Evaluation status and prognostic significance of O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation in pediatric high grade gliomas

Therapeutically targeting the unique disease landscape of pediatric high-grade gliomas

Pediatric high-grade gliomas (pHGG) are a rare yet devastating malignancy of the central nervous system's glial support cells, affecting children, adolescents, and young adults. Tumors of the central nervous system account for the leading cause of pediatric mortality of which high-grade gliomas present a significantly grim prognosis. While the past few decades have seen many pediatric cancers experiencing significant improvements in overall survival, the prospect of survival for patients diagnosed with pHGGs has conversely remained unchanged. This can be attributed in part to tumor heterogeneity and the existence of the blood-brain barrier. Advances in discovery research have substantiated the existence of unique subgroups of pHGGs displaying alternate responses to different therapeutics and varying degrees of overall survival. This highlights a necessity to approach discovery research and clinical management of the disease in an alternative subtype-dependent manner. This review covers traditional approaches to the therapeutic management of pHGGs, limitations of such methods and emerging alternatives. Novel mutations which predominate the pHGG landscape are highlighted and the therapeutic potential of targeting them in a subtype specific manner discussed. Collectively, this provides an insight into issues in need of transformative progress which arise during the management of pHGGs.

Novel Pharmacological Treatment Options in Pediatric Glioblastoma-A Systematic Review

Simple Summary

Childhood glioblastoma is an aggressive brain tumor in children that has a very poor prognosis. Standard therapy includes surgery, irradiation and chemotherapy with temozolomide. So far, there is no effective drug treatment for pediatric glioblastoma patients. This systematic review aims to outline currently available data on novel pharmacological treatment options. None of the included phase II studies showed any benefit regarding overall survival or a prolongation of stable disease. New genomic technologies discovered the biologic heterogeneity of these tumors, demanding more individualized immunotherapeutic and targeted approaches. Autoimmune modulated therapies and further targeting of tumor-specific receptors provide promising preclinical results. Clinical trials aligned to the tumor characteristics are needed to establish effective new therapeutic approaches.

Abstract

Background: Pediatric glioblastoma (GBM) is an aggressive central nervous system tumor in children that has dismal prognosis. Standard of care is surgery with subsequent irradiation and temozolomide. We aimed to outline currently available data on novel pharmacological treatments for pediatric GBM. Methods: We conducted a systematic literature search in PubMed and Embase, including reports published in English from 2010 to 2021. We included randomized trials, cohort studies and case series. Phase I trials were not analyzed. We followed PRISMA guidelines, assessed the quality of the eligible reports using the Newcastle-Ottawa scale (NOS) and the RoB-2 tool and registered the protocol on PROSPERO. Results: We included 6 out of 1122 screened reports. All six selected reports were prospective, multicenter phase II trials (five single-arm and one randomized controlled trial). None of the investigated novel treatment modalities showed any benefit regarding overall or progression free survival. Conclusions: To date, the role of pharmacological approaches regarding pediatric GBM remains unclear, since no novel treatment approach could provide a significant impact on overall or progression free survival. Further research should aim to combine different treatment strategies in large international multicenter trials with central comprehensive diagnostics regarding subgrouping. These novel treatment approaches should include targeted and immunotherapeutic treatments, potentially leading to a more successful outcome.

Childhood Cancer: Occurrence, Treatment and Risk of Second Primary Malignancies

Cancer represents the leading cause of disease-related death and treatment-associated morbidity in children with an increasing trend in recent decades worldwide. Nevertheless, the 5-year survival of childhood cancer patients has been raised impressively to more than 80% during the past decades, primarily attributed to improved diagnostic technologies and multiagent cytotoxic regimens. This strong benefit of more efficient tumor control and prolonged survival is compromised by an increased risk of adverse and fatal late sequelae. Long-term survivors of pediatric tumors are at the utmost risk for non-carcinogenic late effects such as cardiomyopathies, neurotoxicity, or pneumopathies, as well as the development of secondary primary malignancies as the most detrimental consequence of genotoxic chemo- and radiotherapy. Promising approaches to reducing the risk of adverse late effects in childhood cancer survivors include high precision irradiation techniques like proton radiotherapy or non-genotoxic targeted therapies and immune-based treatments. However, to date, these therapies are rarely used to treat pediatric cancer patients and survival rates, as well as incidences of late effects, have changed little over the past two decades in this population. Here we provide an overview of the epidemiology and etiology of childhood cancers, current developments for their treatment, and therapy-related adverse late health consequences with a special focus on second primary malignancies.

Histone H3G34 Mutation in Brain and Bone Tumors

H3G34 mutations occur in both pediatric non-brainstem high-grade gliomas (G34R/V) and giant cell tumors of bone (G34W/L). Glioblastoma patients with G34R/V mutation have a generally adverse prognosis, whereas giant cell tumors of bone are rarely metastatic benign tumors. G34 mutations possibly disrupt the epigenome by altering H3K36 modifications, which may involve attenuating the function of SETD2 at methyltransferase. H3K36 methylation change may further lead to genomic instability, dysregulated gene expression pattern, and more mutations. In this chapter, we summarize the pathological features of each mutation type in its respective cancer, as well as the potential mechanism of their disruption on the epigenome and genomic instability. Understanding each mutation type would provide a thorough background for a thorough understanding of the cancers and would bring new insights for future investigations and the development of new precise therapies.

WHO grade has no prognostic value in the pediatric high-grade glioma included in the HERBY trial

BACKGROUND

The World Health Organization (WHO) adult glioma grading system is questionable in pediatric high-grade gliomas (pHGGs), which are biologically distinct from adult HGGs. We took advantage of the neuropathological review data obtained during one of the largest prospective randomized pHGG trials, namely HERBY (NCT01390948), to address this issue in children with newly diagnosed non-brainstem HGG.

METHODS

HGG diagnosis was confirmed by pre-randomization, real-time central pathology review using WHO 2007 criteria, followed by a consensus review blinded to clinical factors and outcomes. We evaluated association between WHO 2007 grade and other clinical/radiological/biological characteristics and the prognostic value of WHO 2007 grade, midline location, and selected biomarkers (Ki-67 index/Olig2/CD34/EGFR/p53/H3F3A K27M mutation) on overall survival.

RESULTS

Real-time central neuropathological review was feasible in a multicenter study, with a mean time of 2.4 days, and led to the rejection of HGG diagnosis in 20 of 163 cases (12.3%). The different grading criteria and resulting WHO grade were not significantly associated with overall survival in the entire population (n = 118) or in midline and non-midline subgroups. H3F3A K27M mutation was significantly associated with poor outcome. No significant prognostic value was observed for grade, even after regrading H3F3A K27M-mutated midline glioma as grade IV (WHO 2016). Midline location and a high Ki-67 index (≥20%) were associated with poor outcome (P = 0.004 and P = 0.04, respectively). A 10% increase in Ki-67 index was associated with a hazard ratio of 1.53 (95% CI: 1.27-1.83; P < 0.0001).

CONCLUSION

Our findings suggest that WHO grade III versus IV has no prognostic value in pediatric HGG.

Cocaine-induced epigenetic DNA modification in mouse addiction-specific and non-specific tissues

Cocaine-related DNA methylation studies have primarily focused on the specific brain regions associated with drug addiction (e.g., the nucleus accumbens, NAc). To date, no studies have focused on the complex role of both DNA methylation and demethylation in the mechanisms of psychostimulant-induced addiction in the brain and peripheral tissues. Therefore, in this study, we evaluated cocaine treatment and withdrawal (animals were withdrawn from seven days of repeated injections of cocaine that caused behavioral sensitization) effects on epigenetic DNA modifiers (i.e., DNA methyltransferases, [DNMTs] and ten-eleven translocation enzymes [TETs]) in an addiction-specific brain region (NAc), a structure outside the mesolimbic dopaminergic system (cerebellum, Cer), and in peripheral blood cells (PBCs). Using a mouse behavioral sensitization model, we demonstrated that acute cocaine (AC; 0.5 h) treatment significantly decreased Dnmt1, Dnmt3a, Tet1, and Tet2 mRNA levels in the NAc and PBC, whereas at 24 h after AC treatment, Dnmt mRNA expression and enzyme activity levels were significantly increased. Acute procaine treatment caused the opposite effect on the Dnmt3a mRNA level in PBCs; this outcome suggests that the inhibition of voltage-gated sodium channels may be the mechanism that alters Dnmt expression in PBCs. Cocaine withdrawal is associated with increased expression of Dnmts in the NAc, Cer and PBCs and the decreased expression of Tet1 and Tet3 in the NAc. Additionally, cocaine withdrawal increased DNMT but decreased TET activity levels, and these changes were associated with enhanced global and selected candidate gene promoter-region DNA methylation and hydroxymethylation levels in the NAc and PBCs. Together, these data indicate that cocaine treatment and withdrawal affect the expression of epigenetic DNA modifiers in both addiction-specific brain structures and structures outside of the mesolimbic dopaminergic system and PBCs.

Phase II, Open-Label, Randomized, Multicenter Trial (HERBY) of Bevacizumab in Pediatric Patients With Newly Diagnosed High-Grade Glioma

Purpose Bevacizumab (BEV) is approved in more than 60 countries for use in adults with recurrent glioblastoma. We evaluated the addition of BEV to radiotherapy plus temozolomide (RT+TMZ) in pediatric patients with newly diagnosed high-grade glioma (HGG). Methods The randomized, parallel group, multicenter, open-label HERBY trial ( ClinicalTrials.gov identifier: NCT01390948) enrolled patients age ≥ 3 years to ≤ 18 years with localized, centrally neuropathology-confirmed, nonbrainstem HGG. Eligible patients were randomly assigned to receive RT + TMZ (RT: 1.8 Gy, 5 days per week, and TMZ: 75 mg/m² per day for 6 weeks; 4-week treatment break; then up to 12 × 28-day cycles of TMZ [cycle 1: 150 mg/m² per day, days 1 to 5; cycles 2 to 12: 200 mg/m² per day, days 1 to 5]) with or without BEV (10 mg/kg every 2 weeks). The primary end point was event-free survival (EFS) as assessed by a central radiology review committee that was blinded to treatment. We report findings of EFS at 12 months after the enrollment of the last patient. Results One hundred twenty-one patients were enrolled (RT+TMZ [n = 59]; BEV plus RT+TMZ [n = 62]). Central radiology review committee-assessed median EFS did not differ significantly between treatment groups (RT+TMZ, 11.8 months; 95% CI, 7.9 to 16.4 months; BEV plus RT+TMZ, 8.2 months; 95% CI, 7.8 to 12.7 months; hazard ratio, 1.44; P = .13 [stratified log-rank test]). In the overall survival analysis, the addition of BEV did not reduce the risk of death (hazard ratio, 1.23; 95% CI, 0.72 to 2.09). More patients in the BEV plus RT+TMZ group versus the RT+TMZ group experienced one or more serious adverse events (n = 35 [58%] v n = 27 [48%]), and more patients who received BEV discontinued study treatment as a result of adverse events (n = 13 [22%] v n = 3 [5%]). Conclusion Adding BEV to RT+TMZ did not improve EFS in pediatric patients with newly diagnosed HGG. Our findings were not comparable to those of previous adult trials, which highlights the importance of performing pediatric-specific studies.

Molecular mechanisms and therapeutic targets in pediatric brain tumors

Brain tumors are among the leading causes of cancer-related deaths in children. Although surgery, aggressive radiation, and chemotherapy have improved outcomes, many patients still die of their disease. Moreover, those who survive often suffer devastating long-term side effects from the therapies. A greater understanding of the molecular underpinnings of these diseases will drive the development of new therapeutic approaches. Advances in genomics and epigenomics have provided unprecedented insight into the molecular diversity of these diseases and, in several cases, have revealed key genes and signaling pathways that drive tumor growth. These not only serve as potential therapeutic targets but also have facilitated the creation of animal models that faithfully recapitulate the human disease for preclinical studies. In this Review, we discuss recent progress in understanding the molecular basis of the three most common malignant pediatric brain tumors-medulloblastoma, ependymoma, and high-grade glioma-and the implications for development of safer and more effective therapies.

Pediatric glioblastoma: a single institution experience

PURPOSE

The aim of this study was to evaluate characteristics of childhood glioblastoma multiforme, effectiveness of treatment modalities, and detect factors related to outcome.

METHODS

A detailed analysis was performed on a series of 15 patients treated between 2000 and 2013, based on their clinical, radiologic, pathologic, treatment, and follow-up data.

RESULTS

Median survival time of children with glioblastoma was 13.5 months. One- and 2-year overall survival probabilities were 66.7 and 20 %, respectively. There were no significant differences in survival based on patients' gender, age, disease presentation with or without epileptic seizures, signs/symptoms of increased intracranial pressure, or tumor location. The presence of neurological deficit initially, as well as prior to radiotherapy, which was quantified by neurologic function score (NFS), had an impact on overall survival. Children with NFS 0 lived longer compared to others (p = 0.001). Survival of children that underwent gross total resection was longer than that of children that underwent subtotal resection (p = 0.030). Mean survival time of children with gross total resection was 73.5 months, compared to 13 months in children with subtotal resection. There was no significant correlation between outcome and type of radiotherapy. In four patients with gigantocellular glioblastoma, we found no evidence of a better prognosis. Two long-term survivors were recorded. Both of them underwent gross total resection and were assigned a NFS 0.

CONCLUSIONS

Gross total resection is essential for longer overall survival among pediatric patients with glioblastoma and offers a possibility for long-term survival. Severity of neurologic symptoms quantified by NFS can be considered as a potential predictor of outcome.

MGMT testing allows for personalised therapy in the temozolomide era

Adjuvant temozolomide (TMZ)-based chemoradiation is the standard of care for most glioblastoma patients (GBMs); however, a large proportion of these patients do not respond to TMZ. Silencing of the O(6)-methylguanine-DNA methyltransferase (MGMT) promoter is thought to induce chemosensitivity, and testing for methylation may allow for patient stratification; however, this has yet to become routine clinical practice despite an abundance of literature on the subject. The databases PubMed, Embase, The Cochrane Library, Science Direct and Medline were searched for relevant articles published between 1999 and 2015. Articles utilising MGMT testing in glioblastomas, and treatment of glioblastomas with temozolomide were assessed. Immunohistochemistry, methylation-specific PCR (MSP), reverse transcriptase PCR, pyrosequencing and bisulphite sequencing were the main testing methods identified. Nested-MSP techniques produced poor correlation with survival, whilst bisulphite sequencing showed no evident benefit over MSP. Testing is limited by sample quality and contamination; however, efforts are made to minimise this. Strong evidence for MGMT-based personalised therapy was presented in the elderly but remains controversial in the entire GBM population. MGMT testing presents many obstacles yet to be overcome, and these warrant attention prior to the routine implementation of MGMT testing to aid decision making in GBMs. However, there is evidence to support its use, particularly in the elderly.

Molecular Biology in Pediatric High-Grade Glioma: Impact on Prognosis and Treatment

High-grade gliomas are the main cause of death in children with brain tumours. Despite recent advances in cancer therapy, their prognosis remains poor and the treatment is still challenging. To date, surgery followed by radiotherapy and temozolomide is the standard therapy. However, increasing knowledge of glioma biology is starting to impact drug development towards targeted therapies. The identification of agents directed against molecular targets aims at going beyond the traditional therapeutic approach in order to develop a personalized therapy and improve the outcome of pediatric high-grade gliomas. In this paper, we critically review the literature regarding the genetic abnormalities implicated in the pathogenesis of pediatric malignant gliomas and the current development of molecularly targeted therapies. In particular, we analyse the impact of molecular biology on the prognosis and treatment of pediatric high-grade glioma, comparing it to that of adult gliomas.

Glioblastoma: pathology, molecular mechanisms and markers

Recent advances in genomic technology have led to a better understanding of key molecular alterations that underlie glioblastoma (GBM). The current WHO-based classification of GBM is mainly based on histologic features of the tumor, which frequently do not reflect the molecular differences that describe the diversity in the biology of these lesions. The current WHO definition of GBM relies on the presence of high-grade astrocytic neoplasm with the presence of either microvascular proliferation and/or tumor necrosis. High-throughput analyses have identified molecular subtypes and have led to progress in more accurate classification of GBM. These findings, in turn, would result in development of more effective patient stratification, targeted therapeutics, and prediction of patient outcome. While consensus has not been reached on the precise nature and means to sub-classify GBM, it is clear that IDH-mutant GBMs are clearly distinct from GBMs without IDH1/2 mutation with respect to molecular and clinical features, including prognosis. In addition, recent findings in pediatric GBMs regarding mutations in the histone H3F3A gene suggest that these tumors may represent a 3rd major category of GBM, separate from adult primary (IDH1/2 wt), and secondary (IDH1/2 mut) GBMs. In this review, we describe major clinically relevant genetic and epigenetic abnormalities in GBM-such as mutations in IDH1/2, EGFR, PDGFRA, and NF1 genes-altered methylation of MGMT gene promoter, and mutations in hTERT promoter. These markers may be incorporated into a more refined classification system and applied in more accurate clinical decision-making process. In addition, we focus on current understanding of the biologic heterogeneity and classification of GBM and highlight some of the molecular signatures and alterations that characterize GBMs as histologically defined. We raise the question whether IDH-wild type high grade astrocytomas without microvascular proliferation or necrosis might best be classified as GBM, even if they lack the histologic hallmarks as required in the current WHO classification. Alternatively, an astrocytic tumor that fits the current histologic definition of GBM, but which shows an IDH mutation may in fact be better classified as a distinct entity, given that IDH-mutant GBM are quite distinct from a biological and clinical perspective.

Regulation of expression of O6-methylguanine-DNA methyltransferase and the treatment of glioblastoma (Review)

O-6-methylguanine-DNA methyltransferase (MGMT) is an abundantly expressed nuclear protein dealkylating O⁶-methylguanine (O⁶-MG) DNA residue, thus correcting the mismatches of O⁶-MG with a thymine residue during DNA replication. The dealkylating effect of MGMT is relevant not only in repairing DNA mismatches produced by environmental alkylating agents promoting tumor pathogenesis, but also when alkylating molecules are applied in the chemotherapy of different cancers, including glioma, the most common primary tumor of the central nervous system. Elevated MGMT gene expression is known to confer resistance to the treatment with the alkylating drug temozolomide in patients affected by gliomas and, on the contrary, methylation of MGMT gene promoter, which causes reduction of MGMT protein expression, is known to predict a favourable response to temozolomide. Thus, detecting expression levels of MGMT gene is crucial to indicate the option of alkylating agents or to select patients directly for a second line targeted therapy. Further study is required to gain insights into MGMT expression regulation, that has attracted growing interest recently in MGMT promoter methylation, histone acetylation and microRNAs expression. The review will focus on the epigenetic regulation of MGMT gene, with translational applications to the identification of biomarkers predicting response to therapy and prognosis.

Integrated analysis of pediatric glioblastoma reveals a subset of biologically favorable tumors with associated molecular prognostic markers

Pediatric glioblastoma (pedGBM) is amongst the most common malignant brain tumors of childhood and carries a dismal prognosis. In contrast to adult GBM, few molecular prognostic markers for the pediatric counterpart have been established. We, therefore, investigated the prognostic significance of genomic and epigenetic alterations through molecular analysis of 202 pedGBM (1-18 years) with comprehensive clinical annotation. Routinely prepared formalin-fixed paraffin-embedded tumor samples were assessed for genome-wide DNA methylation profiles, with known candidate genes screened for alterations via direct sequencing or FISH. Unexpectedly, a subset of histologically diagnosed GBM (n = 40, 20 %) displayed methylation profiles similar to those of either low-grade gliomas or pleomorphic xanthoastrocytomas (PXA). These tumors showed a markedly better prognosis, with molecularly PXA-like tumors frequently harboring BRAF V600E mutations and 9p21 (CDKN2A) homozygous deletion. The remaining 162 tumors with pedGBM molecular signatures comprised four subgroups: H3.3 G34-mutant (15 %), H3.3/H3.1 K27-mutant (43 %), IDH1-mutant (6 %), and H3/IDH wild-type (wt) GBM (36 %). These subgroups were associated with specific cytogenetic aberrations, MGMT methylation patterns and clinical outcomes. Analysis of follow-up data identified a set of biomarkers feasible for use in risk stratification: pedGBM with any oncogene amplification and/or K27M mutation (n = 124) represents a particularly unfavorable group, with 3-year overall survival (OS) of 5 %, whereas tumors without these markers (n = 38) define a more favorable group (3-year OS ~70 %).Combined with the lower grade-like lesions, almost 40 % of pedGBM cases had distinct molecular features associated with a more favorable outcome. This refined prognostication method for pedGBM using a molecular risk algorithm may allow for improved therapeutic choices and better planning of clinical trial stratification for this otherwise devastating disease.

Impact of tumor location and pathological discordance on survival of children with midline high-grade gliomas treated on Children's Cancer Group high-grade glioma study CCG-945

Children with high-grade glioma (HGG) have a poor prognosis compared to those with low-grade glioma (LGG). Adjuvant chemotherapy may be beneficial, but its optimal use remains undetermined. Histology and extent of resection are important prognostic factors. We tested the hypothesis that patients with midline HGG treated on Children's Cancer Group Study (CCG) CCG-945 have a worse prognosis compared to the entire group. Of 172 children eligible for analysis, 60 had midline tumors primarily localized to the thalamus, hypothalamus and basal ganglia. Time-to-progression and death were determined from the date of initial diagnosis, and survival curves were calculated. Univariate analyses were undertaken for extent of resection, chemotherapy regimen, anatomic location, histology, proliferation index, MGMT status and p53 over-expression. For the entire midline tumor group, 5-year PFS and OS were 18.3 ± 4.8 and 25 ± 5.4 %, respectively. Many patients only had a biopsy (43.3 %). The sub-groups with near/total resection and hypothalamic location appeared to have better PFS and OS. However, the effect of tumor histology on OS was significant for children with discordant diagnoses on central pathology review of LGG compared to HGG. Proliferative index (MIB-1 > 36 %), MGMT and p53 over-expression correlated with poor outcomes. Children treated on CCG-945 with midline HGG have a worse prognosis when compared to the entire group. The midline location may directly influence the extent of resection. Central pathology review and entry of patients on clinical trials continue to be priorities to improve outcomes for children with HGG.

Progression of O⁶-methylguanine-DNA methyltransferase and temozolomide resistance in cancer research

Temozolomide (TMZ) is an alkylating agent that is widely used in chemotherapy for cancer. A key mechanism of resistance to TMZ is the overexpression of O(6)-methylguanine-DNA methyltransferase (MGMT). MGMT specifically repairs the DNA O(6)-methylation damage induced by TMZ and irreversibly inactivates TMZ. Regulation of MGMT expression and research regarding the mechanism of TMZ resistance will help rationalize the clinical use of TMZ. In this review, we provide an overview of recent advances in the field, with particular emphasis on MGMT structure, function, expression regulation, and the association between MGMT and resistance to TMZ.

Paediatric and adult glioblastoma: multiform (epi)genomic culprits emerge

We have extended our understanding of the molecular biology that underlies adult glioblastoma over many years. By contrast, high-grade gliomas in children and adolescents have remained a relatively under-investigated disease. The latest large-scale genomic and epigenomic profiling studies have yielded an unprecedented abundance of novel data and provided deeper insights into gliomagenesis across all age groups, which has highlighted key distinctions but also some commonalities. As we are on the verge of dissecting glioblastomas into meaningful biological subgroups, this Review summarizes the hallmark genetic alterations that are associated with distinct epigenetic features and patient characteristics in both paediatric and adult disease, and examines the complex interplay between the glioblastoma genome and epigenome.

Are pediatric brain tumors on the rise in the USA? Significant incidence and survival findings from the SEER database analysis

INTRODUCTION

Central nervous system tumors are the second most common form of cancer in children between the ages of 1 and 19 years. We aimed to provide the most recent data on the incidence and survival of these tumors in the USA and to assess the literature.

METHODS

Frequency, rates, and survival sessions were calculated using the November 2008 submission for the US Surveillance Epidemiology and End Results Program. Data were collected and analyzed for children and adolescents aged 1 to 19 years with primary brain tumors.

RESULTS

We found that the incidence rate of all pediatric brain tumors has been on a gradual but steady increase from 1973 to 2008 (p < 0.001). The average annual increase was 1.37 %. Our survival analysis of the individual tumors revealed that the 5-year overall survival for children diagnosed between 1974 and 1978 with medulloblastoma was 43.7 %. However, this increased to 62.8 % for children diagnosed between 1999 and 2003. A similar survival trend was also observed when all the other pediatric brain cancer histologies were collectively analyzed (p < 0.001).

CONCLUSIONS

From our study, we can conclude that contrary to previous reports indicating a plateau in the incidence rates of pediatric brain tumors since the mid-1980s, there has been an increase from 1973 to 2008. Potential causes include environmental carcinogens, but more research is needed to investigate the factors behind this sustained rise in incidence over the years.

Molecular diagnostics in paediatric glial tumours

Glial tumours in children have distinct patterns of epigenetic alteration, chromosomal structure, and gene and protein expression that differentiate them from their histological counterparts in adults. Understanding paediatric gliomas at the molecular level provides important prognostic and therapeutic insights, such as which genetic alterations confer a favourable response to adjuvant therapy, or which signalling pathways might be amenable to specific molecularly targeted agents. For clinicians, the ultimate goal is to individualise therapeutic regimens on the basis of the molecular fingerprint of a particular tumour and the prognosis conferred by this profile. In this Review, we examine a series of studies of molecular and genomic analysis of glial tumours in children, and discuss the many clinical insights that these molecular features provide.

MGMT promoter gene methylation in pediatric glioblastoma: analysis using MS-MLPA

PURPOSE

Promoter methylation of the O⁶-methylguanine-DNA-methyltransferase (MGMT) gene is widely recognized as an important predictive factor in the treatment of glioblastoma (GBM) patients with temozolomide. However, data regarding the methylation status of the MGMT promoter in pediatric GBM are yet to be elucidated.

METHODS

Nineteen tissue samples of pediatric GBM were evaluated for the MGMT promoter methylation status using methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA). Methylation status was also evaluated using methylation-specific polymerase chain reaction (MSP) for 17 of the 19 patients. The correlation between MGMT promoter methylation and clinical outcome was assessed.

RESULTS

Three of the 19 patients (16%) showed methylation of the MGMT promoter, according to MS-MLPA, as did 1 of the 17 (6%), according to MSP. The methylation status did not seem to have a definite effect on clinical outcome.

CONCLUSIONS

Pediatric GBMs rarely have methylated MGMT promoters. With a better clinical outcome and lower methylation rate than their adult counterparts, it may be suggested that, for pediatric GBM, MGMT promoter methylation does not play a significant role as a prognostic factor.