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Purpose: MRI-based radiomics models can predict genetic markers in pediatric low-grade glioma (pLGG). These models usually require tumour segmentation, which is tedious and time consuming if done manually. We propose a deep learning (DL) model to automate tumour segmentation and build an end-to-end radiomics-based pipeline for pLGG classification. Methods: The proposed architecture is a 2-step U-Net based DL network. The first U-Net is trained on downsampled images to locate the tumour. The second U-Net is trained using image patches centred around the located tumour to produce more refined segmentations. The segmented tumour is then fed into a radiomics-based model to predict the genetic marker of the tumour. Results: Our segmentation model achieved a correlation value of over 80% for all volume-related radiomic features and an average Dice score of.795 in test cases. Feeding the auto-segmentation results into a radiomics model resulted in a mean area under the ROC curve (AUC) of.843, with 95% confidence interval (CI) [.78-.906] and.730, with 95% CI [.671-.789] on the test set for 2-class (BRAF V600E mutation BRAF fusion) and 3-class (BRAF V600E mutation BRAF fusion and Other) classification, respectively. This result was comparable to the AUC of.874, 95% CI [.829-.919] and.758, 95% CI [.724-.792] for the radiomics model trained and tested on the manual segmentations in 2-class and 3-class classification scenarios, respectively. Conclusion: The proposed end-to-end pipeline for pLGG segmentation and classification produced results comparable to manual segmentation when it was used for a radiomics-based genetic marker prediction model. [ABSTRACT FROM AUTHOR]

The article discusses the IDH-wt?H3-wt diffuse gliomas arising mainly in middle-aged adults and grading for it by World Health Organization (WHO) which is characterized by BRAF mutation, FGFR alteration or MYB or MYBLI rearrangement.

Medulloblastoma is the most common malignant brain tumor in children. Overall survival rates have improved in recent years as a result of risk-stratified treatment regimens. However, medulloblastoma remains associated with substantial mortality, and survivors often experience debilitating neurological, endocrinological, and social sequelae as a result of treatment. Targeted and less toxic therapeutic strategies are therefore needed. In this issue of the JCI, Baryawno et al. report their findings that a large percentage of primary medulloblastomas and medulloblastoma cell lines are infected with human cytomegalovirus (HCMV) and suggest that targeting this virus could provide a new way to treat individuals with medulloblastoma. [ABSTRACT FROM AUTHOR]

Objectives: Currently, the BRAF status of pediatric low-grade glioma (pLGG) patients is determined through a biopsy. We established a nomogram to predict BRAF status non-invasively using clinical and radiomic factors. Additionally, we assessed an advanced thresholding method to provide only high-confidence predictions for the molecular subtype. Finally, we tested whether radiomic features provide additional predictive information for this classification task, beyond that which is embedded in the location of the tumor. Methods: Random forest (RF) models were trained on radiomic and clinical features both separately and together, to evaluate the utility of each feature set. Instead of using the traditional single threshold technique to convert the model outputs to class predictions, we implemented a double threshold mechanism that accounted for uncertainty. Additionally, a linear model was trained and depicted graphically as a nomogram. Results: The combined RF (AUC: 0.925) outperformed the RFs trained on radiomic (AUC: 0.863) or clinical (AUC: 0.889) features alone. The linear model had a comparable AUC (0.916), despite its lower complexity. Traditional thresholding produced an accuracy of 84.5%, while the double threshold approach yielded 92.2% accuracy on the 80.7% of patients with the highest confidence predictions. Conclusion: Models that included radiomic features outperformed, underscoring their importance for the prediction of BRAF status. A linear model performed similarly to RF but with the added benefit that it can be visualized as a nomogram, improving the explainability of the model. The double threshold technique was able to identify uncertain predictions, enhancing the clinical utility of the model. Clinical relevance statement: Radiomic features and tumor location are both predictive of BRAF status in pLGG patients. We show that they contain complementary information and depict the optimal model as a nomogram, which can be used as a non-invasive alternative to biopsy. Key Points: • Radiomic features provide additional predictive information for the determination of the molecular subtype of pediatric low-grade gliomas patients, beyond what is embedded in the location of the tumor, which has an established relationship with genetic status. • An advanced thresholding method can help to distinguish cases where machine learning models have a high chance of being (in)correct, improving the utility of these models. • A simple linear model performs similarly to a more powerful random forest model at classifying the molecular subtype of pediatric low-grade gliomas but has the added benefit that it can be converted into a nomogram, which may facilitate clinical implementation by improving the explainability of the model. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Pediatric high-grade glioma (pHGG) is highly malignant central nervous system tumor and constitute 10% of the pediatric gliomas. Effective treatment needs a functioning multi-disciplinary team including pediatric neuro oncologist, neurosurgeon, neuroradiologist, neuropathologist and radiation oncologist. Despite surgical resection, radiotherapy and chemotherapy, most HGG will recur resulting in early death. A significant proportion of HGG occurs in context of cancer predisposition syndromes like Constitutional Mismatch Repair Deficiency (CMMRD) also known as Biallelic Mismatch Repair Deficiency (bMMRD) characterized by high mutational burden. The incidence of HGG with CMMRD is one per million patients. bMMRD is caused by homozygous germline mutations in one of the four Mis Match Repair (MMR) genes (PMS2, MLH1, MSH2, and MSH6). The use of TMZ is now avoided in CMMRD related HGG due to its limited response and known ability to increase the accumulation of somatic mutations in these patients, increasing the risk of secondary tumors. HGG should be managed under the care of multidisciplinary team to receive optimum treatment. This is particularly important for low middle-income countries (LMIC) with limited resources like Pakistan. [ABSTRACT FROM AUTHOR]

Purpose: Biopsy-based assessment of H3 K27 M status helps in predicting survival, but biopsy is usually limited to unusual presentations and clinical trials. We aimed to evaluate whether radiomics can serve as prognostic marker to stratify diffuse intrinsic pontine glioma (DIPG) subsets. Methods: In this retrospective study, diagnostic brain MRIs of children with DIPG were analyzed. Radiomic features were extracted from tumor segmentations and data were split into training/testing sets (80:20). A conditional survival forest model was applied to predict progression-free survival (PFS) using training data. The trained model was validated on the test data, and concordances were calculated for PFS. Experiments were repeated 100 times using randomized versions of the respective percentage of the training/test data. Results: A total of 89 patients were identified (48 females, 53.9%). Median age at time of diagnosis was 6.64 years (range: 1–16.9 years) and median PFS was 8 months (range: 1–84 months). Molecular data were available for 26 patients (29.2%) (1 wild type, 3 K27M-H3.1, 22 K27M-H3.3). Radiomic features of FLAIR and nonenhanced T1-weighted sequences were predictive of PFS. The best FLAIR radiomics model yielded a concordance of.87 [95% CI:.86–.88] at 4 months PFS. The best T1-weighted radiomics model yielded a concordance of.82 [95% CI:.8–.84] at 4 months PFS. The best combined FLAIR + T1-weighted radiomics model yielded a concordance of.74 [95% CI:.71–.77] at 3 months PFS. The predominant predictive radiomic feature matrix was gray-level size-zone. Conclusion: MRI-based radiomics may predict progression-free survival in pediatric diffuse midline glioma/diffuse intrinsic pontine glioma. [ABSTRACT FROM AUTHOR]

Histone H3 mutations at amino acids 27 (H3K27M) and 34 (H3G34R) are recurrent drivers of pediatric-type high-grade glioma (pHGG). H3K27M mutations lead to global disruption of H3K27me3 through dominant negative PRC2 inhibition, while H3G34R mutations lead to local losses of H3K36me3 through inhibition of SETD2. However, their broader oncogenic mechanisms remain unclear. We characterized the H3.1K27M, H3.3K27M and H3.3G34R interactomes, finding that H3K27M is associated with epigenetic and transcription factor changes; in contrast H3G34R removes a break on cryptic transcription, limits DNA methyltransferase access, and alters mitochondrial metabolism. All 3 mutants had altered interactions with DNA repair proteins and H3K9 methyltransferases. H3K9me3 was reduced in H3K27M-containing nucleosomes, and cis-H3K9 methylation was required for H3K27M to exert its effect on global H3K27me3. H3K9 methyltransferase inhibition was lethal to H3.1K27M, H3.3K27M and H3.3G34R pHGG cells, underscoring the importance of H3K9 methylation for oncohistone-mutant gliomas and suggesting it as an attractive therapeutic target. [ABSTRACT FROM AUTHOR]

We performed genome‐wide methylation analysis on 136 pediatric low‐grade gliomas, identifying a unique cluster consisting of three tumors with oligodendroglioma‐like histology, BRAF p.V600E mutations and recurrent whole chromosome gains of 7 and loss of 10. Morphologically, all showed similar features, including a diffusely infiltrative glioma composed of round nuclei with perinuclear halos, a chicken‐wire pattern of branching capillaries and microcalcification. None showed astrocytic features or characteristics suggestive of high‐grade tumors including necrosis or mitotic figures. All tumors harbored multiple chromosomal copy number abnormalities (>10 chromosomes altered), but none showed 1p/19q co‐deletion or IDH1 p.R132H mutation. Hierarchical clustering and t‐stochastic neighbor embedding analyses from DNA methylation data cluster them more closely to previously described pediatric‐type low‐grade gliomas and separate from adult gliomas. These tumors exhibit distinct clinical features; they are temporal lobe lesions occurring in adolescents and young adults with a prolonged history of seizures and all are alive with no recurrence (follow‐up 3.2 to 13.2 years). We encountered another young adult case with quite similar pathological appearance and molecular status except for TERT promoter mutation. Although the series is small, these may represent a new category of IDH wild‐type low‐grade gliomas which may be confused with "molecular GBM." Further, they highlight the heterogeneity of IDH wild‐type gliomas and the relatively indolent behavior of "pediatric‐type" gliomas. [ABSTRACT FROM AUTHOR]

cIMPACT‐NOW (the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy) was established to provide a forum to evaluate and recommend proposed changes to future CNS tumor classifications. From 2016 to 2019 (Round 1), cIMPACT published four updates. Update 1 clarified the use of the term NOS (Not Otherwise Specified) and proposed use of the additional term NEC (Not Elsewhere Classified). Update 2 issued clarifications regarding two diagnoses: Diffuse Midline Glioma, H3 K27M‐mutant and Diffuse Astrocytoma/Anaplastic Astrocytoma, IDH‐mutant. Update 3 proposed molecular criteria that could be used in the setting of an IDH‐wildtype diffuse or anaplastic astrocytic glioma without histological features of glioblastoma to infer that the tumor would behave similarly to a grade IV glioblastoma. Update 4 suggested that, in children and young adults, subtypes of IDH‐wildtype/H3‐wildtype diffuse gliomas may have distinct clinical features in the setting of a BRAFV600E mutation, FGFR1 alteration, other MAPK pathway alteration, or a MYB or MYBL1 rearrangement. The practical diagnostic relevance of these cIMPACT proposals is highlighted in this summary. [ABSTRACT FROM AUTHOR]

Background: Mutations in the tail of histone H3 (K27M) are frequently found in pediatric midline high-grade glioma's but have rarely been reported in other malignancies. Recently, recurrent somatic nucleotide variants in histone H3 (H3 K27M) have been reported in group A posterior fossa ependymoma (EPN_PFA), an entity previously described to have no recurrent mutations. However, the true incidence of H3 K27M mutations in EPN_PFA is unknown. Methods: In order to discern the frequency of K27M mutations in histone H3 in EPN_PFA, we analyzed 151 EPN_PFA previously profiled with genome-wide methylation arrays using a validated droplet digital PCR assay. Results: We identified only 1 case out of 151 EPN_PFA harboring the K27M mutation indicating that histone mutations are extremely rare in EPN_PFA. Morphologically, this single mutated case is clearly consistent with an ependymoma, and the presence of the K27M mutation was confirmed using immunohistochemistry. Discussion: K27M mutations are extremely rare in EPN_PFA. Routine evaluation of K27M mutations in EPN_PFA is of limited utility, and is unlikely to have any bearing on prognosis and/or future risk stratification. [ABSTRACT FROM AUTHOR]

Hemispheric low-grade gliomas account for the second most common location in pediatric low-grade gliomas (PLGGs) after the cerebellum. The pathological spectrum includes gangliogliomas, dysembryoplastic neuroepithelial tumors (DNETs), diffuse astrocytomas, pilocytic astrocytomas, and pleomorphic xanthoastrocytomas (PXAs), among others. Clinically, hemispheric PLGGs represent a well-recognized cause of intractable epilepsy in children and adolescents. With an excellent long-term outcome, surgery remains the cornerstone and patients with gross total resection typically do not need any further therapies. The recent literature about hemispheric PLGGs was reviewed to provide an up-to-date overview of the molecular and cell biology of these tumors. Hemispheric PLGGs can harbor multiple alterations involving BRAFV600E, FGFR, NTRK, MYB/MYBL1, IDH, and BRAF-KIAA1549 fusions. However, the clinical significance of most of these alterations is still to be defined. The role of RAS/MAPK mutations and other alterations in hemispheric PLGGs is of interest from diagnostic, prognostic, and therapeutic perspectives. Molecular testing for these tumors should be encouraged, since the findings can have an important impact not only in prognosis but also in therapeutic strategies. [ABSTRACT FROM AUTHOR]

Paediatric brain tumours arising in the thalamus present significant diagnostic and therapeutic challenges to physicians due to their sensitive midline location. As such, genetic analysis for biomarkers to aid in the diagnosis, prognosis and treatment of these tumours is needed. Here, we identified 64 thalamic gliomas with clinical follow-up and characterized targeted genomic alterations using newly optimized droplet digital and NanoString-based assays. The median age at diagnosis was 9.25 years (range, 0.63-17.55) and median survival was 6.43 (range, 0.01-27.63) years. Our cohort contained 42 and 22 tumours reviewed as low and high grade gliomas, respectively. Five (12 %) low grade and 11 (50 %) high grade gliomas were positive for the H3F3A/HIST1H3B K27M (H3K27M) mutation. Kaplan-Meier survival analysis revealed significantly worse overall survival for patients harbouring the H3K27M mutation versus H3F3A/ HIST1H3B wild type (H3WT) samples (log-rank p < 0.0001) with a median survival of 1.02 vs. 9.12 years. Mitogen-activated protein kinase (MAPK) pathway activation via BRAF or FGFR1 hotspot mutations or fusion events were detected in 44 % of patients, and was associated with long-term survival in the absence of H3K27M (log-rank p < 0.0001). Multivariate analysis demonstrated H3K27M status and high grade histology to be the most significant independent predictors of poor overall survival with hazard ratios of 6.945 and 7.721 (p < 0.0001), respectively. In contrast, MAPK pathway activation is a predictor of favourable patient outcome, although not independent of other clinical factors. Importantly, we show that low grade malignancies may harbour H3K27M mutations and that these tumours show a dismal survival compared to low grade H3WT cases. Our data strongly supports the inclusion of targeted genetic testing in childhood thalamic tumours to most accurately stratify patients into appropriate risk groups. [ABSTRACT FROM AUTHOR]

Background: The determinants of outcomes for adult survivors of pediatric low-grade glioma (PLGG) are largely unknown.Methods: This study collected population-based follow-up information for all PLGG patients diagnosed in Ontario, Canada from 1985 to 2012 (n = 1202) and determined factors affecting survival. The impact of upfront radiation treatment on overall survival (OS) was determined for a cohort of Ontario patients and an independent reference cohort from the Surveillance, Epidemiology, and End Results database.Results: At a median follow-up of 12.73 years (range, 0.02-33 years), only 93 deaths (7.7%) were recorded, and the 20-year OS rate was 90.1% ± 1.1%. Children with neurofibromatosis type 1 had excellent survival and no tumor-related deaths during adulthood. Adverse risk factors included pleomorphic xanthoastrocytoma (P < .001) and a thalamic location (P < .001). For patients with unresectable tumors surviving more than 5 years after the diagnosis, upfront radiotherapy was associated with an approximately 3-fold increased risk of overall late deaths (hazard ratio [HR], 3.3; 95% confidence interval [CI], 1.6-6.6; P = .001) and an approximately 4-fold increased risk of tumor-related deaths (HR, 4.4; 95% CI, 1.3-14.6; P = .013). In a multivariate analysis, radiotherapy was the most significant factor associated with late all-cause deaths (HR, 3.0; 95% CI, 1.3-7.0; P = .012) and tumor-related deaths (HR, 4.4; 95% CI, 1.3-14.6; P = 0.014). A similar association between radiotherapy and late deaths was observed in the independent reference cohort (P < .001). In contrast to early deaths, late mortality was associated not with PLGG progression but rather with tumor transformation and non-oncological causes.Conclusions: The course of PLGG is associated with excellent long-term survival, but this is hampered by increased delayed mortality in patients receiving upfront radiotherapy. These observations should be considered when treatment options are being weighed for these patients. [ABSTRACT FROM AUTHOR]

Introduction: Diffuse intrinsic pontine glioma (DIPG) and midline high-grade glioma (mHGG) are lethal childhood brain tumors. Spatial genomic heterogeneity has been well-described in adult HGG but has not been comprehensively characterized in pediatric HGG. We performed whole exome sequencing on 38-matched primary, contiguous, and metastatic tumor sites from eight children with DIPG (n = 7) ormHGG (n = 1) collected using a unique MRI-guided autopsy protocol. Validation was performed using Sanger sequencing, Droplet Digital polymerase-chain reaction, immunohistochemistry, and fluorescent in-situ hybridization. Results: Median age at diagnosis was 6.1 years (range: 2.9-23.3 years). Median overall survival was 13.2 months (range: 11.2-32.2 months). Contiguous tumor infiltration and distant metastases were observed in seven and six patients, respectively, including leptomeningeal dissemination in three DIPGs. Histopathological heterogeneity was evident in seven patients, including intra-pontine heterogeneity in two DIPGs, ranging from World Health Organization grade II to IV astrocytoma. We found conservation of heterozygous K27M mutations in H3F3A (n = 4) or HIST1H3B (n = 3) across all primary, contiguous, and metastatic tumor sites in all DIPGs. ACVR1 (n = 2), PIK3CA (n = 2), FGFR1 (n = 2), and MET (n = 1) were also intra-tumorally conserved. ACVR1 was co-mutated with HIST1H3B (n = 2). In contrast, PDGFRA amplification and mutation were spatially heterogeneous, as were mutations in BCOR (n = 1), ATRX (n = 2), and MYC (n = 1). TP53 aberrations (n = 3 patients) varied by type and location between primary and metastatic tumors sites but were intra-tumorally conserved. Conclusion: Spatial conservation of prognostically-relevant and therapeutically-targetable somatic mutations in DIPG and mHGG contrasts the significant heterogeneity of driver mutations seen in adult HGG and supports uniform implementation of diagnostic biopsy in DIPG and mHGG to classify molecular risk groups and guide therapeutic strategy. [ABSTRACT FROM AUTHOR]

The article discusses a study related to supratentorial gliomas which reveals discrete genomic alterations to discriminate discriminate pilocytic astrocytomas, diffuse gliomas, and glioblastoma. Topics discussed includes co-deletion of chromosomes not revealed by loss of heterozygosity analysis for variant allele frequency, assess for the changes by transcriptional analysis of spinal cord astrocytomas, and success in BRAF-mutant cancer types with the BRAFâ€MEK inhibitors.

Diffuse intrinsic pontine glioma (DIPG) is the main cause of brain tumour-related death in children. In the majority of cases diagnosis is based on clinical and MRI findings, resulting in the scarcity of pre-treatment specimens available to study. Our group has developed an autopsy-based protocol to investigate the histologic and biologic spectrum of DIPG. This has also allowed us to investigate the terminal pattern of disease and gain a better understanding of what challenges we are facing in treating DIPG. Here, we review 72 DIPG cases with well documented clinical history and molecular data and describe the pathological features of this disease in relation to clinical and genetic features. Fifty-three of the samples were autopsy material (7 pre-treatment) and 19 were pre-treatment biopsy/surgical specimens. Upon histological review, 62 patients had high-grade astrocytomas (18 WHO grade III and 44 WHO grade IV patients), 8 had WHO grade II astrocytomas, and 2 had features of primitive neuroectodermal tumour (PNET). K27M-H3 mutations were exclusively found in tumours with WHO grade II-IV astrocytoma histology. K27M-H3.1 and ACVR1 mutations as well as ALT phenotype were only found in WHO grade III-IV astrocytomas, while PIK3CA mutations and PDGFRA gains/amplifications were found in WHO grade II-IV astrocytomas. Approximately 1/3 of DIPG patients had leptomeningeal spread of their tumour. Further, diffuse invasion of the brainstem, spinal cord and thalamus was common with some cases showing spread as distant as the frontal lobes. These findings suggest that focal radiation may be inadequate for some of these patients. Importantly, we show that clinically classic DIPGs represent a diverse histologic spectrum, including multiple cases which would fit WHO criteria of grade II astrocytoma which nevertheless behave clinically as high-grade astrocytomas and harbour the histone K27M-H3.3 mutation. This suggests that the current WHO astrocytoma grading scheme may not appropriately predict outcome for paediatric brainstem gliomas. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Gliomas represent the most common type of brain tumor, but show considerable variability in histologic appearance and clinical outcome. The phenotypic differences between types and grades of gliomas have not been explained solely on the grounds of differing oncogenic stimuli. Several studies have demonstrated that some phenotypic differences may be attributed to regional differences in the neural stem cells from which tumors arise. We hypothesized that temporal differences may also play a role, with tumor phenotypic variability reflecting intrinsic differences in neural stem cells at distinct developmental stages. To determine how the tumorigenic potential of lineally related stem cells changes over time, we used a conditional transgenic system that integrates Cre-Lox-mediated and Tet-regulated expression to drive K-rasG12D expression in neuro-glial progenitor populations at different developmental time points. Using this model, we demonstrate that K-rasG12D-induced transformation is dependent on the developmental stage at which it is introduced. Diffuse malignant brain tumors develop during early embryogenesis but not when K-rasG12D expression is induced during late embryogenesis or early postnatal life. We show that differential expression of cell-cycle regulators during development may be responsible for this differing susceptibility to malignant transformation and that loss of p53 can overcome the transformation resistance seen at later developmental stages. These results highlight the interplay between genetic alterations and the molecular changes that accompany specific developmental stages; early progenitors may lack the regulatory mechanisms present at later, more lineage-restrictive, developmental time points, making them more susceptible to transformation. [ABSTRACT FROM AUTHOR]

Glioblastoma multiforme (GBM) is the most common and lethal of all gliomas. The current standard of care includes surgery followed by concomitant radiation and chemotherapy with the DNA alkylating agent temozolomide (TMZ). O6-methylguanine--DNA methyltransferase (MGMT) repairs the most cytotoxic of lesions generated by TMZ, O6-methylguanine. Methylation of the MGMT promoter in GBM correlates with increased therapeutic sensitivity to alkylating agent therapy. However, several aspects of TMZ sensitivity are not explained by MGMT promoter methylation. Here, we investigated our hypothesis that the base excision repair enzyme alkylpurine--DNA--N-glycosylase (APNG), which repairs the cytotoxic lesions N³-methyladenine and N7-methylguanine, may contribute to TMZ resistance. Silencing of APNG in established and primary TMZ-resistant GBM cell lines endogenously expressing MGMT and APNG attenuated repair of TMZ-induced DNA damage and enhanced apoptosis. Reintroducing expression of APNG in TMZ-sensitive GBM lines conferred resistance to TMZ in vitro and in orthotopic xenograft mouse models. In addition, resistance was enhanced with coexpression of MGMT. Evaluation of APNG protein levels in several clinical datasets demonstrated that in patients, high nuclear APNG expression correlated with poorer overall survival compared with patients lacking APNG expression. Loss of APNG expression in a subset of patients was also associated with increased APNG promoter methylation. Collectively, our data demonstrate that APNG contributes to TMZ resistance in GBM and may be useful in the diagnosis and treatment of the disease. [ABSTRACT FROM AUTHOR]

Congenital central nervous system (CNS) tumors are uncommon, accounting for 1% of all childhood brain tumors. They present clinically either at birth or within the first 3 months. Glioblastoma (GBM) only rarely occurs congenitally and has not been fully characterized. We examined clinicopathologic features and genetic alterations of six congenital GBMs. Tumors were seen by neuroimaging as large, complex cerebral hemispheric masses. All showed classic GBM histopathology, including diffuse infiltration, dense cellularity, GFAP-positivity, high mitotic activity, endothelial proliferation and pseudopalisading necrosis. Neurosurgical procedures and adjuvant therapies varied. Survivals ranged from 4 days to 7.5 years; two of the three long-term survivors received chemotherapy, whereas the three short-term survivors did not. Paraffin-embedded tissue sections were used for FISH analysis of EGFR, chromosomes 9p21 ( p16/CDKN2A) and 10q ( PTEN/DMBT1); sequencing of PTEN and TP53; and immunohistochemistry for EGFR and p53. We uncovered 10q deletions in two cases. No EGFR amplifications, 9p21 deletions, or mutations of TP53 or PTEN were noted; however, nuclear p53 immunoreactivity was strong in 5/6 cases. Tumors were either minimally immunoreactive (n = 3) or negative (n = 3) for EGFR. We conclude that congenital GBMs show highly variable survivals. They are genetically distinct from their adult counterparts and show a low frequency of known genetic alterations. Nonetheless, the strong nuclear expression of p53 in these and other pediatric GBMs could indicate that p53 dysregulation is important to tumorigenesis. [ABSTRACT FROM AUTHOR]

Spontaneous tumor regression is a unique feature of pediatric low-grade gliomas (PLGG). We speculated that lack of telomere maintenance is responsible for this behavior. We first looked for evidence of telomerase activity and alternative-lengthening telomeres (ALT) in 56 PLGG. Telomerase activity was observed in 0 of 11 PLGG in contrast to 10 of 13 high-grade pediatric brain tumors. There was no ALT in 45 of 45 samples. We applied Q-FISH to eight patients whose indolent PLGG underwent two metachronous biopsies over a lag of several years. Telomere shortening was observed in the second biopsy in all tumors but not in a normal brain control (P < .0001), indicating that lack of telomere maintenance is associated with continuous telomere erosion. Based on these observations, we observed that younger PLGG patients who exhibit more aggressive and frequently recurrent tumors had significantly longer telomeres than older ones (P = .00014). Tumors with a terminal restriction fragment length of <7.5 did not recur, whereas the presence of longer telomeres (>8.0) conferred a high likelihood of late recurrences in PLGG. Our findings provide a plausible biological mechanism to explain the tendency of PLGG to exhibit growth arrest and spontaneous regression. Telomere maintenance may therefore represent the first known biologic prognostic marker in PLGG. [ABSTRACT FROM AUTHOR]