Review of low-grade gliomas in children--evolving molecular era and therapeutic insights

Pediatric Central Nervous System Tumor Overview and Emerging Treatment Considerations

Pediatric central nervous system (CNS) tumors are the most common solid tumor in children, with the majority being glial in origin. These tumors are classified by the World Health Organization (WHO) as either being low grade (WHO grade 1 and 2) or high grade (WHO grade 3 and 4). Our knowledge of the molecular landscape of pediatric brain tumors has advanced over the last decade, which has led to newer categorizations along with an expansion of therapeutic targets and options. In this review, we will give an overview of common CNS tumors seen in children along with a focus on treatment options and future considerations.

Diffuse paediatric cerebellar glioma: two identical imaging phenotypes of an extremely rare entity with disparate pathology

Although the posterior fossa is a common location for paediatric brain tumours [1], diffuse glioma isolated to the cerebellum is an extremely rare imaging entity. Only two cases of isolated diffuse paediatric cerebellar glioma have been reported in the English language to the best of our knowledge [2, 3], and only one of these cases had a similar imaging phenotype to our cases [3]. Although somewhat similar to Lhermitte-Duclos (dysplastic gangliocytoma of the cerebellum), the appearances are distinct from other neoplastic entities of the paediatric posterior fossa. Clinical presentation and neurological examination findings are vital however to help differentiate other diffuse pathologies involving the cerebellum such as rhombencephalitis. Presented here are two diffuse cerebellar gliomas in children under the age of 3 with near identical imaging phenotypes demonstrating differing histological and molecular genetic profiles.

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.

Pediatric Glioma at the Optic Pathway and Thalamus

Gliomas are the most common pediatric tumors of the central nervous system. In this review, we discuss the clinical features, treatment paradigms, and evolving concepts related to two types of pediatric gliomas affecting two main locations: the optic pathway and thalamus. In particular, we discuss recently revised pathologic classification, which adopting molecular parameter. We believe that our review contribute to the readers' better understanding of pediatric glioma because pediatric glioma differs in many ways from adult glioma according to the newest advances in molecular characterization of this tumor. A better understanding of current and evolving issues in pediatric glioma is needed to ensure effective management decision.

The miR-139-5p regulates proliferation of supratentorial paediatric low-grade gliomas by targeting the PI3K/AKT/mTORC1 signalling

AIMS

Paediatric low-grade gliomas (pLGGs) are a heterogeneous group of brain tumours associated with a high overall survival: however, they are prone to recur and supratentorial lesions are difficult to resect, being associated with high percentage of disease recurrence. Our aim was to shed light on the biology of pLGGs.

METHODS

We performed microRNA profiling on 45 fresh-frozen grade I tumour samples of various histological classes, resected from patients aged ≤16 years. We identified 93 microRNAs specifically dysregulated in tumours as compared to non-neoplastic brain tissue. Pathway analysis of the microRNAs signature revealed PI3K/AKT signalling as one of the centrally enriched oncogenic signalling. To date, activation of the PI3K/AKT pathway in pLGGs has been reported, although activation mechanisms have not been fully investigated yet.

RESULTS

One of the most markedly down-regulated microRNAs in our supratentorial pLGGs cohort was miR-139-5p, whose targets include the gene encoding the PI3K's (phosphatidylinositol 3-kinase) catalytic unit, PIK3CA. We investigated the role of miR-139-5p in regulating PI3K/AKT signalling by the use of human cell cultures derived from supratentorial pLGGs. MiR-139-5p overexpression inhibited pLGG cell proliferation and decreased the phosphorylation of PI3K target AKT and phosphorylated-p70 S6 kinase (p-p70 S6K), a hallmark of PI3K/AKT/mTORC1 signalling activation. The effect of miR-139-5p was mediated by PI3K inhibition, as suggested by the decrease in proliferation and phosphorylation of AKT and p70 S6K after treatment with the direct PI3K inhibitor LY294002.

CONCLUSIONS

These findings provide the first evidence that down-regulation of miR-139-5p in supratentorial pLGG drives cell proliferation by derepressing PI3K/AKT signalling.

Pathology-MRI Correlations in Diffuse Low-Grade Epilepsy Associated Tumors

It is recognized that IDH mutation negative, low-grade epilepsy associated tumors (LEAT) can show diffuse growth patterns and lack the diagnostic hallmarks of either classical dysembryoplastic neuroepithelial tumors (DNT) or typical ganglioglioma. “Nonspecific or diffuse DNT” and more recently “polymorphous low-grade neuroepithelial tumor of the young” have been terms used for these entities. There are few reports on the MRI recognition of these diffuse glioneuronal tumors (dGNT), which is important in planning the extent of surgical resection. In 27 LEATs T1, T2, FLAIR, and postcontrast T1 MRI were evaluated and the pathology reviewed, including immunostaining for NeuN, CD34, MAP2, and IDH1. Each case was then independently classified by pathology or MRI as simple DNT, complex DNT, or dGNT. There was agreement in 23/27 (85%; Kappa score 0.62; p < 0.01). In 4 cases, there was discrepancy in the diagnosis of simple versus complex DNT but 100% agreement achieved for dGNT. DNT showed significantly more expansion of the cortex, cystic change and ventricle extension than dGNT. dGNT showed significantly more subcortical T2w hyperintensity and focal cortical atrophy which correlated on pathology with CD34 expression, cortical neuronal loss and white matter rarefaction. There was no distinct cortical dysplasia component identified by MRI or pathology in any case. This study highlights that dGNT can be reliably discriminated on MRI from DNT.

Pediatric Basal Ganglia Region Tumors: Clinical and Radiologic Features Correlated with Histopathologic Findings

PURPOSE

To summarize the clinical and radiologic features of pediatric basal ganglia region tumors (PBGRT) in correlation with their histopathologic findings to reduce inappropriate surgery and identify tumors that can benefit from maximal safe resection.

METHODS

The records of 35 children with PBGRT treated in our hospital from December 2011 to December 2015 were analyzed retrospectively. The clinical and radiologic features of these tumors were summarized and correlated with their histopathologic diagnosis.

RESULTS

Our series included 15 astrocytomas and 11 germ cell tumors (GCTs). Basal ganglia astrocytomas were characterized by various clinical presentations and an ill-circumscribed mass with the involvement of surrounding structures on neuroimaging and mostly occurred in the first decade of life (n = 10; 66.7%). Basal ganglia GCT mostly occurred in the second decade of life (n = 8; 72.7%) with hemiparesis as the most common symptom (n = 9; 81.8%). The tumors were located predominantly in the caput of caudate nucleus (n = 8; 72.7%) with hemiatrophy as the typical sign (n = 8; 72.7%). Occasionally, other tumors also could occur in this region, including primitive neuroectodermal tumor (n = 1), atypical teratoid/rhabdoid tumor (n = 1), anaplastic ependymoma (n = 1), lymphoma (n = 1), extraventricular neurocytoma (n = 1), gangliogliomas (n = 2), oligodendroglioma (n = 1), and dysembryoplastic neuroepithelial tumor (n = 1).

CONCLUSIONS

Astrocytoma and GCT are the most common PBGRTs. Low-grade astrocytomas could benefit from maximal surgical resection, whereas GCTs merit neoadjuvant chemoradiation therapy followed by second-look surgery. We advocate routine testing of tumor markers and analysis of their clinical and radiologic features to optimize the therapeutic strategy.

Conventional chemotherapy and perspectives for molecular-based oncological treatment in pediatric hemispheric low-grade gliomas

INTRODUCTION

Pediatric low-grade gliomas (PLGG) are the most common primary central nervous system tumor in children. Patients in whom gross total resection can be achieved have an excellent overall (OS) and event-free survival (EFS) and do not require adjuvant therapy. However, children with unresectable tumors often experience multiple progressions and require additional treatment.

CONVENTIONAL CHEMOTHERAPY

Radiotherapy results in long-term tumor control, but it is associated with significant toxicity, making chemotherapy the preferred therapeutic option. Several chemotherapy combinations have been found to be successful in PLGG, but 5-year EFS has been below 60 % with most of them.

MOLECULAR-BASED TREATMENT

Recent molecular advances have led to a better understanding of the molecular pathways involved in the biology of LGG, allowing the development of promising tumor-specific, molecularly targeted therapies.