Alterations in ALK/ROS1/NTRK/MET drive a group of infantile hemispheric gliomas

Novel fusion sarcomas including targetable NTRK and ALK

BACKGROUND

Challenging emerging entities with distinctive molecular signatures may benefit from algorithms for diagnostic work-up.

METHODS

Fusion sarcomas (2020-2021, during pandemic) were diagnosed by clinicoradiology, morphology, phenotype, and next-generation sequencing (NGS).

RESULTS

Six fusion sarcomas in two males and four females involved the chest-wall, neck, or extremities; ages ranged 2-73, median 18 years. Sizes ranged 5.3-25.0, median 9.1 cm. These include high grade 1) TPR-NTRK1 of proximal femur with a larger rounded soft tissue mass, previously considered osteosarcoma yet without convincing tumor matrix. A pathologic fracture necessitated emergency hemipelvectomy (NED) and 2) novel KANK1-NTRK2 sarcoma of bone and soft tissue with spindled pleomorphic to epithelioid features (AWD metastases). 3) Novel ERC1-ALK unaligned fusion, a low grade infiltrative deep soft tissue hand sarcoma with prominent-vascularity, myopericytoid/lipofibromatosis-like ovoid cells, and collagenized stroma, was successfully treated with ALK-inhibitor (Crizotinib), avoiding amputation. These NTRK and ALK tumors variably express S100 and CD34 and were negative for SOX10. 4) and 5) CIC-DUX4 round cell tumors (rapid metastases/demise), one with COVID superinfection, were previously treated as Ewing sarcoma. These demonstrated mild pleomorphism and necrosis, variable myxoid change and CD99 reactivity, and a distinctive dot-like-Golgi WT1 immunostaining pattern. 6) A chest wall/thoracic round cell sarcoma, focal CD34/ keratins/CK7, revealed nuclear-STAT6, STAT6-NAB2 by NGS, confirming malignant solitary fibrous tumor, intermediate-risk-stratification (AWD metastases).

CONCLUSIONS

Recent fusion sarcomas include new KANK1-NTRK2 and ERC1-ALK, the latter successfully treated by targeted-therapy. ALK/NTRK fusion partners TPR and KANK1 suggest unusual high-grade morphology/behavior. Clinicoradiologic, morphologic, and phenotypic algorithms can prompt molecular-targeted immunostains or NGS for final classification and promising inhibitor therapy.

Classification and Treatment of Pediatric Gliomas in the Molecular Era

The overall survival of pediatric gliomas varies over a wide spectrum depending on the tumor grade. Low-grade gliomas have an excellent long-term survival, with a possible burden of surgery, irradiation, and chemotherapy; in contrast, high-grade gliomas generally have a short-term, devastating lethal outcome. Recent advances in understanding their molecular background will transform the classification and therapeutic approaches of pediatric gliomas. Molecularly targeted treatments may acquire a leading role in the primary treatment of low-grade gliomas and may provide alternative therapeutic strategies for high-grade glioma cases in the attempt to avoid the highly unsuccessful conventional therapeutic approaches. This review aims to overview this progress.

The 2021 WHO Classification of Tumors of the Central Nervous System: a summary

The fifth edition of the WHO Classification of Tumors of the Central Nervous System (CNS), published in 2021, is the sixth version of the international standard for the classification of brain and spinal cord tumors. Building on the 2016 updated fourth edition and the work of the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy, the 2021 fifth edition introduces major changes that advance the role of molecular diagnostics in CNS tumor classification. At the same time, it remains wedded to other established approaches to tumor diagnosis such as histology and immunohistochemistry. In doing so, the fifth edition establishes some different approaches to both CNS tumor nomenclature and grading and it emphasizes the importance of integrated diagnoses and layered reports. New tumor types and subtypes are introduced, some based on novel diagnostic technologies such as DNA methylome profiling. The present review summarizes the major general changes in the 2021 fifth edition classification and the specific changes in each taxonomic category. It is hoped that this summary provides an overview to facilitate more in-depth exploration of the entire fifth edition of the WHO Classification of Tumors of the Central Nervous System.

Molecular diagnostics helps to identify distinct subgroups of spinal astrocytomas

Primary spinal cord astrocytomas are rare, hence few data exist about the prognostic significance of molecular markers. Here we analyze a panel of molecular alterations in association with the clinical course. Histology and genome sequencing was performed in 26 spinal astrocytomas operated upon between 2000 and 2020. Next-generation DNA/RNA sequencing (NGS) and methylome analysis were performed to determine molecular alterations. Histology and NGS allowed the distinction of 5 tumor subgroups: glioblastoma IDH wildtype (GBM); diffuse midline glioma H3 K27M mutated (DMG-H3); high-grade astrocytoma with piloid features (HAP); diffuse astrocytoma IDH mutated (DA), diffuse leptomeningeal glioneural tumors (DGLN) and pilocytic astrocytoma (PA). Within all tumor entities GBM (median OS: 5.5 months), DMG-H3 (median OS: 13 months) and HAP (median OS: 8 months) showed a fatal prognosis. DMG-H3 tend to emerge in adolescence whereas GBM and HAP develop in the elderly. HAP are characterized by CDKN2A/B deletion and ATRX mutation. 50% of PA tumors carried a mutation in the PIK3CA gene which is seemingly associated with better outcome (median OS: PIK3CA mutated 107.5 vs 45.5 months in wildtype PA). This exploratory molecular profiling of spinal cord astrocytomas allows to identify distinct subgroups by combining molecular markers and histomorphology. DMG-H3 tend to develop in adolescence with a similar dismal prognosis like GBM and HAP in the elderly. We here describe spinal HAP with a distinct molecular profile for the first time.

Precision medicine in pediatric solid cancers

Despite huge advances in the diagnosis and treatment of pediatric cancers over the past several decades, it remains one of the leading causes of death during childhood in developed countries. The development of new targeted treatments for these diseases has been hampered by two major factors. First, the extremely heterogeneous nature of the types of tumors encountered in this age group, and their fundamental differences from common adult carcinomas, has made it hard to truly get a handle on the complexities of the underlying biology driving tumor growth. Second, a reluctance of the pharmaceutical industry to develop products or trials for this population due to the relatively small size of the 'market', and a too-easy mechanism of obtaining waivers for pediatric development of adult oncology drugs based on disease type rather than mechanism of action, led to significant difficulties in getting access to new drugs. Thankfully, the field has now started to change, both scientifically and from a regulatory perspective, in order to address some of these challenges. In this review, we will examine some of the recent insights into molecular features which make pediatric tumors so unique and how these might represent therapeutic targets; highlight ongoing international initiatives for providing comprehensive, personalized genomic profiling of childhood tumors in a clinically-relevant timeframe, and look briefly at where the field of pediatric precision oncology may be heading in future.

Fusing the Genetic Landscape of Infantile High-Grade Gliomas

In this issue of Cancer Discovery, Clarke and colleagues define the genetic landscape of infantile cerebral high-grade gliomas, which frequently contain alterations in the MAPK pathway, as well as recurrent gene fusions in receptor tyrosine kinases (ALK, ROS1, MET) and neurotrophic receptor kinases (NTRK1-3). Combining their multi-omic profiling data with functional preclinical and clinical studies, this large multi-institutional study provides strong rationale for future classification and molecular subtype-specific therapeutic management of infantile high-grade glioma.See related article by Clarke et al., p. 942.

Association of HMGA2 Polymorphisms with Glioma Susceptibility in Chinese Children

Background

Glioma is a malignant central nervous system tumor in children, with poor outcomes and prognosis. HMGA2 is a proto-oncogene with increased expression in various malignancies.

Methods

We explored the association of HMGA2 polymorphisms with glioma susceptibility in Chinese children using a case-control study (191 cases, 248 controls). HMGA2 single nucleotide polymorphisms (rs6581658 A>G; rs8756 A>C; rs968697 T>C) were genotyped using PCR-based TaqMan.

Results

Increased glioma susceptibility was associated with rs6581658 A>G; AG (adjusted odds ratio (OR) = 1.71, 95% confidence interval (CI) = 1.13–2.58, P = 0.010) or GG (adjusted OR = 3.12, 95% CI = 1.26–7.74, P = 0.014) genotype carriers had significantly raised glioma risk compared with AA genotype carriers. The rs6581658 AG/GG (adjusted OR = 1.85, 95% CI = 1.25–2.73, P = 0.002) and AA/GG (adjusted OR = 2.58, 95% CI = 1.05–6.33, P = 0.038) genotypes were associated with an increased risk of glioma relative to the AA genotype. Subjects with 2–3 risk genotypes had a significantly elevated risk (adjusted OR = 1.93, 95% CI = 1.31–2.84, P = 0.001) relative to those with 0–1 risk genotype.

Conclusion

HMGA2 rs6581658 A>G is associated with glioma susceptibility in Chinese children.

Radiation therapy for infants with cancer

The clinical outcomes for infants with malignant tumors are often worse than older children due to a combination of more biologically aggressive disease in some cases, and increased toxicity-or deintensification of therapies due to concern for toxicity-in others. Especially in infants and very young children, finding the appropriate balance between maximizing treatment efficacy while minimizing toxicity-in particular late side effects-is crucial. We review here the management of malignant tumors in infants and very young children, focusing on central nervous system (CNS) malignancies and rhabdomyosarcoma.

Clinical impact of combined epigenetic and molecular analysis of pediatric low-grade gliomas

BACKGROUND

Both genetic and methylation analysis have been shown to provide insight into the diagnosis and prognosis of many brain tumors. However, the implication of methylation profiling and its interaction with genetic alterations in pediatric low-grade gliomas (PLGGs) are unclear.

METHODS

We performed a comprehensive analysis of PLGG with long-term clinical follow-up. In total 152 PLGGs were analyzed from a range of pathological subtypes, including 40 gangliogliomas. Complete molecular analysis was compared with genome-wide methylation data and outcome in all patients. For further analysis of specific PLGG groups, including BRAF p.V600E mutant gliomas, we compiled an additional cohort of clinically and genetically defined tumors from 3 large centers.

RESULTS

Unsupervised hierarchical clustering revealed 5 novel subgroups of PLGG. These were dominated by nonneoplastic factors such as tumor location and lymphocytic infiltration. Midline PLGG clustered together while deep hemispheric lesions differed from lesions in the periphery. Mutations were distributed throughout these location-driven clusters of PLGG. A novel methylation cluster suggesting high lymphocyte infiltration was confirmed pathologically and exhibited worse progression-free survival compared with PLGG harboring similar molecular alterations (P = 0.008; multivariate analysis: P = 0.035). Although the current methylation classifier revealed low confidence in 44% of cases and failed to add information in most PLGG, it was helpful in reclassifying rare cases. The addition of histopathological and molecular information to specific methylation subgroups such as pleomorphic xanthoastrocytoma-like tumors could stratify these tumors into low and high risk (P = 0.0014).

CONCLUSION

The PLGG methylome is affected by multiple nonneoplastic factors. Combined molecular and pathological analysis is key to provide additional information when methylation classification is used for PLGG in the clinical setting.

Interstitial Deletions Generating Fusion Genes

A fusion gene is the physical juxtaposition of two different genes resulting in a structure consisting of the head of one gene and the tail of the other. Gene fusion is often a primary neoplasia-inducing event in leukemias, lymphomas, solid malignancies as well as benign tumors. Knowledge about fusion genes is crucial not only for our understanding of tumorigenesis, but also for the diagnosis, prognostication, and treatment of cancer. Balanced chromosomal rearrangements, in particular translocations and inversions, are the most frequent genetic events leading to the generation of fusion genes. In the present review, we summarize the existing knowledge on chromosome deletions as a mechanism for fusion gene formation. Such deletions are mostly submicroscopic and, hence, not detected by cytogenetic analyses but by array comparative genome hybridization (aCGH) and/or high throughput sequencing (HTS). They are found across the genome in a variety of neoplasias. As tumors are increasingly analyzed using aCGH and HTS, it is likely that more interstitial deletions giving rise to fusion genes will be found, significantly impacting our understanding and treatment of cancer.

Applicability of spatial transcriptional profiling to cancer research

Spatial transcriptional profiling provides gene expression information within the important anatomical context of tissue architecture. This approach is well suited to characterizing solid tumors, which develop within a complex landscape of malignant cells, immune cells, and stroma. In a single assay, spatial transcriptional profiling can interrogate the role of spatial relationships among these cell populations as well as reveal spatial patterns of relevant oncogenic genetic events. The broad utility of this approach is reflected in the array of strategies that have been developed for its implementation as well as in the recent commercial development of several profiling platforms. The flexibility to apply these technologies to both hypothesis-driven and discovery-driven studies allows widespread applicability in research settings. This review discusses available technologies for spatial transcriptional profiling and several applications for their use in cancer research.

Tumor immune landscape of paediatric high-grade gliomas

Over the last decade, remarkable progress has been made towards elucidating the origin and genomic landscape of childhood high-grade brain tumors. It has become evident that pediatric high-grade gliomas (pHGGs) differ from adult HGGs with respect to multiple defining aspects including: DNA copy number, gene expression profiles, tumor locations within the central nervous system, and genetic alterations such as somatic histone mutations. Despite these advances, clinical trials for children with glioma have historically been based on ineffective adult regimens that fail to take into consideration the fundamental biological differences between the two. Additionally, although our knowledge of the intrinsic cellular mechanisms driving tumor progression has considerably expanded, little is known concerning the dynamic tumor immune microenvironment (TIME) in pHGGs. In this review, we explore the genetic and epigenetic landscape of pHGGs and how this drives the creation of specific tumor sub-groups with meaningful survival outcomes. Further, we provide a comprehensive analysis of the pHGG TIME and discuss emerging therapeutic efforts aimed at exploiting the immune functions of these tumors.

Discovery of a rare GKAP1-NTRK2 fusion in a pediatric low-grade glioma, leading to targeted treatment with TRK-inhibitor larotrectinib

Here we report a case of an 11-year-old girl with an inoperable tumor in the optic chiasm/hypothalamus, who experienced several tumor progressions despite three lines of chemotherapy treatment. Routine clinical examination classified the tumor as a BRAF-negative pilocytic astrocytoma. Copy-number variation profiling of fresh frozen tumor material identified two duplications in 9q21.32–33 leading to breakpoints within the GKAP1 and NTRK2 genes. RT-PCR Sanger sequencing revealed a GKAP1-NTRK2 exon 10–16 in-frame fusion, generating a putative fusion protein of 658 amino acids with a retained tyrosine kinase (TK) domain. Functional analysis by transient transfection of HEK293 cells showed the GKAP1-NTRK2 fusion protein to be activated through phosphorylation of the TK domain (Tyr705). Subsequently, downstream mediators of the MAPK- and PI3K-signaling pathways were upregulated in GKAP1-NTRK2 cells compared to NTRK2 wild-type; phosphorylated (p)ERK (3.6-fold), pAKT (1.8- fold), and pS6 ribosomal protein (1.4-fold). Following these findings, the patient was enrolled in a clinical trial and treated with the specific TRK-inhibitor larotrectinib, resulting in the arrest of tumor growth. The patient’s condition is currently stable and the quality of life has improved significantly. Our findings highlight the value of comprehensive clinical molecular screening of BRAF-negative pediatric low-grade gliomas, to reveal rare fusions serving as targets for precision therapy.

An Update on Pediatric Gliomas

Pediatric gliomas are biologically distinct from adult gliomas. Although recent literature uncovered new genetic alterations, the prognostic implications of these discoveries are still unclear. This article provides an update on the histologic and molecular features with prognostic and/or therapeutic implications in pediatric gliomas.

Pediatric Gliomas: Molecular Landscape and Emerging Targets

Next-generation sequencing of pediatric gliomas has revealed the importance of molecular genetic characterization in understanding the biology underlying these tumors and a breadth of potential therapeutic targets. Promising targeted therapies include mTOR inhibitors for subependymal giant cell astrocytomas in tuberous sclerosis, BRAF and MEK inhibitors mainly for low-grade gliomas, and MEK inhibitors for NF1-deficient BRAF:KIAA fusion tumors. Challenges in developing targeted molecular therapies include significant intratumoral and intertumoral heterogeneity, highly varied mechanisms of treatment resistance and immune escape, adequacy of tumor penetrance, and sensitivity of brain to treatment-related toxicities.

Pediatric Glioma: An Update of Diagnosis, Biology, and Treatment

Simple Summary

Recent research has enhanced our understanding of the diverse biological processes that occur in pediatric gliomas; and molecular genetic analysis has become essential to diagnose and treat these conditions. Because targetable molecular aberrations can be detected in pediatric gliomas, identifying these aberrations is very important. This review provides an overview of pediatric gliomas, and describes recent developments made in strategies for their diagnosis and treatment. Additionally, it presents a current picture of pediatric gliomas in light of advances in molecular genetics, and describes the current scientific progress in gliomas’ treatment using information from recently completed and ongoing clinical trials. The era of incorporating molecular genetic analysis into clinical practice is emerging.

Abstract

Recent research has promoted elucidation of the diverse biological processes that occur in pediatric central nervous system (CNS) tumors. Molecular genetic analysis is essential not only for proper classification, but also for monitoring biological behavior and clinical management of tumors. Ever since the 2016 World Health Organization classification of CNS tumors, molecular profiling has become an indispensable step in the diagnosis, prediction of prognosis, and treatment of pediatric as well as adult CNS tumors. These molecular data are changing diagnosis, leading to new guidelines, and offering novel molecular targeted therapies. The Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy (cIMPACT-NOW) makes practical recommendations using recent advances in CNS tumor classification, particularly in molecular discernment of these neoplasms as morphology-based classification of tumors is being replaced by molecular-based classification. In this article, we summarize recent knowledge to provide an overview of pediatric gliomas, which are major pediatric CNS tumors, and describe recent developments in strategies employed for their diagnosis and treatment.

Advances in the classification and treatment of pediatric brain tumors

PURPOSE OF REVIEW

Recent genetic and molecular findings have impacted the diagnosis, prognosis, and in some instances, treatment strategies for children with pediatric central nervous system tumors. Herein, we review the most up-to-date molecular findings and how they have impacted tumor classification and clinical care.

RECENT FINDINGS

It is now recognized that aberrations of the mitogen-activated protein kinase pathway are present in the majority of pediatric low-grade glioma. Also, there has been the identification of recurrent histone H3 K27M mutations in diffuse intrinsic pontine and other midline gliomas. Medulloblastoma is now divided into four molecular subgroups with distinct characteristics and prognoses. The classification of other unique embryonal tumors is also highlighted. Finally, we present the newest classification of ependymoma; supratentorial ependymomas comprise two subtypes based on expression of the chromosome 11 Open Reading Frame 95-reticuloendotheliosis Viral Oncogene Homolog A or yes-associated protein 1 fusion, whereas posterior fossa ependymomas are divided into two distinct molecular subgroups, posterior fossa-A and posterior fossa-B.

SUMMARY

These advances in the molecular classification of pediatric central nervous system tumors have not only assisted in diagnoses, but they have led to a new era of tumor classification and prognostication. They also have served as drivers for the evaluation of new targeted therapies based upon molecular aberrations with the hope for improved survival outcomes for our patients.

How Fear of COVID-19 Can Affect Treatment Choices for Anaplastic Large Cell Lymphomas ALK+ Therapy: A Case Report

Background: The t (2; 5) chromosomal rearrangement of the ALK gene with nucleophosmin 1 gene (NPM1), resulting in an NPM1–ALK fusion, was first demonstrated in 1994 in anaplastic large cell lymphoma, (ALCL), a T-cell lymphoma responsive to cyclophosphamide, abriblastine, vincristine and prednisone in approximately 80% of cases; refractory cases usually respond favorably to brentuximab vedotin. These treatments are regarded as a bridge to allogeneic hematopoietic stem cell transplantation (allo-SCT). Nowadays, transplant procedures and the monitoring of chemotherapy patients proceed very slowly because the SARS-CoV-2 pandemic has heavily clogged the hospitals in all countries. Results: A 40-year-old Caucasian woman was first seen at our clinical center in June 2020. She had ALCL ALK+, a history of failure to two previous therapeutic lines and was in complete remission after 12 courses of brentuximab, still pending allo-SCT after two failed donor selections. Facing a new therapeutic failure, we requested and obtained authorization from the Italian drug regulatory agency to administer 250 mg of crizotinib twice a day, a drug incomprehensibly not registered for ALCL ALK +. Conclusions: The response to crizotinib was optimal since no adverse event occurred, and CT-PET scans persisted negative; this drug has proved to be a valid bridge to allo-SCT.

Retrospective Validation of a 168-Gene Expression Signature for Glioma Classification on a Single Molecule Counting Platform

Gene expression profiling has been shown to be comparable to other molecular methods for glioma classification. We sought to validate a gene-expression based glioma classification method. Formalin-fixed paraffin embedded tissue and flash frozen tissue collected at the Augusta University (AU) Pathology Department between 2000-2019 were identified and 2 mm cores were taken. The RNA was extracted from these cores after deparaffinization and bead homogenization. One hundred sixty-eight genes were evaluated in the RNA samples on the nCounter instrument. Forty-eight gliomas were classified using a supervised learning algorithm trained by using data from The Cancer Genome Atlas. An ensemble of 1000 linear support vector models classified 30 glioma samples into TP1 with classification confidence of 0.99. Glioma patients in TP1 group have a poorer survival (HR (95% CI) = 4.5 (1.3-15.4), p = 0.005) with median survival time of 12.1 months, compared to non-TP1 groups. Network analysis revealed that cell cycle genes play an important role in distinguishing TP1 from non-TP1 cases and that these genes may play an important role in glioma survival. This could be a good clinical pipeline for molecular classification of gliomas.

Nasopharyngeal papillary adenocarcinoma harboring a fusion of ROS1 with GOPC: A case report

RATIONALE

Nasopharyngeal papillary adenocarcinoma is a region-specific tumor originating from the nasopharyngeal surface epithelium. Owing to its rarity, more attention has been paid to its clinicopathologic features, while little effort has been made to study the gene abnormalities that drive this tumor. We describe the first case of nasopharyngeal papillary adenocarcinoma harboring a fusion of ROS1 with GOPC.

PATIENT CONCERNS

A 22-year-old female patient was diagnosed with nasopharyngeal papillary adenocarcinoma in our hospital, and she had right nasal obstruction for more than 6 months. Nasal endoscopy revealed a mass on the posterior roof of the nasopharynx.

DIAGNOSES

Immunohistochemical staining showed that the tumor cells were diffusely positive for transcription termination factor 1, vimentin, CK19, glypican-3, and CK7, and negative for melanocyte, CK5/6, CK20, P53, P63, S100, smooth muscle actin, p16, PAX8, and thyroglobulin. The Ki-67 index was approximately 5%; EBV-encoded small nuclear RNA was negative.

INTERVENTIONS

The tumor was completely excised on endoscopy with a negative surgical margin.

OUTCOMES

No sign of recurrence was observed during the 3-year follow-up period.

LESSONS

Owing to its rarity, pathologists should be aware of this unusual neoplasm to avoid misdiagnosis. Further studies are needed to further characterize the relationship between ROS1-GOPC fusion and the pathogenesis of this carcinoma and its response to tyrosine kinase inhibitors in relapsed cases.

Canadian Consensus for Biomarker Testing and Treatment of TRK Fusion Cancer in Pediatric Patients

Neurotrophic tyrosine receptor kinase gene fusions (NTRK) are oncogenic drivers present at a low frequency in most tumour types (<5%), and at a higher frequency (>80%) in a small number of rare tumours (e.g., infantile fibrosarcoma [IFS]) and considered mutually exclusive with other common oncogenic drivers. Health Canada recently approved two tyrosine receptor kinase (TRK) inhibitors, larotrectinib (for adults and children) and entrectinib (for adults), for the treatment of solid tumours harbouring NTRK gene fusions. In Phase I/II trials, these TRK inhibitors have demonstrated promising overall response rates and tolerability in patients with TRK fusion cancer who have exhausted other treatment options. In these studies, children appear to have similar responses and tolerability to adults. In this report, we provide a Canadian consensus on when and how to test for NTRK gene fusions and when to consider treatment with a TRK inhibitor for pediatric patients with solid tumours. We focus on three pediatric tumour types: non-rhabdomyosarcoma soft tissue sarcoma/unspecified spindle cell tumours including IFS, differentiated thyroid carcinoma, and glioma. We also propose a tumour-agnostic consensus based on the probability of the tumour harbouring an NTRK gene fusion. For children with locally advanced or metastatic TRK fusion cancer who have either failed upfront therapy or lack satisfactory treatment options, TRK inhibitor therapy should be considered.

Congenital tumors of the central nervous system: an institutional review of 64 cases with emphasis on tumors with unique histologic and molecular characteristics

Congenital brain tumors are rare accounting for 0.5%-1.9% of all pediatric brain tumors. While different criteria have been used to classify a tumor as congenital, those diagnosed prior to 6 months of age are considered to be "probably" congenital in origin. We performed an institutional review of all central nervous system (CNS) tumors (surgical and autopsy specimens from 1990 to 2019) in patients less than 6 months old. Sixty-four unique cases were identified, and these accounted for 2.0% of all CNS tumor specimens at our institution. The most common tumor types were high-grade gliomas, low-grade gliomas and medulloblastomas. Atypical teratoid rhabdoid tumors, choroid plexus tumors and germ cell tumors also accounted for a significant portion of the cohort. Seven tumors were diagnosed prenatally. The most common clinical presentation at diagnosis was increased head circumference. At the conclusion of the study, over half of the patients were alive including all patients with WHO grade I and II tumors. Ninety-two percent of cases were classifiable using the 2016 WHO system, and when available, molecular findings supported the histologic diagnoses. However, several gliomas had unusual histologic features and did not correspond to a well-defined entity. Molecular testing was essential for accurate classification of a subset of these tumors, and several high-grade gliomas exhibited fusions considered unique to infantile gliomas, including those involving the MET, ALK and NTRK genes. To our knowledge, this cohort represents the largest single-institution study of congenital CNS tumors and highlights many ways in which congenital CNS tumors are distinct from CNS tumors of older pediatric patients and adults.

ROS1-dependent cancers - biology, diagnostics and therapeutics

The proto-oncogene ROS1 encodes a receptor tyrosine kinase with an unknown physiological role in humans. Somatic chromosomal fusions involving ROS1 produce chimeric oncoproteins that drive a diverse range of cancers in adult and paediatric patients. ROS1-directed tyrosine kinase inhibitors (TKIs) are therapeutically active against these cancers, although only early-generation multikinase inhibitors have been granted regulatory approval, specifically for the treatment of ROS1 fusion-positive non-small-cell lung cancers; histology-agnostic approvals have yet to be granted. Intrinsic or extrinsic mechanisms of resistance to ROS1 TKIs can emerge in patients. Potential factors that influence resistance acquisition include the subcellular localization of the particular ROS1 oncoprotein and the TKI properties such as the preferential kinase conformation engaged and the spectrum of targets beyond ROS1. Importantly, the polyclonal nature of resistance remains underexplored. Higher-affinity next-generation ROS1 TKIs developed to have improved intracranial activity and to mitigate ROS1-intrinsic resistance mechanisms have demonstrated clinical efficacy in these regards, thus highlighting the utility of sequential ROS1 TKI therapy. Selective ROS1 inhibitors have yet to be developed, and thus the specific adverse effects of ROS1 inhibition cannot be deconvoluted from the toxicity profiles of the available multikinase inhibitors. Herein, we discuss the non-malignant and malignant biology of ROS1, the diagnostic challenges that ROS1 fusions present and the strategies to target ROS1 fusion proteins in both treatment-naive and acquired-resistance settings.

Canadian Pediatric Neuro-Oncology Standards of Practice

Primary CNS tumors are the leading cause of cancer-related death in pediatrics. It is essential to understand treatment trends to interpret national survival data. In Canada, children with CNS tumors are treated at one of 16 tertiary care centers. We surveyed pediatric neuro-oncologists to create a national standard of practice to be used in the absence of a clinical trial for seven of the most prevalent brain tumors in children. This allowed description of practice across the country, along with a consensus. This had a multitude of benefits, including understanding practice patterns, allowing for a basis to compare in future research and informing Health Canada of the current management of patients. This also allows all children in Canada to receive equivalent care, regardless of location.

Cerebrospinal Fluid Penetration and Combination Therapy of Entrectinib for Disseminated ROS1/NTRK-Fusion Positive Pediatric High-Grade Glioma

Targeting oncogenic fusion-genes in pediatric high-grade gliomas (pHGG) with entrectinib has emerged as a highly promising therapeutic approach. Despite ongoing clinical studies, to date, no reports on the treatment of cerebrospinal fluid (CSF) disseminated fusion-positive pHGG exist. Moreover, clinically important information of combination with other treatment modalities such as intrathecal therapy, radiotherapy and other targeted agents is missing. We report on our clinical experience of entrectinib therapy in two CSF disseminated ROS1/NTRK-fusion-positive pHGG cases. Combination of entrectinib with radiotherapy or intrathecal chemotherapy appears to be safe and has the potential to act synergistically with entrectinib treatment. In addition, we demonstrate CSF penetrance of entrectinib for the first time in patient samples suggesting target engagement even upon CSF dissemination. Moreover, in vitro analyses of two novel cell models derived from one case with NTRK-fusion revealed that combination therapy with either a MEK (trametinib) or a CDK4/6 (abemaciclib) inhibitor synergistically enhances entrectinib anticancer effects. In summary, our comprehensive study, including clinical experience, CSF penetrance and in vitro data on entrectinib therapy of NTRK/ROS1-fusion-positive pHGG, provides essential clinical and preclinical insights into the multimodal treatment of these highly aggressive tumors. Our data suggest that combined inhibition of NTRK/ROS1 and other therapeutic vulnerabilities enhances the antitumor effect, which should be followed-up in further preclinical and clinical studies.

Recurrent SPECC1L-NTRK fusions in pediatric sarcoma and brain tumors

The identification of rearrangements driving expression of neurotrophic receptor tyrosine kinase (NTRK) family kinases in tumors has become critically important because of the availability of effective, specific inhibitor drugs. Whole-genome sequencing (WGS) combined with RNA sequencing (RNA-seq) can identify novel and recurrent expressed fusions. Here we describe three SPECC1L–NTRK fusions identified in two pediatric central nervous system cancers and an extracranial solid tumor using WGS and RNA-seq. These fusions arose either through a simple balanced rearrangement or in the context of a complex chromoplexy event. We cloned the SPECC1L–NTRK2 fusion directly from a patient sample and showed that enforced expression of this fusion is sufficient to promote cytokine-independent survival and proliferation. Cells transformed by SPECC1L–NTRK2 expression are sensitive to a TRK inhibitor drug. We report here that SPECC1L–NTRK fusions can arise in a range of pediatric cancers. Although WGS and RNA-seq are not required to detect NTRK fusions, these techniques may be of benefit when NTRK fusions are not suspected on clinical grounds or not identified by other methods.

Genomic characterization of a PPP1CB-ALK fusion with fusion gene amplification in a congenital glioblastoma

ALK (Anaplastic lymphoma kinase) fusion proteins are oncogenic and have been seen in various tumors. PPP1CB-ALK fusions are rare but have been reported in a few patients with low- or high-grade gliomas. However, little is known regarding the mechanism of fusion formation and genomic break points of this fusion. We performed genomic characterization of a PPP1CB-ALK fusion with fusion gene amplification in a congenital glioblastoma. The PPP1CB-ALK consists of exons 1-5 of PPP1CB and exons 20-29 of ALK. The genomic translocation breakpoints were determined by real-time quantitative PCR (RT-qPCR) and Sanger sequencing of genomic DNA. Next generation sequencing, RT-qPCR and fluorescence in situ hybridization analyses demonstrated PPP1CB-ALK amplification. Copy number analyses of genes between PPP1CB and ALK using RT-qPCR suggest that the PPP1CB-ALK is likely the result of local chromothripsis followed by episomal amplification. Transcriptome sequencing demonstrated high-level SOX2 expression and predicted WNT/β-catenin pathway activation, suggesting possible therapeutic approaches.

Advances in Targeted Therapies for Pediatric Brain Tumors

Purpose of Review

Over the last years, our understanding of the molecular biology of pediatric brain tumors has vastly improved. This has led to more narrowly defined subgroups of these tumors and has created new potential targets for molecularly driven therapies. This review presents an overview of the latest advances and challenges of implementing targeted therapies into the clinical management of pediatric brain tumors, with a focus on gliomas, craniopharyngiomas, and medulloblastomas.

Recent Findings

Pediatric low-grade gliomas (pLGG) show generally a low mutational burden with the mitogen-activated protein kinase (MAPK) signaling presenting a key driver for these tumors. Direct inhibition of this pathway through BRAF and/or MEK inhibitors has proven to be a clinically relevant strategy. More recently, MEK and IL-6 receptor inhibitors have started to be evaluated in the treatment for craniopharyngiomas. Aside these low-grade tumors, pediatric high-grade gliomas (pHGG) and medulloblastomas exhibit substantially greater molecular heterogeneity with various and sometimes unknown tumor driver alterations. The clinical benefit of different targeted therapy approaches to interfere with altered signaling pathways and restore epigenetic dysregulation is undergoing active clinical testing. For these multiple pathway-driven tumors, combination strategies will most likely be required to achieve clinical benefit.

Summary

The field of pediatric neuro-oncology made tremendous progress with regard to improved diagnosis setting the stage for precision medicine approaches over the last decades. The potential of targeted therapies has been clearly demonstrated for a subset of pediatric brain tumors. However, despite clear response rates, questions of sufficient blood-brain barrier penetration, optimal dosing, treatment duration as well as mechanisms of resistance and how these can be overcome with potential combination strategies need to be addressed in future investigations. Along this line, it is critical for future trials to define appropriate endpoints to assess therapy responses as well as short and long-term toxicities in the growing and developing child.

Pediatric hemispheric high-grade glioma: targeting the future

Pediatric high-grade gliomas (pHGGs) are a group of tumors affecting approximately 0.85 children per 100,000 annually. The general outcome for these tumors is poor with 5-year survival rates of less than 20%. It is now recognized that these tumors represent a heterogeneous group of tumors rather than one entity. Large-scale genomic analyses have led to a greater understanding of the molecular drivers of different subtypes of these tumors and have also aided in the development of subtype-specific therapies. For example, for pHGG with NTRK fusions, promising new targeted therapies are actively being explored. Herein, we review the clinico-pathologic and molecular classification of these tumors, historical treatments, current management strategies, and therapies currently under investigation.

Effect of surgery and chemotherapy on long-term survival in infants with congenital glioblastoma: an integrated survival analysis

OBJECTIVE

Glioblastoma (GBM) during infancy is rare, and the clinical outcomes of congenital GBM are not well understood. Correspondingly, the aim of this study was to present a long-term survivor case from the authors' institution, and establish an integrated cohort of cases across the published literature to better understand the clinical course of this disease in this setting.

METHODS

The authors report the outcomes of an institutional case of congenital GBM diagnosed within the first 3 months of life, and performed a comprehensive literature search for published cases from 2000 onward for an integrated survival analysis. All cases were integrated into 1 cohort, and Kaplan-Meier estimations, Fisher's exact test, and logistic regression were used to interrogate the data.

RESULTS

The integrated cohort of 40 congenital GBM cases consisted of 23 (58%) females and 17 (42%) males born at a median gestational age of 38 weeks (range 22-40 weeks). Estimates of overall survival (OS) at 1 month was 67%, at 1 year it was 59%, and at 10 years it was 45%, with statistically superior outcomes for subgroups in which patients survived to be treated by resection and chemotherapy. In the overall cohort, multivariable analysis confirmed resection (p < 0.01) and chemotherapy (p < 0.01) as independent predictors of superior OS. Gestational age > 38 weeks (p < 0.01), Apgar scores ≥ 7 at 5 minutes (p < 0.01), absence of prenatal hydrocephalus (p < 0.01), and vaginal delivery (p < 0.01) were associated with greater odds of surgical diagnosis versus autopsy diagnosis.

CONCLUSIONS

Congenital GBM can deviate from the expected poor prognosis of adult GBM in terms of OS. Both resection and chemotherapy confer statistically superior prognostic advantages in those patients who survive within the immediate postnatal period, and should be first-line considerations in the initial management of this rare disease.

Updates in Pediatric Glioma Pathology

Gliomas are a diverse group of primary central nervous system tumors with astrocytic, oligodendroglial, and/or ependymal features and are an important cause of morbidity/mortality in pediatric patients. Glioma classification relies on integrating tumor histology with key molecular alterations. This approach can help establish a diagnosis, guide treatment, and determine prognosis. New categories of pediatric glioma have been recognized in recent years, due to increasing application of molecular profiling in brain tumors. The aim of this review is to alert pediatric pathologists to emerging diagnostic concepts in pediatric glioma neuropathology, emphasizing the incorporation of molecular features into diagnostic practice.

Molecular-Targeted Therapy for Childhood Brain Tumors: A Moving Target

Molecular-targeted therapy is an attractive therapeutic approach for childhood brain tumors. Unfortunately, with some notable exceptions, such treatment has not yet made a major impact on survival or for that matter quality-of-life for children with brain tumors. Limitations include the specificity of any single agent to inhibit the target, the presence of multiple genetic abnormalities within a tumor, the likely presence of escape mechanisms and the frequent use of molecular-targeted therapies in relatively biologically unselected patient populations. Despite these limitations, the MEK inhibitors and the BRAF V600E inhibitors have already demonstrated efficacy and are being compared to standard therapy in trials of treatment-naïve patients. There is also great enthusiasm for molecular-targeted therapies that target selective gene fusions. Given the plasticity of epigenetic changes, the targeting of epigenetic aberrations is also a promising avenue of therapy. Because molecular-targeted therapies frequently target genes and pathways that are critical in normal brain development, the acute, subacute long-term sequelae of molecular-targeted therapies need to be carefully monitored.

Infantile/Congenital High-Grade Gliomas: Molecular Features and Therapeutic Perspectives

Brain tumors in infants account for less than 10% of all pediatric nervous system tumors. They include tumors diagnosed in fetal age, neonatal age and in the first years of life. Among these, high-grade gliomas (HGGs) are a specific entity with a paradoxical clinical course that sets them apart from their pediatric and adult counterparts. Currently, surgery represents the main therapeutic strategy in the management of these tumors. Chemotherapy does not have a well-defined role whilst radiotherapy is rarely performed, considering its late effects. Information about molecular characterization is still limited, but it could represent a new fundamental tool in the therapeutic perspective of these tumors. Chimeric proteins derived from the fusion of several genes with neurotrophic tyrosine receptor kinase mutations have been described in high-grade gliomas in infants as well as in neonatal age and the recent discovery of targeted drugs may change the long-term prognosis of these tumors, along with other target-driven therapies. The aim of this mini review is to highlight the recent advances in the diagnosis and treatment of high-grade gliomas in infants with a particular focus on the molecular landscape of these neoplasms and future clinical applications.

Clinical, radiological and molecular characterization of intramedullary astrocytomas

Intramedullary astrocytomas (IMAs) are rare tumors, and few studies specific to the molecular alterations of IMAs have been performed. Recently, KIAA1549-BRAF fusions and the H3F3A p.K27M mutation have been described in low-grade (LG) and high-grade (HG) IMAs, respectively. In the present study, we collected clinico-radiological data and performed targeted next-generation sequencing for 61 IMAs (26 grade I pilocytic, 17 grade II diffuse, 3 LG, 3 grade III and 12 grade IV) to identify KIAA1549-BRAF fusions and mutations in 33 genes commonly implicated in gliomas and the 1p/19q regions. One hundred seventeen brain astrocytomas were analyzed for comparison. While we did not observe a difference in clinico-radiological features between LG and HG IMAs, we observed significantly different overall survival (OS) and event-free survival (EFS). Multivariate analysis showed that the tumor grade was associated with better OS while EFS was strongly impacted by tumor grade and surgery, with higher rates of disease progression in cases in which only biopsy could be performed. For LG IMAs, EFS was only impacted by surgery and not by grade. The most common mutations found in IMAs involved TP53, H3F3A p.K27M and ATRX. As in the brain, grade I pilocytic IMAs frequently harbored KIAA1549-BRAF fusions but with different fusion types. Non-canonical IDH mutations were observed in only 2 grade II diffuse IMAs. No EGFR or TERT promoter alterations were found in IDH wild-type grade II diffuse IMAs. These latter tumors seem to have a good prognosis, and only 2 cases underwent anaplastic evolution. All of the HG IMAs presented at least one molecular alteration, with the most frequent one being the H3F3A p.K27M mutation. The H3F3A p.K27M mutation showed significant associations with OS and EFS after multivariate analysis. This study emphasizes that IMAs have distinct clinico-radiological, natural evolution and molecular landscapes from brain astrocytomas.

Molecular and clinicopathologic features of gliomas harboring NTRK fusions

Fusions involving neurotrophic tyrosine receptor kinase (NTRK) genes are detected in ≤2% of gliomas and can promote gliomagenesis. The remarkable therapeutic efficacy of TRK inhibitors, which are among the first Food and Drug Administration-approved targeted therapies for NTRK-fused gliomas, has generated significant clinical interest in characterizing these tumors. In this multi-institutional retrospective study of 42 gliomas with NTRK fusions, next generation DNA sequencing (n = 41), next generation RNA sequencing (n = 1), RNA-sequencing fusion panel (n = 16), methylation profile analysis (n = 18), and histologic evaluation (n = 42) were performed. All infantile NTRK-fused gliomas (n = 7) had high-grade histology and, with one exception, no other significant genetic alterations. Pediatric NTRK-fused gliomas (n = 13) typically involved NTRK2, ranged from low- to high-histologic grade, and demonstrated histologic overlap with desmoplastic infantile ganglioglioma, pilocytic astrocytoma, ganglioglioma, and glioblastoma, among other entities, but they rarely matched with high confidence to known methylation class families or with each other; alterations involving ATRX, PTEN, and CDKN2A/2B were present in a subset of cases. Adult NTRK-fused gliomas (n = 22) typically involved NTRK1 and had predominantly high-grade histology; genetic alterations involving IDH1, ATRX, TP53, PTEN, TERT promoter, RB1, CDKN2A/2B, NF1, and polysomy 7 were common. Unsupervised principal component analysis of methylation profiles demonstrated no obvious grouping by histologic grade, NTRK gene involved, or age group. KEGG pathway analysis detected methylation differences in genes involved in PI3K/AKT, MAPK, and other pathways. In summary, the study highlights the clinical, histologic, and molecular heterogeneity of NTRK-fused gliomas, particularly when stratified by age group.

Infant High-Grade Gliomas Comprise Multiple Subgroups Characterized by Novel Targetable Gene Fusions and Favorable Outcomes

Infant high-grade gliomas appear clinically distinct from their counterparts in older children, indicating that histopathologic grading may not accurately reflect the biology of these tumors. We have collected 241 cases under 4 years of age, and carried out histologic review, methylation profiling, and custom panel, genome, or exome sequencing. After excluding tumors representing other established entities or subgroups, we identified 130 cases to be part of an "intrinsic" spectrum of disease specific to the infant population. These included those with targetable MAPK alterations, and a large proportion of remaining cases harboring gene fusions targeting ALK (n = 31), NTRK1/2/3 (n = 21), ROS1 (n = 9), and MET (n = 4) as their driving alterations, with evidence of efficacy of targeted agents in the clinic. These data strongly support the concept that infant gliomas require a change in diagnostic practice and management. SIGNIFICANCE: Infant high-grade gliomas in the cerebral hemispheres comprise novel subgroups, with a prevalence of ALK, NTRK1/2/3, ROS1, or MET gene fusions. Kinase fusion-positive tumors have better outcome and respond to targeted therapy clinically. Other subgroups have poor outcome, with fusion-negative cases possibly representing an epigenetically driven pluripotent stem cell phenotype.See related commentary by Szulzewsky and Cimino, p. 904.This article is highlighted in the In This Issue feature, p. 890.

A Unique Case of a High-Grade Neuroepithelial Tumor With EML4-ALK Fusion in a Five-Month-Old

We present a unique and challenging case of a high-grade neuroepithelial tumor with echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK) fusion in a five-month-old child. This tumor was difficult to classify, with glial and ependymal features, reinforcing the impact of a molecular-based diagnosis in correct classification and management. The patient had two tumor resections and underwent chemotherapy following the Head Start trial treatment regimen. The patient remains well, with no residual disease on MRI 15 months after initial resection. Further studies are needed to determine the frequency of EML4-ALK fusions in these types of tumors and to optimize therapeutic protocols for children and adults, alike, suffering from this disease.

Advances in the molecular classification of pediatric brain tumors: a guide to the galaxy

Central nervous system (CNS) tumors are the most common solid tumor in pediatrics, accounting for approximately 25% of all childhood cancers, and the second most common pediatric malignancy after leukemia. CNS tumors can be associated with significant morbidity, even those classified as low grade. Mortality from CNS tumors is disproportionately high compared to other childhood malignancies, although surgery, radiation, and chemotherapy have improved outcomes in these patients over the last few decades. Current therapeutic strategies lead to a high risk of side effects, especially in young children. Pediatric brain tumor survivors have unique sequelae compared to age-matched patients who survived other malignancies. They are at greater risk of significant impairment in cognitive, neurological, endocrine, social, and emotional domains, depending on the location and type of the CNS tumor. Next-generation genomics have shed light on the broad molecular heterogeneity of pediatric brain tumors and have identified important genes and signaling pathways that serve to drive tumor proliferation. This insight has impacted the research field by providing potential therapeutic targets for these diseases. In this review, we highlight recent progress in understanding the molecular basis of common pediatric brain tumors, specifically low-grade glioma, high-grade glioma, ependymoma, embryonal tumors, and atypical teratoid/rhabdoid tumor (ATRT). © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

A glioneuronal tumor with CLIP2-MET fusion

We report a case of glioneuronal tumor (GNT) with a discovery of novel gene fusion of CLIP2-MET resulting from aberrant chromosome 7 abnormalities. We executed an elaborate genomic study on this case including whole-exome sequencing and RNA sequencing. Genomic analysis of the tumor revealed aberrations in chromosomes 1 and 7 and a CLIP2-MET fusion. Further analysis of the upregulated genes revealed substantial connections with MAPK pathway activation. We concluded that the chromosome 7 abnormalities prompted CLIP2-MET gene fusion which successively leads to MAPK pathway activation. We deliberated that MAPK pathway activation is one of the driver pathways responsible for the oncogenesis of GNT.

Integrated Molecular and Clinical Analysis of 1,000 Pediatric Low-Grade Gliomas

Pediatric low-grade gliomas (pLGG) are frequently driven by genetic alterations in the RAS-mitogen-activated protein kinase (RAS/MAPK) pathway yet show unexplained variability in their clinical outcome. To address this, we characterized a cohort of >1,000 clinically annotated pLGG. Eighty-four percent of cases harbored a driver alteration, while those without an identified alteration also often exhibited upregulation of the RAS/MAPK pathway. pLGG could be broadly classified based on their alteration type. Rearrangement-driven tumors were diagnosed at a younger age, enriched for WHO grade I histology, infrequently progressed, and rarely resulted in death as compared with SNV-driven tumors. Further sub-classification of clinical-molecular correlates stratified pLGG into risk categories. These data highlight the biological and clinical differences between pLGG subtypes and opens avenues for future treatment refinement.

Novel PPP1CB-ALK fusion in spindle cell tumor defined by S100 and CD34 coexpression and distinctive stromal and perivascular hyalinization

A novel group of S100- and CD34-positive spindle cell tumors with distinctive stromal and perivascular hyalinization harboring recurrent gene fusions involving kinases including RAF1, BRAF, NTRK1/2/3, and RET have been recently reported. To our knowledge, no such cases harboring ALK rearrangements have been identified. We report a previously healthy 41-year-old male with a 12-cm intramuscular shoulder mass. The tumor was composed of bland-appearing spindled to epithelioid cells, arranged in a patternless pattern in a background of loose myxoid stroma containing striking amianthoid-like stromal collagen and perivascular rings. In accordance with the previously reported tumors, the tumor cells showed diffuse immunopositivity with S100 and CD34, while lacking SOX10 expression. Targeted RNA-based next-generation sequencing identified a novel serine/threonine-protein phosphatase PP1-beta-catalytic subunit (PPP1CB)-ALK fusion gene. Although ALK break-apart was not detected by FISH, likely due to a paracentric inversion of chromosome 2, the presence of the fusion was confirmed by Sanger sequencing showing a 10-bp linker between exon 6 of PPP1CB and intron 19 of ALK while maintaining reading frame. Subsequent ALK-1 immunostain exhibited diffuse cytoplasmic staining in the tumor cells. Our case expands the molecular genetic spectrum of the distinctive group of spindle cell tumors with CD34/S100+ immunophenotype, supporting the important role of various kinases as drivers of oncogenesis. Awareness of this entity including its unique morphologic and immunophenotypic features as well as its interchangeable kinase gene fusions is crucial for correct classification and potential targeted therapy, particularly in aggressive subsets.

Pediatric low-grade glioma in the era of molecular diagnostics

Low grade gliomas are the most frequent brain tumors in children and encompass a spectrum of histologic entities which are currently assigned World Health Organisation grades I and II. They differ substantially from their adult counterparts in both their underlying genetic alterations and in the infrequency with which they transform to higher grade tumors. Nonetheless, children with low grade glioma are a therapeutic challenge due to the heterogeneity in their clinical behavior – in particular, those with incomplete surgical resection often suffer repeat progressions with resultant morbidity and, in some cases, mortality. The identification of up-regulation of the RAS–mitogen-activated protein kinase (RAS/MAPK) pathway as a near universal feature of these tumors has led to the development of targeted therapeutics aimed at improving responses while mitigating patient morbidity. Here, we review how molecular information can help to further define the entities which fall under the umbrella of pediatric-type low-grade glioma. In doing so we discuss the specific molecular drivers of pediatric low grade glioma and how to effectively test for them, review the newest therapeutic agents and their utility in treating this disease, and propose a risk-based stratification system that considers both clinical and molecular parameters to aid clinicians in making treatment decisions.