Atypical Teratoid Rhabdoid Tumor Research Articles

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

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

RADT-08. BASAL GANGLIA TOXICITY FOLLOWING PROTON THERAPY OF THE PINEAL REGION WITH BILATERAL ACTION-INDUCED MYOCLONUS

Abstract INTRODUCTION We sought to evaluate the toxicity profile for children receiving 54Gy to the pineal region with a significant dose delivered to posterior thalamus and basal ganglia. METHODS We performed a retrospective review of patients treated at a single institution with intensity modulated proton therapy (IMPT) receiving 54Gy to the pineal region. Multiple beam angles were utilized for planning. Patient characteristics and dosimetric data were correlated with late-toxicity and imaging. RESULTS From 2021-2023, six children were treated, and at a median follow-up of 13 months [9-26], all patients remain disease-free. Three patients had non-germinomatous germ cell tumors, 1 low-grade glioma, 1 atypical teratoid rhabdoid tumor (ATRT), and 1 embryonal tumor with multilayered rosettes. Age range was 2.4 to 16.8 years. All patients received chemotherapy prior to IMPT. Neuropsychological evaluation indicated range of intellectual functioning (mean = 98.3 [83-118]). One patient, a 4-year-old female with ATRT, developed T2 changes within the globus pallidus and thalamus on 3 month follow-up. At 5 months, she developed bilateral action-induced myoclonus with corresponding enhancing lesions in the globus pallidus bilaterally. Neuropsychological evaluation at 5 months post-treatment indicated memory impairments. She was treated with dexamethasone without improvement. Between 912 months post-treatment, tremors improved with physical therapy and imaging showed near complete resolution of enhancement within globus pallidus. CONCLUSION One of six children developed grade 3 toxicity manifesting as bilateral action-induced myoclonus with imaging changes in the globus pallidus bilaterally following IMPT and exhibited related neuropsychological deficits. While brainstem toxicity from IMPT is well documented, globus pallidus toxicity is not well characterized. Given the contiguous neuronal tracts with the brainstem, it is logical to apply similar treatment planning techniques, i.e. minimizing hotspots within the globus pallidus and thalamic “core” structures, and being cognizant of LET/RBE effects for treatment involving the pineal region in young children.

LMIC-16. PRE-IRRADIATION CHEMOTHERAPY AND DELAYED RADIATION THERAPY IN INFANTS AND YOUNG CHILDREN WITH WITH CENTRAL NERVOUS SYSTEM EMBRYONAL TUMOURS

Abstract BACKGROUND Established strategies for infants and young children(IYC) with embryonal tumours of the central nervous system(CNSET) - autologous stem-cell rescue(ASCT) and intraventricular chemotherapy(IVCT) – are not universally available. We report the outcomes of IYC with CNSET treated using the strategy of surgery, pre-irradiation chemotherapy and delayed radiation. METHODS Children <3years diagnosed with CNSET- medulloblastoma(MB), atypical teratoid/rhabdoid tumour(ATRT), embryonal tumour with multilayered rosettes(ETMR), CNS primitive neuroectodermal tumours(PNET)- and pineoblastoma(PB),underwent standard evaluation and staging, maximal safe excision, pre-irradiation chemotherapy(cyclophosphamide, etoposide and carboplatin;CEJ) upto 36months of age and either ris-adapted craniospinal with boost or focal irradiation. We performed a retrospective intention-to-treat outcome analysis. RESULTS Of 117children <3years with CNSET treated January2011- December2022, 72 were treated with this strategy.The median age was 25months (range6-35), 49males,histology medulloblastoma-42(58%), ATRT-9(12.5%), PNET-8(11.1%), ETMR-8(11.1%) and PB-5(6.8%); 23(32%) metastatic.The median chemotherapy cycles were 6(range 1-15). 36 children went on to receive RT; CSI in 33 (20standard-dose,13reduced-dose) and focal in 3. At last follow-up, 27children are in remission, 43 have relapsed/progressed (9 received salvage treatment) and 2 died due to chemotherapy toxicity. The 3-year and 5-year event-free-survival(EFS) are 35% and 3-year and 5-year overall-survival(OS) are 41.8% and 40.2%. The 3-year EFS/OS for MB are 51.1%/ 62.8%,PNET 25%/25%,ATRT 11.1%/11.1%,ETMR 12.5%/12.5% and PB 0%. Only metastasis was prognostic in medulloblastoma (HR 2;95% CI 0.86-4.6 for EFS and HR 1.7;95% CI 0.67-4.5 for OS); age, molecular group and histology were not prognostic. Long-term follow-up (n=17) documented >grade2 late effects in all (endocrine-16, neurocognitive-8, vision-3, hearing -8 and neurological-10). CONCLUSION The use of moderate-intensity pre-irradiation chemotherapy is feasible and effective in infants and young children with CNSETs. Despite inferior outcomes compared to ASCT or IVCT,this strategy could be used in resource-limited settings.

BIOM-14. UTILITY OF MIRNA-BASED LIQUID BIOPSY AND RADIOGRAPHIC IMAGING IN PEDIATRIC BRAIN TUMOR PATIENTS

Abstract BACKGROUND MRI is the current gold standard imaging technique for diagnostic evaluation and monitoring of pediatric CNS tumors; however, MRI measures can only provide inference into tumor biology and molecular stratification. miRNAs are an abundant and stable nucleic acid found circulating in blood and cerebrospinal fluid (CSF) and can be utilized as a tumor biomarker. METHODS We hypothesized that correlating miRNA biomarkers with radiological tumor measurements may provide improved diagnostic and monitoring for patients with pediatric brain tumors. Using a cohort of 54 pediatric brain tumors including low grade glioma, ependymoma, germ cell tumor, medulloblastoma, atypical teratoid rhabdoid tumor and high-grade glioma we attempted to combine MRI findings and circulating miRNA data. The miRNA expression was profiled in 33 CSF and 52 plasma samples using the HTG EdgeSeq platform. Clinically acquired, multi-parametric MRI scans at time-points close to liquid biopsy collection were collected retrospectively and used to generate volumetric tumor segmentations. Machine learning methods were implemented to evaluate combinatory features. RESULTS We identified unique miRNA targets that significantly correlated with MRI features, clinical findings, and patient outcomes. In both CSF and plasma, miRNA expression was found to correlate with diagnosis and clinical features including tumor grade and disease burden (p < 0.05). In CSF, miRNA expression was correlated with MRI features including cystic core presence, edema, leptomeningeal disease and tumor location (p <0.05). In plasma, differences in miRNA expression were related to MRI measurements including cystic core volume, location, and leptomeningeal disease (p < 0.05). Combination of miRNA targets for plasma or CSF with imaging-based features significantly improved histology specific multimodal diagnosis predictions. CONCLUSIONS These results demonstrate the potential utility of miRNAs as a pediatric brain tumor biomarker which when combined with imaging features can improve minimally and non-invasive diagnostics and the subsequent management of pediatric brain tumor patients.

IMMU-14. MULTI-INSTITUTION ANALYSIS OF TREATMENT MATCHING STATUS AND OUTCOMES IN PEDIATRIC CNS TUMOR PATIENTS

Abstract BACKGROUND With the advent of immunotherapies and targeted therapies, research is needed to assess how pediatric brain tumor genomic biomarkers may impact treatment modality choice and outcomes. METHODS We conducted a retrospective analysis of 160 pediatric patients (78 male, 82 female) with a median age of 9 years (2 months-26 years) diagnosed with a primary CNS tumor at four academic institutions from 2008-2023. Tumor mutational burden (TMB), treatment type, outcomes, and matching status were analyzed. Matching status refers to the presence of tumor genomic markers that matched with the pharmacologic target. RESULTS Low-grade glioma (N=68, 42.5%) and high-grade glioma (N=36, 22.5%) were the most common tumors. Other tumors included medulloblastoma (N=17, 10.6%), atypical teratoid rhabdoid tumor (N=4, 2.5%), ependymoma (N=8, 5%), ganglioglioma (N=7, 4.4%), other embryonal tumors (N=5, 3.1%), and choroid plexus tumors (N=5, 3.1%). Of the patients who received targeted or immunotherapy (N=30), most patients had matched (N=19) versus unmatched therapy (N=11) and similar survival rates (p=0.44). Although not statistically significant (p=0.065), patients who received standard therapy had higher overall survival rates (N=103/130) compared to those receiving targeted or immunotherapy (N=19/30). When comparing only patients with high TMB tumors (≥3 mutations/megabase), patients were significantly more likely to survive when receiving standard therapy only (N=20/33) versus targeted or immunotherapy (N=1/7) (p=0.026). Notably, targeted and immunotherapy were not used upfront in these cases. Among patients who had progressed or recurrent disease specifically, there was a non-statistically significant trend towards better survival rates for those who received targeted or immunotherapy (p=0.46). CONCLUSIONS Patients with high TMB tumors who received targeted or immunotherapy have worse outcomes than patients with low TMB, or with high TMB receiving standard therapy. High TMB tumors often require therapy for relapsed/refractory disease. These findings are critical for identifying patient subsets in need of alternative treatment options.

QOL-06. RECURRENCE PATTERNS AND SURVEILLANCE IMAGING IN PEDIATRIC BRAIN TUMOR SURVIVORS

Abstract BACKGROUND Surveillance magnetic resonance imaging (MRI) is routinely used to detect recurrence in pediatric central nervous system (CNS) tumors. Frequency of neuroimaging varies with no standardized approach. METHODS A single institution retrospective cohort study evaluated frequency and pattern of recurrences. Pediatric patients (birth to age 21 years) diagnosed with a primary CNS tumor between 1988 and 2011 treated at Lurie Children’s Hospital were included. RESULTS This study included 476 patients; the majority diagnosed with a low-grade glioma (LGG) (n=138; 29%), high grade glioma (HGG) (n=77; 16%), ependymoma (n=70; 15%) or medulloblastoma (n=61; 13%). LGG, HGG and ependymoma patients more commonly had multiply recurrent disease (p=0.08), with ependymoma patients demonstrating ≥2 relapses in 47% of cases. Recurrent disease was identified by imaging more often than clinical symptoms (65% vs 32%; p=<0.01). Treatment at relapse included surgical managment more often than non-surgical approach (59% vs. 41%; p=0.0016) in patients, leading to pathology confirmation of recurrence. Mean time to first relapse for the entire cohort was 2.5 years (range 1 day-24.8 years). Patients diagnosed with meningioma demonstrated the longest mean time to first relapse (74.7 months) whereas those with Atypical Teratoid Rhabdoid Tumor and Choroid plexus carcinoma tended to have the shortest time to relapse (8.9 months and 9 months, respectively). Overall, 22 patients sustained first relapse >10 years from initial diagnosis, including those diagnosed with LGG, medulloblastoma, pineoblastoma, craniopharyngioma, GCT, and meningioma. CONCLUSION With a higher percentage of tumor recurrence/progression seen on neuroimaging before development of symptoms, surveillance imaging is necessary in routine follow up of pediatric CNS tumor survivors. While the study is limited since we did not look at overall survival, earlier detection of recurrence would lead to earlier initiation of treatment and implementation of salvage treatment regimens which can impact survival and quality of life.

DIPG-56. BRAINSTEM TUMOR BIOPSY: A SINGLE INSTITUTE EXPERIENCE OF SAFETY AND FEASIBILITY IN A LOW-MIDDLE INCOME COUNTRY (LMIC)

Abstract BACKGROUND Brainstem tumors account for 10-15% of all pediatric central nervous system tumors and carry a dismal prognosis. These include a wide spectrum of histological diagnosis therefore, in most specialized centers stereotactic biopsies for brainstem tumors are considered safe and standard practice. However, this approach continues to pose a challenge in LMIC’s. METHODS We retrospectively reviewed data of patients presenting with brainstem tumors at Aga Khan University Hospital, Pakistan, between 2014 and 2023. In addition to histopathological analysis, whole-genome sequencing and RNA sequencing were also performed on 6 tumors. RESULTS We identified 39 patients with brainstem tumors; amongst these 56.4% were females. Median age at diagnosis was 9 years (IQR: 5.1-11). Most cases presented with walking difficulty (74%) and cranial nerve palsies (46%). Median duration of symptoms was 30 days (IQR: 20-60). On imaging large proportion were intrinsic pontine tumors (53.8%) followed by brainstem (30.8%) and cerebellopontine angle (15.4%). 21 patients underwent stereotactic biopsy with 86% performed after 2016. 43% were intrinsic pontine tumors. Histopathology analysis showed a wide spectrum with diffuse midline glioma in 28% of cases, pilocytic astrocytoma, anaplastic astrocytoma and ganglioglioma in 33%, 14% and 9% of cases respectively. Rare entities identified included embryonal tumor with multilayered rosettes, atypical teratoid rhabdoid tumor and schwannoma (5%). Biopsies were uneventful in 81% of cases. Complication of biopsy in 2 patients included cranial nerve palsy and subdural hemorrhage. No patient died due to complications of biopsy. Surgical and medical management was altered in 9 patients due to availability of histological diagnosis. CONCLUSIONS We present the first study demonstrating safety and feasibility of stereotactic biopsy for brainstem tumors in LMIC. These biopsies should be considered for atypical brainstem tumors and should be performed in well-equipped tertiary neurosurgical facilities by trained neurosurgeons in LMIC.

ATRT-02. RECAPITULATING THE POST-SURGICAL BRAIN MICROENVIRONMENT OF ATYPICAL TERATOID RHABDOID TUMOURS TO IDENTIFY MEMBRANE PROTEIN CANDIDATES FOR TARGETED THERAPY

Abstract BACKGROUND Atypical Teratoid Rhabdoid Tumours – (AT/RT) are rare and aggressive tumours primarily arising in the hind brain of children under three, conferring median survival of <12 months. Surgery remains the only standard treatment; however tumours recur from post-surgical residual disease. The utilisation of PolyEthylene Glycol Diacrylate – (PEGDA) hydrogel and decellularised human brain cerebellum extracellular matrix aim to recapitulate AT/RT post-surgery brain microenvironments, where we hypothesise AT/RT plasma membrane proteins represent viable molecular therapy targets. METHODS AT/RT and astrocyte membrane protein cellular fractions were extracted and analysed using liquid chromatography-mass spectrometry. Proteomic analyses was integrated to identify differentially expressed AT/RT and astrocyte membrane proteins. RESULTS PEGDA and decellularised brain tissue were biocompatible for AT/RT-astrocyte co-cultured spheroid growth. AT/RT and astrocyte KEGG Pathway analysis revealed more specific oncology-based pathway expression in membrane protein than total protein, thus reinforcing membrane proteins as suitable therapeutic targets. Between the top 20 expressed membrane proteins, only ATP1A1 was shared exclusively between all AT/RT cells and astrocytes, suggesting a potential functional role. Membrane proteins showing shared expression when normalised against each AT/RT cell line included ATP1A1, HSPD1, GNA13 and SLC3A2, indicating biological similarities between AT/RT subtypes. Membrane proteins expressed similarly in AT/RT-MYC subtypes include ATP1A1, SLC7A5 and EEF1A1. ATP1A1 network analyses of AT/RT and astrocyte membrane protein pathways displayed strong interactions with ATP1B1, SLC7A5 and SLC3A2, therefore likely to map common expressed shared pathways. CONCLUSIONS AT/RT membrane protein pathways offer novel therapeutic targets directly amenable for drug repurposing. Future work prioritises proteomic analysis utilising 3D AT/RT spheroids and cerebellum brain tissue to maximise accurately recapitulating AT/RT post-surgical microenvironments.

OTHR-12. GENERATING A COMPREHENSIVE INTERACTIVE PEDIATRIC BRAIN TUMOR VISUALIZATION PORTAL FROM MOLECULAR AND CLINICAL DATA DERIVED FROM TWO MULTI-INSTITUTIONAL PROTOCOLS (SJMB03, SJYC07) AND NON-PROTOCOL PATIENTS TREATED AT ST JUDE CHILDREN’S RESEARCH HOSPITAL

Abstract BACKGROUND Pediatric central nervous system (CNS) tumors represent a diverse group of neoplasms with heterogeneous molecular and clinical characteristics. The need for well-organized, searchable datasets is paramount to enhance our understanding and improve the treatment approaches for these devastating diseases. To illustrate this, we have organized multifaceted data from patients into an interactive portal equipped with cutting-edge visualization tools. METHODS Clinical and molecular data from the SJMB03 and SJYC07 protocols and select published non-protocol St. Jude patients were collated and harmonized. A data dictionary was constructed to record demographic information, treatment details, histology, methylation classification, mutations, chromosomal aberrations, and outcomes. We implemented five visualization techniques - summary plots, sample view, scatter plots, sample matrix, and survival plots. These techniques are interconnected, enabling interaction and “crosstalk”. RESULTS Data from 710 patients with CNS tumors were incorporated: 386 Medulloblastomas (MB); 88 Atypical teratoid Rhabdoid Tumors (ATRT); 54 Ependymomas (EPN); 49 Pineoblastomas (PB); 28 Embryonal Tumors with Multilayered Rosettes (ETMR), 22 Infant-type hemispheric glioma (IHG), 16 High grade glioma (HGG), 13 Choroid Plexus Tumors (CPT); 11 CNS Sarcoma; 8 CNS tumor with BCOR internal tandem duplication (CNS BCOR); 6 CNS neuroblastoma FOXR2 activated (CNS NB FOXR2); 5 Low grade glioma (LGG); and 24 other entities or unclassified tumors. The portal features enabled the creation of custom cohorts. For example, patients with TP53 mutations (n=32; 15 MB, 7 CPT, 6 HGG, 1 CNS Sarcoma, 1 CNS NB FOXR2, 1 PB, 1 unclassified tumor) or DICER1 mutations (n=10; 7 PB, 2 CNS Sarcoma, and 1 ETMR) could be identified, cross-compared and analyzed adjusting for variables at users’ choice. CONCLUSION The integration of molecular and clinical data from multiple sources into an interactive visualization portal presents a comprehensive resource for research and clinical practice. Future work will focus on expanding the portal to integrate more cases/cohorts.

STEM-01. DEVELOPMENT OF A HUMAN-SPECIFIC 3DIN VITRO PAEDIATRIC CEREBELLAR TUMOUR MODEL USING DECELLULARISED BRAIN AUTOPSY TISSUE

Abstract BACKGROUND Medulloblastoma (MB) and Atypical Teratoid/ Rhabdoid Tumours (ATRT) represent paediatric cerebellar tumours with a dismal prognosis. For ATRT in particular, 5-year survival remains at less than 32%. We have developed a 3D in vitro model termed ‘tumoursphere matrix’ which recapitulates in vivo crosstalk between tumour and reactive brain. METHODS AND RESULTS We co-cultured D283 (Group 3-MYC amplified MB) and BT12 (ATRT-MYC) cells with primary human cerebellar astrocytes within a PEGDA hydrogel containing decellularised cerebellar extracellular matrix (ECM) derived from non-disease human autopsy brain. Cerebellar ECM was extensively characterised, showing a significant reduction in cellular material whilst retaining ECM ligands. Reduction of DNA content to 174 ng/mg was corroborated by an absence of nuclei in immunohistochemical staining. Colorimetric assays indicated collagen and glycosaminoglycan retention in decellularised ECM, and Immunofluorescence confirmed retention of fibronectin, laminin and hyaluronic acid. Detection of all ECM ligands was cross-validated by Orbitrap-Secondary Ion Mass Spectrometry. A solubilised ECM/PEGDA hydrogel was used to coat an AggreWell™ plate. Primary human cerebellar astrocytes, D283 and BT12 cells were cultured as spheroids within the ECM/PEGDA hydrogel for 7 days with no significant decrease in cellular viability. Cytokine and Human Matrix Metalloproteinase (MMP) Antibody Arrays showed cytokine and MMP expression in all three cell lines was retained in the presence of ECM material. Furthermore, D283 and BT12 cells were co-cultured with primary astrocytes for 7 days prior to separation using fluorescence activated cell sorting to generate individual cell populations. CONCLUSIONS We have developed a 3D in vitro model which can co-culture cells for over 7 days, whilst recapitulating the in vivo tumour environment. RNA sequencing is currently in progress to identify differentially expressed genes in cerebellar tumour cells upon astrocytic and brain ECM crosstalk. We hypothesise that biochemical signalling underlying this communication will reveal putative therapeutic vulnerabilities.

QOL-42. ANALYSIS OF LATE EVENTS AFTER RADIATION THERAPY FOR PRIMARY PEDIATRIC BRAIN TUMORS

Abstract BACKGROUND Late events after radiation therapy for primary brain tumors consist of secondary malignant neoplasms (SMN) and tumor recurrences. The incidence and biology of late events are not very well described. Therefore, we aimed to identify late events in our institutional cohort and describe their biology. METHODS A retrospective chart review of all irradiated pediatric brain tumor patients treated between 2000 and 2015 at our institution was performed to obtain demographics and clinical data of late events. Late events were defined as intracranial intraaxial SMN or tumor recurrence occurring later than 3 years after radiation therapy. A whole-genome methylation array was employed to identify the methylation class of the late event. RESULTS In the observed period, 267 patients received some form of cranial radiotherapy for primary brain tumor; high-grade glioma (HGG, n=66), medulloblastoma (n=74), ependymoma (n=50), germ-cell tumors (GCT, n=22), low-grade glioma (LGG, n=24), and other diagnoses (n=31). Out of the 174 patients who were alive and without an event after 3 years from the radiation therapy, 30 developed late events (16.8%), and 27 of them were histologically verified. Verified late events consisted of 8 SMNs (29.6%) and 19 primary tumor recurrences. SMNs were mainly radiation-induced gliomas (RIG, n=7) and one atypical teratoid/rhabdoid tumor (ATRT) after craniopharyngioma. All RIG tumors clustered with the “pediatricHGG_RTK1” methylation class. Tumor recurrences consisted of medulloblastomas (Group 4 and Wnt), ependymomas (PFA and ST_ZFTA), GCTs, gliomas (one NF1-associated HGG, one H3-altered thalamic glioma, one diffuse astrocytoma with BRAF-V600E mutation), and craniopharyngiomas. The overall survival rate 5 years after a late event was 39.7%, with a worse survival rate for SMN patients (14.3%) compared to those with recurrences (44.9%) (p=0.05). CONCLUSIONS Late events affected 16.8% of long-term survivors. Strikingly, SMNs represented almost 30% of late events and were associated with a very poor prognosis.

EPID-05. 60 YEARS OF CENTRAL NERVOUS SYSTEM TUMOURS IN THE WEST MIDLANDS, UK

Abstract BACKGROUND The West Midlands Regional Children’s Tumour Registry is a specialist paediatric cancer registry in the West Midlands region of England, representing 9% of the national population. Our aim was to produce an historical, regional overview of central nervous system (CNS) tumour incidence and survival from 1957 onwards. METHODS Paediatric CNS tumour records included in the Registry from 01/01/57 to 31/12/16 were reviewed. There were 1945 cases: 1066 males and 879 females (M:F ratio 1.2:1) aged 0-14 years, resident in the West Midlands and diagnosed with a malignant, uncertain, or benign tumour. Patients were categorised according to the International Classification of Childhood Cancer, Third Edition (ICCC-3). Age and sex-specific incidence rates per million and directly age standardised incidence rates were calculated. Survival by decade of diagnosis was calculated using Kaplan-Meier survival analysis. RESULTS Incidence rates were broadly comparable to national data. Five-year survival for all CNS tumours combined increased from 38.0% [CI 32.2-43.8%] during 1957-1966 to 79.8% [CI 75.4-83.5] for diagnoses 2007-2016. Five-year survival for patients with ependymoma, astrocytoma and medulloblastoma diagnosed 2007-2016 was 95.7% [CI 72.9-99.4], 86.9% [CI 80.3-91.3] and 68.0% [CI 52.0-79.7] respectively: substantially above equivalent national figures. Five-year survival for groups including ‘Other Gliomas’ and Atypical teratoid/rhabdoid tumour (ATRT) had lower than nationally reported survival rates at 53.3% [CI 37.6-66.8] and 9.1% [0.5-33.3] however, small numbers and wide confidence intervals must be considered. CONCLUSIONS Huge improvements in survival, nationally and in the West Midlands, over the past 60 years are attributable to a greater understanding of tumour biology, intensification of multi-agent chemotherapy and new treatments. Despite these gains, certain diagnoses - most prominently ATRT - remain resistant to cure with five-year survival below 10%. Certain diagnoses showed a notable rise in late mortality, demonstrating the importance of long-term follow-up for detecting late effects and subsequent malignancies.

Multiple primary tumors in children: a clinicopathological analysis of four cases

Objective: To investigate the clinicopathological features of children with metachronous or synchronous primary tumors and to identify related genetic tumor syndromes. Methods: The clinicopathological data of 4 children with multiple primary tumors diagnosed in the Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China from 2011 to 2023 were collected. The histological, immunophenotypic and molecular characteristics were examined using H&E staining, immunohistochemical staining, PCR, Sanger sequencing and next-generation sequencing (NGS). The patients were followed up. Results: Case 1 was an 8-year-old boy with the adrenal cortical carcinoma, and 5 years later a poorly differentiated gastric adenocarcinoma was detected. Case 2 was a 2-year-old boy, presented with a left ventricular choroid plexus carcinoma, and a hepatoblastoma was detected 8 months later. Case 3 was a 9-month-old girl, diagnosed with renal rhabdoid tumor first and intracranial atypical teratoid/rhabdoid tumor (AT/RT) 3 months later. Case 4 was a 7-year-old boy and had a sigmoid colon adenocarcinoma 3 years after the diagnosis of a glioblastoma. The morphology and immunohistochemical features of the metachronous or synchronous primary tumors in the 4 cases were similar to the corresponding symptom-presenting/first-diagnosed tumors. No characteristic germ line mutations were detected in cases 1 and 2 by relevant molecular detection, and the rhabdoid tumor predisposition syndrome was confirmed in case 3 using NGS. Case 4 was clearly related to constitutional mismatch repair deficiency as shown by the molecular testing and clinical features. Conclusions: Childhood multiple primary tumors are a rare disease with histological morphology and immunophenotype similar to the symptom-presenting tumors. They are either sporadic or associated with a genetic (tumor) syndrome. The development of both tumors can occur simultaneously (synchronously) or at different times (metachronously). Early identification of the children associated with genetic tumor syndromes can facilitate routine tumor screening and early treatment.

TAZNI: A phase I/II combination trial of tazemetostat with nivolumab and ipilimumab for children with INI1-negative or SMARCA4-deficient tumors.

TPS10077 Background: The prognosis for children with INI1-negative cancers is dismal, with historic 5-year overall survival <30%. These cancers (including malignant rhabdoid tumors [MRT], atypical teratoid rhabdoid tumors [ATRT], epithelioid sarcomas [ES], and poorly differentiated chordomas) have few novel treatment options. These tumors exhibit a heightened dependence on the Polycomb Repressive Complex, whereby EZH2 is the catalytic subunit. Two recent pediatric phase 1/2 trials with EZH2 inhibitor tazemetostat (EZH-102, NCT02601937 and APEC1621C, NCT03213665) demonstrated 17% overall objective response rate, with 19% response in ATRT patients and higher response rates in patients with chordoma and ES. One patient had PR on the phase 2 Pediatric MATCH study and 5 patients had prolonged SD. Studies of INI1-deficient tumors have shown significant immune infiltration, including T-cells with high levels of inhibitory checkpoint receptors. As EZH2 has a role in tumor immunity and tazemetostat increases MHC presentation and immune signaling, we hypothesized that combining EZH2 inhibitor with checkpoint inhibitors may provide benefit for pediatric patients with INI1- or SMARCA4-deficient tumors. Methods: TAZNI is a phase 1/2, multi-center trial of Tazemetostat, Nivolumab and Ipilimumab for children with INI1- or SMARCA4-deficient tumors after upfront therapy. All patients receive standard pediatric nivolumab and ipilimumab doses/dosing schedule with continuous tazemetostat dosing determined by disease strata: Stratum A- subjects with ATRT; Stratum B for all other (non-ATRT) INI1/SMARCA4-deficient tumors. Each stratum is subdivided by disease status: A1/B1- subjects with refractory disease after upfront therapy; A2/B2- subjects with relapsed disease; and A3/B3: subjects with no evidence of disease (NED) after upfront therapy. The study is conducted in 2 parts: Part 1 will be two concurrent “rolling six” phase 1 studies to identify the maximum tolerated dose (MTD) or recommended phase 2 dose (RP2D) by disease stratum. Starting dose level 1 for Stratum A is 900mg/m2 orally BID and for Stratum B: 520mg/m2 orally BID, with one dose escalation and one dose de-escalation planned. Part 2 will be two phase 2 studies to estimate the overall response rate (ORR) in Substrata A1 and A2 (with refractory disease or with relapse, respectively), based on a primary endpoint of ORR (CR+PR) in a Simon’s 2-stage design at the RP2D. All other substrata will be descriptive analyses. Patients may receive up to 26 cycles of therapy. Key inclusion/exclusion criteria include INI1 loss by immunohistochemistry (IHC) or molecular confirmation; age between 6 mo and 21 yo; no prior immunotherapy; limited corticosteroid; and no history or concern for hematologic malignancy. To date, 4 patients have enrolled, and the study is ongoing in the United States. Clinical trial information: NCT05407441 .

Retrospective experience of children with relapsed brain tumors treated with oral combination of axitinib and metronomic etoposide.

Metronomic chemotherapy-based combinations have received interest for relapsed/refractory malignancies. Preclinical and clinical studies showed activity of metronomic etoposide and axitinib. We report our retrospective experience in six children treated with axitinib and metronomic etoposide for refractory/relapsed brain tumors as an "off-label" combination. Three patients with medulloblastoma experienced partial response; one patient with atypical teratoid rhabdoid tumor (ATRT) displays an ongoing stable disease (12months); two patients with medulloblastoma had progressive disease. Grade 3-4 toxicities were observed in two patients (thrombocytopenia, anemia, diarrhea, fatigue). The axitinib-etoposide combination shows signals of efficacy in heavily pretreated patients with relapsed/refractory brain tumors. These results were based on real-world observation and will need formal evaluation in a phase I/II trial.

Atypical Teratoid/Rhabdoid Tumor with Retained SMARCB1 (INI1) Expression and Rare SMARCA4 Gene Mutation: A Case Report of a Pediatric Patient

Atypical teratoid/rhabdoid tumors (AT/RT) are highly aggressive tumors of the central nervous system (CNS), accounting for 1–3% of all pediatric CNS tumors. In general, AT/RTs are associated with biallelic inactivation of SMARCB1, resulting in the loss of expression of the integrase interactor 1 (INI1) protein. In this report, we describe the clinical course of an infant patient who presented with fatigue, postprandial vomiting, and disability of left side movement. Histological examination revealed classical features indicative of rhabdoid tumors, yet an atypical immunohistochemical profile with preserved INI1 expression was observed. Molecular diagnostics further elucidated the presence of a heterozygous frameshift variant, SMARCA4 c.2693del, p.(Asn898Thrfs*12), underscoring the distinctive genetic foundations of the case. Surgical resection of the tumor was administered with subsequent chemotherapy to the patient, but the condition worsened dynamically, and a decision was made to give the patient palliative therapy. We report on a patient with AT/RT caused by a rare mutation of the SMARCA4 gene and an aggressive course of disease to provide more information and characteristics of these tumors.

Central nervous system embryonal tumors with EWSR1-PLAGL1 rearrangements reclassified as INI-1 deficient tumors at relapse

PurposeCentral nervous system (CNS) embryonal tumors are a diverse group of malignant tumors typically affecting pediatric patients that recently have been better defined, and this paper describes evolution of a unique type of embryonal tumor at relapse.MethodsTwo pediatric patients with CNS embryonal tumors with EWSR1-PLAGL1 rearrangements treated at Arkansas Children’s Hospital with histopathologic and molecular data are described.ResultsThese two patients at diagnosis were classified as CNS embryonal tumors with EWSR1-PLAGL1 rearrangements based on histologic appearance and molecular data. At relapse both patient’s disease was reclassified as atypical teratoid rhabdoid tumor (ATRT) based on loss of INI-1, presence of SMARCB1 alterations, and methylation profiling results.ConclusionCNS embryonal tumors with EWSR1-PLAGL1 rearrangements acquire or include a population of cells with SMARCB1 alterations that are the component that predominate at relapse, suggesting treatment aimed at this disease component at diagnosis should be considered.

Plasma miRNA expression profile in pediatric pineal pure germinomas.

Pure germinomas account for 40% of pineal tumors and are characterized by the lack of appreciable tumor markers, thus requiring a tumor biopsy for diagnosis. MicroRNAs (miRNA) have emerged as potential non-invasive biomarkers for germ cell tumors and may facilitate the non-invasive diagnosis of pure pineal germinomas. A retrospective chart review was performed on all patients treated at the Children's Cancer Hospital Egypt diagnosed with a pineal region tumor between June 2013 and March 2021 for whom a research blood sample was available. Plasma samples were profiled for miRNA expression, and DESeq2 was used to compare between pure germinoma and other tumor types. Differentially expressed miRNAs were identified. The area under the curve of the receive;r operating characteristic curve was constructed to evaluate diagnostic performance. Samples from 39 pediatric patients were available consisting of 12 pure germinomas and 27 pineal region tumors of other pathologies, including pineal origin tumors [n = 17; pineoblastoma (n = 13) and pineal parenchymal tumors of intermediate differentiation (n = 4)] and others [n = 10; low-grade glioma (n = 6) and atypical teratoid rhabdoid tumor (n = 4)]. Using an adjusted p-value <0.05, three miRNAs showed differential expression (miR-143-3p, miR-320c, miR-320d; adjusted p = 0.0058, p = 0.0478, and p = 0.0366, respectively) and good discriminatory power between the two groups (AUC 90.7%, p < 0.001) with a sensitivity of 25% and a specificity of 100%. Our results suggest that a three-plasma miRNA signature has the potential to non-invasively identify pineal body pure germinomas which may allow selected patients to avoid the potential surgical complications.

Long-Term Survival of a Child with Atypical Teratoid-Rhabdoid Tumor and Acute Lymphoblastic Leukemia: A Case Report

Atypical teratoid-rhabdoid tumor (AT/RT) is a rare but one of the most aggressive embryonal tumors of the central nervous system (CNS), most often occurring in children under 3 years of age. AT/RT accounts for about 1–2% of all CNS neoplasms and has a very poor prognosis, high risk of secondary tumor development, recurrence and/or metastasis in patients in remission and limited therapeutic potential. The clinical manifestations are usually symptoms of increased intracranial pressure. The mainstay of tumor treatment is complex chemotherapy combined with radiation therapy. A clinical case of sequential occurrence of two cancers (AT/RT and leukemia) in a 3-year-old girl is presented.

153 Spatial Transcriptomic Profiling of T Cell Exhaustion Markers in Atypical Teratoid Rhabdoid Tumor Subtypes

INTRODUCTION: Atypical teratoid/rhabdoid tumor (ATRT) is one of the most common brain tumors in pediatric populations. Despite advances in treatment, overall survival remains poor and novel effective therapies are needed. METHODS: Tumor purities of 49 atypical ATRT tumors, encompassing 3 epigenetic subtypes (MYC, SHH, TYR) were estimated using known mRNA expression signatures of stromal and immune cells. Using the purity estimates and bulk tumor expression values, non-negative linear regression was implemented to estimate the average expression of each gene in the stromal and tumor compartments for each subtype. RESULTS: Compared to other subtypes, SHH-ATRTs expressed relatively higher levels of T-cell immunoglobulin domain and mucin domain protein 3 (TIM-3) and its ligand GAL9. MYC-ATRTs expressed higher levels of numerous T cell inhibitory receptors including lymphocyte activation gene 3 protein (LAG-3), band T lymphocyte attenuator (BTLA), cytotoxic T lymphocyte antigen-4 (CTLA-4), and programmed cell death protein 1 (PD-1). CONCLUSIONS: The predicted stromal and tumor compartment deconvolution yielded previously unrecognized expression patterns of T cell exhaustion markers which should be evaluated further to develop effective targeted therapies for ATRT.