuropathological and molecularly-confirmed diagnosis of ETMR were included. Outcome of 18 patients treated with carboplatin-etoposide-induction followed by tandem-high-dose chemotherapy (“CARBO-ETO+HDCT”) with stage-stratified radiotherapy administered in case of persistant disease, relapse or progression were compared to patients treated with HIT-SKK chemotherapy ± radiotherapy (n=9) or other regimens (n=8). RESULTS Median age at diagnosis was 2.9(1.0–5.3) years. Metastases at diagnosis were detected in 9 patients (26%). For the entire cohort of n=35, 5-year overall survival (OS) was 26.7%, and progression-free survival (PFS) was 18.5%. Five-year OS for patients with CARBO-ETO+HDCT, SKK chemotherapy or other regimens was 44.4%, 13.0% and 0%, respectively (p=0.006). Five-year PFS was 33.3%, 0% and 0%, respectively (p=0.119). Of 10 survivors, n=8 were treated with CARBO-ETO+HDCT; n=4 had craniospinal, n=2 local and n=4 no radiotherapy. Impact of initial gross-total-resection (p=0.231) and non-metastatic disease (p=0.097) was limited. CONCLUSIONS We show improved survival with carboplatin-etoposide-induction followed by tandem-high-dose chemotherapy, indicating that a cure is possible for some patients. However, despite intensive treatment, outcome is unsatisfactory and innovative therapies urgently need to be included in an upfront setting.

Ependymoma represents a heterogeneous disease affecting the entire neuraxis. Extensive molecular profiling efforts have identified molecular ependymoma subgroups based on DNA methylation. However, the intratumoral heterogeneity and developmental origins of these groups are only partially understood, and effective treatments are still lacking for about 50% of patients with high-risk tumors. We interrogated the cellular architecture of ependymoma using single cell/nucleus RNA-sequencing to analyze 24 tumor specimens across major molecular subgroups and anatomic locations. We additionally analyzed ten patient-derived ependymoma cell models and two patient-derived xenografts (PDXs). Interestingly, we identified an analogous cellular hierarchy across all ependymoma groups, originating from undifferentiated neural stem cell-like populations towards different degrees of impaired differentiation states comprising neuronal precursor-like, astro-glial-like, and ependymal-like tumor cells. While prognostically favorable ependymoma groups predominantly harbored differentiated cell populations, aggressive groups were enriched for undifferentiated subpopulations. Projection of transcriptomic signatures onto an independent bulk RNA-seq cohort stratified patient survival even within known molecular groups, thus refining the prognostic power of DNA methylation-based profiling. Furthermore, we identified novel potentially druggable targets including IGF- and FGF-signaling within poorly prognostic transcriptional programs. Ependymoma-derived cell models/PDXs widely recapitulated the transcriptional programs identified within fresh tumors and are leveraged to validate identified target genes in functional follow-up analyses. Taken together, our analyses reveal a developmental hierarchy and transcriptomic context underlying the biologically and clinically distinct behavior of ependymoma groups. The newly characterized cellular states and underlying regulatory networks could serve as basis for future therapeutic target identification and reveal biomarkers for clinical trials.

Neuroendocrine tumors (NETs) are rare neoplasms predominantly arising in the GI-tract or the lungs of adults. To date, only ten cases of primary CNS NETs have been reported with just three of them describing a neuroendocrine carcinoma (NEC) in patients aged 34–77 years and none occurring in a child. We report on a previously healthy 5-year-old boy, who presented with headaches, nausea and vomiting and was diagnosed with a left cerebellar solid mass with a cystic component, radiologically suggestive of a pilocytic astrocytoma. After gross-total resection, histological analysis revealed an epithelial tumor growing in a nest-like pattern with a very high mitotic frequency, staining positive for CK8, CK18 and CK19. Chromogranin A and synaptophysin expression indicated a neuroendocrine differentiation. Molecular analysis of the tumor tissue revealed a KRAS- splice-site mutation (c451-3C>T). After extensive search for an extracranial primary, including Ga-68 DOTANOC-PET-CT, the diagnosis of a primary CNS NEC was made, and proton irradiation was performed. However, the patient developed an in-field recurrence just five weeks after the end of radiotherapy. The tumor was re-resected en-bloc, showing vital tumor tissue, demonstrating its aggressiveness. Chemotherapy consisting of etoposide, cisplatin and ifosfamide was initiated. After two cycles chemotherapy was continued with etoposide and carboplatin for another four cycles. The patient remains disease free one year after the end of relapse-treatment, supporting the beneficial effect of platinum- and etoposide-based chemotherapy for this tumor entity. Physical exam revealed a sagittal synostosis with a mild dolichocephaly. Interestingly, the KRAS-mutation was discovered to be a maternal germline mutation, previously described as likely benign. However, alterations of the RAS/MAPK pathway have been described in NECs and in craniosynostosis cases. It remains to be elucidated whether the KRAS-mutation is merely a variant of uncertain significance or might have been implicated in the development of this exceptional tumor.

Background Ependymomas account for up to 10% of childhood CNS tumors and have a high rate of tumor recurrence despite gross total resection. Recently, classification into molecular ependymoma subgroups has been established, but the mechanisms underlying the aggressiveness of certain subtypes remain widely enigmatic. The aim of this study was to dissect the clinical and biological role of telomerase reactivation, a frequent mechanism of cancer cells to evade cellular senescence, in pediatric ependymoma. Methods We determined telomerase enzymatic activity, hTERT mRNA expression, promoter methylation, and the rs2853669 single nucleotide polymorphism located in the hTERT promoter in a well-characterized cohort of pediatric intracranial ependymomas. Results In posterior fossa ependymoma group A (PF-EPN-A) tumors, telomerase activity varied and was significantly associated with dismal overall survival, whereas telomerase reactivation was present in all supratentorial RelA fusion-positive (ST-EPN-RELA) ependymomas. In silico analysis of methylation patterns showed that only these two subgroups harbor hypermethylated hTERT promoters suggesting telomerase reactivation via epigenetic mechanisms. Furthermore, chromosome 1q gain, a well-known negative prognostic factor, was strongly associated with telomerase reactivation in PF-EPN-A. Additional in silico analyses of gene expression data confirmed this finding and further showed enrichment of the E-twenty-six factor, Myc, and E2F target genes in 1q gained ependymomas. Additionally, 1q gained tumors showed elevated expression of ETV3, an E-twenty-six factor gene located on chromosome 1q. Conclusion Taken together we describe a subgroup-specific impact of telomerase reactivation on disease progression in pediatric ependymoma and provide preliminary evidence for the involved molecular mechanisms.

Brain tumors are comprised of cells with heterogeneous genetic and transcriptional states, resulting in substantial phenotypic diversity. This diversity is particularly evident in embryonal tumor with multilayered rosettes (ETMR), which shows a striking bi-phasic pattern for which it is named. A better understanding of its underlying molecular makeup is urgently needed to develop more effective therapeutic strategies that eliminate all malignant cell types underlying ETMR initiation, maintenance, progression, and relapse. Furthermore, the cellular origin of ETMR is currently poorly understood. We used plate-based single-cell RNA sequencing to assess the intratumoral heterogeneity in 6 fresh and 4 snap-frozen surgical biopsies, following a workflow that we have previously established to study pediatric high grade gliomas, medulloblastomas, and ependymomas. Computational analyses conducted on >4,000 single cells identified cellular hierarchies ranging from a proliferative, undifferentiated cell population to more differentiated, predominantly neural-like progeny in all samples. Patient-derived cell line and xenograft models partially recapitulated this hierarchy. We further integrated transcriptional programs identified in single cells with available datasets of the developing normal brain, as well as with programs identified in other pediatric brain tumor entities, to inform both putative cellular origins and ETMR-specific oncogenic pathways. These timely results provide unparalleled insights into the molecular underpinnings of the phenotypic heterogeneity observed in ETMR. Analyses aimed at further integrating malignant cell type abundances with genetic alterations and clinical annotations, and therapeutical targeting of malignant cell populations using in-vitro models are currently ongoing.

Central nervous system high-grade neuroepithelial tumor with BCL6-corepressor alteration (CNS HGNET-BCOR) is a recently discovered molecular brain tumor entity characterized by genomic alterations of BCOR, a central component of a non-canonical polycomb repressive complex. However, the underlying oncogenic mechanisms and their consequences for tumor-specific anti-cancer therapy remain widely enigmatic. We systematically analyzed genomics, transcriptomics, and drug-sensitivity patterns in three tumor-derived models (two cell-lines, one primary cell-culture) from three consecutive intracranial CNS HGNET-BCOR metastases of one patient. All models harbored a unique frameshift mutation within BCOR resulting in a truncated protein lacking functionally important c-terminal protein domains. Re-expression of BCOR wild-type in our CNS HGNET-BCOR cell-models resulted in decreased cell proliferation and increased apoptosis. Interestingly, genes downregulated upon re-expression of BCOR wild-type were also derepressed in CNS HGNET-BCOR tumor tissues harboring BCOR-alterations different from our case (e.g. internal tandem duplication in BCOR). Via comparison with a chromatin immunoprecipitation DNA-sequencing dataset, we determined that a significant proportion of the corresponding gene promoters are occupied by BCOR in BCOR wild-type cancer cells. An additional drug-screen demonstrated hypersensitivity of CNS HGNET-BCOR cells against histone deacetylase inhibitors and histone methyltransferase inhibitors. Matching of drug sensitivity patterns to upregulated target-genes determined bortezomib, dasatinib, and crizotinib as promising tumor-specific therapeutics against CNS HGNET-BCOR. Taken together, our results suggest that dysfunction of BCOR-mediated gene repression determines the oncogenic behavior and transcriptomic profile of CNS HGNET-BCOR. Moreover, we provide preliminary results for potential pharmacological interventions against this aggressive tumor type.

Pediatric medulloblastoma is considered a highly heterogeneous disease and a new strategy of risk stratification to optimize therapeutic outcomes is required. We aimed to investigate a new risk-stratification approach based on expression profiles of medulloblastoma cohorts. We analyzed gene expression profiles of 30 primary medulloblastomas and detected strong evidence that poor survival outcome was significantly associated with mRNA expression profiles of 17p loss. However, it was not supported in independent cohorts from previously published data (n = 100). We speculated that this discrepancy might come from complex conditions of two important prognostic determinants: loss of tumor suppressors (chromosome 17p) and high expression of oncogenes c-myc (MYCC) or N-myc (MYCN). When patients were stratified into 5 or 7 subgroups based on simultaneous consideration of these 2 factors while defining the Wnt group as independent, obviously different survival expectancies were detected between the subgroups. For instance, predicted 5-year survival probabilities ranged from 19% to 81% in the 5 subgroups. We also found that age became a significant prognostic marker after adjusting for 17p, MYCC, and MYCN status. Diminished survival in age

Epigenetic profiling has shown that a proportion of cases diagnosed as CNS PNET in the past can be assigned to other tumour entities with similar morphological appearance. In an international effort to re-analyze CNS-PNET aiming for disease-specific re-evaluation of survival data and the development of diagnostic guidelines providing the basis for improved therapeutic approaches, 256 tumours diagnosed and treated as CNS-PNET in the last two decades in 17 countries were reviewed by a panel of neuropathologists according to today’s standards of clinical neuropathological diagnostics including immunohistochemical and molecular pathological assays. The majority of cases were also independently analyzed by methylation array hybridization and classified by random forest algorithm. In this unique cohort, we identified 20 different tumor entities including frequent high grade gliomas. 41% of cases were confirmed as CNS-PNET (now termed CNS-embryonal tumors (CNS-ET) according to the revised WHO-classification) representing two main entities: ETMR displayed typical histopathological features, LIN28A expression and/or C19MC alteration. The other represented a group of tumors with variable degrees of differentiation along neuroblastic/ganglionic lines, corresponding to the WHO diagnoses CNS-(Ganglio)-neuroblastoma or CNS-ET, NOS. The vast majority of these tumors could be assigned to the FOXR2 CNS-NB group by methylation array-based classification. Crossvalidation of neuropathological and epigenetic classification proved that methylation classification represents a useful complimentary tool in the differential diagnosis of CNS-ET. Re-evaluation of prototypic tumors and cases with discrepant diagnoses enabled us to develop an optimized diagnostic algorithm to securely delineate this tumor type from other entities with largely divergent clinical and biological behaviour.

Patients with recurrent malignant CNS tumors have a poor prognosis irrespective of salvage therapy applied. We used a metronomic antiangiogenic combination therapy and report on the response of individual tumor types to this approach. Since 2006, 81 patients with various recurrent malignant brain tumors started treatment with an antiangiogenic multidrug-regimen at the Medical University of Vienna. Therapy consisted of daily oral thalidomide, fenofibrate, celecoxib, and 21-day cycles of low dose oral etoposide alternating with cyclophosphamide augmented with IV bevacizumab and intraventricular therapy (etoposide and liposomal cytarabine). Excluding the 10 patients with recurrent medulloblastoma treated in the formal international protocol (MEMMAT; ClinicalTrials.gov Identifier: NCT01356290), 71 patients were treated according to the same strategy “off trial”. Diagnoses were medulloblastoma (n=20), atypical teratoid rhabdoid tumor (ATRT) (n=11), ependymoma (n=9), high grade glioma/diffuse intrinsic pontine glioma (HGG/DIPG) (n=9), and various other entities in the remaining patients. As of the end of 2017, 3-year and 5-year OS for the 20 patients with recurrent medulloblastoma was 64.2 ± 10.9% and for the 11 patients with recurrent ATRT 45.7 ± 16.6% and 30.5 ± 16.7%, respectively. Remission could be maintained after discontinuation of treatment in a certain percentage of patients with medulloblastoma, ATRT and ependymoma. Patients with HGG and DIPG did not respond to this approach. The proposed antiangiogenic regimen seems most promising in medulloblastoma and ATRT and possibly also ependymoma. In a number of other tumor entities time to progression could be prolonged while maintaining good quality of life.

BACKGROUND: Malignant brain tumors carry a high risk for leptomeningeal dissemination, but tumor cells floating in the CSF are often not affected by systemic and/or antiangiogenic chemotherapy. Since liposomal cytarabine was removed from the market, alternatives for intraventricular therapy are desperately needed. We report on our experience with an intraventricular therapy consisting of alternating cycles of etoposide, aqueous cytarabine and topotecan. PATIENTS AND METHODS: Between 2008 and 2017, 26 patients aged 1 to 17 years (median 7 years) with various malignant brain tumors received intraventricular therapy via an Ommaya reservoir, consisting of alternating etoposide 0.5mg on five consecutive days (1 and 2 and 1 and 2 and

BACKGROUND: Prognosis of patients with recurrent medulloblastoma and atypical teratoid rhabdoid tumor (ATRT) is dismal despite intensive therapy including high-dose chemotherapy with stem cell rescue. We report on 28 patients with recurrent medulloblastoma and ATRT treated with an alternative approach to conventional chemotherapy that targets neovascularisation by interfering with tumor angiogenesis at various levels. Patients and METHODS: From 11/2006 to 06/2016, 28 patients were diagnosed with recurrent embryonal tumors, 20 with a recurrent medulloblastoma (13 first, 7 multiple recurrences) and eight with recurrent ATRT (5 first, 3 multiple), three had germ line mutations. Treatment consisted of an antiangiogenic multidrug-regime including IV bevacizumab, oral thalidomide, celecoxib, fenofibrate, and etoposide alternating with cyclophosphamide, and augmented with intraventricular therapy (etoposide and liposomal cytarabine). Median age at start of antiangiogenic therapy was 10 (1–24) years for medulloblastoma and 1.5 (1–13) years for ATRT. Results: As of 11/2016, 12/20 patients with medulloblastoma are alive at a median of 25 (12–97) months after their last recurrence. 8/12 surviving patients are currently in CR for 97, 94, 93, 29, 27, 23, 19 and 18 months, five off therapy for 79, 62, 60, 22 and 18 months, three are in PR 23, 12 and 2 months after their last recurrence and one patient has stable disease 12 months after her last recurrence. 5-year-OS is 57.6 ± 13.2%. One patient died of an accident in CR 23 months after initiation of antiangiogenic therapy and one patient with a very good PR died of a septicemia seven months after his last recurrence. Two patients had prior been treated with the same antiangiogenic approach and had recurred 67 and 40 months after their last recurrence while off therapy for 36 and 21 months and both patients are in remission again, one off therapy for 18 months. 3/8 patients with ATRT are alive. Follow-up since last recurrence is 72, 27 and 24 months and all patients are off therapy for 52, 14 and 13 months. One patient died of another cause without evidence of tumor at autopsy 54 months after recurrence and while off therapy for 46 months. One surviving patient with a germ line mutation and a fourth recurrence was prior treated with the same approach albeit without intrathecal therapy. He recurred 78 months after his last recurrence while off therapy for 36 months. He is again in CR and off therapy for 13 months. Therapy is primarily outpatient, was generally well tolerated, and toxicities were manageable. CONCLUSION: The proposed antiangiogenic regimen is currently being evaluated for medulloblastomas in an international phase II protocol (MEMMAT; ClinicalTrials.gov Identifier: NCT01356290). The same approach seems to be also efficacious in recurrent ATRTs and warrants further evaluation.

HG-85. INTER-OBSERVER AGREEMENT IN NEUROPATHOLOGICAL HGG DIAGNOSIS : EXPERIENCE OF THE PRE-RANDOMISATION CENTRAL REVIEW IN THE HERBY TRIAL Pascale Varlet1, Marie-Cecile Le Deley2, Felice Giangaspero3, Christine Haberler4, Thomas S. Jacques5, Dominique Figarella-Branger6, Torsten Pietsch7, Felipe Andreiuolo1, Darren Hargrave5, Maura Massimino8, Tim Jaspan9, Chris Jones10, Amedeo A. Azizi11, Adela Canete12, Eric Bouffet13, Helen Smith14, Josep Garcia14, Gilles Vassal2, and Jacques Grill2; Sainte-Anne Hospital, Paris, France; Institut Gustave Roussy, Villejuif, France; Sapienza UniversityofRome,Roma, Italy; InstituteofNeurology,Wien,Austria; Great Ormond Street Hospital, London, UK; Hopital de la Timone, Marseille, France; University of Bonn, Bonn, Germany; Fondazione IRCCS Istituto Nazionale Tumori, Milan, Italy; University Hospital, Nottingham, UK; InstituteofCancerResearch,Sutton,UK;UniversitatsKlinik furKinderund Jugendheilkunde, Wien, Austria; H.U. LA FE, Valencia, Spain; Hospital for Sick Children, Toronto, ON, Canada; F. Hoffmann-La Roche Ltd, Basel, Switzerland In previous large paediatric multicentre trials for High-Grade Glioma (HGG), highproportions of diagnosticdisagreementacrossneuropathologists were reported. The HERBY trial is a Phase-II open-label, randomised, multicentre trial evaluating bevacizumab in paediatric patients with newly diagnosed supratentorial HGG. METHODS: Confirmation of HGG diagnosis by reference pathology was mandatory before randomisation, followed by a review by five independent expert neuropathologists. Inter-observer agreement was assessed using Cohen’s Kappa coefficients. RESULTS: Slides from 169/187 patients screened for eligibility were centrally reviewed, within 3 days in 69% of cases. HGG diagnosis was centrally confirmed in 149 cases (88%), whereas diagnosis was low-grade glioma in 5% (n 1⁄4 8), anaplastic ganglioglioma/PXA (n 1⁄4 8), miscellaneous diagnoses (n 1⁄4 4). 124 patients entered the randomised trial. Three cases were not confirmed by the pathology panel (reclassified in grade II oligodendroglioma or anaplastic gangliogliomas). The Kappa coefficient between local and reference pathologistwasmoderate for the subtype and substantial for the WHO grade (Kappa 1⁄4 0.45 and 0.68, respectively). Agreement varied according to the initial diagnosis with the confirmation of subtype and grade for 23% cases of oligodendroglioma or mixed oligo-astrocytoma, 76% of WHO grade III astrocytoma and 95% of glioblastoma. The review panel registered some degree of discordance for subtype or grade in 52% cases, with dispersed conclusions from the experts (. 3 out of 5) in 10% cases. However, Kappa coefficient reached 85% for the grading between the reference pathologist and the consensus. These data highlight the interest and feasibility of a pre-randomised real-time central neuropathological review in multicentre trials. Neuro-Oncology 18:iii48–iii77, 2016. doi:10.1093/neuonc/now073.81 #The Author(s) 2016. Published by Oxford University Press on behalf of the Society for Neuro-Oncology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

LG-40. UNUSUAL NON-PILOCYTIC HISTOPATHOLOGICAL FEATURES OF PEDIATRIC INFRATENTORIAL GLIOMAS WITH BRAF FUSION GENE: A REPORT OF 2 CASES Christine Haberler1, Andreas Kiefer2, Barbara Jauk2, Christian Dorfer1, Thomas Czech1, Giles Vince2, Manuela Badiali3, and Irene Slavc1; Medical University of Vienna, Vienna, Austria; Academic Hospital of Klagenfurt, Klagenfurt, Austria; Microcitemico Hospital, Cagliari, Italy Genomic profiling studies have unraveled distinct molecular changes in different pediatric glioma entities. High grade gliomas commonly harbor H3F3A mutations or PDGFRA amplifications, diffuse low grade gliomas frequently display mutations in the FGFR1 or MYB1 gene, and pilocytic astrocytomas are characterized by MAPK pathway alterations including BRAF fusions and mutations. We report two infratentorial tumors with unusual morphological features. Patient 1 is a 15-year-old girl with a 6 months history of headache and a 4.5x4.5x6 cm cerebellar cystic tumor with contrast enhancement. A near gross total resection was performed. Histopathologically, the tumor was partly clear-celled but showed focally also some rosettes reminiscent of a RGNT. Vascular proliferations in a nonpilocytic tumor raised the suspicion of a malignant glioma. Patient 2, a 4-year-old girl presented with cephalea/strabism and had a cystic 2,8 x 2,9 x 2,5 cm tumor in the pineal region, radiologically compatible with a pilocytic astrocytoma. A gross total resection was performed. Histopathologically, ependymoma-like features with perivascular pseudorosettes, clear cells and vascular proliferations were present. In both cases immunhistochemical expression pattern confirmed a glioma without H3F3A K27M and BRAF V600E mutation, however classification and grading were difficult. Sequencing revealed in both tumors a KIAA1549– BRAF fusion. As this alteration is predominantly but not exclusively found in pilocytic astrocytomas and histopathologically no clear-cut signs ofmalignancy werepresent, no adjuvant treatment was administered. Both patients show no tumor recurrence/progression 32 and 21 months postoperatively. These cases emphasize the importance of molecular analyses in tumors with unusual morphological feature. Neuro-Oncology 18:iii78–iii96, 2016. doi:10.1093/neuonc/now075.40 #The Author(s) 2016. Published by Oxford University Press on behalf of the Society for Neuro-Oncology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Thalamic tumors are rare neoplastic lesions usually of glial lineage representing about 2- 5% of all pediatric brain tumors. We report on our experience in the management of thalamic tumors in children and analyze the current role of surgery in a multimodal treatment approach. We retrospectively reviewed the medical charts of all children treated at our institution for a thalamic tumor since March 1992. Neuroimaging data were reviewed for anatomic location, contrast enhancement, solid and cystic components, and extent of resection. Tumors primarily localized in the basal ganglia, hypothalamus, pineal gland and optic pathway were excluded. All histologic specimens were reexamined for the study by one neuropathologist. From 1992 to 2014, 36 children with a thalamic tumor were identified. The median age at diagnosis was 9.2 (range 1-19) years with a male:female ratio of 1:1. Tumors were unilateral in 29 and bilateral in 7 patients. Histology was pilocytic astrocytoma (PA, WHO I) in 10 patients, astrocytoma WHO II or glioma NOS in 7 patients, glioma WHO III or IV in 17, and atypical teratoid rhabdoid tumor (ATRT) in 2 patients. Surgery consisted of a GTR in 6, STR in 9, PR in 9, and biopsy in 12 patients. 22/26 WHO II-IV tumors were irradiated and all WHO III and IV tumors received adjuvant chemotherapy. 3/10 patients with PA received chemotherapy. 5-year OS for the whole cohort was 56.2 ± 8.6% and 5-year EFS was 47.6 ± 8.7%. For the 2 patients with ATRT and the 10 with PA the 5-year OS was 100% versus 36.1 ± 10.1% for the remaining patients. Gross total tumor removal is recommended for PA. In unilateral non-pilocytic tumors the attempt at extensive resection should be decided on individually since most tumors will be candidates for adjuvant treatment. Bilateral thalamic tumors should initially be biopsied.

BACKGROUND: Glioblastoma constitutes the most common primary malignant brain tumor in adults. Its aggressive disease course is mediated by a hitherto poorly understood interplay of rapid tumor progression and therapy-related effects. Crucial factors include - amongst hypoxia, angiogenesis, and others - an immune response upfront and/or as a consequence to combined chemo-radiotherapy. Herein, we aim at a systematic morphological characterization of this immune response based on a homogenous series of paired pre- and posttherapeutic glioblastoma samples. PATIENTS AND METHODS: A total of 15 glioblastoma patients newly diagnosed from 2005-2010 at the Medical University of Vienna were included in the analysis. All patients underwent neursurgical resection followed by standard radio- and TMZ-chemotherapy. At time of tumor recurrence second surgery was performed in all cases. Information on clinical characteristics and last follow-up were available. The tumor-associated immune response was semiquantitatively assessed using immunohistochemistry for anti-HLA-DR, CD3, and CD8. In addition, tumor-associated eosinophilia was assessed on conventional HE stains. RESULTS: Median age at diagnosis was 54 ys (range 21-69 ys). Median time from first to second surgery was 12.0 mths (range 1-26 mths) and median overall survival was 46.0 mths of the total cohort. While tumor-infiltrating CD3+ and CD8+ T-lymphocytes did not show a significant difference between first and second surgery (p = 0.07 and p = 0.3, respectively), a significant increase of HLA-DR+ microglia/macrophages (p = 0.01) was observed at time of tumor recurrence in the majority of cases (10/15; 66.7%). No unequivocal differences in overall survival were observed for those patients with enhanced microglial/macrophage response at time of tumor recurrence (log rank test; p = 0.34). A single case showed massive infiltration of eosinophils at second surgery only. This case differed from others by young age at diagnosis (26 ys), positive IDH-1 mutational and MGMT methylation status, short time to second surgery (1 mth) and exceptional favorable overall survival with stable disease at 84 mths. No peripheral eosinophilia or prior history of atopic disease was noted. Further screening for anti-neuronal/glial antibodies on a tissue-based assay did not yield a positive result. CONCLUSION: Although the small sample size implies cautious interpretation, we observed a significant increase of tumor-infiltrating microglia/macrophages in glioblastoma samples obtained after first-line therapy, while no significant differences were observed for tumor-infiltrating CD3+ and CD8+ T-lymphocytes. Of note, a single patient showed prominent tumor-associated eosinophilia upon second surgery which was associated with long-term survival.

Low grade gliomas (LGG) comprise a spectrum of different tumor entities corresponding to WHO grade I and II, including pilocytic astrocytoma, diffuse glioma and glioneuronal tumors. LGG in children differ in histologic distribution, molecular profile, localisation in the CNS and outcome from LGGs in adults. We report on a series of patients treated at a single center over 20 years. PATIENTS: Between 1993 and 2012, 339 consecutive patients with a median age of 8 years (range 4 months - 18 years, p25 = 3.7 years, p75 = 13.4 years) were treated at the Medical University of Vienna. 19.5% of the patients were