Development and pilot validation of a novel disfigurement severity scale for plexiform neurofibromas in children with neurofibromatosis type 1

BACKGROUND/AIMS

We developed an observer disfigurement severity scale for neurofibroma-related plexiform neurofibromas to assess change in plexiform neurofibroma-related disfigurement and evaluated its feasibility, reliability, and validity.

METHODS

Twenty-eight raters, divided into four cohorts based on neurofibromatosis type 1 familiarity and clinical experience, were shown photographs of children in a clinical trial (NCT01362803) at baseline and 1 year on selumetinib treatment for plexiform neurofibromas (n = 20) and of untreated participants with plexiform neurofibromas (n = 4). Raters, blinded to treatment and timepoint, completed the 0-10 disfigurement severity score for plexiform neurofibroma on each image (0 = not at all disfigured, 10 = very disfigured). Raters evaluated the ease of completing the scale, and a subset repeated the procedure to assess intra-rater reliability.

RESULTS

Mean baseline disfigurement severity score for plexiform neurofibroma ratings were similar for the selumetinib group (6.23) and controls (6.38). Mean paired differences between pre- and on-treatment ratings was -1.01 (less disfigurement) in the selumetinib group and 0.09 in the control (p = 0.005). For the disfigurement severity score for plexiform neurofibroma ratings, there was moderate-to-substantial agreement within rater cohorts (weighted kappa range = 0.46-0.66) and agreement between scores of the same raters at repeat sessions (p > 0.05). In the selumetinib group, change in disfigurement severity score for plexiform neurofibroma ratings was moderately correlated with change in plexiform neurofibroma volume with treatment (r = 0.60).

CONCLUSION

This study demonstrates that our observer-rated disfigurement severity score for plexiform neurofibroma was feasible, reliable, and documented improvement in disfigurement in participants with plexiform neurofibroma shrinkage. Prospective studies in larger samples are needed to validate this scale further.

Zebrafish-A Suitable Model for Rapid Translation of Effective Therapies for Pediatric Cancers

Pediatric cancers are the leading cause of disease-related deaths in children and adolescents. Most of these tumors are difficult to treat and have poor overall survival. Concerns have also been raised about drug toxicity and long-term detrimental side effects of therapies. In this review, we discuss the advantages and unique attributes of zebrafish as pediatric cancer models and their importance in targeted drug discovery and toxicity assays. We have also placed a special focus on zebrafish models of pediatric brain cancers-the most common and difficult solid tumor to treat.

Four distinct ipsilateral vestibular schwannomas: A case of mosaic NF2-related schwannomatosis

OBJECTIVES

Distinguishing between sporadic and germline/mosaic NF2-related schwannomatosis is important to ensure that patients have appropriate long-term care. With this report, we describe a unique case of a patient with 4 ipsilateral schwannomas and identify a combination of sequencing modalities that can accurately diagnose mosaic NF2-related schwannomatosis.

METHODS

We present a 32-year-old woman with a familial history of vestibular schwannoma in her father and right-sided schwannomas involving the apical and basal turns of cochlea, lateral semicircular canal, and internal auditory canal (IAC). Genetic analysis of blood and frozen tissue from 2 tumors (intralabyrinthine and IAC tumors) was performed using next-generation sequencing (NGS), multiplex ligation-dependent probe amplification (MLPA), and optical genome mapping (OGM).

RESULTS

Germline testing for NF2, LZTR1, and SMARCB1 was negative. Tumor genetic testing revealed a shared NF2 pathogenic variant between the 2 tumors ("first hit") but distinct "second hit" NF2 variants, including mosaic loss of chromosome 22 in the IAC tumor seen only with OGM, consistent with mosaic NF2-related schwannomatosis.

CONCLUSIONS

Multimodality sequencing, including NGS, MLPA, and OGM, was required to ensure appropriate diagnosis of mosaic NF2-related schwannomatosis in this patient. A similar approach can be used for other patients with multiple ipsilateral tumors and suspected tumor predisposition.

The Brain Tumor Segmentation (BraTS) Challenge 2023: Focus on Pediatrics (CBTN-CONNECT-DIPGR-ASNR-MICCAI BraTS-PEDs)

Pediatric tumors of the central nervous system are the most common cause of cancer-related death in children. The five-year survival rate for high-grade gliomas in children is less than 20\%. Due to their rarity, the diagnosis of these entities is often delayed, their treatment is mainly based on historic treatment concepts, and clinical trials require multi-institutional collaborations. The MICCAI Brain Tumor Segmentation (BraTS) Challenge is a landmark community benchmark event with a successful history of 12 years of resource creation for the segmentation and analysis of adult glioma. Here we present the CBTN-CONNECT-DIPGR-ASNR-MICCAI BraTS-PEDs 2023 challenge, which represents the first BraTS challenge focused on pediatric brain tumors with data acquired across multiple international consortia dedicated to pediatric neuro-oncology and clinical trials. The BraTS-PEDs 2023 challenge focuses on benchmarking the development of volumentric segmentation algorithms for pediatric brain glioma through standardized quantitative performance evaluation metrics utilized across the BraTS 2023 cluster of challenges. Models gaining knowledge from the BraTS-PEDs multi-parametric structural MRI (mpMRI) training data will be evaluated on separate validation and unseen test mpMRI dataof high-grade pediatric glioma. The CBTN-CONNECT-DIPGR-ASNR-MICCAI BraTS-PEDs 2023 challenge brings together clinicians and AI/imaging scientists to lead to faster development of automated segmentation techniques that could benefit clinical trials, and ultimately the care of children with brain tumors.

Early prognostication of overall survival for pediatric diffuse midline gliomas using MRI radiomics and machine learning: a two-center study

Background

Diffuse midline gliomas (DMG) are aggressive pediatric brain tumors that are diagnosed and monitored through MRI. We developed an automatic pipeline to segment subregions of DMG and select radiomic features that predict patient overall survival (OS).

Methods

We acquired diagnostic and post-radiation therapy (RT) multisequence MRI (T1, T1ce, T2, T2 FLAIR) and manual segmentations from two centers of 53 (internal cohort) and 16 (external cohort) DMG patients. We pretrained a deep learning model on a public adult brain tumor dataset, and finetuned it to automatically segment tumor core (TC) and whole tumor (WT) volumes. PyRadiomics and sequential feature selection were used for feature extraction and selection based on the segmented volumes. Two machine learning models were trained on our internal cohort to predict patient 1-year survival from diagnosis. One model used only diagnostic tumor features and the other used both diagnostic and post-RT features.

Results

For segmentation, Dice score (mean [median]±SD) was 0.91 (0.94)±0.12 and 0.74 (0.83)±0.32 for TC, and 0.88 (0.91)±0.07 and 0.86 (0.89)±0.06 for WT for internal and external cohorts, respectively. For OS prediction, accuracy was 77% and 81% at time of diagnosis, and 85% and 78% post-RT for internal and external cohorts, respectively. Homogeneous WT intensity in baseline T2 FLAIR and larger post-RT TC/WT volume ratio indicate shorter OS.

Conclusions

Machine learning analysis of MRI radiomics has potential to accurately and non-invasively predict which pediatric patients with DMG will survive less than one year from the time of diagnosis to provide patient stratification and guide therapy.

Long-term safety and efficacy of selumetinib in children with neurofibromatosis type 1 on a phase 1/2 trial for inoperable plexiform neurofibromas

BACKGROUND

Selumetinib shrank inoperable symptomatic plexiform neurofibromas (PN) in children with neurofibromatosis type 1 (NF1) and provided clinical benefit for many in our previously published phase 1/2 clinical trials (SPRINT, NCT01362803). At the data cutoff (DCO) of the prior publications, 65% of participants were still receiving treatment. This report presents up to 5 years of additional safety and efficacy data from these studies.

METHODS

This manuscript includes data from the phase 1 and phase 2, stratum 1 study which included participants with clinically significant PN-related morbidity. Participants received continuous selumetinib dosing (1 cycle = 28 days). Safety and efficacy data through February 27, 2021 are included. PN response assessed by volumetric magnetic resonance imaging analysis: Confirmed partial response (cPR) ≥20% decrease from baseline on 2 consecutive evaluations. Phase 2 participants completed patient-reported outcome measures assessing tumor pain intensity (Numeric Rating Scale-11) and interference of pain in daily life (pain interference index).

RESULTS

For the 74 children (median age 10.3 years; range 3-18.5) enrolled, overall cPR rate was 70% (52/74); median duration of treatment was 57.5 cycles (range 1-100). Responses were generally sustained with 59% (44) lasting ≥ 12 cycles. Tumor pain intensity (n = 19, P = .015) and pain interference (n = 18, P = .0059) showed durable improvement from baseline to 48 cycles. No new safety signals were identified; however, some developed known selumetinib-related adverse events (AEs) for the first time after several years of treatment.

CONCLUSIONS

With up to 5 years of additional selumetinib treatment, most children with NF1-related PN had durable tumor shrinkage and sustained improvement in pain beyond that previously reported at 1 year. No new safety signals were identified; however, ongoing monitoring for known selumetinib-related AEs is needed while treatment continues.

Optical genome mapping identifies a novel pediatric embryonal tumor with a ZNF532::NUTM1 fusion

The molecular characteristics of pediatric brain tumors have not only allowed for tumor subgrouping but have led to the introduction of novel treatment options for patients with specific tumor alterations. Therefore, an accurate histologic and molecular diagnosis is critical for optimized management of all pediatric patients with brain tumors, including central nervous system embryonal tumors. We present a case where optical genome mapping identified a ZNF532::NUTM1 fusion in a patient with a unique tumor best characterized histologically as a central nervous system embryonal tumor with rhabdoid features. Additional analyses including immunohistochemistry for NUT protein, methylation array, whole genome, and RNA-sequencing was done to confirm the presence of the fusion in the tumor. This is the first description of a pediatric patient with a ZNF532::NUTM1 fusion, yet the histology of this tumor is similar to that of adult cancers with ZNF::NUTM1 fusions reported in the literature. Although rare, the distinct pathology and underlying molecular characteristics of the ZNF532::NUTM1 tumor separates this from other embryonal tumors. Therefore, screening for this or similar NUTM1 rearrangements should be considered for all patients with unclassified central nervous system tumors with rhabdoid features to ensure accurate diagnosis. Ultimately, with additional cases, we may be able to better inform therapeutic management for these patients. © 2023 The Pathological Society of Great Britain and Ireland.

Surveillance imaging and early surgical intervention for improved CNS tumor outcomes in children with Li-Fraumeni syndrome: Children's National Hospital experience and literature review

OBJECTIVE

Li-Fraumeni syndrome (LFS) is a cancer predisposition syndrome caused by germline mutations in the TP53 gene. CNS tumors are the fourth most common tumor type in LFS, and recent screening guidelines demonstrate that early tumor detection is associated with improved long-term survival. However, there is a paucity of data regarding surgical intervention when lesions are identified in asymptomatic patients on surveillance imaging. The authors investigated this through their cohort and literature review.

METHODS

The cohort consisted of children seen in the Pediatric Cancer Genetics Program at Children's National Hospital between August 2012 and August 2021. The authors also include a PubMed (MEDLINE) literature search of articles from 2006 to 2021 related to surveillance and CNS tumors in patients with LFS. Studies in which CNS tumors were not identified or detailed patient information was not provided were excluded. Patients from the selected articles and the authors' cohort were added for further analysis.

RESULTS

Between August 2012 and August 2021, 10 children with LFS and CNS tumors were assessed at Children's National Hospital: 4 who were known carriers of the TP53 mutation had CNS lesions found on surveillance imaging, whereas 6 presented with symptomatic CNS lesions and were either known or subsequently found to have germline TP53 mutations. The literature search identified 148 articles, 7 of which were included in this review. Patients from the literature and the present cohort were added for a total of 56 CNS lesions. A majority of the low-grade CNS lesions (22/24, 92%) were found on surveillance protocols in asymptomatic patients, whereas the majority of the high-grade lesions (22/26, 85%) presented in symptomatic patients who were not undergoing routine surveillance or as the initial diagnosis of LFS. The authors noted a significant survival advantage in pediatric patients with low-grade lesions, with an overall survival of 100% at 30 months. Minor limitations of the study include patient sample size and limitations in the patient cohort due to this being a retrospective rather than a prospective study.

CONCLUSIONS

Data presented in this study support surveillance protocols in LFS and demonstrate the importance of dedicated CNS imaging and early surgical intervention when lesions are identified. Systematic review registration no.: CRD42022372610 (www.crd.york.ac.uk/prospero).

Case report: Tisagenlecleucel for treatment of relapsed B- acute lymphoblastic leukemia in a patient with CHEK2 mutation

Background

Germline Checkpoint Kinase 2 gene (CHEK2) mutations can increase the risk of solid tumors. Recently, they have been identified as risk factors for hematologic malignancies. However, to the best of our knowledge, B-acute lymphoblastic leukemia (B-ALL) has never been described as a presenting manifestation of germline CHEK2 mutation. Chimeric antigen receptor-T (CAR-T) cell therapy directed against CD19 antigen (tisagenlecleucel) is a novel cellular therapy for treatment of relapsed/refractory (R/R) B-ALL. The use of tisagenlecleucel has not been described in patients with CHEK2 mutation.

Case Presentation

We describe a case of a pediatric patient with a heterozygous pathogenic germline CHEK2 mutation (c.1100delC; p.Thr367Metfs*15) successfully treated with tisagenlecleucel for relapsed B-ALL to avoid hematopoietic cell transplant (HCT). The twelve-year-old boy was diagnosed with National Cancer Institute (NCI) high-risk B-ALL (white blood cell count >50,000/mcL), with no extramedullary disease. Cytogenetic analysis revealed normal karyotype but fluorescent in situ hybridization (FISH) showed 93% positivity for CRLF2::P2RY8 rearrangement. He was treated as per Children's Oncology Group (COG) AALL1131 therapy and achieved a complete remission. Seven months after diagnosis, he was found to have papillary thyroid carcinoma with no evidence of metastatic disease. The patient underwent a total thyroidectomy with central lymph node biopsy and radioactive iodine therapy. The patient's biological mother and fraternal twin brother carry the same germline CHEK2 mutation with no history of malignancy. The biological father tested negative for the familial mutation. The patient's genetic panel also identified three variants of unclear significance: CDKN2A (c.37 °C > T; p.Arg124Cys), FLCN (c.62G > A; p.Cys21Tyr) and SDHAF2 (c.139A > G; p.Met47Val). Extended family history also revealed a diagnosis of anaplastic thyroid cancer in maternal uncle at the age of 44 years. Fifteen months after diagnosis the patient had a relapse of B-ALL (both medullary and extramedullary with blasts in CSF), which was successfully treated with tisagenlecleucel. The patient remains in remission 3 years after receiving tisagenlecleucel.

Conclusion

As conventional chemotherapy and radiation can potentially increase the risk of DNA damage and development of secondary malignancies, CD19 CAR-T therapy (tisagenlecleucel) can be used as a substitute for intensive re-induction chemotherapy and HCT in patients with a germline CHEK2 mutation.

INNV-16. SPINAL POST-TREATMENT SURVEILLANCE IN MEDULLOBLASTOMA – A SYSTEMATIC REVIEW OF THE LITERATURE AND CLINICAL TRIALS

BACKGROUND

Monitoring for dissemination in medulloblastoma involves spinal MRIs (sMRIs) and lumbar punctures (LPs). The frequency and duration of these studies vary depending on risk of dissemination; general practice varies between and within institutions. Our goal is to review the current practice in post-treatment monitoring via examination of published data, clinical trial standards, and expert practice.

METHODS

We reviewed the available literature and accessible clinical trial protocols. Using PRISMA guidelines, we conducted searches of Ovid MEDLINE, Embase, and PubMed to identify studies which detailed relapse rates and patterns, and recommended practice for patients with medulloblastoma aged 3-21 years. Eligible studies from 1990 to present were included.

RESULTS

Thirteen multi-institutional clinical trials from North America and Europe were analyzed for frequency of post-therapy surveillance with LPs/sMRIs. Several studies (n=8) recommend LPs/sMRIs every 3-6 months in standard risk and every 3 months in high risk disease for two years when initially completing therapy, and then often diverge in frequency after 2 years. Some studies (n=5) did not include post-treatment recommendations. Cumulative data on relapse from available clinical trial reports and single institution studies (n=673 relapses) demonstrated local failure rate of 18.4%, distant failure of 49.1%, and combined distant and local failure of 32.5%. Spine-only relapses were reported to occur in approximately 13-20%, with one small study reporting spine-only relapse rate of 37.5%.

DISCUSSION

Patterns of recurrence in medulloblastoma have shifted over time as therapeutic approaches have evolved, including more spinal-only recurrences. Standardized guidance regarding surveillance could have significant impact on clinical detection and streamline management to minimize unnecessary examinations. Early detection of recurrent disease could optimize treatment options for providers and families, whether focusing on curative approaches or quality of life.

EOLP-04. A CALL TO ACTION TO INCREASE ACCESS TO POST-MORTEM BRAIN TUMOR DONATIONS: GIFT FROM A CHILD

Implementation of access to donate post mortem tissue among pediatric brain tumor patients remains a challenge[DSM1] . Previous attempts to develop a post-mortem network have been jeopardized by barriers such as a lack of education, logistical coordination of donation, and difficulties effectively communicating the benefit of post-mortem donations to families. [CC2] Utilizing feedback from patients’ families, clinicians, and researchers, standard operating procedures (SOP) were developed and utilized by six “tissue navigators” (TN) working across institutions. Tissue navigators are critical in implementation of access to donate as they serve as a liaison between patients’ families and clinical team to ensure post-mortem tissue is procured correctly and respectfully. From 2018 through 2021, there has been an increase in donations, which has led to establishment of tumor cell cultures translating rapidly to clinical development, and a growing network of centers participating in GFAC procedures. Donations have been facilitated at over 75 institutions. GFAC has coordinated 146 donations in this 3-year launch timeframe, with nearly half from families outside GFAC’s primary institutional network. Barriers to implementation were addressed with the design of GFAC’s SOPs, which lead to the successful implementation of access to donation. GFAC is developing CME training for clinicians and researchers to address communication of post-mortem donation, continuing awareness campaigns with collaborators in the field, advocating for families to receive feedback on the donation, and expanding on the SOPs as more is learned from clinicians and families.

Management of neurofibromatosis type 1-associated plexiform neurofibromas

Plexiform Neurofibromas (PN) are a common manifestation of the genetic disorder neurofibromatosis type 1 (NF1). These benign nerve sheath tumors often cause significant morbidity, with treatment options limited historically to surgery. There have been tremendous advances over the past two decades in our understanding of PN, and the recent regulatory approvals of the MEK inhibitor selumetinib are reshaping the landscape for PN management. At present, there is no agreed upon PN definition, diagnostic evaluation, surveillance strategy, or clear indications for when to initiate treatment and selection of treatment modality. In this review, we address these questions via consensus recommendations from a panel of multidisciplinary NF1 experts.

Circulating tumor DNA sequencing provides comprehensive mutation profiling for pediatric central nervous system tumors

Molecular profiling of childhood CNS tumors is critical for diagnosis and clinical management, yet tissue access is restricted due to the sensitive tumor location. We developed a targeted deep sequencing platform to detect tumor driver mutations, copy number variations, and heterogeneity in the liquid biome. Here, we present the sensitivity, specificity, and clinical relevance of our minimally invasive platform for tumor mutation profiling in children diagnosed with CNS cancer.

DIPG-47. TSO500ctDNA sequencing reveals oncogenic mutations and copy number variations in the liquid biome of children with diffuse midline glioma

BACKGROUND: Molecular profiling of childhood CNS tumors is critical for diagnosis and clinical management, yet tissue access is restricted due to sensitive neuroanatomical locations. Moreover, CNS tumors including diffuse midline glioma (DMG) exhibit mutational heterogeneity and clonal evolution, which cannot be captured by upfront diagnostic biopsy alone. To address the lack of tumor visibility, and tprovide opportunity for longitudinal sampling, we validated and optimized a commercially available deep sequencing platform for analysis of circulating tumor DNA (TSO500ctDNA^TM). METHODS: In a proof-of-concept study, we defined the sensitivity, specificity, and clinical relevance of our novel ctDNA platform via analysis of paired tissue, CSF, and blood from children with DMG (n=10). Paired samples were assessed for concordance and sequencing results were compared to digital droplet PCR (ddPCR) detection of prognostic H3K27M mutation. RESULTS: DMG associated mutations in genes including H3-3A, H3C2, TP53, and ACVR1 were detected in ctDNA, including in CSF samples with low (<5ng) starting DNA input. Of 9 H3K27M mutations identified in tumor, 8 were present in CSF and 3 in plasma/serum, for a positive percent agreement with tumor results of 89% and 33%, respectively. Among CSF samples, H3.3K27M was detected in 6/6 cases, and H3.1K27M in 2/3 cases, with variant allele frequencies comparable to ddPCR results. CNVs including PDGFRA, KIT, and MDM4 gains were detected in CSF and paired tumor. Low frequency events including ACVR1, PIK3CA activating mutations and KRAS amplification were detected in CSF but absent from paired tumor, indicating tissue heterogeneity. Strategies to optimize ctDNA detection, including optimization of ctDNA isolation and adjustment of library QC metrics, were identified. CONCLUSION: Targeted ctDNA deep sequencing is feasible, can inform on clinically relevant tumor mutation and CNV profiling, and provides an opportunity for longitudinal monitoring of tumor genomic evolution in the liquid biome of children with CNS tumors.

NFB-20. Pre-clinical models of Mismatch Repair Deficient Gliomas

INTRODUCTION: Lynch syndrome and Biallelic Mismatch Repair Deficiency (BMMRD) are hereditary tumor predisposition syndromes, resulting from one or two (respectively) germline alterations in DNA mis-match repair (MMR) genes. Currently, there are few treatments for mismatch repair deficient (MMRD) gliomas, in part due to a lack of suitable pre-clinical models for drug testing. The purpose of this study is to develop and characterize pre-clinical models of MMRD gliomas. METHODS: Primary cells were developed from patients diagnosed with MMRD gliomas and characterized through immunofluorescence staining (IF) for different cell type markers, western blot assays, and genome and transcriptome analysis. Murine models were generated through intracranial injection of mCherry-luciferase reporter expressing primary cells, and mice were monitored for evidence of engraftment and clinical symptoms. Drug screening on the cell lines was performed to identify potential therapeutic agents for in-vivo testing. RESULTS: The cell lines had similar characteristics as the primary glial tumors by IF staining and genome and transcriptome analysis. Adult NSG mice developed tumors around three weeks after intercranial transplantation of the tumor cells. These tumors closely resembled the primary patient tumors on histology. Preliminary drug testing on the cell lines showed efficacy of ONC201, ONC206, and RM006 against MMRD gliomas with IC50 concentrations of 1.77 μM, 185 nM, and 699 nM respectively. CONCLUSION: The generation of pre-clinical MMRD glioma models can lead to improved understanding of tumorigenesis, allowing for the identification of targetable molecules, and supporting novel treatment development.

DIPG-48. MRI volumetric and machine learning based analyses predict survival outcome in pediatric diffuse midline glioma

INTRODUCTION: Diffuse midline glioma (DMG) is a fatal childhood CNS tumor. Magnetic resonance imaging (MRI) is the gold standard for DMG diagnosis and monitoring of response to therapy. Leveraging novel MRI analytical approaches, including volumetric and machine learning based analyses, may aid in the prediction of patient overall survival (OS) and help to identify high-risk cases. METHODS: T1- and T2-weighted MR images were retrospectively collected from children and young adults diagnosed with DMG (n=43). MRI features, including manually determined 3D tumor volume (T2), T1 contrast-enhancing tumor volume, T1 relative to T2 volume (T1/T2), tumor relative to whole brain volume, tumor average intensity, and tumor heterogeneity (i.e., intensity skewness and kurtosis), were evaluated at upfront diagnosis. MRI features were analyzed to identify significant predictors of OS outcome, which was defined as OS shorter, or longer, than one year from diagnosis. A support vector machine was used to predict OS outcomes using combinations of these features. RESULTS: The presence of T1 contrast-enhancing tumor at diagnosis (p=0.01), and a high T1/T2 ratio (>25%, p=0.009), predicted significantly shorter median OS. Moreover, feature selection identified T2 mean intensity (p<0.001), T2 image intensity skew (p=0.006), T1/T2 ratio (p=0.02), and T1 volume relative to whole brain (p=0.03) as significant predictors of OS outcome (short versus long). Combining T2 mean intensity, T2 image skew, T1 segment kurtosis and patient gender resulted in OS outcome prediction accuracy of 83.3% (sensitivity=85%, specificity=81.8%, n=42 cases).CONCLUSION: We have identified MRI volume and imaging features that significantly predict OS outcome in children diagnosed with DMG. Our findings provide a framework for incorporating MRI volumetric and machine learning analyses into the clinical setting, allowing for the customization of treatment based on tumor risk characteristics.

Risk factors for treatment-refractory and relapsed optic pathway glioma in children with neurofibromatosis type 1

BACKGROUND

Nearly one-third of patients with neurofibromatosis type 1-associated optic pathway glioma (NF1-OPG) fail frontline chemotherapy; however, little is known about risk factors for treatment failure.

METHODS

We performed a retrospective multi-institutional cohort study to identify baseline risk factors for treatment-refractory/relapsed disease and poor visual outcome in children with NF1-OPG. Refractory/relapsed NF1-OPG was defined as a requirement of two or more treatment regimens due to progression or relapse.

RESULTS

Of 111 subjects eligible for inclusion, adequate clinical and visual data were available for 103 subjects from 7 institutions. Median follow-up from the initiation of first chemotherapy regimen was 95 months (range 13-185). Eighty-four (82%) subjects received carboplatin-based frontline chemotherapy. Forty-five subjects (44%) experienced refractory/relapsed disease, with a median time of 21.5 months (range 2-149) from the initiation of first treatment to the start of second treatment. The proportion of patients without refractory/relapsed disease at 2 and 5 years was 78% and 60%. In multivariable analyses, age less than 24 months at initial treatment, posterior tumor location, and familial inheritance were associated with refractory/relapsed NF1-OPG by 2 years. Both age less than 24 months and posterior tumor location were associated with refractory/relapsed NF1-OPG by 5 years. Subjects with moderate to severe vision loss at last follow-up were more likely to have posterior tumor location, optic disc abnormalities, or abnormal visual acuity at initial treatment.

CONCLUSION

Young age, posterior tumor location, and optic disc abnormalities may identify patients with the greatest likelihood of refractory/relapsed NF1-OPG and poor visual outcomes, and who may benefit from newer treatment strategies.

OUP accepted manuscript

BACKGROUND

Selumetinib was recently approved for the treatment of inoperable symptomatic plexiform neurofibromas (PNs) in children with neurofibromatosis type 1 (NF1). This parallel phase II study determined the response rate to selumetinib in children with NF1 PN without clinically significant morbidity.

METHODS

Children with NF1 and inoperable PNs, which were not yet causing clinically significant morbidity but had the potential to cause symptoms, received selumetinib at 25 mg/m2 orally twice daily (1 cycle = 28 days). Volumetric magnetic resonance imaging analysis and outcome assessments, including patient-reported (PRO), observer-reported, and functional outcome measures were performed every 4 cycles for 2 years, with changes assessed over time. A confirmed partial response (cPR) was defined as PN volume decrease of ≥20% on at least 2 consecutive scans ≥3 months apart.

RESULTS

72% of subjects experienced a cPR on selumetinib. Participants received selumetinib for a median of 41 cycles (min 2, max 67) at data cutoff. Approximately half of the children rated having some target tumor pain at baseline, which significantly decreased by pre-cycle 13. Most objectively measured baseline functions, including visual, motor, bowel/bladder, or airway function were within normal limits and did not clinically or statistically worsen during treatment.

CONCLUSIONS

Selumetinib resulted in PN shrinkage in most subjects with NF1 PN without clinically significant morbidity. No new PN-related symptoms developed while on selumetinib, and PRO measures indicated declines in tumor-related pain intensity. This supports that selumetinib treatment may prevent the development of PN-related morbidities, though future prospective studies are needed to confirm these results.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT01362803.

Targeting integrated epigenetic and metabolic pathways in lethal childhood PFA ependymomas

Childhood posterior fossa group A ependymomas (PFAs) have limited treatment options and bear dismal prognoses compared to group B ependymomas (PFBs). PFAs overexpress the oncohistone-like protein EZHIP (enhancer of Zeste homologs inhibitory protein), causing global reduction of repressive histone H3 lysine 27 trimethylation (H3K27me3), similar to the oncohistone H3K27M. Integrated metabolic analyses in patient-derived cells and tumors, single-cell RNA sequencing of tumors, and noninvasive metabolic imaging in patients demonstrated enhanced glycolysis and tricarboxylic acid (TCA) cycle metabolism in PFAs. Furthermore, high glycolytic gene expression in PFAs was associated with a poor outcome. PFAs demonstrated high EZHIP expression associated with poor prognosis and elevated activating mark histone H3 lysine 27 acetylation (H3K27ac). Genomic H3K27ac was enriched in PFAs at key glycolytic and TCA cycle–related genes including hexokinase-2 and pyruvate dehydrogenase. Similarly, mouse neuronal stem cells (NSCs) expressing wild-type EZHIP (EZHIP-WT) versus catalytically attenuated EZHIP-M406K demonstrated H3K27ac enrichment at hexokinase-2 and pyruvate dehydrogenase, accompanied by enhanced glycolysis and TCA cycle metabolism. AMPKα-2, a key component of the metabolic regulator AMP-activated protein kinase (AMPK), also showed H3K27ac enrichment in PFAs and EZHIP-WT NSCs. The AMPK activator metformin lowered EZHIP protein concentrations, increased H3K27me3, suppressed TCA cycle metabolism, and showed therapeutic efficacy in vitro and in vivo in patient-derived PFA xenografts in mice. Our data indicate that PFAs and EZHIP-WT–expressing NSCs are characterized by enhanced glycolysis and TCA cycle metabolism. Repurposing the antidiabetic drug metformin lowered pathogenic EZHIP, increased H3K27me3, and suppressed tumor growth, suggesting that targeting integrated metabolic/epigenetic pathways is a potential therapeutic strategy for treating childhood ependymomas.

Feasibility of magnetic resonance-guided high-intensity focused ultrasound treatment targeting distinct nodular lesions in neurofibromatosis type 1

Background

Patients with Neurofibromatosis Type 1 (NF1) and plexiform neurofibromas (PN) often have radiographically diagnosed distinct nodular lesions (DNL) which can cause pain and weakness. Magnetic resonance-guided high intensity focused ultrasound (MR-HIFU) can precisely and accurately deliver heat to thermally ablate target tissue. The aim of this study is to evaluate whole-body MRIs from patients with NF1 and DNL, applying volumetrics and a consistent treatment planning approach to determine the feasibility of MR-HIFU ablation of DNL.

Methods

A retrospective review of whole-body MRI scans from patients with NF1 and PN from CNH and NCI was performed. DNL are defined as lesions >3 cm, distinct from PN and lacking the “central dot” feature. Criteria for MR-HIFU thermal ablation include target location 1–8 cm from skin surface; >1 cm from visible plexus, spinal canal, bladder, bowel, physis; and ability to ablate ≥50% of lesion volume. Lesions in skull and vertebral body were excluded.

Results

In 26 patients, 120 DNL were identified. The majority of DNL were located in an extremity (52.5%). Other sites included head/neck (7%), chest (13%), and abdomen/pelvis (28%). The predefined HIFU ablation criteria was not met for 47.5% of lesions (n = 57). The main limitation was proximity to a vital structure or organ (79%). Complete and partial HIFU ablation was feasible for 25% and 27.5% of lesions, respectively.

Conclusion

Based on imaging review of lesion location, technical considerations and ability to target lesions, thermal ablation with MR-HIFU may be a feasible noninvasive alternative for symptom management in patients with NF1 and symptomatic DNL.

OMIC-12. PREVALENCE AND SPECTRUM OF GERMLINE PATHOGENIC VARIANTS IN CANCER PREDISPOSITION GENES ACROSS THE CHILDREN’S BRAIN TUMOR NETWORK (CBTN)

Germline variants are known to contribute to the pathogenesis of specific central nervous system (CNS) tumor subtypes; however, a large pan-pediatric brain and nervous system cancer germline susceptibility study has not been performed. To define the prevalence and spectrum of pathogenic variants in known cancer predisposition genes (CPGs; n=200), we analyzed whole genome sequencing (WGS) data from 880 pediatric subjects across 19 different cancer types in the Children’s Brain Tumor Network (CTBN). Data were aligned using BWA. Variants were called using GATK and annotated with SnpEff and ANNOVAR. After quality control, variants with a minor allele frequency (MAF) < 0.1% in Gnomad 2.11 or ExAC were retained. Pathogenicity was assessed with American College of Medical Genetics (ACMG) guidelines using a lab-developed modification of ClinVar and InterVar. Automated pathogenic/likely pathogenic (P-LP) calls were manually reviewed by two cancer predisposition clinicians and a bioinformatician. Frequency of P-LP variants was assessed and gene burden testing was performed against Gnomad3.1 (without cancer samples) using Fisher’s exact test with Bonferroni adjustment. We observed 214 P-LP variants involving 190 unique individuals (21.6% of cohort). As expected, the most frequent variants were observed in NF1, NF2, and TP53(n=40 variants in 21% of individuals). ATM, TSC2 and CHEK2 variants (n=23) were observed in another 12% of individuals. An increased burden of P-LP variants was observed for 5 of these 6 genes (p = 1.7x10^-25 to 1.4x10^-2, CHEK2 p=5.5x10^-2). We also identified 5 variants in BRCA2 (3 in high-grade glioma), 7 in REQC helicases (BLM, WRN, REQL4), and 16 variants in Fanconi anemia genes. Overall, cases harbored increased burden in P-LP variants in CPG genes (p=8.8x^-18) and the subset of DNA repair genes (p=4.7x10^-4). In conclusion we confirmed the association of variants in established predisposition genes while potentially identifying novel variants and genes associated in CNS tumors.

Survival Benefit for Individuals With Constitutional Mismatch Repair Deficiency Undergoing Surveillance

Constitutional mismatch repair deficiency syndrome (CMMRD) is a lethal cancer predisposition syndrome characterized by early-onset synchronous and metachronous multiorgan tumors. We designed a surveillance protocol for early tumor detection in these individuals.

LGG-55. OUTCOME OF BRAF V600E PEDIATRIC GLIOMAS TREATED WITH TARGETED BRAF INHIBITION

Children with pediatric gliomas harboring BRAF V600E mutation have a poor outcome with current chemoradiation strategies. Our aim was to study the role of targeted BRAF inhibition in these tumors. We collected clinical, imaging, molecular and outcome information from BRAF V600E glioma patients treated with BRAFi across 29 centers from multiple countries. Sixty-seven patients were treated with BRAFi (56 pediatric low grade gliomas, PLGG and 11 pediatric high grade gliomas, PHGG) for up to 5.6 years. Objective responses were observed in 80% of PLGGs compared to 28% with conventional chemotherapy (p<0.001). These responses were rapid (median, 4 months), and sustained in 86% of tumors up to 5 years while on therapy. PLGG which discontinued BRAFi, 76.5% (13/17) progressed rapidly after discontinuation (median 2.3 months). However, upon re-challenge with BRAFi therapy, 90% achieved an objective response. Poor prognostic factors to conventional therapies, such as concomitant homozygous deletion of CDKN2A, were not associated with a lack of response to BRAFi. In contrast, only 36% of PHGG responded to BRAFi with all but one tumor progressing within 18 months. In PLGG, responses translated to 3-year progression-free survival of 49.6% (95%CI, 35.3% to 69.5%) vs 29.8% (95% CI, 20% to 44.4%) for BRAFi vs chemotherapy respectively (p=0.02). The use of BRAFi results in robust and durable responses while on therapy in BRAF V600E PLGG. Prospective studies are required to determine long-term survival and functional outcomes with BRAFi therapy in childhood gliomas.

NFB-09. ENROLLMENT AND CLINICAL CHARACTERISTICS OF NEWLY DIAGNOSED, NEUROFIBROMATOSIS TYPE 1 ASSOCIATED OPTIC PATHWAY GLIOMA (NF1-OPG): PRELIMINARY RESULTS FROM AN INTERNATIONAL MULTI-CENTER NATURAL HISTORY STUDY

INTRODUCTION

Because treatment and clinical management decisions for children with NF1-OPG remain challenging, we sought to establish evidence-based guidelines. We prospectively enrolled children with newly-diagnosed NF1-OPGs, and gathered standardized clinical neuro-oncology and ophthalmology assessments.

METHODS

Only children with NF1 and newly diagnosed OPGs, confirmed by central review, were eligible. Indications for obtaining the initial MRI, as well as factors associated with the decision to treat with chemotherapy or observe without treatment, were obtained. Quantitative visual acuity (VA), other ophthalmic features, and imaging were captured at standard time points. Goal enrollment is 250 subjects.

RESULTS

One-hundred thirty-three children (52% female) from 20 institutions met inclusion criteria, and were included in this preliminary analysis. Eighty-six percent of subjects were able to perform quantitative VA testing at enrollment. The most common reasons for the diagnostic MRI included screening related to NF1 diagnosis (36.8%), ophthalmologic concerns (29.3%), and non-ophthalmologic concerns (24.8%), such as headache. To date, twenty subjects have initiated treatment with chemotherapy, twelve (9%) at the time of the initial OPG diagnosis. Median age at OPG diagnosis was 3.1 years. Age and sex distribution were similar in subjects immediately entering the observation and treatment arms (median age 3.0 versus 3.5 years, respectively).

CONCLUSION

Most children with NF1-OPGs are observed at time of their initial OPG diagnosis, rather than treated. Importantly, a large proportion of children are able to complete quantitative VA testing at enrollment. Once enrollment is complete, these data will help to establish evidence-based guidelines for clinical management of NF1-OPGs.

PATH-14. GENETIC SUSCEPTIBILITY AND OUTCOMES OF PEDIATRIC, ADOLESCENT AND YOUNG ADULT IDH-MUTANT ASTROCYTOMAS

INTRODUCTION

Previously thought to be rare, recent case series have shown that IDH mutations in young patients are more common than previously described. In this study, we analyzed IDH-mutant tumors to determine clinical significance of these mutations in children, adolescents and young adults.

METHODS

Through this multi-institution study (10 institutions), we collected 64 IDH1/2-mutant infiltrating astrocytoma specimens from 58 patients aged 4–26 (M:F, 0.4:0.6). Specimens included 46 low-grade (LGG) and 18 high-grade (HGG) astrocytomas. Tumor sequencing data (n=45), germline sequencing data (n=37) and outcome data (n=40) was analyzed.

RESULTS

Similar to adults, most sequenced tumors had a co-mutation in the TP53 gene, while ATRX mutations were less common and primarily seen in HGGs. Approximately 60% (n=21) of patients with germline data available had a mutation in a cancer predisposition gene. Mismatch repair (MMR) mutations were most common (n=12; MSH6 n=9), followed by TP53mutations (n=7). All patients with MMR gene mutations had HGGs and poor progression free (PFS=10% at 2 years, mean TTP=9 months) and overall (OS &lt;30% at 2 years) survival. Despite an OS of 90% at 5 years, many LGG patients had tumor progression/recurrence requiring additional treatment (PFS= 80% at 2 yrs, 40% at 5 yrs, mean TTP=3.5 years). Four LGG tumors (2 with TP53+ATRXloss, 2 with TP53 loss+1p19q co-deletion) underwent malignant transformation.

CONCLUSION

IDH-mutant tumors in pediatric patients are strongly associated with cancer predisposition and increased risk for progression/recurrence or malignant transformation. Routine screening for IDH1/2 mutations in children with grade 2–4 astrocytomas could greatly impact patient management.

Clinicopathologic Features of Diencephalic Neuronal and Glioneuronal Tumors

Neuronal/mixed glioneuronal tumors are central nervous system neoplasms composed of neoplastic neuronal cell components or a mixture of glial and neuronal elements. They occur in cerebral hemispheres, posterior fossa, and spinal cord. Compared with other tumors at these locations, diencephalic neuronal/glioneuronal tumors are very rare and therefore not well characterized. We hereby performed clinicopathologic evaluation on 10 neuronal/glioneuronal tumors arising from the diencephalic region. Morphologically, these tumors resemble their histologic counterparts in other locations, except that lymphocytic infiltrates and microcalcifications are more common than Rosenthal fibers or eosinophilic granular bodies. The BRAFV600 mutation rate is 75%. Given the high percentage of samples being small biopsy specimens, the subtle histologic features and molecular findings greatly aided in establishing the pathologic diagnosis in several cases. At a median follow-up of 42 months, 71% of the tumors demonstrated radiological recurrence or progression, with median progression-free survival of 18 months. Recurrence/progression is observed in tumors across different histologic subtypes, necessitating additional therapies in 56% of the cases. Despite their bland histology, diencephalic neuronal/glioneuronal tumors are not clinically indolent. Their frequent recurrences warrant a close follow-up, and the prevalent BRAF mutation makes MAPK pathway inhibition a plausible treatment option when conventional therapies fail.

Harmonization of postmortem donations for pediatric brain tumors and molecular characterization of diffuse midline gliomas

Children diagnosed with brain tumors have the lowest overall survival of all pediatric cancers. Recent molecular studies have resulted in the discovery of recurrent driver mutations in many pediatric brain tumors. However, despite these molecular advances, the clinical outcomes of high grade tumors, including H3K27M diffuse midline glioma (H3K27M DMG), remain poor. To address the paucity of tissue for biological studies, we have established a comprehensive protocol for the coordination and processing of donated specimens at postmortem. Since 2010, 60 postmortem pediatric brain tumor donations from 26 institutions were coordinated and collected. Patient derived xenograft models and cell cultures were successfully created (76% and 44% of attempts respectively), irrespective of postmortem processing time. Histological analysis of mid-sagittal whole brain sections revealed evidence of treatment response, immune cell infiltration and the migratory path of infiltrating H3K27M DMG cells into other midline structures and cerebral lobes. Sequencing of primary and disseminated tumors confirmed the presence of oncogenic driver mutations and their obligate partners. Our findings highlight the importance of postmortem tissue donations as an invaluable resource to accelerate research, potentially leading to improved outcomes for children with aggressive brain tumors.

A Pediatric Case of Transformed Mycosis Fungoides in a BRCA2 Positive Patient

Cutaneous T-cell lymphomas are very rare in children. Although mycosis fungoides is the most common of these rare cutaneous T-cell lymphomas in children, transformation to an aggressive malignancy remains extremely uncommon, and there are no clear guidelines for clinical management in the pediatric population. In addition, the increased usage of next-generation sequencing for pediatric patients with unusual malignancies may result in the discovery of pathogenic germline mutations, though the association between these mutations and the patient's cancer is not always clear. We present here a unique pediatric case of transformed mycosis fungoides in a patient with BRCA2 mutation.

Outcomes of BRAF V600E Pediatric Gliomas Treated With Targeted BRAF Inhibition

PURPOSE

Children with pediatric gliomas harboring a BRAF V600E mutation have poor outcomes with current chemoradiotherapy strategies. Our aim was to study the role of targeted BRAF inhibition in these tumors.

PATIENTS AND METHODS

We collected clinical, imaging, molecular, and outcome information from patients with BRAF V600E-mutated glioma treated with BRAF inhibition across 29 centers from multiple countries.

RESULTS

Sixty-seven patients were treated with BRAF inhibition (pediatric low-grade gliomas [PLGGs], n = 56; pediatric high-grade gliomas [PHGGs], n = 11) for up to 5.6 years. Objective responses were observed in 80% of PLGGs, compared with 28% observed with conventional chemotherapy (P < .001). These responses were rapid (median, 4 months) and sustained in 86% of tumors up to 5 years while receiving therapy. After discontinuation of BRAF inhibition, 76.5% (13 of 17) of patients with PLGG experienced rapid progression (median, 2.3 months). However, upon rechallenge with BRAF inhibition, 90% achieved an objective response. Poor prognostic factors in conventional therapies, such as concomitant homozygous deletion of CDKN2A, were not associated with lack of response to BRAF inhibition. In contrast, only 36% of those with PHGG responded to BRAF inhibition, with all but one tumor progressing within 18 months. In PLGG, responses translated to 3-year progression-free survival of 49.6% (95% CI, 35.3% to 69.5%) versus 29.8% (95% CI, 20% to 44.4%) for BRAF inhibition versus chemotherapy, respectively (P = .02).

CONCLUSION

Use of BRAF inhibition results in robust and durable responses in BRAF V600E-mutated PLGG. Prospective studies are required to determine long-term survival and functional outcomes with BRAF inhibitor therapy in childhood gliomas.

Selumetinib in Children with Inoperable Plexiform Neurofibromas

BACKGROUND

No approved therapies exist for inoperable plexiform neurofibromas in patients with neurofibromatosis type 1.

METHODS

We conducted an open-label, phase 2 trial of selumetinib to determine the objective response rate among patients with plexiform neurofibromas and to assess clinical benefit. Children with neurofibromatosis type 1 and symptomatic inoperable plexiform neurofibromas received oral selumetinib twice daily at a dose of 25 mg per square meter of body-surface area on a continuous dosing schedule (28-day cycles). Volumetric magnetic resonance imaging and clinical outcome assessments (pain, quality of life, disfigurement, and function) were performed at least every four cycles. Children rated tumor pain intensity on a scale from 0 (no pain) to 10 (worst pain imaginable).

RESULTS

A total of 50 children (median age, 10.2 years; range, 3.5 to 17.4) were enrolled from August 2015 through August 2016. The most frequent neurofibroma-related symptoms were disfigurement (44 patients), motor dysfunction (33), and pain (26). A total of 35 patients (70%) had a confirmed partial response as of March 29, 2019, and 28 of these patients had a durable response (lasting ≥1 year). After 1 year of treatment, the mean decrease in child-reported tumor pain-intensity scores was 2 points, considered a clinically meaningful improvement. In addition, clinically meaningful improvements were seen in child-reported and parent-reported interference of pain in daily functioning (38% and 50%, respectively) and overall health-related quality of life (48% and 58%, respectively) as well as in functional outcomes of strength (56% of patients) and range of motion (38% of patients). Five patients discontinued treatment because of toxic effects possibly related to selumetinib, and 6 patients had disease progression. The most frequent toxic effects were nausea, vomiting, or diarrhea; an asymptomatic increase in the creatine phosphokinase level; acneiform rash; and paronychia.

CONCLUSIONS

In this phase 2 trial, most children with neurofibromatosis type 1 and inoperable plexiform neurofibromas had durable tumor shrinkage and clinical benefit from selumetinib. (Funded by the Intramural Research Program of the National Institutes of Health and others; ClinicalTrials.gov number, NCT01362803.).

Molecularly Targeted Agents in the Therapy of Pediatric Brain Tumors

Pediatric brain tumors are the leading cause of cancer-related death in children. Recent advances in sequencing techniques, and collaborative efforts to encode the mutational landscape of various tumor subtypes, have resulted in the identification of recurrent mutations that may present as actionable targets in these tumors. A number of molecularly targeted agents are approved or in development for the treatment of various tumor types in adult patients. Similarly, these agents are increasingly being incorporated into pediatric clinical trials, allowing for a targeted approach to treatment. However, due to the genetic heterogeneity of these tumors, focused clinical trials in pediatric patients are challenging and regulatory hurdles may delay access to therapeutic compounds that are in regular use in adult patients. The tumor site-agnostic clinical development of TRK inhibitors for pediatric solid tumors is a current example of how the combination of genetic testing and innovative clinical trial design can accelerate the clinical development of targeted agents for pediatric patients.

Somatic Mosaicism of IDH1 R132H Predisposes to Anaplastic Astrocytoma: A Case of Two Siblings

Anaplastic astrocytomas are aggressive glial cancers that present poor prognosis and high recurrence. Heterozygous IDH1 R132H mutations are common in adolescent and young adult anaplastic astrocytomas. In a majority of cases, the IDH1 R132H mutation is unique to the tumor, although rare cases of anaplastic astrocytoma have been described in patients with mosaic IDH1 mutations (Ollier disease or Maffucci syndrome). Here, we present two siblings with IDH1 R132H mutant high grade astrocytomas diagnosed at 14 and 26 years of age. Analysis of IDH^R132H mutations in the siblings' tumors and non-neoplastic tissues, including healthy regions of the brain, cheek cells, and primary teeth indicate mosaicism of IDH^R132H. Whole exome sequencing of the tumor tissue did not reveal any other common mutations between the two siblings. This study demonstrates the first example of IDH1 R132H mosaicism, acquired during early development, that provides an alternative mechanism of cancer predisposition.

PDCT-08. SUPERIOR OUTCOME FOR BRAF V600E PEDIATRIC GLIOMAS TREATED WITH TARGETED BRAF INHIBITION

BACKGROUND

Children with pediatric low grade glioma’s (PLGG) harboring BRAF V600E mutation have poor outcome due to relative resistance to chemo-radiation and higher risk of malignant transformation. However, the role of targeted BRAF inhibition in these tumors is poorly defined.

METHODS

We assembled an international cohort of children with BRAF V600E mutant gliomas treated with BRAF inhibition, from 29 centers participating in the PLGG taskforce, and collected response, survival and molecular parameters.

RESULTS

Sixty-seven patients were treated with BRAFi (56 PLGG and 11 high grade gliomas) for a median time of 17.4 months (6 – 61 months), with 13 PLGG treated upfront. Objective responses was observed in 80% of PLGG patients compared to 28% with conventional chemotherapy (p< 0.001). Rapid responses were observed in most PLGG patients (median of 4 months), sustained in 86% of tumors up to 5 years while on therapy. In contrast, only 36% of PHGG responded to BRAFi with all but one tumor progressing within 18 months. Seventeen patients with PLGG discontinued BRAFi and 76.5% (13/17) progressed rapidly after discontinuation (median time 2.3 months). However, upon re-challenge with BRAFi therapy, 90% achieved an objective response. Poor prognostic factors to conventional therapies such as concomitant homozygous deletion of CDKN2A or H3K27M mutation were not associated with lack of response to BRAFi. Overall these responses translated to 2-year progression-free survival of 0.636 (95%CI 0.505–0.802) and 0.43 (95% CI 0.32–0.57) for BRAFi and chemotherapy treated BRAF V600E PLGG respectively (p=0.003).

CONCLUSION

The use of BRAFi results in objective, robust and durable responses in BRAF V600E PLGG and is associated with favorable survival. Larger prospective studies will be required to determine appropriate regiments, and long-term functional outcomes with BRAFi therapy in childhood gliomas.

Gliomas in the context of Li-Fraumeni syndrome: An international cohort

1517

Background: Li-Fraumeni syndrome (LFS) is a cancer predisposition syndrome associated with germline mutation in the TP53 tumor suppressor gene. As a result of increased awareness and surveillance imaging, more asymptomatic low-grade brain lesions are being identified, raising important questions regarding the management of those patients. Sporadic low-grade gliomas (LGG) in the pediatric age rarely transform to malignant lesions, whereas the prognosis of high-grade gliomas (HGG) is grim in all age groups. Although HGG is a hallmark of LFS, little is known of the natural history of these lesions in this syndrome. Methods: For this multi-institutional retrospective study, anonymized clinicopathologic data from TP53 mutation carriers with gliomas were collected and analysed. Results: Our cohort included 61 patients, of whom 71% (n = 45) were children or young adults (age < 25 years). 39% of patients with known family history of cancer had a close relative with a brain tumor. Of 31 patients with low grade lesions at presentation, 83% (n = 26) were identified through surveillance. Five-year progression free survival (PFS) for these patients was 48%, though two patients progressed later. Furthermore, at 5 years 25% of these patients had biopsy proven malignant transformation to HGG. This “transformation free survival” rate did not plateau, as at 7 years 56% of patients transformed. When considering death from a brain tumor, the 5- and 10- year overall survival (OS) for the LGG group was 100% and 83%, respectively. Additional 3 patients succumbed to other LFS related malignancies. For the HGG group, consisting of 30 patients, the 5 year OS was 35% (median follow-up 19.5 months), comparing favorably with the sporadic HGG population as reported in the literature. Almost all of these patients presented with clinical symptoms. Notably, 12 (40%) of them had a prior malignancy. Conclusions: Our analysis suggests that the risk of transformation of LGG in the setting of LFS is high and warrants ongoing surveillance. Interestingly, there are a considerable number of long- term survivors in our HGG group, although the median follow up is still short. Further study to examine potential genotype- phenotype correlations in germline TP53 mutation carriers will inform strategies to identify those patients at highest risk of glioma progression.

Liquid biopsy for pediatric central nervous system tumors

Central nervous system (CNS) tumors are the most common solid tumors in children, and the leading cause of cancer-related death. Over the past decade, molecular profiling has been incorporated into treatment for pediatric CNS tumors, allowing for a more personalized approach to therapy. Through the identification of tumor-specific changes, it is now possible to diagnose, assign a prognostic subgroup, and develop targeted chemotherapeutic treatment plans for many cancer types. The successful incorporation of informative liquid biopsies, where the liquid biome is interrogated for tumor-associated molecular clues, has the potential to greatly complement the precision-based approach to treatment, and ultimately, to improve clinical outcomes for children with CNS tumors. In this article, the current application of liquid biopsy in cancer therapy will be reviewed, as will its potential for the diagnosis and therapeutic monitoring of pediatric CNS tumors.

Pediatric low-grade gliomas: next biologically driven steps

Despite the fact that they are not typically life-threatening, low-grade gliomas (LGGs) remain a significant clinical challenge in pediatric neuro-oncology due to comorbidities associated with these tumors and/or their treatments, and their propensity to multiply recurs. LGGs, in total the most common brain tumors arising in childhood, can often become a chronic problem requiring decades of management. The Second International Consensus Conference on Pediatric Low-Grade Gliomas held in Padua, Italy in 2016 was convened in an attempt to advance the pace of translating biological discoveries on LGGs into meaningful clinical benefit. Topics discussed included: the implications of our growing biological understanding of the genomics underlying these tumors; the assessment of the model systems available; the implications of the molecular and histopathologic differences between adult and pediatric diffuse gliomas; and steps needed to expedite targeted therapy into late-stage clinical trials for newly diagnosed cases. Methods for the diagnostic assessment of alterations in the Ras/mitogen-activated protein kinase pathway, typical for these tumors, were also considered. While the overall tone was positive, with a consensus that progress is being and will continue to be made, the scale of the challenge presented by this complex group of tumors was also acknowledged. The conclusions and recommendations of the meeting panel are provided here as an outline of current thinking and a basis for further discussion.

Blood-brain barrier-adapted precision medicine therapy for pediatric brain tumors

Targeted chemotherapeutics provide a promising new treatment option in neuro-oncology. The ability of these compounds to penetrate the blood-brain barrier is crucial for their successful incorporation into patient care. "CNS Targeted Agent Prediction" (CNS-TAP) is a multi-institutional and multidisciplinary translational program established at the University of Michigan for evaluating the central nervous system (CNS) activity of targeted therapies in neuro-oncology. In this report, we present the methodology of CNS-TAP in a series of pediatric and adolescent patients with high-risk brain tumors, for which molecular profiling (academic and commercial) was sought and targeted agents were incorporated. Four of five of the patients had potential clinical benefit (partial response or stable disease greater than 6 months on therapy). We further describe the specific drug properties of each agent chosen and discuss characteristics relevant in their evaluation for therapeutic suitability. Finally, we summarize both tumor and drug characteristics that impact the ability to successfully incorporate targeted therapies into CNS malignancy management.