Looking beyond year 1 in the molecular era of pediatric brain tumor diagnosis: confirmatory testing of germline variants found on tumor sequencing

Purpose

Somatic molecular profiling of pediatric brain tumors aids with the diagnosis and treatment of patients with a variety of high- and low-grade central nervous system neoplasms. Here, we report follow-up targeted germline evaluation for patients with possible germline variants following tumor only testing in the initial year in which somatic molecular testing was implemented at a single institution.

Patients and Methods

Somatic testing was completed for all tumors of the central nervous system (CNS) undergoing diagnostic workup at Seattle Children's Hospital during the study period of November 2015 to November 2016. Sequencing was performed in a College of American Pathologists-accredited, Clinical Laboratory Improvements Amendments-certified laboratory using UW-OncoPlex™ assay (version 5), a DNA-based targeted next generation sequencing panel validated to detect genetic alterations in 262 cancer-related genes. We tracked subsequent clinical evaluation and testing on a subgroup of this cohort found to have potential germline variants of interest.

Results

Molecular sequencing of 88 patients' tumors identified 31 patients with variants that warranted consideration of germline testing. To date, 19 (61%) patients have been tested. Testing confirmed germline variants for ten patients (31% of those identified for testing), one with two germline variants (NF1 and mosaic TP53). Eight (26%) patients died before germline testing was sent. One patient (13%) has not yet had testing.

Conclusion

Clinically validated molecular profiling of pediatric brain tumors identifies patients who warrant further germline evaluation. Despite this, only a subset of these patients underwent the indicated confirmatory sequencing. Further work is needed to identify barriers and facilitators to this testing, including the role of genetic counseling and consideration of upfront paired somatic-germline testing.

Everolimus for Children With Recurrent or Progressive Low-Grade Glioma: Results From the Phase II PNOC001 Trial

PURPOSE

The PNOC001 phase II single-arm trial sought to estimate progression-free survival (PFS) associated with everolimus therapy for progressive/recurrent pediatric low-grade glioma (pLGG) on the basis of phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway activation as measured by phosphorylated-ribosomal protein S6 and to identify prognostic and predictive biomarkers.

PATIENTS AND METHODS

Patients, age 3-21 years, with progressive/recurrent pLGG received everolimus orally, 5 mg/m2 once daily. Frequency of driver gene alterations was compared among independent pLGG cohorts of newly diagnosed and progressive/recurrent patients. PFS at 6 months (primary end point) and median PFS (secondary end point) were estimated for association with everolimus therapy.

RESULTS

Between 2012 and 2019, 65 subjects with progressive/recurrent pLGG (median age, 9.6 years; range, 3.0-19.9; 46% female) were enrolled, with a median follow-up of 57.5 months. The 6-month PFS was 67.4% (95% CI, 60.0 to 80.0) and median PFS was 11.1 months (95% CI, 7.6 to 19.8). Hypertriglyceridemia was the most common grade ≥3 adverse event. PI3K/AKT/mTOR pathway activation did not correlate with clinical outcomes (6-month PFS, active 68.4% v nonactive 63.3%; median PFS, active 11.2 months v nonactive 11.1 months; P = .80). Rare/novel KIAA1549::BRAF fusion breakpoints were most frequent in supratentorial midline pilocytic astrocytomas, in patients with progressive/recurrent disease, and correlated with poor clinical outcomes (median PFS, rare/novel KIAA1549::BRAF fusion breakpoints 6.1 months v common KIAA1549::BRAF fusion breakpoints 16.7 months; P < .05). Multivariate analysis confirmed their independent risk factor status for disease progression in PNOC001 and other, independent cohorts. Additionally, rare pathogenic germline variants in homologous recombination genes were identified in 6.8% of PNOC001 patients.

CONCLUSION

Everolimus is a well-tolerated therapy for progressive/recurrent pLGGs. Rare/novel KIAA1549::BRAF fusion breakpoints may define biomarkers for progressive disease and should be assessed in future clinical trials.

Somatic Versus Germline: A Case Series of Three Children With ATM-Mutated Medulloblastoma

Somatic versus Germline-A Case Series of Three Children with ATM- mutated Medulloblastoma.

The type II RAF inhibitor tovorafenib in relapsed/refractory pediatric low-grade glioma: the phase 2 FIREFLY-1 trial

BRAF genomic alterations are the most common oncogenic drivers in pediatric low-grade glioma (pLGG). Arm 1 (n = 77) of the ongoing phase 2 FIREFLY-1 (PNOC026) trial investigated the efficacy of the oral, selective, central nervous system-penetrant, type II RAF inhibitor tovorafenib (420 mg m-2 once weekly; 600 mg maximum) in patients with BRAF-altered, relapsed/refractory pLGG. Arm 2 (n = 60) is an extension cohort, which provided treatment access for patients with RAF-altered pLGG after arm 1 closure. Based on independent review, according to Response Assessment in Neuro-Oncology High-Grade Glioma (RANO-HGG) criteria, the overall response rate (ORR) of 67% met the arm 1 prespecified primary endpoint; median duration of response (DOR) was 16.6 months; and median time to response (TTR) was 3.0 months (secondary endpoints). Other select arm 1 secondary endpoints included ORR, DOR and TTR as assessed by Response Assessment in Pediatric Neuro-Oncology Low-Grade Glioma (RAPNO) criteria and safety (assessed in all treated patients and the primary endpoint for arm 2, n = 137). The ORR according to RAPNO criteria (including minor responses) was 51%; median DOR was 13.8 months; and median TTR was 5.3 months. The most common treatment-related adverse events (TRAEs) were hair color changes (76%), elevated creatine phosphokinase (56%) and anemia (49%). Grade ≥3 TRAEs occurred in 42% of patients. Nine (7%) patients had TRAEs leading to discontinuation of tovorafenib. These data indicate that tovorafenib could be an effective therapy for BRAF-altered, relapsed/refractory pLGG. ClinicalTrials.gov registration: NCT04775485 .

Children's Oncology Group's 2023 blueprint for research: Central nervous system tumors

Tumors of the central nervous system (CNS) are a leading cause of morbidity and mortality in the pediatric population. Molecular characterization in the last decade has redefined CNS tumor diagnoses and risk stratification; confirmed the unique biology of pediatric tumors as distinct entities from tumors that occur in adulthood; and led to the first novel targeted therapies receiving Food and Drug Administration (FDA) approval for children with CNS tumors. There remain significant challenges to overcome: children with unresectable low-grade glioma may require multiple prolonged courses of therapy affecting quality of life; children with high-grade glioma have a dismal long-term prognosis; children with medulloblastoma may suffer significant short- and long-term morbidity from multimodal cytotoxic therapy, and approaches to improve survival in ependymoma remain elusive. The Children's Oncology Group (COG) is uniquely positioned to conduct the next generation of practice-changing clinical trials through rapid prospective molecular characterization and therapy evaluation in well-defined clinical and molecular groups.

Therapeutic HDAC inhibition in hypermutant diffuse intrinsic pontine glioma

Constitutional mismatch repair deficiency (CMMRD) is a cancer predisposition syndrome associated with the development of hypermutant pediatric high-grade glioma, and confers a poor prognosis. While therapeutic histone deacetylase (HDAC) inhibition of diffuse intrinsic pontine glioma (DIPG) has been reported; here, we use a clinically relevant biopsy-derived hypermutant DIPG model (PBT-24FH) and a CRISPR-Cas9 induced genetic model to evaluate the efficacy of HDAC inhibition against hypermutant DIPG. We screened PBT-24FH cells for sensitivity to a panel of HDAC inhibitors (HDACis) in vitro, identifying two HDACis associated with low nanomolar IC50s, quisinostat (27 nM) and romidepsin (2 nM). In vivo, quisinostat proved more efficacious, inducing near-complete tumor regression in a PBT-24FH flank model. RNA sequencing revealed significant quisinostat-driven changes in gene expression, including upregulation of neural and pro-inflammatory genes. To validate the observed potency of quisinostat in vivo against additional hypermutant DIPG models, we tested quisinostat in genetically-induced mismatch repair (MMR)-deficient DIPG flank tumors, demonstrating that loss of MMR function increases sensitivity to quisinostat in vivo. Here, we establish the preclinical efficacy of quisinostat against hypermutant DIPG, supporting further investigation of epigenetic targeting of hypermutant pediatric cancers with the potential for clinical translation. These findings support further investigation of HDAC inhibitors against pontine high-grade gliomas, beyond only those with histone mutations, as well as against other hypermutant central nervous system tumors.

EPCT-05. Phase Ib study of unesbulin (PTC596) in children with newly diagnosed diffuse intrinsic pontine glioma (DIPG) and high-grade glioma (HGG): A report from the COllaborative Network for NEuro-Oncology Clinical Trials (CONNECT)

BACKGROUND: The B-cell-specific Moloney murine leukemia virus integration site-1 (BMI-1) protein, implicated in self-renewal and DNA-damage signaling, is highly expressed in DIPG and HGG. Preclinically, BMI-1 modulation by unesbulin (PTC596 [which mediates hyperphosphorylation and subsequent degradation of BMI-1]) leads to DIPG/HGG cell proliferation blockade, mitotic abnormalities, and tumor cell sensitization to radiation-induced DNA damage. METHODS: This phase Ib study sought to determine the maximally tolerated dose/ recommended phase 2 dose (RP2D) of unesbulin administered concurrently with radiotherapy and adjuvantly in children with newly diagnosed DIPG or HGG. Patients were enrolled according to a Rolling-6 design and received oral unesbulin twice weekly during radiotherapy and as maintenance therapy. RESULTS: Twenty-seven patients enrolled (median age: 8.5 years [range: 2-18]), including 18 patients with DIPG and nine patients with HGG. Unesbulin was administered in capsule formulation in the first nine patients, then tablet formulation for subsequent patients. Within the capsule formulation group, three dose-limiting toxicities (DLTs) were observed in two patients on dose level 2 (grade 4 neutropenia). Within the tablet formulation group, four DLTs were experienced by three patients on dose level 2 (grade 3 ALT elevation, grade 3 dehydration/vomiting, grade 3 decreased ejection fraction, grade 4 neutropenia). Dose level 1 was declared the RP2D, and six additional patients enrolled in the expansion cohort at this dose without DLTs. Most common drug-related grade 3/4 toxicities were neutropenia (48%), leucopenia (35%), and elevated ALT (26%). Similar pharmacokinetic profiles were observed for capsule and tablet formulations, consistent with adult data. Survival outcomes and genomics results will be shared at time of presentation. CONCLUSIONS: The RP2D of unesbulin in children newly diagnosed with DIPG or HGG is 200mg/m2 twice weekly, concurrent with and following radiotherapy. The recently opened surgical cohort will assess intratumoral pharmacokinetics and inhibition of tumor BMI-1 signaling, with results forthcoming.

EPCT-06. Phase I study of ribociclib and everolimus post-radiotherapy in children with newly diagnosed diffuse intrinsic pontine glioma (DIPG) and high-grade glioma (HGG): Updated report from the COllaborative Network for NEuro-Oncology Clinical Trials (CONNECT)

BACKGROUND: Dual inhibition of CDK4/6 and mTOR in DIPG and pediatric HGG has strong biologic rationale, given prevalent genetic alterations resulting in upregulated cell cycle and PI3K/mTOR pathways in these diseases, as well as non-overlapping agent toxicities. This study sought to evaluate safety/tolerability and determine the recommended phase 2 dose (RP2D) of ribociclib and everolimus among children with newly diagnosed DIPG and HGG post-radiotherapy. METHODS: Patients were enrolled according to a Rolling-6 design and received oral ribociclib and everolimus once daily for 21 and 28 days, respectively, starting 2-4 weeks post-completion of radiotherapy. All HGG and biopsied DIPG patients were screened for RB protein presence by immunohistochemistry. Pharmacokinetics and survival data were analyzed.

RESULTS: Nineteen patients enrolled (median age: 8 years [range: 2-18]). Three patients enrolled at each of dose levels 1 and 2 without dose-limiting toxicities (DLTs). Thirteen patients enrolled at dose level 3, with one patient experiencing a DLT (grade 3 infection). One patient came off therapy prior to cycle 9 due to cardiac toxicity. The most common grade 3/4 toxicities were neutropenia (33%), leucopenia (17%), and lymphopenia (11%). Steady-state everolimus exposures in combination were 1.9±0.9-fold higher than single-agent administration. Median overall survival (OS) for 15 patients with DIPG was 13.9 months, with 12-, 24-, and 36-month OS of 53.3%, 38.9%, and 38.9%. Median event-free survival for four patients with HGG was 10.5 months. Among patients with tumor molecular profiling, two longer survivors (OS: 20, &gt;37 months) had evidence of cell cycle upregulation with CDKN2A/B deletion and CDK4 overexpression identified. CONCLUSIONS: The combination of ribociclib and everolimus was well-tolerated post-radiotherapy in children with newly diagnosed DIPG and HGG, with a RP2D of ribociclib 170 mg/m2 days 1-21 and everolimus 1.5 mg/m2 days 1-28. Results will inform a molecularly-guided phase II study currently underway to evaluate efficacy.

Phase I study of ribociclib and everolimus in children with newly diagnosed DIPG and high-grade glioma: A CONNECT pediatric neuro-oncology consortium report

Background

Genomic aberrations in the cell cycle and PI3K/Akt/mTOR pathways have been reported in diffuse intrinsic pontine glioma (DIPG) and high-grade glioma (HGG). Dual inhibition of CDK4/6 and mTOR has biologic rationale and minimal overlapping toxicities. This study determined the recommended phase 2 dose (RP2D) of ribociclib and everolimus following radiotherapy in children with DIPG and HGG.

Methods

Patients were enrolled according to a Rolling-6 design and received ribociclib and everolimus once daily for 21 and 28 days, respectively. All patients with HGG and biopsied DIPG were screened for retinoblastoma protein presence by immunohistochemistry. Pharmacokinetics were analyzed.

Results

Nineteen patients enrolled (median age: 8 years [range: 2-18]). Three patients enrolled at each dose level 1 and 2 without dose-limiting toxicities (DLT). Thirteen patients were enrolled at dose level 3, with one patient experiencing a DLT (grade 3 infection). One patient came off therapy before cycle 9 due to cardiac toxicity. The most common grade 3/4 toxicities were neutropenia (33%), leucopenia (17%), and lymphopenia (11%). Steady-state everolimus exposures in combination were 1.9 ± 0.9-fold higher than single-agent administration. Median overall survival for 15 patients with DIPG was 13.9 months; median event-free survival for four patients with HGG was 10.5 months. Two longer survivors had tumor molecular profiling identifying CDKN2A/B deletion and CDK4 overexpression.

Conclusion

The combination of ribociclib and everolimus following radiotherapy in children with newly diagnosed DIPG and HGG was well tolerated, with a RP2D of ribociclib 170 mg/m² and everolimus 1.5 mg/m². Results will inform a molecularly guided phase II study underway to evaluate efficacy.

Two cases of pineal anlage tumor with molecular analysis

Pineal anlage tumor is a rare pediatric tumor with clinical and histological features overlapping with pineoblastoma. Two patients with pineal anlage tumor, a 13-month-old female and an 11-month-old male, underwent subtotal resection, high-dose chemotherapy with autologous stem cell rescue, and radiation. Neither had tumor progression 50 months after diagnosis. The tumors underwent next-generation sequencing on a panel of 340 genes. Chromosomal copy gains and losses were present and differed between the tumors. No mutations or amplifications, including none specific to pineoblastoma, were identified.

Vorinostat and isotretinoin with chemotherapy in young children with embryonal brain tumors: A report from the Pediatric Brain Tumor Consortium (PBTC-026)

BACKGROUND

Embryonal tumors of the CNS are the most common malignant tumors occurring in the first years of life. This study evaluated the feasibility and safety of incorporating novel non-cytotoxic therapy with vorinostat and isotretinoin to an intensive cytotoxic chemotherapy backbone.

METHODS

PBTC-026 was a prospective multi-institutional clinical trial for children <48 months of age with newly diagnosed embryonal tumors of the CNS. Treatment included three 21-day cycles of induction therapy with vorinostat and isotretinoin, cisplatin, vincristine, cyclophosphamide, and etoposide; three 28-day cycles of consolidation therapy with carboplatin and thiotepa followed by stem cell rescue; and twelve 28-day cycles of maintenance therapy with vorinostat and isotretinoin. Patients with M0 medulloblastoma (MB) received focal radiation following consolidation therapy. Molecular classification was by DNA methylation array.

RESULTS

Thirty-one patients with median age of 26 months (range 6-46) received treatment on study; 19 (61%) were male. Diagnosis was MB in 20 and supratentorial CNS embryonal tumor in 11. 24/31 patients completed induction therapy within a pre-specified feasibility window of 98 days. Five-year progression-free survival (PFS) and overall survival (OS) for all 31 patients were 55 ± 15 and 61 ± 13, respectively. Five-year PFS was 42 ± 13 for group 3 MB (n = 12); 80 ± 25 for SHH MB (n = 5); 33 ± 19 for embryonal tumor with multilayered rosettes (ETMR, n = 6).

CONCLUSION

It was safe and feasible to incorporate vorinostat and isotretinoin into an intensive chemotherapy regimen. Further study to define efficacy in this high-risk group of patients is warranted.

Predictors of mortality and tumor recurrence in desmoplastic infantile ganglioglioma and astrocytoma-and individual participant data meta-analysis (IPDMA)

PURPOSE

Desmoplastic infantile astrocytoma (DIA) and desmoplastic infantile ganglioglioma (DIG) are classified together as grade I neuronal and mixed neuronal-glial tumor of the central nervous system by the World Health Organization (WHO). These tumors are rare and have not been well characterized in terms of clinical outcomes. We aimed to identify clinical predictors of mortality and tumor recurrence/progression by performing an individual patient data meta-analysis (IPDMA) of the literature.

METHODS

A systematic literature review from 1970 to 2020 was performed, and individualized clinical data for patients diagnosed with DIA/DIG were extracted. Aggregated data were excluded from collection. Outcome measures of interest were mortality and tumor recurrence/progression, as well as time-to-event (TTE) for each of these. Participants without information on these outcome measures were excluded. Cox regression survival analyses were performed to determine predictors of mortality and tumor recurrence / progression.

RESULTS

We identified 98 articles and extracted individual patient data from 188 patients. The cohort consisted of 58.9% males with a median age of 7 months. The majority (68.1%) were DIGs, while 24.5% were DIAs and 7.5% were non-specific desmoplastic infantile tumors; DIAs presented more commonly in deep locations (p = 0.001), with leptomeningeal metastasis (p = 0.001), and was associated with decreased probability of gross total resection (GTR; p = 0.001). Gender, age, and tumor pathology were not statistically significant predictors of either mortality or tumor recurrence/progression. On multivariate survival analysis, GTR was a predictor of survival (HR = 0.058; p = 0.007) while leptomeningeal metastasis at presentation was a predictor of mortality (HR = 3.27; p = 0.025). Deep tumor location (HR = 2.93; p = 0.001) and chemotherapy administration (HR = 2.02; p = 0.017) were associated with tumor recurrence/progression.

CONCLUSION

Our IPDMA of DIA/DIG cases reported in the literature revealed that GTR was a predictor of survival while leptomeningeal metastasis at presentation was associated with mortality. Deep tumor location and chemotherapy were associated with tumor recurrence / progression.

Efficacy of Carboplatin and Isotretinoin in Children With High-risk Medulloblastoma: A Randomized Clinical Trial From the Children's Oncology Group

Importance

Brain tumors are the leading cause of disease-related death in children. Medulloblastoma is the most common malignant embryonal brain tumor, and strategies to increase survival are needed.

Objective

To evaluate therapy intensification with carboplatin as a radiosensitizer and isotretinoin as a proapoptotic agent in children with high-risk medulloblastoma in a randomized clinical trial and, with a correlative biology study, facilitate planned subgroup analysis according to World Health Organization consensus molecular subgroups of medulloblastoma.

Design, Setting, and Participants

A randomized clinical phase 3 trial was conducted from March 2007 to September 2018. Analysis was completed in September 2020. Patients aged 3 to 21 years with newly diagnosed high-risk medulloblastoma from Children's Oncology Group institutions within the US, Canada, Australia, and New Zealand were included. High-risk features included metastasis, residual disease, or diffuse anaplasia.

Interventions

Patients were randomized to receive 36-Gy craniospinal radiation therapy and weekly vincristine with or without daily carboplatin followed by 6 cycles of maintenance chemotherapy with cisplatin, cyclophosphamide, and vincristine with or without 12 cycles of isotretinoin during and following maintenance.

Main Outcomes and Measures

The primary clinical trial end point was event-free survival, using the log-rank test to compare arms. The primary biology study end point was molecular subgroup classification by DNA methylation array.

Results

Of 294 patients with medulloblastoma, 261 were evaluable after central radiologic and pathologic review; median age, 8.6 years (range, 3.3-21.2); 183 (70%) male; 189 (72%) with metastatic disease; 58 (22%) with diffuse anaplasia; and 14 (5%) with greater than 1.5-cm2 residual disease. For all participants, the 5-year event-free survival was 62.9% (95% CI, 55.6%-70.2%) and overall survival was 73.4% (95% CI, 66.7%-80.1%). Isotretinoin randomization was closed early owing to futility. Five-year event-free survival was 66.4% (95% CI, 56.4%-76.4%) with carboplatin vs 59.2% (95% CI, 48.8%-69.6%) without carboplatin (P = .11), with the effect exclusively observed in group 3 subgroup patients: 73.2% (95% CI, 56.9%-89.5%) with carboplatin vs 53.7% (95% CI, 35.3%-72.1%) without (P = .047). Five-year overall survival differed by molecular subgroup (P = .006): WNT pathway activated, 100% (95% CI, 100%-100%); SHH pathway activated, 53.6% (95% CI, 33.0%-74.2%); group 3, 73.7% (95% CI, 61.9%-85.5%); and group 4, 76.9% (95% CI, 67.3%-86.5%).

Conclusions and Relevance

In this randomized clinical trial, therapy intensification with carboplatin improved event-free survival by 19% at 5 years for children with high-risk group 3 medulloblastoma. These findings further support the value of an integrated clinical and molecular risk stratification for medulloblastoma.

Trial Registration

ClinicalTrials.gov Identifier: NCT00392327.

Optimal therapeutic targeting by HDAC inhibition in biopsy-derived treatment-naïve diffuse midline glioma models

BACKGROUND

Diffuse midline gliomas (DMGs), including diffuse intrinsic pontine gliomas (DIPGs), have a dismal prognosis, with less than 2% surviving 5 years postdiagnosis. The majority of DIPGs and all DMGs harbor mutations altering the epigenetic regulatory histone tail (H3 K27M). Investigations addressing DMG epigenetics have identified a few promising drugs, including the HDAC inhibitor (HDACi) panobinostat. Here, we use clinically relevant DMG models to identify and validate other effective HDACi and their biomarkers of response.

METHODS

HDAC inhibitors were tested across biopsy-derived treatment-naïve in vitro and in vivo DMG models with biologically relevant radiation resistance. RNA sequencing was performed to define and compare drug efficacy and to map predictive biomarkers of response.

RESULTS

Quisinostat and romidepsin showed efficacy with low nanomolar half-maximal inhibitory concentration (IC50) values (~50 and ~5 nM, respectively). Comparative transcriptome analyses across quisinostat, romidepsin, and panobinostat showed a greater degree of shared biological effects between quisinostat and panobinostat, and less overlap with romidepsin. However, some transcriptional changes were consistent across all 3 drugs at similar biologically effective doses, such as overexpression of troponin T1 slow skeletal type (TNNT1) and downregulation of collagen type 20 alpha 1 chain (COL20A1), identifying these as potential vulnerabilities or on-target biomarkers in DMG. Quisinostat and romidepsin significantly (P < 0.0001) inhibited in vivo tumor growth.

CONCLUSIONS

Our data highlight the utility of treatment-naïve biopsy-derived models; establishes quisinostat and romidepsin as effective in vivo; illuminates potential mechanisms and/or biomarkers of DMG cell lethality due to HDAC inhibition; and emphasizes the need for brain tumor-penetrant versions of potentially efficacious agents.

MR imaging features of diffuse intrinsic pontine glioma and relationship to overall survival: report from the International DIPG Registry

BACKGROUND

This study describes imaging features of diffuse intrinsic pontine glioma (DIPG) and correlates with overall survival (OS) and histone mutation status in the International DIPG Registry (IDIPGR).

METHODS

Four hundred cases submitted to the IDIPGR with a local diagnosis of DIPG and baseline MRI were evaluated by consensus review of 2 neuroradiologists; 43 cases were excluded (inadequate imaging or alternative diagnoses). Agreement between reviewers, association with histone status, and univariable and multivariable analyses relative to OS were assessed.

RESULTS

On univariable analysis imaging features significantly associated with worse OS included: extrapontine extension, larger size, enhancement, necrosis, diffusion restriction, and distant disease. On central review, 9.5% of patients were considered not to have DIPG. There was moderate mean agreement of MRI features between reviewers. On multivariable analysis, chemotherapy, age, and distant disease were predictors of OS. There was no difference in OS between wild-type and H3 mutated cases. The only imaging feature associated with histone status was the presence of ill-defined signal infiltrating pontine fibers.

CONCLUSIONS

Baseline imaging features are assessed in the IDIPGR. There was a 9.5% discordance in DIPG diagnosis between local and central review, demonstrating need for central imaging confirmation for prospective trials. Although several imaging features were significantly associated with OS (univariable), only age and distant disease were significant on multivariable analyses. There was limited association of imaging features with histone mutation status, although numbers are small and evaluation exploratory.

Cutaneous reactions to pediatric cancer treatment part II: Targeted therapy

Cancer remains a leading cause of morbidity and mortality among children. Targeted therapies may improve survivorship; however, unique side-effect profiles have also emerged with these novel therapies. Changes in hair, skin, and nails-termed dermatologic adverse events (AEs)-are among the most common sequelae and may result in interruption or discontinuation of therapy. Though dermatologic AEs have been detailed in adults, these findings are not well described in the pediatric population. We reviewed the literature to characterize dermatologic AEs to anticancer targeted therapies available as of July 2020 and summarized the spectrum of clinical findings as well as treatment recommendations for children. Dermatologic AEs are among the most common AEs reported in pediatric patients receiving targeted therapy, but morphologic and histologic descriptions are often lacking in current publications. Pediatric dermatologists are uniquely poised to recognize specific morphology of dermatologic AEs and make recommendations for prevention and treatment that may improve quality of life and enable ongoing cancer therapy.

EPEN-54. ACNS0831, PHASE III RANDOMIZED TRIAL OF POST-RADIATION CHEMOTHERAPY IN PATIENTS WITH NEWLY DIAGNOSED EPENDYMOMA AGES 1 TO 21 YEARS

PURPOSE

The primary objective of this study is to determine the EFS and OS of children with gross total and near totally resected ependymoma (EPN) treated with post-operative focal radiation therapy (RT) followed by randomization to either RT alone or RT + 4 cycles of maintenance chemotherapy with vincristine, cisplatin, cyclophosphamide and etoposide. Secondary objectives include estimating the EFS and OS of children not randomized, evaluation of neurobehavioral and quality of life (QoL) endpoints, and EPN biomarkers.

RESULTS

479 patients enrolled, 451 were eligible. Of 325 eligible randomized patients, 161 were randomized to RT alone and 164 to RT + maintenance chemotherapy. Age range (1–21 years, median 4.9 years). The planned primary analysis was based on intent-to-treat, irrespective of actual treatment received. Based on the data available as of 12/31/2019, estimated 3-year EFS in the RT + maintenance chemotherapy vs. RT arms were 78% vs. 72%, respectively, which did not meet statistical criteria to establish the benefit of maintenance chemotherapy post RT (1-sided log-rank p-value=0.074). Due to significant noncompliance (30.5% in the RT + maintenance vs 4.3% in the RT arm), a planned secondary “as treated” analysis was performed. With median follow-up of 42.6 months among patients without events, the 3 year EFS estimates for patients who received any chemotherapy (n=114) vs. those who received RT only (n=196) were 80% vs. 71%, respectively (1-sided p-value = 0.0121).

CONCLUSION

Early results in this randomized trial suggest that there may be some EPN patients who benefit from maintenance chemotherapy. Genomic analyses are ongoing.

Differential trajectories of neurocognitive functioning in females versus males following treatment for pediatric brain tumors

BACKGROUND

Female and male trajectories of cerebellar and lobar brain structures are sexually dimorphic, making sex a potential candidate moderator of neurocognitive late effects from radiation treatment. We sought to evaluate longitudinal neurocognitive functioning in male versus female children treated for posterior fossa brain tumors.

METHODS

Fifty-one female and 63 male survivors of posterior fossa tumors completed neuropsychological testing at 2 timepoints. We included patients treated with surgical resection, chemotherapy, and radiation therapy. Multilevel mixed modeling was used to predict IQ score as a function of patient sex following treatment (~2 or ~4 years post treatment). Effect sizes were used as a measure of clinical significance.

RESULTS

Multilevel models resulted in a significant sex by time interaction (F = 6.69, P = 0.011). Females' cognitive scores were considerably higher compared with males at 4 years posttreatment. Females demonstrated an average improvement of 7.61 standard score IQ points compared with a decline of 2.97 points for males at 4 years follow-up. Effect sizes for female IQ compared with male IQ at 4 years posttreatment were between 0.8 and 0.9.

CONCLUSION

Trajectories of neurocognitive functioning following posterior fossa tumor treatment differed between female and male children. Sexual dimorphism in radiation late effects may alter treatment decisions in children. Research into sex-specific neuroprotective mechanisms underlying neurocognitive development following pediatric brain tumor treatments is warranted.

Characterization of the immune microenvironment of diffuse intrinsic pontine glioma: implications for development of immunotherapy

Background

Diffuse intrinsic pontine glioma (DIPG) is a uniformly fatal CNS tumor diagnosed in 300 American children per year. Radiation is the only effective treatment and extends overall survival to a median of 11 months. Due to its location in the brainstem, DIPG cannot be surgically resected. Immunotherapy has the ability to target tumor cells specifically; however, little is known about the tumor microenvironment in DIPGs. We sought to characterize infiltrating immune cells and immunosuppressive factor expression in pediatric low- and high-grade gliomas and DIPG.

Methods

Tumor microarrays were stained for infiltrating immune cells. RNA was isolated from snap-frozen tumor tissue and Nanostring analysis performed. DIPG and glioblastoma cells were co-cultured with healthy donor macrophages, T cells, or natural killer (NK) cells, and flow cytometry and cytotoxicity assays performed to characterize the phenotype and function, respectively, of the immune cells.

Results

DIPG tumors do not have increased macrophage or T-cell infiltration relative to nontumor control, nor do they overexpress immunosuppressive factors such as programmed death ligand 1 and/or transforming growth factor β1. H3.3-K27M DIPG cells do not repolarize macrophages, but are not effectively targeted by activated allogeneic T cells. NK cells lysed all DIPG cultures.

Conclusions

DIPG tumors have neither a highly immunosuppressive nor inflammatory microenvironment. Therefore, major considerations for the development of immunotherapy will be the recruitment, activation, and retention of tumor-specific effector immune cells.

Beyond the Blood: CSF-Derived cfDNA for Diagnosis and Characterization of CNS Tumors

Genetic data are rapidly becoming part of tumor classification and are integral to prognosis and predicting response to therapy. Current molecular tumor profiling relies heavily on tissue resection or biopsy. Tissue profiling has several disadvantages in tumors of the central nervous system, including the challenge associated with invasive biopsy, the heterogeneous nature of many malignancies where a small biopsy can underrepresent the mutational profile, and the frequent lack of obtaining a repeat biopsy, which limits routine monitoring to assess therapy response and/or tumor evolution. Circulating tumor, cell-free DNA (cfDNA), has been proposed as a liquid biopsy to address some limitations of tissue-based genetics. In cancer patients, a portion of cfDNA is tumor-derived and may contain somatic genetic alterations. In central nervous system (CNS) neoplasia, plasma tumor-derived cfDNA is very low or absent, likely due to the blood brain barrier. Interrogating cfDNA in cerebrospinal fluid (CSF) has several advantages. Compared to blood, CSF is paucicellular and therefore predominantly lacks non-tumor cfDNA; however, patients with CNS-limited tumors have significantly enriched tumor-derived cfDNA in CSF. In patients with metastatic CNS disease, mutations in CSF cfDNA are most concordant with the intracranial process. CSF cfDNA can also occasionally uncover additional genetic alterations absent in concurrent biopsy specimens, reflecting tumor heterogeneity. Although CSF is enriched for tumor-derived cfDNA, absolute quantities are low. Highly sensitive, targeted methods including next-generation sequencing and digital PCR are required to detect mutations in CSF cfDNA. Additional technical and bioinformatic approaches also facilitate enhanced ability to detect tumor mutations in CSF cfDNA.

Unusual Radiographic Presentation of Intracranial Mature Teratoma and Resection via Supraorbital Approach

BACKGROUND

Primary intracranial teratomas account for <1% of intracranial masses during childhood after infancy. When supratentorial, they commonly occur in the pineal and suprasellar regions, demonstrating multilocularity, areas of fat, and calcifications and increasing enhancement correlating with decreased maturity. However, the presence of a teratoma as a mobile fat lesion within a large unilocular suprasellar cyst is rarely documented in this patient population.

CASE DESCRIPTION

We present the first pediatric case of a suprasellar mature teratoma presenting as a mobile fat suppressing lesion within a large unilocular suprasellar cyst and describe a supraorbital approach with adjunctive use of the endoscope for resection. We also provide a literature review of other cases presenting with similar radiographic findings.

CONCLUSIONS

Mature teratomas may manifest atypically as unilocular cystic lesions with a central mobile fatty component and are treated by gross total surgical resection. The supraorbital approach with adjunctive use of an endoscope can provide adequate exposure for resection with optimal cosmetic outcome.

Desmoplastic Infantile Ganglioglioma/Astrocytoma (DIG/DIA) Are Distinct Entities with Frequent BRAFV600 Mutations

Desmoplastic infantile ganglioglioma (DIG) and desmoplastic infantile astrocytoma (DIA) are extremely rare tumors that typically arise in infancy; however, these entities have not been well characterized in terms of genetic alterations or clinical outcomes. Here, through a multi-institutional collaboration, the largest cohort of DIG/DIA to date is examined using advanced laboratory and data processing techniques. Targeted DNA exome sequencing and DNA methylation profiling were performed on tumor specimens obtained from different patients (n = 8) diagnosed histologically as DIG/DIGA. Two of these cases clustered with other tumor entities, and were excluded from analysis. The remaining 16 cases were confirmed to be DIG/DIA by histology and by DNA methylation profiling. Somatic BRAF gene mutations were discovered in 7 instances (43.8%); 4 were BRAFV600E mutations, and 3 were BRAFV600D mutations. Three instances of malignant transformation were found, and sequencing of the recurrence demonstrated a new TP53 mutation in one case, new ATRX deletion in one case, and in the third case, the original tumor harbored an EML4-ALK fusion, also present at recurrence. DIG/DIA are distinct pathologic entities that frequently harbor BRAFV600 mutations. Complete surgical resection is the ideal treatment, and overall prognosis is excellent. While, the small sample size and incomplete surgical records limit a definitive conclusion about the risk of tumor recurrence, the risk appears quite low. In rare cases with wild-type BRAF, malignant progression can be observed, frequently with the acquisition of other genetic alterations.Implications: DIG/DIA are a distinct molecular entity, with a subset frequently harboring either BRAF V600E or BRAF V600D mutations. Mol Cancer Res; 16(10); 1491-8. ©2018 AACR.

A phase 1/2 dose-finding, safety, and activity study of cabazitaxel in pediatric patients with refractory solid tumors including tumors of the central nervous system

BACKGROUND

This phase 1/2 study (NCT01751308) evaluated cabazitaxel in pediatric patients. Phase 1 determined the maximum tolerated dose (MTD) in patients with recurrent/refractory solid tumors, including central nervous system (CNS) tumors. Phase 2 evaluated activity in pediatric recurrent high-grade glioma (HGG) or diffuse intrinsic pontine glioma (DIPG).

PROCEDURE

In phase 1, a 3 + 3 dose-escalation study design was followed. Cabazitaxel was administered at a starting dose of 20 mg/m² . Dose-limiting toxicities (DLTs) during cycle 1 were assessed to determine the MTD. Tumor response and cabazitaxel pharmacokinetics were also assessed. In phase 2, patients received cabazitaxel at the MTD determined in phase 1. Tumor responses were assessed every 9 weeks (modified Response Assessment in Neuro-oncology criteria). Progression-free survival and cabazitaxel pharmacokinetics were evaluated, and overall survival was estimated.

RESULTS

In phase 1, 23 patients were treated, including 19 with CNS tumors. One patient had a partial response; five had stable disease for >3 cycles. Common adverse events included fatigue, diarrhea, nausea and vomiting, febrile neutropenia, and hypersensitivity reactions. Two of three DLTs (febrile neutropenia) occurred with a dose of 35 mg/m² ; the MTD was 30 mg/m² . Slightly higher cabazitaxel clearance was observed compared with adult trials. In phase 2, 16 patients (eight HGG and eight DIPG) were enrolled; 11 were evaluable for response and five withdrew (three due to anaphylaxis). All 11 patients progressed within four cycles. No responses were observed; the study was stopped due to futility.

CONCLUSIONS

The safety profile of cabazitaxel was consistent with previous studies. The MTD (30 mg/m² ) was higher than the adult MTD. Cabazitaxel did not demonstrate activity in recurrent/refractory HGG or DIPG.

Pediatric Phase I Trial and Pharmacokinetic Study of Trebananib in Relapsed Solid Tumors, Including Primary Tumors of the Central Nervous System ADVL1115: A Children's Oncology Group Phase I Consortium Report

Purpose: Trebananib is a first-in-class antiangiogenic peptibody (peptide-Fc fusion protein) that inhibits Angiopoietin 1 and 2. A pediatric phase 1 trial was performed to define trebananib dose-limiting toxicities (DLT), recommended phase 2 dose (RP2D), and pharmacokinetics (PK).Experimental Design: Trebananib was administered by weekly infusion. Three dose levels (10, 15, or 30 mg/kg/dose) were evaluated using a rolling-six design. Part 2 evaluated a cohort of subjects with primary central nervous system (CNS) tumors. Pharmacokinetic sampling and analysis of peripheral blood biomarkers was performed during the first 4 weeks. Response was evaluated after 8 weeks. Correlative studies included angiogenic protein expression and DCE-MRI.Results: Thirty-seven subjects were enrolled (31 evaluable for toxicity) with median age 12 years (range, 2 to 21). Two of 19 evaluable non-CNS subjects developed DLT at the 30 mg/kg dose level, including venous thrombosis and pleural effusion. In the CNS cohort, 3/12 subjects developed DLT, including decreased platelet count, transient ischemic attack, and cerebral edema with headache and hydrocephalus. Other grade 3 or 4 toxicities included lymphopenia (n = 4), anemia, thrombocytopenia, neutropenia, vomiting, and hypertension (n = 1 each). Response included stable disease in 7 subjects, no partial or complete responses. Two subjects continued study treatment with prolonged stable disease for 18 cycles (neuroblastoma) and 26 cycles (anaplastic astrocytoma). Pharmacokinetics appeared linear over 3 dose levels. Correlative studies demonstrated increased PlGF and sVCAM-1, but no change in endoglin or perfusion by DCE-MRI.Conclusions: Trebananib was well tolerated in pediatric patients with recurrent or refractory solid or CNS tumors. RP2D is 30 mg/kg. Clin Cancer Res; 23(20); 6062-9. ©2017 AACR.

NKG2D ligand expression in pediatric brain tumors

Adult brain tumors establish an immunosuppressive tumor microenvironment as a modality of immune escape, with several immunotherapies designed to overcome this barrier. However, the relationship between tumor cells and immune cells in pediatric brain tumor patients is not as well-defined. In this study, we sought to determine whether the model of immune escape observed in adult brain tumors is reflected in patients with pediatric brain tumors by evaluating NKG2D ligand expression on tissue microarrays created from patients with a variety of childhood brain tumor diagnoses, and infiltration of Natural Killer and myeloid cells. We noted a disparity between mRNA and protein expression for the 8 known NKG2D ligands. Surprisingly, high-grade gliomas did not have increased NKG2D ligand expression compared to normal adjacent brain tissue, nor did they have significant myeloid or NK cell infiltration. These data suggest that pediatric brain tumors have reduced NK cell-mediated immune surveillance, and a less immunosuppressive tumor microenvironment as compared to their adult counterparts. These data indicate that therapies aimed to improve NK cell trafficking and functions in pediatric brain tumors may have a greater impact on anti-tumor immune responses and patient survival, with fewer obstacles to overcome.

Description of a new oncogenic mechanism for atypical teratoid rhabdoid tumors in patients with ring chromosome 22

Atypical teratoid rhabdoid tumors of the central nervous system are rare, highly malignant, embryonal tumors most often occurring in children under age 3 years. Most are due to a somatic change in tumor suppressor gene SMARCB1 followed by a second-hit, typically loss of heterozygosity, best detected on immunohistochemical staining. Despite the noteworthy genetic homogeneity of atypical teratoid rhabdoid tumors, relatively little is known about the oncogenic mechanisms that lead to biallelic inactivation of SMARCB1. Herein, we describe a patient with constitutional ring chromosome 22, Phelan-McDermid syndrome and atypical teratoid rhabdoid tumor of the brain. During mitosis, sister chromatids of a ring chromosome may form interlocking and dicentric rings, resulting in chromosomal loss, complex karyotypes, and ongoing somatic variation. We hypothesized that the inherent instability of the patient's ring chromosome could lead to mosaic monosomy chromosome 22, resulting in allelic inactivation of the tumor-suppressor gene SMARCB1 and AT/RT if a second-hit occurred. Utilizing high-density microarray technology to analyze peripheral blood and tumor tissue, we confirmed this oncogenic mechanism, previously undescribed in patients with atypical teratoid rhabdoid tumors. Our data demonstrate chromosomal loss as a consequence of ring chromosome instability serving as the first hit in oncogenesis. This rare but possibly under-recognized mechanism is important to note in children with ATRT and syndromic features. Further investigation is warranted to assess if this oncogenic mechanism has management and/or prognostic implications. © 2016 Wiley Periodicals, Inc.

Growth plate abnormalities in pediatric cancer patients undergoing phase 1 anti-angiogenic therapy: a report from the Children's Oncology Group Phase I Consortium

BACKGROUND

Pre-clinical studies suggest that anti-angiogenic agents may be toxic to the developing growth plate. The purpose of this study was to evaluate the incidence of growth plate abnormalities in children with refractory cancer undergoing anti-angiogenic therapy.

PROCEDURE

Targeted radiographic studies from 53 subjects enrolled on six separate Children's Oncology Group Phase 1 and Pilot Consortium clinical trials evaluating new anti-cancer agents interfering with angiogenesis were reviewed. Subjects received tyrosine kinase inhibitors with anti-angiogenic effects (n = 35), monoclonal antibodies targeting vascular endothelial growth factor (VEGF) (n = 13), or angiopoietin (n = 5). Radiographs of their distal femur/proximal tibia were obtained at baseline. Follow-up radiographs were obtained after odd-numbered treatment cycles in patients with open growth plates who did not experience disease progression prior to cycle 3.

RESULTS

Baseline and follow-up growth plate radiographs were acquired in 48/53 (90%) of patients. Five patients (9.4%), all of whom received a specific VEGF/VEGFR blocking agent (sunitinib [n = 1] or pazopanib [n = 4]), had growth plate abnormalities. Four patients had growth plate widening that was apparent on at least two successive radiographs, but was not confirmed by MRI. The fifth patient had progressive growth plate widening and evidence of physeal cartilage hypertrophy on MRI. Subsequent off treatment radiographs showed that the growth plate changes were reversible.

CONCLUSION

Growth plate abnormalities occur in a small, but relevant number of patients undergoing anti-angiogenic therapy. These results support the need for growth plate monitoring in children with open growth plates who are receiving anti-angiogenic therapy, and for improved methods to assess toxicity of anti-angiogenic agents to the developing skeleton.

Survival of pediatric patients after relapsed osteosarcoma: the St. Jude Children's Research Hospital experience

BACKGROUND

Chemotherapy has improved the outcome of patients with newly diagnosed osteosarcoma, but its role in relapsed disease is unclear.

METHODS

We reviewed the records of all patients who were treated for relapsed high-grade osteosarcoma at our institution between 1970 and 2004. Postrelapse event-free survival (PREFS) and postrelapse survival (PRS) were estimated, and outcome comparisons were made using an exact log-rank test.

RESULTS

The 10-year PREFS and PRS of the 110 patients were 11.8% ± 3.5% and 17.0% ± 4.3%, respectively. Metastasis at initial diagnosis (14%), and relapse in lung only (75%) were not significantly associated with PREFS or PRS. Time from initial diagnosis to first relapse (RL1) ≥18 months (43%), surgery at RL1 (76%), and ability to achieve second complete remission (CR2, 56%) were favorably associated with PREFS and PRS (P  ≤  0.0002). In patients without CR2, chemotherapy at RL1 was favorably associated with PREFS (P = 0.01) but not with PRS. In patients with lung relapse only, unilateral relapse and number of nodules ( ≤ 3) were associated with better PREFS and PRS (P  ≤  0.0005); no patients with bilateral relapse survived 10 years. The median PREFS after treatment with cisplatin, doxorubicin, methotrexate, and ifosfamide was 3.5 months (95% confidence interval, 2.1-5.2), and the median PRS was 8.2 months (95% confidence interval, 5.2-15.1).

CONCLUSIONS

Late relapse, surgical resection, and unilateral involvement (in lung relapse only) favorably impact outcome after relapse. Surgery is essential for survival; chemotherapy may slow disease progression in patients without CR2. These data are useful for designing clinical trials that evaluate novel agents.

A procedure to statistically evaluate agreement of differential expression for cross-species genomics

MOTIVATION

Animal models play a pivotal role in translation biomedical research. The scientific value of an animal model depends on how accurately it mimics the human disease. In principle, microarrays collect the necessary data to evaluate the transcriptomic fidelity of an animal model in terms of the similarity of expression with the human disease. However, statistical methods for this purpose are lacking.

RESULTS

We develop the agreement of differential expression (AGDEX) procedure to measure and determine the statistical significance of the similarity of the results of two experiments that measure differential expression across two groups. AGDEX defines a metric of agreement and determines statistical significance by permutation of each experiment's group labels. Additionally, AGDEX performs a comprehensive permutation-based analysis of differential expression for each experiment, including gene-set analyses and meta-analytic integration of results across studies. As an example, we show how AGDEX was recently used to evaluate the similarity of the transcriptome of a novel model of the brain tumor ependymoma in mice to that of a subtype of the human disease. This result, combined with other observations, helped us to infer the cell of origin of this devastating human cancer.

AVAILABILITY

An R package is currently available from www.stjuderesearch.org/site/depts/biostats/agdex and will shortly be available from www.bioconductor.org.

Histology predicts a favorable outcome in young children with desmoplastic medulloblastoma: a report from the children's oncology group

BACKGROUND

Contemporary therapy for medulloblastoma results in adverse neurocognitive effects on young children, particularly those under the age of 3. Stratification of patients by risk group may allow toxic treatment to be avoided.

METHODS

Seventy-six patients diagnosed with medulloblastoma and enrolled on CCG-9921 underwent central review of pathology, and histologic subtype was designated as desmoplastic or nondesmoplastic. Nonparametric event-free survival (EFS) and survival (OS) curves were computed using the product limit (Kaplan-Meier) estimates, and the log-rank test was used to compare survival according to histologic subtype.

RESULTS

Patients with desmoplastic medulloblastoma experienced a favorable EFS of 77% ± 9% and OS of 85% ± 8% compared with EFS of 17% ± 5% and OS of 29% ± 6% for patients with tumors in the nondesmoplastic group (P < .0001 for both EFS and OS comparisons). Patients without disease progression did not receive radiation therapy.

CONCLUSIONS

Children less than 3 with desmoplastic histology of medulloblastoma represent a lower-risk group for whom reduction of therapy, including elimination of radiation therapy, is an appropriate strategy.

Cross-species genomics matches driver mutations and cell compartments to model ependymoma

Understanding the biology that underlies histologically similar but molecularly distinct subgroups of cancer has proven difficult because their defining genetic alterations are often numerous, and the cellular origins of most cancers remain unknown. We sought to decipher this heterogeneity by integrating matched genetic alterations and candidate cells of origin to generate accurate disease models. First, we identified subgroups of human ependymoma, a form of neural tumour that arises throughout the central nervous system (CNS). Subgroup-specific alterations included amplifications and homozygous deletions of genes not yet implicated in ependymoma. To select cellular compartments most likely to give rise to subgroups of ependymoma, we matched the transcriptomes of human tumours to those of mouse neural stem cells (NSCs), isolated from different regions of the CNS at different developmental stages, with an intact or deleted Ink4a/Arf locus (that encodes Cdkn2a and b). The transcriptome of human supratentorial ependymomas with amplified EPHB2 and deleted INK4A/ARF matched only that of embryonic cerebral Ink4a/Arf(-/-) NSCs. Notably, activation of Ephb2 signalling in these, but not other, NSCs generated the first mouse model of ependymoma, which is highly penetrant and accurately models the histology and transcriptome of one subgroup of human supratentorial tumour. Further, comparative analysis of matched mouse and human tumours revealed selective deregulation in the expression and copy number of genes that control synaptogenesis, pinpointing disruption of this pathway as a critical event in the production of this ependymoma subgroup. Our data demonstrate the power of cross-species genomics to meticulously match subgroup-specific driver mutations with cellular compartments to model and interrogate cancer subgroups.