bluuebunny/crossref_metadata_2025 huggingface dataset:
HGG-51. Uncovering therapeutic vulnerabilities in mismatch repair-deficient gliomas
Authors: Boynton Adam , Pal Sangita , Johnston Ryan , Currimjee Naomi , Qian Kenin , Touat Mehdi , Persky Nicole , Goodale Amy , Berstler James , Miller Lisa , Guletsky Alex , Ligon Keith L , Beroukhim Rameen , Bandopadhayay Pratiti
Published: June 2022

INTRODUCTION: We have observed that approximately 26% of recurrent gliomas acquire hypermutation following treatment with temozolomide (TMZ). Intriguingly, 91% of these tumors harbor mutations in mismatch repair (MMR) genes. Since MMR deficiency confers resistance to TMZ, strategies to target MMR-deficient gliomas stand to impact many patients. METHODS: We ablated the MMR genes MSH2, MSH6, MLH1, and PMS2 using an all-in-one sgRNA-CRISPR/Cas9 expression vector to generate isogenic MMR knockouts in patient-derived glioma cell lines. We characterized the gene expression profiles of these MMR-deficient glioma models and leveraged high-throughput drug screens and genome-scale CRISPR/Cas9 dropout screens to identify therapeutic vulnerabilities induced by loss of MMR. RESULTS: We show that loss of each major MMR gene confers resistance to TMZ. Gene set enrichment analysis of our MMR-deficient knockouts shows enrichment of several hallmark gene sets including DNA repair and G2M checkpoint signatures, and our genome-wide CRISPR dropout screen reveals that MMR-deficient cells are preferentially dependent on a number of genes involved in DNA repair and cell cycle, along with several other pathways. Lastly, the high-throughput drug repurposing (REPO) screen shows that loss of MMR confers differential dependencies to small molecule inhibitors. CONCLUSIONS: Using CRISPR/Cas9 to knock out individual MMR pathway members allows us to systematically study the response of MMR-deficient cells to alkylating agents in an isogenic context. Importantly, these isogenic models reveal that MMR-deficient glioma cells possess novel genetic dependencies and sensitivities to small molecules, which may inform future therapies for MMR-deficient tumors.
HGG-62. Molecularly guided treatment of mismatch repair-deficient pediatric brain tumors
Authors: Crotty Erin , Cole Bonnie , Stasi Shannon , Vitanza Nicholas , Paulson Vera , Lockwood Christina , Leary Sarah
Published: June 2022

Mismatch repair (MMR)-deficient brain tumors, defined by high tumor mutational burden (TMB) and alterations in MMR or DNA proofreading genes, may harbor therapeutic vulnerabilities to immune checkpoint inhibition (ICI) and resistance to temozolomide. We report a single-institution experience incorporating a personalized genomics approach for pediatric brain tumor patients with high TMB. Tumor and peripheral blood samples were obtained at surgery or autopsy and molecular profiling performed by UWOncoPlex, a multiplexed DNA sequencing panel. Treatment and survival information was obtained by medical records review. Tumor types included high-grade glioma (10, including 1 DIPG), and desmoplastic/nodular medulloblastoma (1). Metachronous tumors were present in three patients and median age at diagnosis was 11.5 years (range 8 – 18). Constitutional predisposition included MMR deficiency (CMMRD), Lynch syndrome, and polymerase proofreading deficiency (PPD). All patients had localized disease, with gross total resection achieved in 6/11 (55%). All received radiation (RT), with concurrent temozolomide delivered in HGG (9). 7/9 patients (78%) with HGG had radiographic progression following RT/temozolomide. Five patients received ICI with pembrolizumab (4), nivolumab/ipilimumab (2), or nivolumab alone (1). Two patients progressed on pembrolizumab then had partial responses to dual nivolumab/ipilimumab. Another patient had a complete response to pembrolizumab and remains disease-free nearly 1 year after discontinuing drug due to reactivated skin GHVD. While not statistically significant in this small cohort, median survival of ICI-treated patients (5) compared to those who received alternative therapies (6) was 40.4 vs. 17.7 months. Patients with durable responses >18 months to ICI (3) included one who underwent surgical debulking following nivolumab, and two patients molecularly classified as CMMRD + somatic PPD. This series highlights the importance of integrating molecular findings and identification of high TMB early in clinical diagnosis and supports the use of ICI to achieve durable responses in children with MMR-deficient brain tumors.
IMG-01. Quantitative Direct Sodium (23Na) MRI in Pediatric Gliomas
Authors: Bhatia Aashim
Published: June 2022

BACKGROUND: The treatment of pediatric gliomas is typically assessed with proton (1H) MRI, which can have limitations. 23Na MRI has been shown in adult brain tumors to measure intra-tumoral total sodium concentration as a correlate of tumor proliferation. 23Na MRI sodium studies in pediatric patients are lacking. PURPOSE: (1) To compare total sodium concentration (TSC) between pediatric glioma and non-neoplastic brain tissue using 23Na MRI; (2) Compare tissue conspicuity of bound sodium concentration (BSC) using 23Na MRI dual echo relative to TSC imaging. MATERIALS AND METHODS: TSC was measured in: (1) non-neoplastic brain tissues and (2) three types of manually segmented gliomas [diffuse intrinsic brainstem glioma (DIPG), recurrent supratentorial low-grade glioma (LGG), and high-grade glioma (HGG)] on sodium MRI images co-registered with proton MRI. In a subset of patients, serial changes in both TSC and BSC (dual echo 23Na MRI) were assessed for tissue conspicuity using voxel-based parametric maps. RESULTS: Twenty-six pediatric patients with gliomas (median age of 12.0 years, range 4.9 – 23.3 years) were scanned with 23Na MRI. Uninvolved tissues demonstrated a range of TSC values similar to published adult values. DIPG treated with RT demonstrated higher TSC values than the uninvolved infratentorial tissues (P<0.001). Recurrent supratentorial LGG and HGG exhibited higher TSC values than the uninvolved white matter (WM) and gray matter (GM) (P<0.002 for LGG, and P<0.02 for HGG). The dual echo 23Na MRI suppresses the sodium signal within both CSF and necrotic foci, resulting in improved conspicuity of both non-neoplastic and neoplastic, compared to serial TSC imaging. CONCLUSION: Quantitative 23Na MRI of pediatric gliomas demonstrates a range of values that are higher than non-neoplastic tissues. Dual echo 23Na MRI of BCS improves tissue conspicuity relative to TSC imaging. Future studies are needed to determine the value of 23Na MRI in delineating therapeutic responses in pediatric gliomas.
IMMU-06. Landscape of adaptive immunity of childhood brain cancers
Authors: Raphael Itay , Chikina Maria , Broniscer Alberto , Pollack Ian , Rajasundaram Dhivyaa , Kohanbash Gary
Published: June 2022

T lymphocytes have a unique ability to recognize a vast array of antigens prompted by an enormous T cell receptor (TCR) repertoire. Characterization of tumor-infiltrating T cells (TILs) is key to understand MHC-restricted anti-tumor immunity and for developing T cell-centered immunotherapies such as adoptive cell therapy and tumor vaccines. In the current work, we investigated RNA-Seq data from 997 pediatric brain tumor patients and performed a large-scale comprehensive examination of the immunogenomic and TCR landscape of TILs across the entire spectrum of pediatric brain tumors. We show that the relative ratio between T cell diversity (clonality) and T cell abundance within each sample, represented by the clonal expansion index (CEI), is a strong predictor of prognosis both within and between tumor types. Interestingly, we show that CEI was strongly associated with molecular subgroups of medulloblastoma but not with known tumor-genomic features of these subgroups. Investigation of TCR clones recognizing a common recurrent tumor-antigen across patients based on CDR3 homology and characteristics, reveals 9 TCR clusters which are tumor type restricted with defined prognoses and HLA dominance. Using computational immunogenomics and machine learning-based investigations of these clusters yielded novel putative HLA-restricted tumor antigens which could bind and activate the clusters’ specific TCRs. Importantly, our framework grounded the foundations for developing a precision medicine approach of T cell-centered immunotherapies. These findings have major implications for understanding the interplay between T cell and tumor genomic, and for developing new immunotherapies for children with brain tumors.
IMMU-07. Interim analysis of the HIT-HGG Rez Immunvac study - Dendritic cell vaccination with partial Treg depletion and double checkpoint blockade in children with relapsed high-grade gliomas.
Authors: Eyrich Matthias , Krauss Jürgen , Ghaffari Maryam , Caruana Ignazio , Rachor Johannes , Monoranu Camelia-Maria , Bison Brigitte , Rückriegel Stefan , Wölfl Matthias , Miller Elisabeth , Schlegel Paul-Gerhardt , Kramm Christof
Published: June 2022

Relapses of high-grade gliomas show an aggressive course and survival 6 months after (sub-)total re-resection was only 62% in former HIT-HGG trials. Immunotherapy by induction of tumor-specific T cells through active immunization might help to control glioma regrowth. In the HIT-HGG-Rez Immunovac trial (Eudra-CT 2013-000419-26) we investigate whether a therapeutic vaccine (autologous dendritic cells loaded with tumor lysate, DCV) combined with Treg-depletion and double checkpoint-inhibition (CI, anti-PD-1/anti-CTLA4) is able to increase the number of patients alive 6 months after relapse. Here, we report interim results after 50% of the intended patients (n=25) have been recruited. 13 children and adolescents (mean age 12.7±4.0 y) with relapsed glioblastomas were screened for the trial so far. Three patients were screening failures, 10 patients received study treatment. Of these, 2 patients are currently vaccinated, so that 8 patients were evaluable for this interim analysis. 5 SAEs have been reported so far, none of them was limiting. 4 patients with gross total or subtotal resection at time of relapse had an overall survival (OS) of 13.2±4.0 months and a 6-month survival rate of 100%, which compares favourably to historical controls. 4 partially resected patients survived only 5.1±1.3 months and 6-months OS was 25%. Treg-depletion lead to a reduction of CD4+CD127-CD25+ T-cells of 45%, the majority of patients exhibited a tumor-specific T-cell response. We conclude that DCV in combination with partial Treg-depletion and CI is feasible, safe, and related with immunological responses. Double CI was not associated with unexpected toxicities. In (sub-)totally resected patients, immunotherapy seems to confer a survival advantage. For the completion of the trial we aim to include more patients with (sub-)totally resectable tumors to gain more insight into the nature and duration of the induced immune response. This trial is supported by Bristol Myers-Squibb (CA209-7JA).
IMMU-12. Exploring and modulating the tumour immune microenvironment to facilitate the selection of immunotherapies for paediatric-type diffuse high-grade glioma
Authors: Cockle Julia , Bjerke Lynn , Mackay Alan , Grabovska Yura , Burford Anna , Molinari Valeria , Pereira Rita , Boult Jessica , Robinson Simon , Carvalho Diana Martins , Clarke Matthew , Titley Ian , Yara Erika , Straathof Karin , Wennerberg Erik , Becher Oren , Castro Maria , Melcher Alan , Jones Chris
Published: June 2022

Immune cells have the potential to selectively eradicate high-risk brain tumours such as paediatric-type diffuse high-grade glioma (PDHGG). We aim to characterize the tumour immune microenvironment (TIME) of intra-cranial syngeneic mouse models of diffuse hemispheric glioma, H3G34 (DHG-H3G34) and diffuse midline glioma, H3K27 (DMG-H3K27). We also demonstrate how an oncolytic reovirus (Reolysin) can “heat-up” the TIME of our syngeneic models. Orthotopic immunocompetent mouse models of DHG-H3G34 (C57BL/6, NRASG12V + shp53 + shATRX +/- H3.3G34R) and DMG-H3K27 (Nestin-Tv-a/p53fl/fl, RCAS-ACVR1R206H + RCAS-H3.1K27M) were profiled using single-cell RNA-sequencing (scRNA-seq) (10x genomics), a 22-colour custom flow cytometry immune panel and spatial transcriptomics. Differential marker expression was validated with immunohistochemistry and immunofluorescence in tissue sections. Syngeneic mouse tumours treated systemically with Reolysin were also profiled to evaluate the effects of the oncolytic virus on the TIME. Cell type predictions in scRNA-seq using singleR, ssGSEA and expression of individual marker genes suggested that the predominant immune cell types within hemispheric tumours were monocytes (11-21%) and macrophages (10-19%) with much smaller proportions of CD4+ and CD8+ T-cells (4-10%). By contrast, much smaller proportions of monocytes (2%) and macrophages (3%) were observed in the H3.1K27M pontine model. Flow cytometry, immunohistochemistry and immunofluorescence validated scRNA-seq immune profiles and characterised signalling of the PD-1/PD-L1 checkpoint pathway. Spatial transcriptomics allowed immune cell populations to be positioned within tumour sections and showed significant co-localization of CD4+ and CD8+ lymphocytes at tumour margins. Treatment of syngeneic mouse tumours with Reolysin resulted in reduced tumour volumes and altered the TIME, in particular increasing cytotoxic T-cell tumour infiltration. Our results highlight immunological heterogeneity within molecular subgroups of PDHGG and demonstrate ability of a systemically delivered oncolytic virus, Reolysin, to “heat-up” the TIME, contributing to a more immune actionable profile. Future work will help to identify optimal combinations for the next generation of immunotherapies in PDHGG.
LGG-07. Novel CRISPR/Cas9 induced KIAA1549:BRAF fusion model for preclinical studies of pediatric gliomas
Authors: Patel Krupesh , Zhao Guisheng , Huang Shih-Ming , Karakousi Triantafyllia , Nicolaides Theodore , Papagiannakopoulos Thales
Published: June 2022

BACKGROUND: Pediatric Low Grade Gliomas (pLGG) are the most common group of central nervous system (CNS) tumors in children and cause significant morbidities. Pilocytic astrocytoma (PA) is the most frequent pLGG. KIAA1549:BRAF fusion is a well-established oncogenic driver in PA. Oncogene induced senescence (OIS) has prevented establishing PA cultures for in vitro and in vivo studies. Here we look at a novel NIH-3T3 fibroblast model harboring KIAA1549:BRAF fusion gene via CRISPR/Cas9 somatic genome engineering technology.

OBJECTIVES: Establishing that the CRISPR/Cas9 edited NIH-3T3 fibroblast model with the KIAA1549:BRAF fusion is valuable for in vitro and in vivo studies without early OIS. DESIGN/METHOD: CRISPR/Cas9 editing technology was used to establish a KIAA1549:BRAF fusion positive cell model. This cell model was studied in vitro with MEK inhibitor cobimetinib (GDC-0973) and using WST-1 viability assay, clonogenic assay, senescence β-galactosidase staining, and western blot. In vivo murine models with subcutaneous fusion positive NIH-3T3 fibroblast tumors were treated with GDC-0973. Survival studies and tissue studies were subsequently done. RESULTS: A fusion positive NIH-3T3 fibroblast model was successfully established. Increased BRAF cDNA expression and higher levels of p-ERK were observed. In vitro studies showed decreased viability with GDC-0973. Clonogenic assay showed qualitative and quantitative decreases in viable cells. P-ERK target inhibition was established without induction of senescence. In vivo studies demonstrated successful subcutaneous tumor implantation, therapy efficacy, and target inhibition. CONCLUSION: CNS tumors, most commonly pLGG, in children cause significant morbidities. KIAA1549:BRAF fusion is an oncogenic driver in PA. In vitro and in vivo studies are important for pre-clinical models. OIS has prevented establishing adequate fusion positive animal cell models. Here we have demonstrated a successful CRISPR/Cas9 edited fusion positive NIH-3T3 fibroblast model.
LGG-10. Evaluation of the chemotherapy efficacy of children with optic pathway glioma in a tertiary hospital in China
Authors: Li Miao , Du Shuxu , Tian Yongji , Zhang Jin , Gao Wenchao , Xiao Jinjing , Gong Xiaojun , Sun Yanling , Wu Wanshui , Sun Liming
Published: June 2022

OBJECTIVE: In order to analyze the chemotherapy efficacy of children with optic pathway glioma (OPG), the clinical, treatment and prognosis factors of children with OPG who received the German International Society of Pediatric Oncology (SIOP) low-grade glioma (LGG) 2004 regimen chemotherapy, were retrospectively analyzed. METHOD: From September 2014 to October 2019, a total of 60 patients with OPG were enrolled and accept LGG 2004 chemotherapy in the Department of Pediatrics, Beijing Shijitan Hospital, Capital Medical University, China. The progression-free survival (PFS) rates and overall survival (OS) rates were analyzed by the Kaplan-Meier method. Both univariate and multivariate analyses were performed using the Cox-proportional hazards model. The test standard α=0.05. RESULTS: Until January 1st, 2022, all children were alive, and the clinical symptoms were improved at any degree, and well tolerated during the whole treatment. The median follow-up time was 3.7 years (range 2.3-7.1 years), the average time of objective response was 6.8 months (range from 2 to 21 months), and the 5 year PFS rates were 73.0 ± 7.24 %. However, about 3 to 8 months later, 8 cases (age <4 years) relapsed which attained partial remission (PR) at the end of the whole therapy. These relapsed cases were performed the LGG 2004 regimen again, and all had an objective response after 4~6 courses of treatment. In addition, two children (age>8 years old) progressed rapidly during treatment, and had to be performed local radiotherapy and reached complete remission (CR). Another two cases with BRAF V600E mutation, reached a significant remission after 3 months of targeted therapy with selumetinib. Furthermore, the COX multivariate analysis shows that spinal metastasis is an independent risk factor of prognosis of children with OPG. CONLUSIONS: Chemotherapy can improve the clinical efficacy of children with OPG, which is better when combining with bevacizumab and/or targeted therapy.
LGG-16. Retrospective and integrative analyses of molecular characteristics and their specific imaging parameters in pediatric grade 1 gliomas.
Authors: Courant Marie , Lhermitte Benoit , Guerin Eric , Chammas Agathe , Reita Damien , Sebastia Consuelo , Douzal Valérie , Gabor Flaviu , Salmon Alexandra , Todeschi Julien , Coca Andres Hugo , Vincent Florence , Entz-Werlé Natacha
Published: June 2022

Pediatric low-grade gliomas (PLGG) are the most common brain tumors diagnosed during childhood and represent a heterogeneous group associating variable molecular abnormalities. To go further and develop specific statistical patterns integrating altogether tumor molecular background, imaging features and patient outcome, a retrospective study was performed in a group of non-NF1 grade 1 PLGGs. So, 78 children, followed from 2004 to 2017, were retrospectively reported. Their therapeutic management comprised surgery or surgery plus chemotherapies (e.g., carboplatin and vincristine). In this population, radiological and molecular patterns were pooled statistically to be able to identify specific prognostic subgroups. Considering all 78 patients, 59 had only a surgical removal and 19 patients were treated with post-operative chemotherapy. Twelve progressions were reported in the partially resected and chemotherapeutic groups, whereas 4 deaths occurred only in the highly treated patients. As expected, PLGG with BRAF pV600E and/or CDKN2A loss exhibited poor outcomes. Nevertheless, we were able to evidence statistically significant associations between molecular characteristics and their specific imaging presentation on diagnostic and 24-week MRIs. In the chemo-treated patients, the molecularly good risk situations were significantly linked to the presence of a large tumor cyst at diagnosis (> 50% of the tumor volume (TV)) and the appearance during treatment of a higher cystic proportion that we called “cystic conversion”. So, additionally to the WHO prognostic molecular patterns, precise MRI characteristics (notably cystic part proportions onto TV) were associated to BRAF p.V600E PLGGs, as well as to the more frequent molecular KIAA1549-BRAF fused PLGGs. To summarize, absence on diagnostic MRI of cystic parts and/or cystic conversion at 6-month chemotherapy time point were significantly linked to a worst prognosis and response to treatment. In future studies, these imaging features might be considered as innovative prognostic markers to use during treatment.
LGG-20. Defining subgroups in low grade gliomas by their immune and stromal microenvironment
Authors: Körner Meik , Spohn Michael , Schüller Ulrich , Bockmayr Michael
Published: June 2022

Immunologic treatment options are still uncommon in low grade gliomas, although such therapies might be beneficial for inoperable and aggressive cases. Knowledge on immune and stromal cells in low grade gliomas, which is a mandatory prerequisite for such approaches, is still scarce. We therefore gathered published gene-expression data from 400 low grade gliomas as well as 302 high grade gliomas in order to quantify 10 microenvironment cell populations. First, we investigated general differences in the microenvironment of low- and high-grade gliomas. Lower-grade and high-grade tumors cluster together, respectively, and show a general similarity within and distinct differences between these groups, the main difference being a higher infiltration of fibroblasts and T-cells in high-grade gliomas. Among the analysed entities, gangliogliomas and pleomorphic xanthoastrocytomas presented the highest overall immune cell infiltration. Further analyses of the low-grade gliomas presented three distinct microenvironmental signatures of immune cell infiltration, which can be divided into T-cell/dendritic/natural killer cell-, neutrophilic/B lineage/natural killer cell-, and monocytic/vascular/stromal-dominated immune clusters. These clusters correlated with tumor location, age, and histological diagnosis, but not with sex or progression-free survival. Our work shows that low- and high-grade gliomas can be characterized and differentiated by their immune cell infiltration. Low grade gliomas cluster into three distinct immunologic tumor microenvironments, which may be of further interest for upcoming immunotherapeutic research.
LGG-29. Use of Bevacizumab in Pediatric Low-grade Glioma: Ten-year experience in a single center
Authors: Rafael Margarida Simão , Cruz Ofelia , Perez-Jaume Sara , Santa-María Vicente , Lavarino Cinzia , Salvador Hector , Muchart Jordi , Hinojosa Jose , Suñol Mariona , Morales Andrés
Published: June 2022

PURPOSE: Pediatric low-grade gliomas (PLGG) have excellent overall survival but frequently need non-surgical therapy at diagnosis or after progression at unresectable sites such as the optic pathway. Chemotherapy side effects have led to the need for better-tolerated regimens with a sustained response. Bevacizumab, a humanized anti-VEGF monoclonal antibody has been used in monotherapy and/or in combination for these entities. Here we present our experience with its use in PLGG. METHODS: A retrospective, observational, single-institution study between 2008-2018 was performed, reporting the short-term outcomes of safety and efficacy of bevacizumab in progressive PLGG. RESULTS: Twenty-six patients with a median age at diagnosis of 3.32 years old [0.12-14.7] and the median age at the treatment of 8.11 years old [0.41-16.82] were included in the study. Nineteen had optic pathway gliomas and chiasmatic-hypothalamic gliomas (73.1%), 9 of them (47.4%) associated with neurofibromatosis type 1 (NF1). Fourteen non-NF1 tumors were molecularly studied, disclosing BRAF-KIAA1549 fusion transcript in 9 and BRAF V600E mutation in 2. Bevacizumab was administered in combination with other agent(s) in 16 of the 35 treatment courses. Responses were assessed at 3, 6, 12 months, and at the end of treatment. Progression-free survival at 12 months was 94%, and no severe adverse events were observed. CONCLUSIONS: In our series, Bevacizumab in PLGG showed short-term clinical efficacy with a favorable toxicity profile. Larger and long-term prospective studies may determine whether the response is conditioned upon different clinical or molecular features.
LGG-31. Pediatric low-grade gliomas with FGFR1 mutations and spontaneous hemorrhage: case series
Authors: Campion Stephani , Aguilar-Bonilla Ana E , Elbabaa Samer , Smith Amy A
Published: June 2022

Pediatric low-grade gliomas (pLGG) are the most common pediatric CNS neoplasms. Thanks to the advent of molecular tumor diagnostics, we have begun exploring the clinical relevance of FGFR1 (c.1632C>A; p.N546K) mutations in the pLGG population. However, the risk of spontaneous hemorrhage in pLGG patients harboring FGFR1 mutations is even less understood. We present four pLGG cases with FGFR1 mutation and hemorrhagic episodes. Patient 1 presented with an intraventricular hemorrhage and leptomeningeal disease. Pathology was consistent with suprasellar pilocytic astrocytoma, FGFR1, and PTPN11 mutations. Initial therapy consisted of Carboplatin/Vinblastine per ADVL0515. The patient has had several recurrences, and treatment regimens have included ACNS0223, Everolimus, and A9952 regimen A. Patient 2 was diagnosed with an optic pathway glioma, and pathology confirmed FGFR1, MEK2, PTPN11, and NF1 splice site mutations. The patient also has a history of Noonan’s Syndrome and has undergone several chemotherapy regimens, including A9952 Regimen A, COG MATCH with Erdafitinib, and Avastin. The best tumor response was seen while on Avastin. The patient has presented with two episodes of intratumoral hemorrhage, both after treatment with Avastin. Patient 3 presented with a sudden brain stem hemorrhage and underwent a biopsy and debulking. The pathology was consistent with a pilocytic astrocytoma with an FGFR1 mutation confirmed by Next-generation sequencing (NGS). Treatment regimens for this patient include A9952 Regimen A and Vinblastine. Patient 4 presented with acute headache and vomiting and was found to have a hemorrhagic suprasellar mass. The patient underwent tumor debulking, and pathology was consistent with low-grade glioma. NGS revealed FGFR1 and KRAS mutations. The patient received therapy as per A9952 Regimen A. Greater surveillance of this molecular and clinical finding is warranted to uncover the association between FGFR1 mutations and hemorrhage in patients with low-grade gliomas.
LGG-35. Dyslipidemia in children treated with BRAF inhibitors for brain tumor, a new side effect? A single center retrospective study
Authors: Crocco Marco , Verrico Antonio , Milanaccio Claudia , Piccolo Gianluca , Gaggero Gabriele , De Marco Patrizia , Iurilli Valentina , Profio Sonia Di , Calevo Maria Grazia , Casalini Emilio , Iorgi Natascia Di
Published: June 2022

The targeted therapies for brain tumors are innovative and promising oncological treatments and as a result their use has expanded widely. BRAF inhibitors (BRAFi) in recent years have played a central role in disease control of unresectable BRAF-mutated pediatric low-grade gliomas (LGG). Understanding the side effects of these drugs is crucial for clinical practice. The aim of the study was to investigate retrospectively the acute and long-term effects of vemurafenib on lipid metabolism in children treated for an LGG. Children (n=6) treated with vemurafenib at the mean age of 8.41±6.1 exhibited early alterations in plasma lipid profile as demonstrated after 1 month (n=4) by high plasma levels of Low-Density Lipoprotein (LDL 139.5±51.5,mg/dL), Total Cholesterol (TC 221.5±42.1,mg/dL) and Triglycerides (TG 107.8±44.4,mg/dL). Despite dietary recommendations, dyslipidemia persisted 3 months later (LDL 148.8±40.2,mg/dL; TC 238±36.5,mg/dL; TG 115±45.6,mg/dL; n=4) and at long distance follow-up (38±23,months) after treatment with vemurafenib: LDL 139.2±49.1,mg/dL; TC 216.5±38.4,mg/dL; TG 129.7±83.4 mg/dL. This potential side effect suddenly resolved itself in the only patient in which a change of therapy was made (to the combination of dabrafenib and trametinib). BMI was compatible with overweight/obesity at baseline (mean BMI-SDS 0.9±1.8) in 2 patient and normal in 4 patients: during follow-up BMI remained stable in 5 patients and increased in 1 patient. Our findings highlight that Vemurafenib could be associated with an increased risk of dyslipidemia independently of weight. This risk should be anticipated by the identification of high-risk patients and managed by close monitoring of metabolic parameters during routinely follow-up. The association of dabrafenib with trametinib seem not be associated to dyslipidemia, yet more data are needed to explore the hypothesis about the possible role to reduce the risk of dyslipidemia.
LGG-47. Single-cell RNA Sequencing Reveals Immunosuppressive Myeloid Cell Diversity During Malignant Progression in Glioma
Authors: Rajendran Sakthi , Peterson Clayton , Canella Alessandro , Hu Yang , Gross Amy , Cam Maren , Serin-Harmanci Akdes , Distefano Rosario , Nigita Giovanni , Wang Wesley , Hester Mark , Miller Katherine , Elemento Olivier , Roberts Ryan , Holland Eric , Rao Ganesh , Mardis Elaine , Rajappa Prajwal
Published: June 2022

Myeloid cells and macrophages have been shown to promote immunosuppression in high-grade gliomas (HGG), however their roles in malignant progression of low-grade glioma (LGG) are poorly understood. Here, we investigated the heterogeneity of the immune microenvironment during glioma progression using a murine model that recapitulates the malignant progression of low to high-grade glioma. To that end, we performed single-cell RNA sequencing on CD45+ immune cells isolated from animals bearing no tumor (NT), LGG, and HGG. We observed an increased infiltration of CD4+ T cells, CD8+ T cells, B cells, and natural killer cells in the tumor microenvironment of LGG, whereas this infiltration was abrogated in HGG. Our study identified two distinct macrophage clusters across all 3 samples, with signatures of bone marrow derived and resident macrophages, respectively. These macrophages showed an immune-activated phenotype (Stat1, Tnf, Cxcl9 and Cxcl10) in LGG, but then evolved to a more immunosuppressive state (Lgals3, Apoc1 and Id2) in HGG, restricting T cell recruitment and activation. In addition, we identified CD74 and macrophage migration inhibition factor (MIF) as potential targets for both these distinct macrophage populations, based on their increased expression in LGG and HGG compared to NT. Targeting these factors during the LGG therapeutic window may inhibit myeloid cells and intra-tumoral macrophages and attenuate their immunosuppressive properties and impair malignant progression.
LGG-50. Human induced pluripotent stem cell engineering establishes a humanized mouse platform for pediatric low-grade glioma modeling
Authors: Anastasaki Corina , Chatterjee Jit , Cobb Olivia , Scheaffer Suzanne , Sanapala Shilpa , Costa Amanda , Wilson Anna , Garbow Joel , Rodriguez Fausto , Gutmann David
Published: June 2022

A major obstacle to identifying improved treatments for pediatric low-grade brain tumors (gliomas) is the inability to reproducibly generate human xenografts. To surmount this barrier, we leveraged human induced pluripotent stem cell (hiPSC) engineering to generate low-grade glioma (LGG) lesions representing the two most common pediatric pilocytic astrocytoma-associated molecular alterations, NF1 loss and KIAA1549:BRAF fusion. Using hiPSCs, we identified the susceptible cells of origin for these tumors, and demonstrated that the resulting tumors retain LGG histologic features for at least 6 months in vivo. Finally, this platform enabled the successful long-term growth of patient-derived pLGGs in vivo. Taken together, these avatars establish tractable experimental humanized platforms to elucidate the pathogenesis of childhood brain tumors.
LGG-52. Volumetry-based response characterization of recurrent pediatric low-grade gliomas in PNOC clinical Neuro-oncology trials
Authors: von Reppert Marc , Lin MingDe , Bousabarah Khaled , Familiar Ariana , Velasco Ryan , Waanders Angela , Vossough Arastoo , Haddock Amanda , Nicolaides Theodore , Swanson Kristin , Kazerooni Anahita , Kline Cassie , Nabavizadeh Ali , Haas-Kogan Daphne , Prados Michael , Rubin Joshua , Mueller Sabine , Aboian Mariam
Published: June 2022

BACKGROUND: Endpoints in clinical trials using novel treatments are evaluated by RANO criteria, which provide an estimate of tumor size from two-dimensional measurements along the most prominent axial slice. However, pediatric low-grade gliomas (pLGG) commonly have variegated shapes with solid and cystic components, potentially resulting in misevaluation of true tumor volume and thus, ultimately, trial outcome. OBJECTIVES: We aim to characterize treatment response through volumetric assessment of progressive/recurrent pLGGs treated with single-agent everolimus on PNOC001 clinical trial. We seek to identify clinically relevant criteria that provide added value to response assessment beyond 2D measurements. METHODS: In a cohort of 44 patients we performed 3D-segmentation of solid, cystic and whole tumor within our PACS-framework and compared results to previously carried-out central imaging review by RANO criteria which had yielded 15 PD, 27 SD, 2 PR and 0 CR. RESULTS: 8 tumors were solid only and 36 had a mixed solid-cystic appearance. When evaluating the entire tumor (i.e. solid and cystic components combined) and using the same RANO cutoff criteria, one case changed from PR to SD, one changed from SD to PR, 3 changed from SD to PD, and 7 changed from PD to SD, resulting in an overall discordance of 27% of cases. CONCLUSION: We propose that incorporation of volumetrics into response assessment provides additional and potentially more accurate information beyond RANO-based measurements. It is crucial to note that the above-reported changes represent numerical discrepancies as opposed to true-to-reality changes in clinical outcome. Determining representative thresholds for the deployment of volumetric measures in clinical trials will be critical. Future work will include data from the PNOC002 clinical trial and evaluate inter-reader agreement and reader discordance. With the availability of PACS-based 3D-tools in neuroradiology practice, well-defined volumetric criteria could be incorporated prospectively into treatment response analysis in clinical trials.
LGG-60. Development and implementation of a complementary diagnostic tool to detect targetable pathways in pediatric glioma patients
Authors: Nobre Liana , Levine Adrian , Milos Scott , Johnson Monique , Laxer Benjamin , Ryall Scott , Siddaway Robert , Tabori Uri , Hawkins Cynthia
Published: June 2022

Pediatric Low grade gliomas are mainly driven by MAPK alterations including mutations in BRAF (BRAF fusions and BRAFV600) and FGFR. This has led to the study of BRAF, MEK and more recently FGFR inhibitors resulting in variable responses. We hypothesize that differing levels of RAS_MAPK coupled with alternate pathway activation may be driving this variability. To address this, we designed a custom NanoString assay that integrates proteomic and transcriptomic profiling of 4 key cancer-related, actionable pathways (MAPK, PI3K-AKT-mTOR, JAK-STAT, and NFkB) with robust results on formalin-fixed paraffin embedded tissue, including archival samples up to approximately 15 years old. We validated this assay using 15 gold standard cell lines with defined changes in each pathway including both isogenic activating mutations and perturbation with inhibitors. These findings were confirmed using data from the Cancer Cell Line Encyclopedia. The panel was further validated using a cohort of 40 low grade glioma samples with available RNAseq data where the RNA expression signatures had high concordance between assays. We have currently run the assay on over 200 surgical tumor samples, including 206 gliomas, 15 ependymomas, 11 medulloblastomas, 14 high grade gliomas and 10 control normal brain specimens. Findings indicate significant variability in pathway activations between tumors, although PLGG overall have higher MAPK activation scores than control tissue and other tumor types, a subset of these tumors have increased activity in PIK , JAK and NFKB pathways, underscoring the importance of integrating transcriptomic and proteomic information in precision oncology treatments. Finally, single cell RNA sequencing data from pilocytic astrocytomas demonstrates significant heterogeneity in pathway activation states within the tumor cells, as well as high pathway activations in some tumor associated microglia. This raises further research questions regarding the role of tumor heterogeneity in treatment failures and the impact of targeted therapies on the tumor immune microenvironment.
LGG-61. Cerebrospinal fluid as a source for liquid biopsy in pediatric gliomas
Authors: Nobre Liana , Johnson Monique , Siddaway Robert , Sheth Javal , Ryall Scott , Ku Michelle , Lyn Rodney , Stucklin Ana , Zapotocky Michal , Tabori Uri , Hawkins Cynthia
Published: June 2022

Central nervous system neoplasms are currently the leading cause of morbidity and mortality among childhood cancers, gliomas account for 50% of these cases. The last decade has seen a massive growth in our understanding of the genetic underpinnings of these cancers, including the discovery of multiple diagnostic, prognostic and therapeutic markers. However, molecular characterization of these tumours requires a biopsy, with no added therapeutic benefit particularly in unresectable tumors. Liquid biopsy is a minimally-invasive alternative to biopsies which enables molecular characterization to diagnose, monitor response to therapy, and potentially predict progression/recurrence. We here present the results of a customized capture based NGS panel including 21 commonly altered genes present in pediatric and AYA gliomas coupled with low pass whole genome as a diagnostic and monitoring liquid biopsy tool. To assess for common fusions, exonic and intronic regions of specific genes are covered to capture different breakpoints. To establish the sensitivity and specificity of this assay we have used a commercially available control (SeraseqR) with 18 known mutated genes of interest and a in house control sample with two additional mutations. Samples with low ctDNA concentration (10 ng) and a limit of detection as low as 0.5% variant allele frequency, had a sensitivity of 83% and specificity of 100%. At higher concentrations (30 ng of ctDNA) we achieved a sensitivity and specificity of 100 %. We are currently finalizing the validation steps ctDNA samples extracted from CSF collected intra-surgically, through ventricular shunt or lumbar puncture. Twenty-two samples have been tested with additional 40 samples in processing. Driver alterations were identified in 16/22 samples, with additional 3/4 samples having concordant CNV alterations between tumor and CSF. This work supports further implementation of CSF use as a minimal invasive source of diagnostic and monitoring sample in children and adolescent patients with gliomas.
LGG-62. Weight change in pediatric patients treated with MEK inhibitors: a retrospective cohort study
Authors: Hyun Bahng Hye , Malvar Jemily , Chi Yueh-Yun , Framson Celia , Robison Nathan
Published: June 2022

BACKGROUND: MEK inhibition is an emerging treatment strategy in pediatric tumors characterized by activation of the Ras-Raf-MEK-ERK pathway, including low-grade glioma (LGG) and neurofibromatosis 1 (NF1)-associated tumors. Preliminary clinical experience suggests that MEK inhibitors (MEKi) may be associated with weight gain in children, which has not been a reported toxicity in adults. METHODS: 35 patients > 1 and < 21 years old treated at CHLA with MEKi between October 2013 and May 2019 were identified. Data was collected at t = 0 (baseline), t = 3 months, t = 6 months, t = 12 months, and t = 24 months, as well as pre- and post-treatment time points. Weight change was categorized as no change (change in Z-score [-0.25, +0.25]), weight gain (change in Z-score > 0.25), and weight loss (change in Z-score > -0.25). RESULTS: Weight gain and weight loss were seen in 11 (34.4%) and 8 (25%) patients, respectively, after 6 months on therapy. Weight gain reversed in 4 out of 5 patients with post-treatment data. There was no clear association between weight outcome and hypothesized covariates (including hypothalamic location and NF1 status). Notably, significant weight gain was seen across baseline weight spectrum, including patients who had underweight and severely overweight BMI percentiles at baseline. CONCLUSION: Our findings preliminarily suggest that MEK inhibition may be associated with clinically significant weight change, especially weight gain, in a subset of children and young adults. Reversal upon drug cessation suggests a causal relationship. Further prospective and mechanistic investigation is needed.
MEDB-03. Medulloblastoma cerebrospinal fluid reveals hypoxic indicators (metabolites and lipids) and cancer-specific RNAs
Authors: Lee Bongyong , Mohamad Iqbal , Pokhrel Rudramani , Murad Rabi , Yuan Menglang , Stapleton Stacie , Bettegowda Chetan , Jallo George , Eberhart Charles G , Garrett Timothy , Perera Ranjan J
Published: June 2022

Medulloblastoma (MB) is the most common malignant brain tumor in children. There remains an unmet need for diagnostics to sensitively detect the disease, particularly recurrences. Cerebrospinal fluid (CSF) provides a window into the central nervous system, and liquid biopsy of CSF could provide a relatively non-invasive means for disease diagnosis. There has yet to be an integrated analysis of the transcriptomic, metabolomic, and lipidomic changes occurring in the CSF of children with MB. CSF samples from patients with (n=40) or without (n=11; no cancer) MB were subjected to RNA-sequencing and high-resolution mass spectrometry to identify RNA, metabolite, and lipid profiles. Differentially expressed transcripts, metabolites, and lipids were identified and their biological significance assessed by pathway analysis. Multivariate analysis method DIABLO (R package mixOmics) was used to integrate the molecular changes characterizing the CSF of MB patients. Differentially expressed transcripts, metabolites, and lipids in CSF were discriminatory for the presence of MB but not the exact molecular subtype. One hundred ten genes and ten circular RNAs were differentially expressed in MB CSF compared to normal representing TGF-β signaling, TNF-a signaling via NF-kB, and adipogenesis pathways. Tricarboxylic acid cycle and other metabolites (malate, fumarate, succinate, α-ketoglutarate, hydroxypyruvate, N-acetyl-aspartate) and total triacylglycerols were significantly upregulated in MB CSF compared to normal CSF. Although the transcriptomic, metabolomic, and lipid signatures in CSF to differentiate MB subgroup separation was challenging, we were able to identify a group of omics signatures that could separate cancer from normal CSF. Metabolic and lipidomic profiles both contained indicators of tumor hypoxia. Our approach provides several candidate signatures that deserve further validation, including the novel circular RNA circ_463, and insights into the impact of MB on the CSF microenvironment.
MEDB-05. Survival and prognostic factors in childhood medulloblastoma: A China single center experience from 2006 to 2015
Authors: Liang zhuangzhuang , Cao liangliang , Zhao yang , Wang baocheng , Tian shuaiwei , Wang jiajia , Ma jie
Published: June 2022

OBJECTIVE: Medulloblastoma (MB) is a malignant embryonal tumor that develops especially in childhood, with overall survival (OS) at 5 years of up to 70%. The aim of the study is to explore the clinical profile and outcome among the histo-molecular subgroups in Chinese children. METHODS: A total of 93 patients of MB who underwent surgical treatment at Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine from January 2006 to December 2015. The clinical profile, treatment, and survival patterns are discussed. The relevant statistical analysis was done using SPSS software, version 21.0. RESULTS: At the most recent follow-up date, 15 (16.1%) had been lost to follow-up，78 cases were tested for RNA-seq, of which 54 cases were successful, and 24 cases failed the quality control due to sample quality problems.The male-to-female ratio was 2.4:1, and the patients’ mean age at diagnosis was 5 years (ranged from 4 months to 11 years).The estimated 5-year overall survival and progression-free survival, based on Kaplan-Meier analysis, were 55.1% ± 5.6% and 40.9% ± 5.7%.Multivariate survival analysis showed that progression -free survival were significantly affected by extent of surgery (P=0.026) and postoperative radiotherapy(P＜0.001).Preoperative metastasis (P=0.032) and postoperative radiotherapy (P=0.001) had a significant influence on overall survival. While，the molecular subtypes showed no statistically significant differences in 5-year PFS and 5-year OS. CONCLUSION: Extent of resection of MB and postoperative radiotherapy were the important clinical prognostic factors for survival. In the future, we will continue to expand cases and study the clinical characteristics and prognostic risk factors of different molecular types of medulloblastoma in Chinese children,and to improve the survival rate of children with medulloblastoma.
MEDB-07. Long-term medical and functional outcomes of medulloblastoma survivors: a population-based, matched cohort study
Authors: Coltin Hallie , Pequeno Priscila , Liu Ning , Tsang Derek S , Taylor Michael D , Bouffet Eric , Nathan Paul C , Ramaswamy Vijay
Published: June 2022

BACKGROUND: Most medulloblastoma survivors suffer from late treatment-related sequelae. There are no population-based studies examining such late effects in a dedicated cohort of medulloblastoma survivors. METHODS: Using a provincial pediatric cancer registry, all 5+ year medulloblastoma survivors diagnosed between 1987-2015 in Ontario, Canada were identified and matched to cancer-free population controls based on age, sex, and geographical location. Cases were followed from the index date (five years from latest of diagnosis, or relapse or subsequent malignancy prior to age 18 years) until December 31, 2020 or censorship (death, or relapse or new cancer after age 18 years). Clinical data were linked to administrative health databases to estimate cumulative incidences and cause-specific hazard ratios (HR) of mortality, hospitalizations, strokes, hearing loss requiring a hearing aid, and receipt of homecare services between cohorts, accounting for matching and competing risks. RESULTS: We identified 230 cases [65.7% female; median diagnostic age: 7y, interquartile range (IQR) 4-10; median attained age: 24y, IQR 18-31] and 1150 controls. One hundred eighty-seven (81.3%) received craniospinal irradiation. Ten-year survival probability after index was 92.4% in cases and 99.4% in controls (HR 21.5, 95% CI 9.8-54.0). Cases were at higher risk for hospitalizations (HR 3.4, 95% CI 2.7-4.3), stroke (HR 45.6, 95% CI 12.8-289.8), hearing loss (HR 96.3, 95% CI 39.7-317.3), and requiring homecare services (HR 7.9, 95% CI 5.8-10.9). By 10 years after index, 4.8% (95% CI 2.2-9.0) of survivors had experienced a stroke compared to 0.1% (95% CI 0.01-0.7) of controls. CONCLUSIONS: Survivors of childhood medulloblastoma experienced an increased risk of mortality and serious morbidity compared to population controls. Consideration for mitigation strategies or early interventions in preventing neurovascular sequelae and hearing loss is warranted, as are dedicated supports for survivors.