Pediatric Intracranial Ependymoma Research Articles

[Pediatric Intracranial Ependymoma - Recommendations for First-Line Treatment from the German HIT-MED study group].

Biological subtypes of ependymoma (EPN) have been introduced by the recent WHO classification and appear to have great impact on the clinical course, but have not yet found their way into clinical risk stratification. Further, the overall unfavorable prognosis underlines the fact that current therapeutic strategies need further evaluation for improvement. To date, there is no international consensus regarding first-line treatment for children with intracranial EPN. Extent of resection is known to be the most important clinical risk factor, leading to the consensus that consequent evaluation for re-surgery of postoperative residual tumor needs to have highest priority. Furthermore, efficacy of local irradiation is unquestioned and recommended for patients aged>1 year. In contrast, efficacy of chemotherapy is still under discussion. The European trial SIOP Ependymoma II aims at evaluating efficacy of different chemotherapy elements, leading to the recommendation to include German patients. The BIOMECA study, as biological accompanying study, aims at identifying new prognostic parameters. These results might help to develop targeted therapies for unfavorable biological subtypes. For patient who are not qualified for inclusion into the interventional strata, the HIT-MED Guidance 5.2 provides specific recommendations. This article is meant as an overview of national guidelines regarding diagnostics and treatment as well as of treatment according to the SIOP Ependymoma II trial protocol.

Why haven't we solved intracranial pediatric ependymoma? Current questions and barriers to treatment advances.

Pediatric intracranial ependymoma has seen a recent exponential expansion of biological findings, rapidly dividing the diagnosis into several subgroups, each with specific molecular and clinical characteristics. While such subdivision may complicate clinical conclusions from historical trials, this knowledge also provides an opportunity for interrogating the major clinical and biological questions preventing near-term translation into effective therapy for children with ependymoma. In this article, we briefly review some of the most critical clinical questions facing both patient management and the construct of future trials in childhood ependymoma, as well as explore some of the current barriers to efficient translation of preclinical discovery to the clinic.

Pediatric intracranial ependymoma—a single-center clinical analysis and literature review

Background: Pediatric intracranial ependymoma (EPN) is an important central nervous system neoplasm, and has a high recurrence rate. The data on Chinese children with EPN are limited. This study sought to explore the characteristics of pediatric EPN at a single center in China.

Does Gross Total Resection Improve Progression-Free and Overall Survival in Pediatric Intracranial Ependymomas? Single-Center Clinical Experience Of 61 Cases

To share our clinical experience of 25 years and identify prognostic factors for progression-free and overall survival in pediatric intracranial ependymomas. In total, 61 children who were treated between 1995 and 2020 in a single institution were included in the study. Medical records of the patients were retrospectively reviewed to obtain and analyze the following data: patient age at first surgery, sex, presenting symptoms, hydrocephalus and any invasive treatment, anatomic site, extent of resection, pathologic grade, time to progression, and time to death. Progression-free and overall survival rates and affecting factors were analyzed by Kaplan-Meier method. Dysphagia, number of surgeries, and spinal seeding were associated with progression free and overall survival in univariate analysis. The extent of resection, World Health Organization grade, and visual problems were also associated with progression whereas sex was associated with overall survival. Cox regression identified the extent of resection and single surgery as an independent prognostic factor for progression-free survival. No independent factor was found for overall survival. This single center experience of 25 years confirms the beneficial effect of gross total resection on disease progression. Although spinal seeding seems to affect survival rates, greater number of cases are needed to reveal its full effect.

EPEN-01. Response assessment in pediatric intracranial ependymoma: recommendations from the Response Assessment in Pediatric Neuro-Oncology (RAPNO) working group

Abstract INTRODUCTION: Ependymomas remain a major cause of cancer-related death in childhood and adolescence, with recurrence occurring in up to 50% of patients. Despite exciting molecular advances in understanding ependymoma tumorigenesis and recurrence, MRI remains the mainstay for assessing objective response to therapy and duration of disease stability. Standardized response assessment criteria for clinical trials studying pediatric intracranial ependymoma are critically needed in order to accurately compare results between studies. METHODS: To generate these standardized response criteria in pediatric intracranial ependymoma, a multidisciplinary team of pediatric neuro-oncologists, neuroradiologists, neurosurgeons, radiation oncologists, and molecular biologists formed the Response Assessment in Pediatric Neuro-Oncology (RAPNO) working group. The expert members reviewed relevant published literature, assessed current clinical practices, and engaged in iterative discussions to provide consensus recommendations for objective response assessment in pediatric intracranial ependymoma for use in prospective clinical trials. RECOMMENDATIONS AND CONCLUSIONS: The primary sequences for detecting and measuring disease and assessing radiologic response to therapy should be the contrast-enhanced T1-weighted sequence or T2-weighted sequence (T2 or T2-FLAIR) depending on which sequence the tumor is best visualized. When metastatic disease is present, only the three largest lesions will be followed in addition to any residual disease at the primary tumor focus. Importantly, the RAPNO working group notes that radiologic response to therapy is of limited value in clinical trials of patients with ependymoma, since most patients enroll on clinical trials with either no evidence of disease or only minimal disease. In recurrent or progressive disease that cannot be resected, true radiologic disease response to therapy is less clinically meaningful as a study endpoint than event-free and/or overall survival (representing prolonged stable disease) but may provide a signal of efficacy worthy of future exploration in patients with complete to near complete resections.

Prognostic Factors and Histopathological Features of Pediatric Intracranial Ependymomas: Nationwide Brain Tumor Registry-based Study of Japan.

To assess the clinicopathological features and prognostic factors of pediatric intracranial ependymomas and to explore the current diagnostic practice, we analyzed clinical data from the Brain Tumor Registry of Japan (BTRJ). Data of fifty children under 18 years of age diagnosed with intracranial ependymoma were extracted from the BTRJ database. Cases were reviewed for overall survival (OS) and progression-free survival (PFS), with attention to gender, preoperative Karnofsky performance status score, location of the tumor, the extent of resection, World Health Organization (WHO) histopathological grading, and adjuvant therapy. The median age at diagnosis was 6.1 years, ranging from 7 months to 17.6 years. Based on the WHO histopathological grading, 27 patients were classified under grade 2 (54%) and 23 patients were classified under grade 3 (46%). Gross total resection (GTR) was achieved in 30 patients (60%). The median follow-up time was 65 months. Five-year PFS and OS were 47.2 ± 7.3% and 73.3 ± 6.7%, respectively. GTR was associated with longer OS (P = 0.02). The histopathological grading was not an independent prognostic factor for the OS. Mitosis and microvascular proliferation were higher among patients with grade 3 than in those with grade 2, which aided in deciding the WHO grade. This nationwide study revealed the characteristics and outcomes of patients with childhood ependymomas. GTR was the factor most consistently associated with improved survival. In contrast, the histopathological grading in this cohort was not a significant prognostic factor. More reproducible and practical criteria for the diagnosis of intracranial ependymomas should be further pursued in future studies.

Treatment and outcome of pediatric intracranial ependymoma after first relapse.

Almost 50% of children with intracranial ependymoma experience disease relapse, and their outcomes areextremely poor. The aim of this study was to investigate optimal salvage treatment for pediatric intracranial ependymoma after the first relapse and to identify prognostic factors affecting survival. We conducted a retrospective analysis of 159 children who underwent initial treatment for intracranial ependymoma at Beijing Tiantan Hospital from 2013 to 2017. Relapse was observed in 73 patients (73/159;45.9%), with a median age of 7.2 ± 3.5years old. Molecular subgrouping analysis identified H3K27me3-negative PF-EPNs in 74% of patients, ST-RELA EPNs in 21% of patients, and H3K27me3-positive PF-EPNs in 5% of patients. The 5-year event-free survival(EFS) and overall survival(OS) rates after first relapse were 21.1% (95% CI 16.0-26.2) and 30.5% (95% CI 19.8-30.8), respectively. Patients with GTR at first relapse had higher 5-year EFS and 5-year OS than those with STR (P = 0.031 and P = 0.003) or no surgery (P = 0.007 and P = 0.001). Radiotherapy or re-radiotherapy at first relapse significantly prolonged 5-year EFS and OS (both P < 0.001). Patients with H3K27me3-negative PF-EPN had worse 5-year EFS and OS than those with ST-RELA EPN (P = 0.001 and P = 0.002). Multivariate analysis showed that both tumor resection and radiotherapy at first relapse had independent prognostic significance for survival (all P < 0.05). Children with recurrent intracranial EPN have poor outcomes, andsurgery and radiotherapy at first relapse should be encouraged to improve their prognosis.

Cell-of-Origin and Genetic, Epigenetic, and Microenvironmental Factors Contribute to the Intra-Tumoral Heterogeneity of Pediatric Intracranial Ependymoma.

Simple SummaryIntra-cranial ependymoma (EPN) accounts for approximately 10% of pediatric brain tumors. The current therapeutic strategies have not significantly improved prognosis, which is still dismal in nearly 40% of patients. Major challenges for treatment are chemorefractoriness of EPN, tendency to recur, and high intra-tumoral heterogeneity (ITH). It is increasingly emerging that stalled neurodevelopmental programs driven by cancer stem cells (CSCs)/progenitor cells are at the root of oncogenesis and ITH of pediatric brain tumors, including EPN. This is the first review that examines how genetic and heritable epigenetic alterations and environmental selection forces drive ITH of pediatric intra-cranial EPN in the perspective of the CSC model. This review also summarizes how improvement in the single-cell technology has deepened the comprehension of the complexity, cell-of-origin, and developmental trajectories of EPN, paving the way for novel therapeutic options.Intra-tumoral heterogeneity (ITH) is a complex multifaceted phenomenon that posits major challenges for the clinical management of cancer patients. Genetic, epigenetic, and microenvironmental factors are concurrent drivers of diversity among the distinct populations of cancer cells. ITH may also be installed by cancer stem cells (CSCs), that foster unidirectional hierarchy of cellular phenotypes or, alternatively, shift dynamically between distinct cellular states. Ependymoma (EPN), a molecularly heterogeneous group of tumors, shows a specific spatiotemporal distribution that suggests a link between ependymomagenesis and alterations of the biological processes involved in embryonic brain development. In children, EPN most often arises intra-cranially and is associated with an adverse outcome. Emerging evidence shows that EPN displays large intra-patient heterogeneity. In this review, after touching on EPN inter-tumoral heterogeneity, we focus on the sources of ITH in pediatric intra-cranial EPN in the framework of the CSC paradigm. We also examine how single-cell technology has shed new light on the complexity and developmental origins of EPN and the potential impact that this understanding may have on the therapeutic strategies against this deadly pediatric malignancy.

376P Nucleolin and its prognostic value in pediatric patients with intracranial ependymoma: A systematic review and meta-analysis

Nucleolin (NCL) is one of several potential molecular biomarkers that have been suggested as predictors for pediatric intracranial ependymomas. However, few studies have assessed whether NCL is an optimal prognostic marker to predict outcome in pediatric intracranial ependymoma. Thus, this systematic review and meta-analysis aimed to examine the prognostic role of NCL in predicting the outcome of patients with intracranial ependymoma.

EPEN-02. EVALUATION OF TREATMENT OUTCOMES AND EXPRESSION OF EMT-RELATED TRANSCRIPTION FACTORS AS NOVEL THERAPEUTIC TARGETS IN PEDIATRIC EPENDYMOMA

OBJECTIVEIntracranial ependymomas are common brain tumors in children. However, prognosis, especially in young children, remains poor because of the chemo- and radioresistant properties of intracranial ependymomas. Furthermore, effective treatments for intracranial ependymomas remain a challenge. The epithelial-to-mesenchymal transition (EMT) is important for invasion and metastasis in many cancers. This study aimed to evaluate and compare treatment outcomes with the expression of EMT-related transcription factors in pediatric ependymomas.MATERIAL AND METHODSMedical and radio-imaging data of 22 (11 boys, 11 girls) patients aged <15 years with intracranial ependymomas were reviewed from January 1983 to December 2018. Six cases were subdivided into clinicopathological-molecular subgroups and immunohistochemically analyzed for Slug and ZEB.RESULTSThe median age at the start of treatment was 5 years (range 8 months–15 years) (9 cases were aged <3 years). The median progression-free survival (PFS) was 25.6 (range, 0.8–383.5) months; the median overall survival (OS) was 81.9 (range, 2.9–383.5) months. Extent of resection and malignant histology were significant prognostic factors for OS and PFS in multivariate analysis. There were 6 cases (2 cases of PFA, 2 of PFB, 1 of ST and 1 case of ST-RELA). Nuclear expression of ZEB1 was found in all tumors; however, that of Slug increased only in PFA and PFB tumors, which were associated with a poor prognosis.CONCLUSIONExpression of EMT-related transcription factors was increased in pediatric ependymomas. These data suggest that EMT is a novel therapeutic target for treating pediatric intracranial ependymomas.

RTHP-09. SINGLE INSTITUTION’S EXPERIENCE FOR PEDIATRIC INTRACRANIAL EPENDYMOMA TREATED WITH ADJUVANT RADIOTHERAPY

Abstract PURPOSE To investigate long term outcomes of pediatric intracranial ependymoma treated with maximal safe resection followed by radiotherapy in single institution. METHODS Between 1983 and 2016, 42 pediatric patients received adjuvant radiotherapy after surgery. There were 19 and 23 grade II and III ependymomas, and total resection could be performed in 50% of patients. There were 4 patients with initial leptomeningeal seeding, and craniospinal irradiation (CSI) was the component of adjuvant treatment in 5 patients including them. Local radiotherapy (median 54 Gy (range, 45–60 Gy) was performed in all the rest patients excluding three with whole-brain radiotherapy. RESULTS With a median follow-up of 89 months, 14 patients (33%) experienced recurrences after radiotherapy (m/c: intracranial, 79%, all within tumor bed). The 5- and 10-year progression-free survival (PFS) rates were 70% and 63%, and overall survival (OS) rates were 85% and 78%, respectively. The recurrence rates were significantly higher in patients younger than 3 years (64% vs. 23%, p = 0.024) or with subtotal resection (STR) (52% vs. 15%, p = 0.009). In multivariate analyses, age and STR were significant factors for PFS (p = 0.007 and 0.028, respectively). There was no independent prognostic factor for OS on multi-variate analysis. Fourteen patients experienced recurrence. Among them, all of 6 grade II cases showed local recurrence. Four grade II cases (67%) underwent aggressively salvage treatments such as resection, stereotactic radiosurgery were still under observation. However, 75% of 8 grade III recurrent cases were expired, despite aggressive salvage treatments. All 3 patients with seeding recurrent were grade III and died from disease. CONCLUSION Local adjuvant radiotherapy showed favorable survival in pediatric ependymoma. Even if recurrence occurs, aggressive salvage treatment would be needed for grade II ependymoma.

The Value of High-Dose Radiotherapy in Pediatric Intracranial Ependymoma

The Value of High-Dose Radiotherapy in Pediatric Intracranial Ependymoma

Outcome of postoperative radiation therapy for pediatric intracranial ependymoma: a single-institution review.

To report outcome of postoperative radiotherapy (RT) in both new and recurrent grade II and III intracranial ependymomas in children treated at Ramathibodi Hospital. Between 2006 and 2017, 24 pediatric intracranial ependymomas treated with postoperative RT were retrospectively reviewed. The median age at diagnosis was 44.5months (range, 4-165months). There were 14 (58%) males. Fourteen (58%) patients had infratentorial tumor. The median maximal diameter of tumor at diagnosis was 4.45cm (range, 2.2-10cm). Fourteen (58%) patients had anaplastic tumor. Gross total resections were performed in 14 (58%) patients. The median prescribed dose was 54Gy (range, 45-60Gy). The median total treatment time was 43days (range, 37-78days). The median clinical follow-up time was 44.5months (range, 1-146months). There were nine recurrences, five of which occurred at the primary tumor site. The estimated 5-year progression-free survival rate was 56%. The estimated 5-year overall survival rate was 75%. Extent of resection was the only factor associated with improved progression-free survival and overall survival after univariate testing. Six from nine patients with recurrent diseases underwent further surgery or further RT. These six patients had better median overall survival than the three who did not. Acute complication was mostly transient and tolerable. No late radiation effect was found. Postoperative radiation is an effective treatment. GTR is associated with better PFS and OS. Aggressive salvage local treatments for recurrent patients can result in good overall survival. Longer follow-up is needed in account for late relapse.

Re-irradiation of locally recurrent pediatric intracranial ependymoma: Experience of the French society of children’s cancer

PurposeThis study aimed to evaluate retrospectively the clinical results of re-irradiation for children with a locally recurrent brain ependymoma. Methods33 full-dose re-irradiations were delivered to 31 children with a recurrent brain ependymoma after a standard treatment. Each child was followed up with clinical and MRI examinations. We evaluated overall survival, local recurrence free-survival and short term toxicity according to CTCAE 4.0 scale. ResultsWith a median follow-up of 37 months (range, 0 to 107), median local recurrence free-survival was 31 months (range, 2 to 63) and median overall survival was 34 months (range, 3 to 63). It was significantly higher in patients who underwent surgery first, compared with re-irradiation only. Cumulated dosimetric data were available for 22 patients. On average, maximal BED to brain stem was 106,2 Gyα/β3 (±35,4) for infratentorial re-irradiation. No acute toxicity grade >2 was reported and 1 case of brain radionecrosis treated successfully with steroids was reported after radiosurgery. ConclusionLocal recurrence of brain ependymoma can be treated with full-dose re-irradiation, which can be hypofractionated with an acceptable short term toxicity in spite of high total doses delivered to OARs, especially brain stem.

MicroRNA expression in pediatric intracranial ependymomas and their potential value for tumor grading.

Intracranial ependymoma represents one of the most common pediatric central nervous system malignancies, and exhibits a wide range of clinical behavior from relatively indolent lesions to highly malignant anaplastic ependymomas. Due to the heterogeneous nature of this disease there is lack of prognostic markers, which would reliably predict the outcome of patients. MicroRNAs (miRNAs) have emerged as important molecules in cancer biology during past decade; however, very little is known about their role in ependymomas. The aim of the present study was to evaluate expression of miRNAs in archived formalin-fixed paraffin-embedded (FFPE) samples of pediatric intracranial ependymomas. The expression of miRNAs were examined in 29 samples of ependymoma and we observed that miR-135a-3p, miR-137, miR-17-5p, miR-181d and let-7d-5p were upregulated. In addition, a significantly higher expression of miR-203a was detected in Grade III tumors suggesting its possible use as a prognostic or diagnostic marker. The present study also demonstrated that storage of (FFPE) ependymoma samples for >20 years did not result in a deterioration of miRNAs. The present findings broaden the presently available knowledge regarding miRNA expression in ependymomas and provide further evidence for the employment of miRNA analysis as a supplementary method for the morphological assessment of ependymoma samples.

Pediatric intracranial ependymoma: correlating signs and symptoms at recurrence with outcome in the second prospective AIEOP protocol follow-up.

The aims of patients' radiological surveillance are to: ascertain relapse; apply second-line therapy; accrue patients in phase 1/2 protocols if second-line therapy is not standardized/curative; and assess/treat iatrogenic effects. To lessen the emotional and socioeconomic burdens for patients and families, we ideally need to establish whether scheduled radiological surveillance gives patients a better outcome than waiting for symptoms and signs to appear. We analyzed a prospective series of 160 newly-diagnosed and treated pediatric/adolescent patients with intracranial ependymoma, comparing patients with recurrent disease identified on scheduled MRI (the RECPT group; 34 cases) with those showing signs/symptoms of recurrent disease (the SYMPPT group; 16 cases). The median follow-up was 67months. No significant differences emerged between the two groups in terms of gender, age, tumor grade/site, shunting, residual disease, or type of relapse (local, distant, or concomitant). The time to relapse (median 19months; range 5-104) and the MRI follow-up intervals did not differ between the SYMPPT and RECPT groups. The presence of signs/symptoms was an unfavorable factor for overall survival (OS) after recurrence (5-year OS: 8% vs. 37%, p = 0.001). On multivariable analysis, an adjusted model confirmed a significantly worse OS in the SYMPPT than in the RECPT patients. Symptomatic relapses carried a significantly worse survival for ependymoma patients than recurrences detected by MRI alone. It would therefore be desirable to identify recurrences before symptoms develop. Radiological follow-up should be retained in ependymoma patient surveillance because there is a chance of salvage treatment for relapses found on MRI.

Establishment of primary cell culture and an intracranial xenograft model of pediatric ependymoma: a prospect for therapy development and understanding of tumor biology.

BackgroundEpendymoma (EPN), the third most common pediatric brain tumor, is a central nervous system (CNS) malignancy originating from the walls of the ventricular system. Surgical resection followed by radiation therapy has been the primary treatment for most pediatric intracranial EPNs. Despite numerous studies into the prognostic value of histological classification, the extent of surgical resection and adjuvant radiotherapy, there have been relatively few studies into the molecular and cellular biology of EPNs.ResultsWe elucidated the ultrastructure of the cultured EPN cells and characterized their profile of immunophenotypic pluripotency markers (CD133, CD90, SSEA-3, CXCR4). We established an experimental EPN model by the intracerebroventricular infusion of EPN cells labeled with multimodal iron oxide nanoparticles (MION), thereby generating a tumor and providing a clinically relevant animal model. MRI analysis was shown to be a valuable tool when combined with effective MION labeling techniques to accompany EPN growth.ConclusionsWe demonstrated that GFAP/CD133+CD90+/CD44+ EPN cells maintained key histopathological and growth characteristics of the original patient tumor. The characterization of EPN cells and the experimental model could facilitate biological studies and preclinical drug screening for pediatric EPNs.MethodsIn this work, we established notoriously challenging primary cell culture of anaplastic EPNs (WHO grade III) localized in the posterior fossa (PF), using EPNs obtained from 1 to 10-year-old patients (n = 07), and then characterized their immunophenotype and ultrastructure to finally develop a xenograft model.

Treatment challenges and outcomes for pediatric intracranial ependymoma at a single institution in Iran

ABSTRACTBackground: The scarcity of information on pediatric ependymoma in Iran motivated this study. Our main objectives were to determine outcomes, identify clinical management challenges at a nongovernment hospital in Iran, and devise guidelines for improving care.Procedure: A retrospective chart review was performed for pediatric patients with ependymoma who were younger than 15 years and treated at MPCTRC between 2007 and 2015. Records included patient demographics, treatment regimens used, duration of follow-up, and outcomes. Clinical outcomes [ie, 3-year overall survival (OS) and progression-free survival (PFS)] were determined based on the age at diagnosis (younger or older than 3 years) by using the Kaplan–Meier method.Results: In total, 73 eligible patients were enrolled; 20 patients were in the younger group, and 53 were in the older group. The majority (91.8%, n = 67) of patients underwent initial gross-total or partial surgical resection, and 6 (8.2%) had a biopsy. Twenty-one patients experienced ependymoma recurrence. The median time to relapse was 1 year. The median duration of follow-up and PFS were 25 and 17 months, respectively. The 3-year OS and PFS were 61% and 59.5%, respectively. At the time of this project, 27 patients had died, and 35 were alive with no evidence of disease.Conclusion: Our study demonstrated inferior outcomes of Iranian children with ependymoma. To improve our care for these children, a paradigm shift must occur that includes radiation therapy as standard of care, second-look surgery, a multidisciplinary team approach, and potentially twinning initiatives.

Outcomes following proton therapy for pediatric ependymoma

Background: Proton therapy can reduce the low and intermediate radiation dose to uninvolved brain tissue in children with intracranial ependymomas, which may improve functional outcomes and reduce second malignancies in survivors. Accordingly, ependymoma has become the most common pediatric tumor treated with proton therapy, yet data on efficacy and toxicity are limited.Material and methods: Between June 2007 and February 2017, 179 children (≤21 years old) with nonmetastatic grade II/III intracranial ependymoma received proton therapy at our institution. Median age, 3.5 years (range, 0.7–21); 58% were male. Most (66%) tumors were in the posterior fossa and classified as WHO grade III (67%). 27% underwent multiple operations to maximize the extent of resection; ultimately 85% had a gross total or near total tumor resection before radiotherapy. 33% received preradiation chemotherapy. Median radiation dose in children ≤3 years old, 54 Gy(RBE). Most (>90%) children over 3 years old received 59.4 Gy(RBE). Patient and treatment variables were assessed for correlation with disease control.Results: Median follow-up, 3.2 years. 3-year local control, progression-free survival, and overall survival rates were 85%, 76%, and 90%, respectively. First site of progression was local, metastatic, or simultaneous in 14, 17 and 6 patients, respectively. On multivariate analysis, subtotal resection was associated with inferior local control (67% vs. 88%; p ≤ .01) and progression-free survival (59% vs. 79%; p < .05). Male sex was associated with inferior progression-free (67% vs. 87%; p< .05) and overall survival (84% vs. 99%; p < .01). The 3-year CTCAE grade 2 + brainstem toxicity rate was 5.5% (95% CI: 2.9–10.2), including 1 grade 5 toxicity.Conclusions: This series of proton therapy for pediatric intracranial ependymoma demonstrates disease control comparable to photon series without unexpected toxicity. Subtotal resection and male sex were associated with inferior disease control. Additional follow-up to quantify the expected reductions in late toxicity with proton therapy is ongoing.

PATH-32. MOLECULAR HETEROGENEITY AMONG PEDIATRIC POSTERIOR FOSSA EPENDYMOMA

Previously, we have identified nine distinct molecular groups of ependymoma across all age groups, three in each major anatomical compartment of the CNS: spinal, posterior fossa, and supratentorial. These nine molecular groups are genetically, epigenetically, transcriptionally, demographically, and clinically distinct. Pediatric intracranial ependymomas are either affiliated with the RELA and YAP1 supratentorial groups or with the posterior fossa PFA group. RELA and YAP1 ependymomas harbor recurrent and distinct fusion genes that drive the disease, but PFA ependymomas lack significant recurrent mutations, and the specific oncogenic events underlying these tumors remain undefined. Observing distinct outcomes among children with PFA ependymomas, we tested the hypothesis that further molecular diversity with clinical utility, including possible novel genetic alterations, may exist among these tumors. Genome-wide DNA methylation profiles of 675 pediatric PFA ependymomas were analyzed by unsupervised consensus hierarchical clustering and t-distributed stochastic neighbor embedding (tsne), which identified not only three major distinct molecular subgroups of PFA ependymoma: PFA-1, PFA-2, and PFA-3, but additional small subgroups that segregate within PFA-1 and PFA-2. Subgroups were characterized by distinct clinical and genetic characteristics; most PFA-3 tumors harbored 1q gain and occurred in children significantly older than those with PFA-1 and PFA-2 tumors. Some of the small subgroups demonstrated distinctive copy number alterations or gene mutations, e.g. H3 K27M. Outcome data revealed considerable heterogeneity among the different subgroups, overall survival at 5 years was >90% for one subgroup, but <20% for two others. We conclude that further molecular refinement of pediatric PFA ependymomas has clinical utility and the potential for enhanced risk assessment or therapeutic stratification. In addition, identification of PFA subgroups and further molecular heterogeneity within these subgroups may help to identify the drivers of PFA ependymomas.