IDH Wild-type Tumors Research Articles

Differences in spatial distribution between WHO 2016 low-grade glioma molecular subgroups.

BackgroundSeveral studies reported a correlation between anatomic location and genetic background of low-grade gliomas (LGGs). As such, tumor location may contribute to presurgical clinical decision-making. Our purpose was to visualize and compare the spatial distribution of different WHO 2016 gliomas, frequently aberrated single genes and DNA copy number alterations within subgroups, and groups of postoperative tumor volume.MethodsAdult grade II glioma patients (WHO 2016 classified) diagnosed between 2003 and 2016 were included. Tumor volume and location were assessed with semi-automatic software. All volumes of interest were mapped to a standard reference brain. Location heatmaps were created for each WHO 2016 glioma subgroup, frequently aberrated single genes and copy numbers (CNVs), as well as heatmaps according to groups of postoperative tumor volume. Differences between subgroups were determined using voxelwise permutation testing.ResultsA total of 110 IDH mutated astrocytoma patients, 92 IDH mutated and 1p19q co-deleted oligodendroglioma patients, and 22 IDH wild-type astrocytoma patients were included. We identified small regions in which specific molecular subtypes occurred more frequently. IDH-mutated LGGs were more frequently located in the frontal lobes and IDH wild-type tumors more frequently in the basal ganglia of the right hemisphere. We found no localizations of significant difference for single genes/CNVs in subgroups, except for loss of 9p in oligodendrogliomas with a predilection for the left parietal lobes. More extensive resections in LGG were associated with frontal locations.ConclusionsWHO low-grade glioma subgroups show differences in spatial distribution. Our data may contribute to presurgical clinical decision-making in LGG patients.

Interrelationships between molecular subtype, anatomical location, and extent of resection in diffuse glioma: a systematic review and meta-analysis

BackgroundThe introduction of the 2016 WHO Classification of Tumors of the Central Nervous System has resulted in tumor groupings with improved prognostic value for diffuse glioma patients. Molecular subtype, primarily based on IDH-mutational status and 1p/19q-status, is a strong predictor of survival. It is unclear to what extent this finding may be mediated by differences in anatomical location and surgical resectability among molecular subgroups. Our aim was to elucidate possible correlations between (1) molecular subtype and anatomical location and (2) molecular subtype and extent of resection.MethodsWe performed a systematic review of literature searching for studies on molecular subtype in relation to anatomical location and extent of resection. Only original data concerning adult participants suffering from cerebral diffuse glioma were included. Studies adopting similar outcomes measures were included in our meta-analysis.ResultsIn the systematic analysis for research questions 1 and 2, totals of 20 and 9 studies were included, respectively. Study findings demonstrated that IDH-mutant tumors were significantly more frequently located in the frontal lobe and less often in the temporal lobe compared with IDH-wildtype gliomas. Within the IDH-mutant group, 1p/19q-codeleted tumors were associated with more frequent frontal and less frequent temporal localization compared with 1p/19q-intact tumors. In IDH-mutant gliomas, greater extent of resection was achieved than in IDH-wildtype tumors.ConclusionsGenetic profile of diffuse cerebral glioma influences their anatomical location and seems to affect tumor resectability.

DNA methylation, transcriptome and genetic copy number signatures of diffuse cerebral WHO grade II/III gliomas resolve cancer heterogeneity and development

BackgroundDiffuse lower WHO grade II and III gliomas (LGG) are slowly progressing brain tumors, many of which eventually transform into a more aggressive type. LGG is characterized by widespread genetic and transcriptional heterogeneity, yet little is known about the heterogeneity of the DNA methylome, its function in tumor biology, coupling with the transcriptome and tumor microenvironment and its possible impact for tumor development.MethodsWe here present novel DNA methylation data of an LGG-cohort collected in the German Glioma Network containing about 85% isocitrate dehydrogenase (IDH) mutated tumors and performed a combined bioinformatics analysis using patient-matched genome and transcriptome data.ResultsStratification of LGG based on gene expression and DNA-methylation provided four consensus subtypes. We characterized them in terms of genetic alterations, functional context, cellular composition, tumor microenvironment and their possible impact for treatment resistance and prognosis. Glioma with astrocytoma-resembling phenotypes constitute the largest fraction of nearly 60%. They revealed largest diversity and were divided into four expression and three methylation groups which only partly match each other thus reflecting largely decoupled expression and methylation patterns. We identified a novel G-protein coupled receptor and a cancer-related ‘keratinization’ methylation signature in in addition to the glioma-CpG island methylator phenotype (G-CIMP) signature. These different signatures overlap and combine in various ways giving rise to diverse methylation and expression patterns that shape the glioma phenotypes. The decrease of global methylation in astrocytoma-like LGG associates with higher WHO grade, age at diagnosis and inferior prognosis. We found analogies between astrocytoma-like LGG with grade IV IDH-wild type tumors regarding possible worsening of treatment resistance along a proneural-to-mesenchymal axis. Using gene signature-based inference we elucidated the impact of cellular composition of the tumors including immune cell bystanders such as macrophages.ConclusionsGenomic, epigenomic and transcriptomic factors act in concert but partly also in a decoupled fashion what underpins the need for integrative, multidimensional stratification of LGG by combining these data on gene and cellular levels to delineate mechanisms of gene (de-)regulation and to enable better patient stratification and individualization of treatment.

Controversies in the Therapy of Low-Grade Gliomas.

In the context of the new WHO classification system, all low-grade gliomas must have an IDH mutation, with or without 1p/19q codeletion. Upon discovery of the tumor, maximal safe surgical resection is the most appropriate first step due to the current inability to differentiate between IDH mutant and IDH wild-type tumors by imaging alone. In the postoperative setting, based on the synthesis and interpretation of the available data, we recommend utilizing conventional radiation therapy and PCV in all high-risk-low-grade gliomas. For patients felt to be in a low risk category, we recommend maintaining a low threshold to initiate treatment. In the setting of tumor recurrence, consideration of all treatment options is reasonable, but treatment with alkylator therapy has the strongest supporting data.

Awake craniotomies for epileptic gliomas: intraoperative and postoperative seizure control and prognostic factors.

Awake craniotomy is well-established for tumors resected in eloquent brain areas. Whether awake craniotomy provides improved seizure control in patients with epileptic gliomas has not been well evaluated. This study analyzed the incidence, risk factors and outcome of seizures during and following awake craniotomies for patients presenting with epilepsy and glioma. Forty-one patients undergoing awake craniotomies for epileptic gliomas were retrospectively analyzed. Postoperative seizure was defined as either early (postoperative day 7 + before) or late onset (after postoperative day 7). Neurologic function was assessed with modified Rankin Scales (mRS) and seizure outcome was assessed using International League Against Epilepsy (ILAE) classification. Multivariable logistic regression was used for clinical variables associated with postoperative seizures. Three patients (7.3%) had intraoperative seizures however did not fail the awake craniotomies. Mean mRS before and after the awake craniotomies were 2.4 and 2.1, respectively (P = 0.032). Fourteen (34.1%) patients had early seizures, which caused longer hospitalization than those without early seizures (P = 0.03). Surgical resection to isocitrate dehydrogenase 1 (IDH1) mutation tumors, comparing to IDH1 wild type tumors, caused better postoperative seizure control. 6-month late seizure freedom was achieved in 33 patients (80.5%). Early seizure recurrence (odds ratio = 30.75; P = 0.039) and postoperative mRS ≥ 3 (odds ratio = 7.00; P = 0.047) were independent risk factors for late seizures. Intraoperative seizures could be well-controlled during awake craniotomies. Early postoperative seizures extended hospitalization and strongly predicted late seizure recurrence. Awake craniotomies benefited long-term seizure control in patients with epileptic gliomas.

Abstract PR15: The oncometabolite R-2-Hydroxyglutarate suppresses the innate immune microenvironment of IDH1-mutated gliomas via aryl hydrocarbon receptor signaling

Abstract Background: IDH1-mutated gliomas are associated with less abundant and phenotypically skewed innate and adaptive immune cell infiltrates compared to IDH1 wild-type tumors. Despite this, the most frequent mutation—IDH1R132H—represents a clonal shared neoantigen and mutations in IDH are associated with a more favorable prognosis. While the tumor cell-intrinsic consequences of the oncometabolite R-2-hydroxyglutarate (R-2-HG) accumulating in IDH1-mutated gliomas as a result of a neomorphic enzymatic function are well-characterized, potential direct paracrine effects of R-2-HG influencing the glioma immune microenvironment remain incompletely understood. Aim: This study aimed at characterizing the impact of the oncometabolite R-2-HG on the innate immune microenvironment of IDH1-mutated gliomas. Methods and Results: By means of comprehensive analyses of expression datasets from human gliomas and syngeneic murine tumor models as well as transporter studies, we demonstrate that R-2-HG is imported by both microglia and macrophages via SLC family transporters and suppresses their function in a paracrine manner. Functional analyses of microglia and macrophages indicate an R-2-HG-driven induction of tolerogenicity as evidenced by accumulation of IL10 and TGFβ and suppression of MHC-II expression, which results in impaired activation of antigen-specific T-cells and activation of immune checkpoint molecules. Multilevel signature profiling of human tumor-infiltrating as well as primary immune cells was complemented by reporter gene assays and pathway analyses and revealed that R-2-HG activates the cytosolic transcription factor aryl hydrocarbon receptor (AHR), a key immunomodulatory target of immunosuppressive tryptophan metabolism. By means of knockout models, the observed immunosuppressive phenotype was shown to be AHR-dependent. Functional relevance of R-2-HG-mediated, AHR-driven impairment of myeloid cell immunity was demonstrated in vivo by pharmacologic AHR inhibition, increasing the efficacy of checkpoint blockade. Conclusion: R-2-HG impairs antitumor immunity in IDH1-mutated gliomas by activating the AHR in innate immune cells, thus suppressing the innate immune microenvironment by compromising antigen presentation and activation of antigen-specific T-cells. This, together with recent findings on inhibitory effects on T-cell immunity, represents a novel mechanism of immune evasion of an immunogenic driver mutation and opens a novel therapeutic approach to IDH1-mutated gliomas. Citation Format: Mirco Friedrich, Lukas Bunse, Theresa Bunse, Edward Green, Tobias Kessler, Stefan Pusch, Katrin Deumelandt, Rafael Carretero, Andreas von Deimling, Francisco J Quintana, Wolfgang Wick, Michael Platten. The oncometabolite R-2-Hydroxyglutarate suppresses the innate immune microenvironment of IDH1-mutated gliomas via aryl hydrocarbon receptor signaling [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr PR15.

Molecular features and clinical outcomes in surgically treated low-grade diffuse gliomas in patients over the age of 60.

WHO grade II gliomas are uncommon in patients over the age of 60, and there is a lack in consensus regarding their management. We present molecular tumor characteristics as well as clinical outcomes in patients over the age of 60 undergoing surgical resection of a WHO grade II glioma. After receiving IRB approval, patients were identified through the UCSF Brain Tumor Center. Pathologic diagnosis was completed using WHO 2016 grading criteria. Twenty-six patients with a mean age of 66years met inclusion criteria with a median follow-up of 5.2years. Diagnoses included diffuse astrocytoma IDH-mutant (19.2%), diffuse astrocytoma IDH-wildtype (26.9%), Oligodendroglioma IDH-mutant and 1p/19q-codeleted (50%), and a rare case of mixed oligoastrocytoma (3.9%). 66% of astrocytoma IDH-wildtype tumors possessed TERT mutation. Median extent of resection was 75.4%. Progression-free (PFS) and overall survival (OS) were 23.5 and 62.6months, respectively. Shorter PFS was associated with the astrocytoma IDH-wildtype subtype despite similar extent of resection and adjuvant treatment rates compared to the other subtypes. OS did not differ between subtypes. Malignant transformation and death were associated with larger preoperative and residual tumor volume. Older patients with diffuse gliomas may safely undergo aggressive treatment with surgical resection and adjuvant therapy. Elderly patients with low grade gliomas have worse clinical outcomes compared to their younger counterparts. This may be due to an increased frequency of diffuse astrocytoma IDH-wildtype tumors in this age group.

Surgical management of lower-grade glioma in the spotlight of the 2016 WHO classification system.

According to the 2016 WHO classification lower-grade gliomas consist of three groups: IDH-mutated and 1p/19q co-deleted, IDH-mutated and IDH-wildtype tumors. The aim of this study was to evaluate the impact of surgical therapy for lower-grade gliomas with a particular focus on the molecular subgroups. This is a bi-centric retrospective analysis including 299 patients, who underwent treatment for lower-grade glioma between 1990 and 2016. All tumors were re-classified according to the 2016 WHO classification. Data concerning baseline and tumor characteristics, overall survival, different treatment modalities and functional outcome were analyzed. A total of 112 (37.5%) patients with IDH-mutation and 1p/19q co-deletetion, 86 (28.8%) patients with IDH-mutation and 101 (33.8%) patients with IDH-wildtype tumors were identified. The median overall survival (mOS) differed significantly between the groups (p < 0.001). Surgical resection was performed in 226 patients and showed significantly improved mOS compared to the biopsy group (p = 0.001). Gross total resection (GTR) was associated with better survival (p = 0.007) in the whole cohort as well as in the IDH-mutated and IDH-wildtype groups compared to partial resection or biopsy. IDH-wildtype patients presented a significant survival benefit after combined radio-chemotherapy compared to radio- or chemotherapy alone (p = 0.02). Good clinical status (NANO) was associated with longer OS (p = 0.001). The impact of surgical treatment on the outcome of lower-grade gliomas depends to a great extent on the molecular subtype of the tumors. Patients with more aggressive tumors (IDH-wildtype) seem to profit from more intensive treatment like GTR, multiple resections and combined radio-/chemotherapy.

GENE-11. SMALL TERMINAL ALTERATIONS AND ALTERNATIVE LENGTHENING OF TELOMERES ARE A FEATURE OF IDH-MUTANT, 1p/19q NON-CODELETED GLIOMAS

Gliomas are typified by genetic variability and instability. The full potential of molecular genetics to classify tumors has not been realized. We previously proposed a novel glioma classification system that increases the sensitivity and specificity of diagnosis and improve prognostication. We have completed copy number array mutational analyses and a targeted next-generation sequencing 50-gene glioma panel on 148 Mayo Clinic formalin-fixed paraffin-embedded gliomas with subsequent data validation performed on 419 gliomas from the TCGA. Median age at resection was 49 years (range: 17–80; 95% 46.5–51.6 years). There were 36 (24.3%) IDH-mutant, 1p/19q codeleted oligodendrogliomas; 46 (31.1%) IDH-mutant, 1p/19q non-codeleted astrocytomas and 66 (44.6%) IDH-wildtype gliomas. Small terminal alterations (STAs) defined as copy number variations (CNVs) IDH-mutant, 1p/19q non-codeleted tumors. Acquisition of 32 STAs was observed in 47% IDH-mutant, 1p/19q non-codeleted versus 27% IDH-wildtype tumors (P=1.8x10-5). In the TCGA dataset, these were seen in 67% versus 26% respectively (P=2.8x10-16). STAs were glioma subclass-specific and did not correlate with overall genetic instability as determined manually or with a computational method. ATRX loss was observed in 27 of 41 (65.9%) tumors with an ATRX mutation versus 20 of 106 (18.9%) ATRX-wildtype tumors (P=1.3x10-7). ATRX loss also correlated with the alternative lengthening of telomeres (ALT) phenotype and was seen in 25 of 31 (80.6%) ALT-positive versus 7 of 55 (12.7%) ALT-negative tumors (P=1.5x10-9). STAs were present in 19 of 32 (59.4%) ALT-positive cases and 8 of 35 (22.9%) ALT-negative cases (P=0.0061). IDH-mutant, 1p/19q non-codeleted astrocytomas have a high prevalence of STAs. This is associated with ATRX loss and the ALT. These alterations do not appear to have de novo implications for survival but may provide novel diagnostic tools and therapeutic targets.

IDH1R132H is intrinsically tumor-suppressive but functionally attenuated by the glutamate-rich cerebral environment.

Recurrent heterozygous mutation of isocitrate dehydrogenase 1 gene (IDH1), predominantly resulting in histidine substitution at arginine 132, was first identified in glioma. The biological significance of IDH1R132H, however, has been controversial, and its prevalent association with glioma remains enigmatic. Although recent studies indicate that IDH1R132H is nonessential to tumor growth or even anti-tumor growth, whether IDH1R132H initiates gliomagenesis remains obscure. In this study, we report that IDH1R132H is intrinsically tumor-suppressive but the activity can be attenuated by glutamate—the cerebral neurotransmitter. We observed that IDH1R132H was highly suppressive of subcutaneous tumor growth driven by platelet-derived growth factor B (PDGFB), but IDH1R132H tumor growth and glioma penetrance were virtually indistinguishable from those of IDH1-wildtype tumors in orthotopic models. In vitro, addition of glutamate compromised IDH1R132H inhibition of neurosphere genesis, indicating glutamate promotion of oncogenic dominance. Furthermore, we observed that IDH1R132H expression was markedly decreased in tumors but became more permissible upon the deletion of tumor-suppressor gene Cdkn2a. To provide direct evidence for the opposing effect of IDH1R132H on PDGFB-driven glioma development, we explored tandem expression of the two molecules from a single transcript to preclude selection against IDH1R132H expression. Our results demonstrate that when juxtaposed with oncogenic PDGFB, IDH1R132H overrides the oncogenic activity and obliterates neurosphere genesis and gliomagenesis even in the glutamate-rich microenvironment. We propose therefore that IDH1R132H is intrinsically suppressive of glioma initiation and growth but such tumor-suppressive activity is compromised by the glutamate-rich cerebral cortex, thereby offering a unifying hypothesis for the perplexing role of IDH1R132H in glioma initiation and growth.

Abstract 5325: 5-hydroxymethylcytosine profiling identifies differential targeting in IDH1 mutant versus IDH1 wild-type high-grade gliomas

Abstract Glioblastoma demonstrates significant epigenetic dysregulation with subgroup differences highlighted by the Glioma CpG-Island Methylator Phenotype (G-CIMP) seen in IDH1 mutant tumors. 5-hydroxymethylcytosine (5hmC) has been implicated in IDH1 wild-type gliomas, however its role in IDH1 mutant tumors remains incompletely understood. We examined 5hmC profiles in high grade (WHO III/IV) IDH1 mutant (n = 12) and IDH1 wild-type (n = 9) tumors through parallel processing of samples using bisulfite (BS) and oxidative bisulfite (OxBS) conversion, with subsequent analysis on the Illumina MethylationEPIC Beadchip platform. Hydroxymethylation profiles were correlated with gene expression measured using the Affymetrix Human Gene 2.0 ST array platform. Cumulative density plots for mean 5hmC β-value across IDH1 mutant and wild-type tumors demonstrated 5hmC accumulation predominantly within the top 10th percentile of probes. No significant difference in global 5hmC levels between IDH1 mutant versus wild-type tumors was evident. Mean 5hmC β-values were 4.6%% and 3.8% for IDH1 mutant and wild-type tumors across all probes, respectively. To focus on regions with greatest 5hmC abundance, we assessed probes among the top 1% mean 5hmC β-values. In addition to probes with high 5hmC abundance, differentially hydroxymethylated (DHMR) regions were identified using the R package ChAMP, comparing IDH1 mutant to wild-type tumors. At the probe level, top 1% and DHMR probes demonstrated a relative increase in 5hmC among IDH1 mutant tumors versus IDH1 wild-type. Top 1% and DHMR probes were enriched for enhancer and super-enhancer regions in both IDH1 mutant and IDH1 wild-type tumors, however enhancer and super-enhancers targeted only partially overlapped. Pathway enrichment analysis for top 1% probe gene targets and DHMR-associated genes identified pathways implicated in glioma pathogenesis. Among genes characteristically ‘hypermethylated' in G-CIMP + tumors, 28/50 were methylated while 22/50 were hypermethylated in our IDH1 mutant cohort, suggesting that 5hmC contributes to overall methylation of G-CIMP target genes. 5hmC marked the most highly expressed genes in our tumor cohort, with increased expression associated with gene body hydroxymethylation. Among 1367 genes differentially expressed between IDH1 mutant and wild-type tumors, 48 demonstrated a positive significant Spearman correlation between probe 5hmC β-value and gene expression (r ≥ 0.5, p &amp;lt; 0.05), including genes implicated in gliomagenesis as well as novel candidates. This correlation was most evident for genes upregulated in the IDH1 mutant cohort. Citation Format: Wioletta Glowacka, Harshika Jain, Makiko Okura, Abulizi Maimaitiming, Romina Nejad, Mamatjan Yasin, Hamza Farooq, Kenneth Aldape, Paul Kongkham. 5-hydroxymethylcytosine profiling identifies differential targeting in IDH1 mutant versus IDH1 wild-type high-grade gliomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5325.

Abstract 1243: Elucidating the molecular pathogenesis of familial glioma

Abstract INTRODUCTION: In recent years, the molecular characterization of sporadically arising diffuse gliomas has identified recurrent driving alterations and delineated molecularly and clinically distinct subclasses of disease. However, less is known about the molecular nature of gliomas that are familial in origin. To address this question, we integrated germline and somatic genomic data to characterize the molecular pathogenesis of 20 tumors arising in unrelated individuals with a family history of glioma collected through the Gliogene International Consortium. METHODS: FFPE tumor specimens were sectioned and reviewed to localize neoplastic tissue for DNA extraction. Library preparation, exome plus targeted capture, and paired-end sequencing on the Illumina HiSeq 2000 platform was performed at the Baylor College of Medicine Human Genome Sequencing Center. Single-nucleotide variants and indels were called with respect to germline DNA sequencing data for each case using MuTect2. Copy number profiling was performed on the Illumina HumanOmniExpress BeadChip and analyzed using GenomeStudio v2.0. Genotypes at known glioma risk polymorphisms were determined from germline DNA profiled on the Illumina Infinium OncoArray and rare, predicted deleterious germline mutations were identified from germline whole-exome sequencing data. RESULTS: Tumor exome sequencing was completed at an average read depth of 116X and we detected a median of 54 non-silent somatic mutations per tumor across the 20 tumors profiled. All three molecular subtypes of sporadic glioma were represented, including IDH-mutant, 1p/19q codeleted (n=3), IDH-mutant, 1p/19q intact (n=7), and IDH-wildtype tumors (n=10). Characteristic subtype-specific mutations and copy number alterations (e.g., TP53 and ATRX mutations among IDH-mutant, 1p/19q intact tumors) were observed, and the frequencies of recurrent alterations were comparable to sporadic glioma cases analyzed by The Cancer Genome Atlas. Notably, all 20 cases had alterations in genes regulating telomere length; 17 had acquired mutations in ATRX or the TERT promoter as typically seen in sporadic glioma, while three instead had germline mutations in telomere shelterin complex genes POT1 or TERF2. Frequencies of known common glioma risk alleles were similar to those among sporadic cases and correlations between risk alleles and specific somatic mutations were not observed. CONCLUSIONS: This study illustrates: 1) the complementarity of inherited and acquired alterations in driving gliomagenesis in some individuals with a familial predisposition to the disease; and 2) that the molecular characteristics of familial tumors profiled largely recapitulate what is known about sporadic glioma. In the majority of cases, the source of germline genetic susceptibility is not known but does not appear to be conferred by common risk polymorphisms. Citation Format: Daniel I. Jacobs, Kazutaka Fukumura, Matthew N. Bainbridge, Georgina N. Armstrong, Donna M. Muzny, Beatrice Melin, Jason T. Huse, Melissa L. Bondy. Elucidating the molecular pathogenesis of familial glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1243.

IDH wild-type WHO grade II diffuse low-grade gliomas. A heterogeneous family with different outcomes. Systematic review and meta-analysis

WHO grade II diffuse low-grade gliomas (DLGGs) were recently divided into sub-groups on the basis of their molecular profiles. IDH wild-type (IDH-wt) tumors seem to be associated with unfavorable prognoses due to biological similarities to glioblastomas. The authors performed a systematic review and meta-analysis of literature examining epidemiology, clinical characteristics, management, and the outcome of IDH-wt grade II DLGGs. According to PRISMA guidelines, a comprehensive review of studies published from January 2009 to October 2017 was carried out. The authors identified series that examined the prevalence rate, clinical and radiological characteristics, treatment, and outcome of IDH-wt DLGGs. Variables influencing outcomes were analyzed using a random-effects meta-analysis model. Finally, a meta-regression analysis was performed to examine the impact of therapeutic strategies on the effect-size. Twenty-two studies were included in this systematic review. The IDH-wt prevalence rate was 22.9% (95% CI 18.4-27.4%). The hazard ratio for this molecular subgroup in the DLGGs population was 3.46 (95% CI 2.24-5.36; p < 0.001), and the heterogeneity was significant (I2= 85%, τ2 = 0.88) (HR range 1.28-376). Nonetheless, publication bias did not affect the analysis (p = 0.176). The meta-regression revealed that the extent of resection and post-operative chemotherapy affected the outcome in the IDH-wt subgroup (p < 0.001 and 0.015, respectively), with no significant association of the HR with the rate of RT or RT + CHT. The prevalence of IDH-wt tumors is approximately 23% of DLGGs. The absence of IDH mutation is associated with a heterogeneous outcome, and its therapeutic relevance for postoperative management remains unclear. Maximal surgical resection improves the overall survival in the DLGGs population, beyond molecular status. Further molecular stratification is needed to better understand IDH-wt behavior and therapeutic response.

Molecular classification of patients with grade II/III glioma using quantitative MRI characteristics.

Molecular markers of WHO grade II/III glioma are known to have important prognostic and predictive implications and may be associated with unique imaging phenotypes. The purpose of this study is to determine whether three clinically relevant molecular markers identified in gliomas-IDH, 1p/19q, and MGMT status-show distinct quantitative MRI characteristics on FLAIR imaging. Sixty-one patients with grade II/III gliomas who had molecular data and MRI available prior to radiation were included. Quantitative MRI features were extracted that measured tissue heterogeneity (homogeneity and pixel correlation) and FLAIR border distinctiveness (edge contrast; EC). T-tests were conducted to determine whether patients with different genotypes differ across the features. Logistic regression with LASSO regularization was used to determine the optimal combination of MRI and clinical features for predicting molecular subtypes. Patients with IDH wildtype tumors showed greater signal heterogeneity (p = 0.001) and lower EC (p = 0.008) within the FLAIR region compared to IDH mutant tumors. Among patients with IDH mutant tumors, 1p/19q co-deleted tumors had greater signal heterogeneity (p = 0.002) and lower EC (p = 0.005) compared to 1p/19q intact tumors. MGMT methylated tumors showed lower EC (p = 0.03) compared to the unmethylated group. The combination of FLAIR border distinctness, heterogeneity, and pixel correlation optimally classified tumors by IDH status. Quantitative imaging characteristics of FLAIR heterogeneity and border pattern in grade II/III gliomas may provide unique information for determining molecular status at time of initial diagnostic imaging, which may then guide subsequent surgical and medical management.

P.051 5-hydroxymethylcytosine profiling identifies differential targeting in IDH1 mutant versus IDH1 wild-type high-grade gliomas

Background: Gliomas demonstrate epigenetic dysregulation highlighted by the Glioma CpG-Island Methylator Phenotype (G-CIMP) seen in IDH1 mutant tumors. IDH1 mutation perturbs the balance between 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) by inhibiting TET-mediated active demethylation. The role 5hmC plays in IDH1 mutant tumors remains poorly understood. Methods: We profiled 5hmC in high grade IDH1 mutant (n = 12) and wild-type (n = 9) tumors on the Illumina MethylationEPIC Beadchip. We examined regions with high 5hmC abundance (top 1% probes), and differentially hydroxymethylated regions (DHMR). 5hmC profiles were correlated with gene expression. Results: Mean 5hmC b-values were 4.6%% and 3.8% for IDH1 mutant and wild-type tumors, respectively. Top 1% and DHMR probes demonstrated increased 5hmC among IDH1 mutants. 5hmC enriched for enhancer and super-enhancers. Among G-CIMP target genes, 22/50 were hydroxymethylated in our IDH1 mutant cohort, suggesting that 5hmC contributes to their overall methylation. Gene expression was associated with gene body 5hmC. 48 genes differentially expressed between IDH1 cohorts showed a positive Spearman correlation between 5hmC and gene expression, in particular for genes upregulated in IDH1 mutants. Conclusions: Locus-specific gain of 5hmC, targeting regulatory regions and associated with over-expressed genes, suggests a significant role for 5hmC in IDH1 mutant HGG.

Exploring cellular subpopulations in glioblastoma and matched organoids using single-cell RNA-seq

Background: Gliomas are the most common and fatal adult brain tumor with distinct genomic subgroups defined by isocitrate dehydrogenase (IDH) mutation status. Mutations in IDH result in overproduction of the oncometabolite 2-hydroxyglutarate (2HG). The landscape of metabolic changes that define gliomas has not previously been explored. Methods: We performed liquid chromotography-mass spectrometry (LC-MS) to examine over 700 metabolites on 90 fresh-frozen glioma samples (30 IDH-wildtype, 30 IDH-mutant 1p/19q codeleted, 30 IDH-mutant 1p/19q non-codeleted) from our institutional biobank. R and S enantiomers of 2HG were quantified using high pressure liquid chromatography tandem mass spectrometry coupled with a CHIROBIOTIC R column. Genome wide DNA methylation was performed on all tumors using Illumina 850k EPIC array. Unsupervised consensus clustering of differentially expressed metabolites and methylated post-processed probes was performed. Copy number variations were determined based on intensity values of the methylation array. Survival of unsupervised cluster groups was determined using the Kaplan-Meier Estimate. Results: Unsupervised clustering of 689 metabolites revealed 2 distinct subgroups of gliomas associated with recurrence-free survival (RFS, P = 0.021). IDH mutant tumours were found in both cluster groups where as IDH-wildtype tumors were found only in Group 2. Group 2 IDH-mutant tumors had unfavourable PFS, higher R/S-2HG levels, and higher proportion of copy number alterations (4q, 9p, 13q, 17q) compared to group 1 IDH-mutant tumors (P=0.048, P=0.0194, P&lt;0.0001 respectively) compared to group 1 IDH-mutant tumors. (P= p=0.048). . Conclusions: Metabolic profiling of gliomas reveals 2 distinct subtypes of IDH-mutant independent of 1p/19q codeletion status with differing survival patterns and large scale chromosomal alterations that may be driven by varying levels of R/S-2HG.

Targetable Gene Fusions Associate With the IDH Wild-Type Astrocytic Lineage in Adult Gliomas.

Gene fusions involving oncogenes have been reported in gliomas and may serve as novel therapeutic targets. Using RNA-sequencing, we interrogated a large cohort of gliomas to assess for the incidence of targetable genetic fusions. Gliomas (n = 390) were profiled using the ArcherDx FusionPlex Assay. Fifty-two gene targets were analyzed and fusions with preserved kinase domains were investigated. Overall, 36 gliomas (9%) harbored a total of 37 potentially targetable fusions, the majority of which were found in astrocytomas (n = 34). Within this lineage 11% (25/235) of glioblastomas, 12% (5/42) of anaplastic astrocytomas, 8% (2/25) of grade II astrocytomas, and 33% (2/6) of pilocytic astrocytoma harbored targetable fusions. Fusions were significantly more frequent in IDH wild-type tumors (12%, n = 31/261) relative to IDH mutants (4%; n = 4/109) (p = 0.011). No fusions were seen in oligodendrogliomas. The most frequently observed therapeutically targetable fusions were in FGFR (n = 12), MET (n = 11), and NTRK (n = 8). Several additional novel fusions that have not been previously described in gliomas were identified including EGFR:VWC2 and FGFR3:NBR1. In summary, targetable gene fusions are enriched in IDH wild-type high-grade astrocytic tumors, which will influence enrollment in and interpretation of clinical trials of glioma patients.

Basic principles of diagnosis and treatment of gliomas

Traditionally, gliomas were classified based on histopathological features alone. The revised World Health Organization (WHO) classification of tumors of the central nervous system from 2016 integrated molecular features into the histopathological diagnosis. To summarize key aspects of the WHO classification from 2016 and implications for the clinical management of glioma patients. An overview of novel treatment approaches is also provided. Oligodendrogliomas are defined independently of their histopathological appearance by the simultaneous presence of amutation in the isocitrate dehydrogenase (IDH)-1 or IDH-2 gene and co-deletion of chromosome arms 1p and 19q. Astrocytomas are classified based on the presence or absence of mutations in IDH. Astrocytic tumors with wild-type IDH comprise approximately 90% of glioblastomas, the most common malignant primary brain tumor in adults. The extent of resection is afavorable prognostic factor in diffuse gliomas. Postoperatively, most patients are treated with a combination of radiotherapy and alkylating agent chemotherapy. In IDH wild-type astrocytic tumors, hypermethylation of the promoter of the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) gene is predictive for benefit from the alkylating agent temozolomide. Most novel treatment approaches that are currently being assessed in clinical trials aim at reprogramming the immune system to specifically eradicate tumor cells, but the efficacy of such approaches in gliomas remains to be demonstrated. To date the classical treatment modalities comprising surgery, radiotherapy and chemotherapy remain the mainstay of glioma treatment. The integration of molecular features into the classification of gliomas is abasis for personalized treatment approaches.

Metabolic characterization of isocitrate dehydrogenase (IDH) mutant and IDH wildtype gliomaspheres uncovers cell type-specific vulnerabilities

BackgroundThere is considerable interest in defining the metabolic abnormalities of IDH mutant tumors to exploit for therapy. While most studies have attempted to discern function by using cell lines transduced with exogenous IDH mutant enzyme, in this study, we perform unbiased metabolomics to discover metabolic differences between a cohort of patient-derived IDH1 mutant and IDH wildtype gliomaspheres.MethodsUsing both our own microarray and the TCGA datasets, we performed KEGG analysis to define pathways differentially enriched in IDH1 mutant and IDH wildtype cells and tumors. Liquid chromatography coupled to mass spectrometry analysis with labeled glucose and deoxycytidine tracers was used to determine differences in overall cellular metabolism and nucleotide synthesis. Radiation-induced DNA damage and repair capacity was assessed using a comet assay. Differences between endogenous IDH1 mutant metabolism and that of IDH wildtype cells transduced with the IDH1 (R132H) mutation were also investigated.ResultsOur KEGG analysis revealed that IDH wildtype cells were enriched for pathways involved in de novo nucleotide synthesis, while IDH1 mutant cells were enriched for pathways involved in DNA repair. LC-MS analysis with fully labeled 13C-glucose revealed distinct labeling patterns between IDH1 mutant and wildtype cells. Additional LC-MS tracing experiments confirmed increased de novo nucleotide synthesis in IDH wildtype cells relative to IDH1 mutant cells. Endogenous IDH1 mutant cultures incurred less DNA damage than IDH wildtype cultures and sustained better overall growth following X-ray radiation. Overexpression of mutant IDH1 in a wildtype line did not reproduce the range of metabolic differences observed in lines expressing endogenous mutations, but resulted in depletion of glutamine and TCA cycle intermediates, an increase in DNA damage following radiation, and a rise in intracellular ROS.ConclusionsThese results demonstrate that IDH1 mutant and IDH wildtype cells are easily distinguishable metabolically by analyzing expression profiles and glucose consumption. Our results also highlight important differences in nucleotide synthesis utilization and DNA repair capacity that could be exploited for therapy. Altogether, this study demonstrates that IDH1 mutant gliomas are a distinct subclass of glioma with a less malignant, but also therapy-resistant, metabolic profile that will likely require distinct modes of therapy.

Effectiveness of Stereotactic Radiotherapy and Bevacizumab for Recurrent High-Grade Gliomas: A Potential Therapy for Isocitrate Dehydrogenase Wild-Type Recurrent High-Grade Gliomas.

This study aimed to evaluate the efficacy of stereotactic radiotherapy combined with bevacizumab (SRT-Bv) compared with Bv treatment for recurrent high-grade gliomas (HGGs). Data for patients with recurrent HGGs who received SRT and Bv (n= 29) or Bv (n= 29) between June 2014 and September 2016 were retrospectively analyzed. All patients received conventional radiotherapy (total, 60 Gy) before this study. SRT was administered at a median dose of 42 Gy in 3-7 fractions. The recurrence pattern was classified into 3 groups: in-field, marginal, and out-field. The median overall survival in the SRT-Bv group was significantly longer than that in the Bv group (10.4 vs. 5.6 months; P= 0.02). In patients with isocitrate dehydrogenase wild-type tumors, the SRT-Bv treatment significantly prolonged survival more than the Bv treatment (10.9 vs. 8.2 months; P= 0.01). The World Health Organization grade and presence or absence of SRT were significant prognostic factors in the univariate analysis. Besides brain edema in 2 cases and asymptomatic subdural hematoma in 1 case, no other severe adverse effect due to SRT-Bv treatment was recorded. The pattern of recurrence was as follows: in-field, 2 cases (7%); marginal, 8 cases (28%); out-field, 11 cases (38%); no recurrence on radiologic findings, 6 cases (21%); and uncertain, 2 cases (7%). SRT-Bv treatment significantly prolonged survival duration more than Bv treatment and provides good local control in patients with recurrent HGGs, especially those with isocitrate dehydrogenase wild-type tumors.