II-III Gliomas Research Articles

Analysis of clinical outcome risk factors in glioma

Abstract In this paper, survival curves and Cox regression models were used to form an integrated disease risk factor model. Stepwise Cox regression models using the AIC criterion and the BIC criterion were included in the comparative models, penalties were imposed on the regression parameters for variable selection, and important covariates were selected to analyze censored data so as to analyze the dependence of dichotomous outcome events and survival time on the covariates. Applying the model of this paper to investigate postoperative infection and seizure risk in glioma, the results showed that 104 strains of pathogenic bacteria were detected. Gram-positive bacteria were the most prevalent infection-causing organisms with 67 strains, with Streptococcus grass-green and Staphylococcus epidermidis being the most common. There were 34 strains (32.69%) of gram-negative bacteria, and Acinetobacter baumannii was the most common one. 3 strains (2.88%) of fungi were present. Cox regression analysis was used to screen for five independent risk factors for surgical site infections in patients undergoing glioma surgery: neutrophil ratio, lymphocyte ratio, surgical grade (III), duration of antibiotic use, and postoperative day three temperature. The presence or absence of preoperative epilepsy has an impact on the prognosis of glioma patients, with fluctuating seizures being the most common postoperative condition in patients with grade II-III gliomas, which often recur after 12 months of seizure-free epilepsy. To sum up, the findings of this report are highly instructive in determining the prognosis for glioma treatment.

The diagnostic challenge of lack of choline level elevation on 1H-MR spectroscopy in grade II-III gliomas.

The accurate diagnosis of brain tumour is very important in modern neuro-oncology medicine. Magnetic resonance spectroscopy (MRS) is supposed to be a promising tool for detecting cancerous lesions. However, the interpretation of MRS data is complicated by the fact that not all cancerous lesions exhibit elevated choline (Cho) levels. The main goal of our study was to investigate the lack of Cho lesion /Cho ref elevation in the population of grade II-III gliomas. 89 cases of gliomas grade II and III were used for the retrospective analysis - glioma (astrocytoma or oligodendroglioma) grade II (74 out of 89 cases [83%]) and III (15 out of 89 cases [17%]) underwent conventional MRI extended by MRS before treatment. Histopathological diagnosis was obtained either by biopsy or surgical resection. Gliomas were classified to the group of no-choline elevation when the ratio of choline measured within the tumour (Cho lesion ) to choline from NABT (Cho ref ) were equal to or lower than 1. Significant differences were observed between ratios of Cho lesion /Cr lesion calculated for no-choline elevation and glial tumour groups as well as in the NAA lesion /Cr lesion ratio between the no-choline elevation group and glial tumour group. With consistent data concerning choline level elevation and slightly lower NAA value, the Cho lesion /NAA lesion ratio is significantly higher in the WHO II glial tumour group compared to the no-choline elevation cases ( p < 0.000). In the current study the results demonstrated possibility of lack of choline elevation in patients with grade II-III gliomas, so it is important to remember that the lack of elevated choline levels does not exclude neoplastic lesion.

Human cytomegalovirus and isocitrate dehydrogenase status in glioma: association and prognosis value in Moroccan population.

Human cytomegalovirus (HCMV) and isocitrate dehydrogenase (IDH) have been separately associated to gliomas. IDH is a molecular marker considered in the histo-molecular classification of gliomas as well as in their management and prognosis. However, even if oncomodulatory properties were attributed to HCMV, its association to gliomas remains a controversy. Most of the studies that investigated this association used the histological classification of gliomas; nevertheless, in 2016, the World Health Organization recommended the introduction of molecular characteristics to refine this classification. The aims of this study were to determine the prevalence of HCMV in glioma patients, the association between HCMV and IDH with gliomas and subsequently their associations with survival of patients in a Moroccan cohort. A series of 102 gliomas and 32 controls were analyzed by nested PCR (nPCR) to determine the HCMV status. PCR and sequencing were used to determine the IDH subtypes in tumors samples. IDH mutation and HCMV status were correlated to the characteristics of the tumors using SPSS, whereas the survival curves were obtained by the Kaplan-Meier method and the log rank test. HCMV shows significant association with gliomas with a detection rate of 30.4% and no case in the control group. The IDH mutation was identified in 40.9-50% of grade II-III gliomas and in 10.9% of grade IV gliomas. A significant association was obtained between survival in patients with glioblastomas and IDH/HCMV status. Glioblastoma patients with HCMV+ and IDHwt had a poor prognostic. HCMV was detected exclusively in tumor cases and was significantly associated with poor prognosis in patients with gliomas and particularly with glioblastomas. The worst overall survival was significantly seen in patients with gliomas HCMV+/IDHwt. So, it will be of interest to consider HCMV and IDH status in gliomas management strategies.

INNV-20. RADIOGRAPHIC RESPONSE AND SEIZURE CONTROL IN IDH1 MUTANT GLIOMA PATIENTS USING IVOSIDENIB

Abstract Isocitrate dehydrogenase 1 (IDH1) is commonly mutated in grade II-III gliomas, and the mutant enzyme leads to the production of the oncometabolite 2-hydroxyglutarate (2-HG). 2-HG is responsible for the gliomagenesis associated with these tumors and the promotion of seizures via glutamate receptors. Ivosidenib, a small molecule oral mIDH1 inhibitor, has shown promise in clinical trials to treat IDH1 mutant gliomas, and providers can utilize this agent in IDH1 mutant glioma patients. We evaluated our IDH1 mutant glioma patients treated off-label with ivosidenib and described the radiographic response and seizure control in this cohort when ivosidenib was initiated between October 2020 to February 2021. Radiographic response was determined using RANO criteria, and seizure control was determined by comparing seizures per month before and after initiation of ivosidenib. All patients represented received single-agent ivosidenib dosed at 500 mg orally once a day. One patient required a dose reduction to 250 mg orally once a day because of drug-induced diarrhea. In our cohort of six patients, patient age range was 31 to 74 years with four female patients and two male patients. Diagnoses represented were astrocytoma, IDH1 mutant (n=3) oligodendroglioma (WHO), IDH1 mutant, 1p19q co-deleted (n=2), and anaplastic astrocytoma IDH1 mutant (n=1). Three patients experienced a reduction of seizure frequency, two patients did not have seizures before or after therapy, and one patient remained with the same level of seizures (1 seizure/month). Radiographic responses recorded included three patients with stable disease, two patients with minor responses, and one patient with a partial response. Treatment with ivosidenib is ongoing for this cohort of mIDH1 glioma patients. Updated information on prolonged disease control and seizure control in this cohort of IDH1 mutant glioma patients will be presented. Therapeutics, such as ivosidenib, can lead to improved seizure control and radiographic outcomes in IDH1 mutant glioma patients.

Identification of De Novo Pyrimidine Synthesis as a Targetable Vulnerability in a Novel IDH1 Mutant Engineered Astrocytoma Model

<h3>Purpose/Objective(s)</h3> Despite high prevalence of IDH1-R132H mutations in grade II-III gliomas, effective therapies remain limited. We sought to identify tumor-specific vulnerabilities induced by the IDH1-R132H oncogene and test the translational relevance of targeting them using a new genetically engineered mouse model (GEMM) of IDH1 mutant anaplastic astrocytoma. <h3>Materials/Methods</h3> We conducted a synthetic lethality screen using isogenic IDH1 mutant and IDH1 wild-type (WT) glioma cells and a novel drug screening platform developed by our group, called MAPS. To create a GEMM of anaplastic astrocytoma, we developed a strategy to engineer Tp53, Atrx, Pik3ca, and Idh1 mutations in the brains of adult mice. We intracranially injected adeno-associated virus (AAV) expressing Cre recombinase and CRISPR sgRNAs targeting murine Atrx and Tp53 genes into 4 mouse strains: 1) LSL-Cas9; 2) LSL-Cas9; LSL-Pik3ca^H1047R, 3) LSL-Cas9; LSL-Idh1^R132H, and 4) LSL-Cas9; LSL-Idh1^R132H; LSL-Pik3ca^H1047R. <h3>Results</h3> Our screen revealed that IDH1 mutant cells are hypersensitive to drugs targeting enzymes in the de novo pyrimidine nucleotide synthesis pathway, including dihydroorotate dehydrogenase (DHODH). We demonstrated that these cytotoxic effects are on-target and are associated with increased DNA damage in IDH1 mutant cells. Next, we showed that IDH1 mutant patient-derived glioma stem-like cell lines (GSCs) are also hyperdependent on de novo pyrimidine synthesis compared to IDH1 WT lines. In addition, we found that the novel brain penetrant DHODH inhibitor, BAY2402234 (currently undergoing testing in leukemia patients), decreased tumor growth in an orthotopic xenograft model of IDH1 mutant, but not IDH1 WT, glioblastoma. We then sought to create and use a GEMM of IDH1 mutant anaplastic astrocytoma to test whether dependence on de novo pyrimidine synthesis manifests across tumor grade. Following intracranial AAV injection (see methods), astrocytomas preferentially formed after 9-14 months in mice carrying both Idh1 and Pik3ca conditional alleles. These tumors histologically resembled grade III astrocytomas, expressed astrocytoma lineage markers, and displayed elevated (R)-2-hydroxyglutarate. To create an additional model with shorter tumor latency, we performed secondary transplants of GSCs derived from our GEMM into recipient mice. We found that BAY2402234 blocked tumor growth in these orthotopic astrocytoma allografts. <h3>Conclusion</h3> Our findings establish IDH1 mutations as predictive biomarkers of DHODH inhibitor efficacy in gliomas across tumor grade, highlight BAY2402234 as a candidate glioma therapeutic, and unveil new genetically faithful mouse models of IDH1 mutant glioma. In addition, we show that BAY2402234 induces preferential DNA damage in IDH1 mutant cells, thereby supporting evaluation of BAY2402234 as a potential tumor-selective radiosensitizer.

343MO Clinical features and DNA methylation patterns in long- and short-term survivors of WHO grade II-III glioma

WHO grade II-III gliomas affect rather young individuals and are characterized by a heterogenous survival prognosis ranging from months to years. Postoperative treatment prolongs survival but potentially impacts long-term quality of life and cognitive functioning. Therefore, refined prognostic stratification models are needed to guide future treatment studies.

Correlation of &lt;sup&gt;11&lt;/sup&gt;C-Methionine Combined Positron Emission and Computed Tomography and Ki-67 Proliferation Index in Pretreatment Assessment of Cerebral Gliomas

The purpose of the study was to explore the correlation between 11С-methionine (Met) uptake measured by combined positron emission and computed tomography (PET/CT) in newly diagnosed cerebral gliomas and tumor proliferative activity as measured by Ki-67 labeling index (Ki-67 LI).The results of PET/CT with 11С-methionine (PET-Met) of 236 adult patients with pretreated glial brain tumors were included in retrospective analysis. The final diagnosis of glioma according to WHO classification of CNS tumors (2007) was based on both histology and immunohistochemistry using Ki-67 antibodies. On PET-Met tumor-to normal brain uptake ratio (TBR) was calculated by dividing maximum Met uptake in the tumor (hot spot 10 mm in diameter) to activity concentration in the contralateral cortex. The Spearmen rank correlation test was used to analyze the relationships between TBR and Ki-67 LI.PET-Met analysis showed that TBR increases with an increase in the aggressiveness of the glial tumor. The differences of TBR values between gliomas grade II vs III and grade III vs IV were significant (p &lt; 0,001). Among grades II-III gliomas Met uptake was significantly higher in oligodendroglial and mixed gliomas than in astrocytomas (p &lt; 0,001), but the differences did not depend on Ki-67 LI.Correlation analysis demonstrated significant correlation between Ki-67 LI and TBR values (r = 0,49, p &lt; 0,05, Spearman rank test). With analyzing glioma subgroups TBR values correlated with Ki-67 LI in diffuse astrocytomas (r = 0,52, p &lt; 0,05), oligodendrogliomas (r = 0,40, p &lt; 0,05), oligoastrocytomas (r = 0,47, p &lt; 0,05) and in high-grade gliomas (r = 0,45, p &lt; 0,05) but not in low-grade gliomas. Comparison between TBR value and Ki-67 LI in each glioma showed a lack of coincidence in 22 % of cases (high Met uptake but low Ki-67 LI and vice versa). The main reasons for such discrepancies were tumor molecular biology or incorrect biopsy target.Met uptake in diffuse gliomas correlates with proliferative activity which justifies the use of PET-Met for glioma grading. In case of mismatch between two biomarkers one should rely on the indicator that implies a higher aggressiveness of the glioma.

R-2-HG in AML… friend or foe?

R-2-HG in AML… friend or foe?

An integrative analysis of genome-wide 5-hydroxymethylcytosines in circulating cell-free DNA detects noninvasive diagnostic markers for gliomas.

BackgroundGliomas, especially the high-grade glioblastomas (GBM), are highly aggressive tumors in the central nervous system (CNS) with dismal clinical outcomes. Effective biomarkers, which are not currently available, may improve clinical outcomes through early detection. We sought to develop a noninvasive diagnostic approach for gliomas based on 5-hydroxymethylcytosines (5hmC) in circulating cell-free DNA (cfDNA).MethodsWe obtained genome-wide 5hmC profiles using the 5hmC-Seal technique in cfDNA samples from 111 prospectively enrolled patients with gliomas and 111 age-, gender-matched healthy individuals, which were split into a training set and a validation set. Integrated models comprised 5hmC levels summarized for gene bodies, long noncoding RNAs (lncRNAs), cis-regulatory elements, and repetitive elements were developed using the elastic net regularization under a case–control design.ResultsThe integrated 5hmC-based models differentiated healthy individuals from gliomas (area under the curve [AUC] = 84%; 95% confidence interval [CI], 74–93%), GBM patients (AUC = 84%; 95% CI, 74–94%), WHO II-III glioma patients (AUC = 86%; 95% CI, 76–96%), regardless of IDH1 (encoding isocitrate dehydrogenase) mutation status or other glioma-related pathological features such as TERT, TP53 in the validation set. Furthermore, the 5hmC biomarkers in cfDNA showed the potential as an independent indicator from IDH1 mutation status and worked in synergy with IDH1 mutation to distinguish GBM from WHO II-III gliomas. Exploration of the 5hmC biomarkers for gliomas revealed relevance to glioma biology.ConclusionsThe 5hmC-Seal in cfDNA offers the promise as a noninvasive approach for effective detection of gliomas in a screening program.

EPID-08. PRE-SURGERY IMMUNE PROFILES OF ADULT GLIOMA PATIENTS

Abstract Changes in glioma patients’ immune profiles over the course of disease may predict outcomes. DNA based immunomethylomics quantifies blood immune cells based on cell specific DNA methylation signatures. To assess changes in immune profiles, we are longitudinally collecting blood samples from glioma patients pre-surgery and at other clinically relevant time points. Here we report patients’ pre-surgery immune profiles. All patients underwent biopsy or resection of a presumed new glioma or recurrent lower grade glioma. Blood DNA methylation was assessed with Illumina EPIC methylation arrays. Relative cell fractions of CD4, CD8, B-cells, natural killer cells, monocytes, and neutrophils, were estimated via our validated deconvolution algorithm. Total nucleated cell counts from Nexcelom cytometry were used to compute absolute cell counts. Other measures include total lymphocytes, CD4/CD8 ratio, neutrophil to lymphocyte ratio (NLR), and lymphocyte to monocyte ratio (LMR)). The first 125 participants includes 56 newly diagnosed glioblastomas (GBM), 28 newly diagnosed grade II-III gliomas, and 41 recurrent grade II-III gliomas. Median patient age is 49 years. 53 (43%) had recent dexamethasone exposure. In overall non-parametric analyses, most cell subsets, especially CD4, differed across grade, diagnosis group, WHO classification and dexamethasone exposure. In post-hoc pairwise analyses, immune profiles of IDH wildtype GBM patients who had taken dexamethasone differed from patients with GBM or grade II-III glioma who had not taken dexamethasone; they had clinically relevant and statistically significantly lower absolute CD4 counts, total white cell counts, and percent of total lymphocytes, and higher absolute neutrophil counts, NLR and LMR. However, some dexamethasone naïve GBM patients also had altered immune profiles. Comparisons of relative immune cell fractions with those from 454 non-glioma controls from the UCSF Adult Glioma Study showed that across grade and WHO classification, for the most part, immune profiles of glioma patients not exposed to dexamethasone did not differ from controls.

MPC-01 PROGNOSTIC ROLE OF TERT PROMOTER IMPROVES THE STRATIFICATION OF IDH-MUTATED LOWER GRADE GLIOMA

TERT promoter mutation is associated with favorable prognosis and 1p/19q codeletion in IDH-mutated gliomas. The current diagnostic system, however, did not incorporate this change as a diagnostic marker in this entity. We investigated the value of prognostication incorporating TERT using the Japanese original cohort of 560 IDH-mutated adult gliomas. We collected the information of molecular status of IDH, TERT and 1p/19q and patient clinical data including Karnofsky performance status (KPS). TERT mutation and 1p/19q codeletion were found in 303 and 285 cases, respectively. For the purpose of this study, the patient cohort was divided into four groups by a combination of 1p/19q and TERT status, and the characteristics of 1p/19q intact-TERT mutated group (Astro-TERT group) (n=24) were dissected in light of the differences comparing with 1p/19q intact-TERT wild (Astro-group, n=251) or 1p/19q codeleted-TERT mutated (Oligo-group, n=279) cases. Astro-TERT group with any grade showed intermediate overall survival between the Oligo-group and Astro-group although the survival differences were not statistically significant (median OS: not reached (NR) versus NR, and 106 months, respectively. p>0.05). In grade II-III gliomas, the survival curve of the Astro-TERT group overlapped with that of the Oligo-group while the Astro-TERT group showed short survival as well as the Astro-group. We further conducted subgroup analysis by adjusting KPS in grade II-III tumors. In the subgroup with favorable KPS (90–100) and gradeII-III (n=438), The OS of Astro-TERT group (median NR) was significantly longer survival than that of Astro-group (median NR p=0.032), and was comparable with that of the Oligo-group (median NR, p>0.05). Thus, TERT promoter status provides the additional information for prognostication at least in grade II-III gliomas in the current diagnostic system.

PATH-37. PROGNOSTIC ROLE OF TERT PROMOTER MUTATIONS IMPROVES THE STRATIFICATION OF IDH-MUTATED LOWER GRADE GLIOMA

Abstract TERT promoter mutation is associated with 1p/19q codeletion and favorable prognosis in IDH-mutated gliomas. Prognostic and diagnostic significance of TERT promoter mutation is well-recognized in IDH-wildtype glioblastomas, but not in IDH-mutated gliomas. We investigated prognostic efficacy of TERT mutation in a cohort of 560 Japanese IDH-mutated adult gliomas. The molecular status of IDH, TERT and 1p/19q and patient clinical data including Karnofsky performance status (KPS) were collected in all cases. TERT mutations and 1p/19q codeletions were found in 303 and 285 cases, respectively. The patient cohort was divided into four groups by a combination of the 1p/19q and TERT status. The characteristics of 1p/19q intact-TERT mutated group (Astro-TERT group, n=24) were compared with those of 1p/19q intact-TERT wild (Astro-group, n=251) or 1p/19q codeleted-TERT mutated (Oligo-group, n=279) cases. Astro-TERT group with any grade showed intermediate overall survival between the Oligo-group and Astro-group although the survival differences were not statistically significant (median overall survival (OS) not reached (NR) versus NR, and 106 months, respectively. p &gt;0.05). We further conducted subgroup analysis by adjusting KPS and WHO grade as Cox regression analysis for survival indicated the unfavorable survival impact of KPS &lt; 90 and WHO grade IV. In the subgroup with favorable KPS (90–100) and grade II-III (n=438), The OS of Astro-TERT group (median NR) was significantly longer survival than that of Astro-group (median 120.2 months, p=0.032), and was comparable with that of the Oligo-group (median NR, p &gt;0.05). On the other hand, OS of none of the molecular groups significantly differ in poorer KPS subgroups (p &gt;0.05). In grade IV tumors, the OS of the Astro-TERT group (NR) was comparable with that of Astro-group (29 months, p=0.19) rather than Oligo-group (NR, p=0.051). Thus, TERT promoter status provides a valuable prognostic information for IDH-mutated grade II-III gliomas in the current molecular diagnostic system.

TMOD-04. CHARACTERIZATION OF MUTANT IDH1 OLIGODENDROGLIOMAS

Abstract Gliomas are the most common primary central nervous system malignancy in adults, but the molecular mechanisms responsible for their development and progression are not fully understood. Recent genomic analysis of World Health Organization grade II-III gliomas identifies 3 molecular subtypes of low grade glioma: no IDH mutation; IDH mutation without 1p/19q co-deletion; and IDH mutation with 1p/19q co-deletion. The latter, categorized as oligodendroglioma, commonly expresses loss of function mutations in CIC, FUBP1, and activation of PIK3CA. However, it is unknown if any of these mutations are sufficient to promote glioma development in cooperation with mutant IDH. Furthermore, research in oligodendroglioma is hampered by the lack of in vivo models of this specific glioma subtype. By utilizing the established RCAS/TVA somatic cell gene delivery method, mutant IDH1 can be expressed in the brains of mice. The tumorgenicity of other mutated genes associated with oligodendroglioma can be determined using additional methods such as conditional gene knockout and in vivo CRISPR-Cas9 mediated deletion. A mouse model for oligodendroglioma may identify new targetable genetic drivers of oligodendroglioma that will be useful for testing novel therapeutic strategies.

Demethylation and epigenetic modification with 5-azacytidine reduces IDH1 mutant glioma growth in combination with temozolomide.

Isocitrate deyhydrogenase (IDH) mutant glioma comprises the majority of grades II-III gliomas and nearly all secondary glioblastomas. These progressive gliomas arise from mutations in IDH1 or IDH2 that pathologically produce D-2-hydroxyglutarate (2HG), which interferes with cell reactions using alpha ketoglutarate, leading to a hypermethylated genome and epigenetic dysregulation of gene expression initiating tumorigenesis. Human IDH1 wild type (wt) and IDH1 R132H cell lines and patient-derived xenografts (PDXs) were used to evaluate the FDA-approved DNA demethylating agent 5-azacytidine (5-aza). Cell growth, protein and gene expression, chromatin immunoprecipitation, and nucleosome position assays were performed in 5-aza treated cells. To evaluate antitumor activity in vivo, 5-aza was administered alone and in combination with temozolomide (TMZ) in a PDX glioma model harboring IDH1 R132H mutation. 5-Aza treatment has been found to reduce cell growth and increase expression of glial fibrillary acid protein (GFAP). Chromatin immunoprecipitation and nucleosome position assay showed that the mechanism of increased GFAP expression induction is associated with histone modification and nucleosome repositioning of the GFAP promoter, respectively. In vivo, 5-aza treatment extended survival in IDH1 R132H mutant but not in an IDH1 wt glioma model. Additionally, 5-aza enhances the therapeutic effect of the DNA damaging agent TMZ in both subcutaneous and orthotopic PDX models of IDH1 R132H mutant glioma. 5-Aza provided a survival benefit as a single agent but worked best in combination with TMZ in 2 different IDH1 R132H mutant glioma models.

Genetic and Epigenetic Features of Rapidly Progressing IDH-Mutant Astrocytomas.

IDH-mutant astrocytomas are significantly less aggressive than their IDH-wildtype counterparts. We analyzed The Cancer Genome Atlas dataset (TCGA) and identified a small group of IDH-mutant, WHO grade II-III astrocytomas (n = 14) with an unexpectedly poor prognosis characterized by a rapid progression to glioblastoma and death within 3 years of the initial diagnosis. Compared with IDH-mutant tumors with the typical, extended progression-free survival in a control group of age-similar patients, the tumors in the rapidly progressing group were characterized by a markedly increased level of overall copy number alterations ([CNA]; p = 0.006). In contrast, the mutation load was similar, as was the methylation pattern, being consistent with IDH-mutant astrocytoma. Two of the gliomas (14%) in the rapidly progressing, IDH-mutant group but none of the other grade II-III gliomas in the TCGA (n = 283) had pathogenic mutations in genes (FANCB and APC) associated with maintaining chromosomal stability. These results suggest that chromosomal instability can negate the beneficial effect of IDH mutations in WHO II-III astrocytomas. The mechanism of the increased CNA is unknown but in some cases appears to be due to mutations in genes with a role in chromosomal stability. Increased CNA could serve as a biomarker for tumors at risk for rapid progression.

A high 18F-FDOPA uptake is associated with a slow growth rate in diffuse Grade II-III gliomas.

In diffuse Grade II-III gliomas, a high 3,4-dihydroxy-6-(18F)-fluoro-L-phenylalanine (18F-FDOPA)positron emission tomography (PET) uptake, with a standardized uptake value (SUVmax)/contralateral brain tissue ratio greater than 1.8, was previously found to be consistently associated with the presence of an isocitrate dehydrogenase (IDH) mutation, whereas this mutation is typically associated with a better prognosis. This pilot study was aimed to ascertain the prognostic value of this high 18F-FDOPA uptake in diffuse Grade II-III gliomas with regard to the velocity of diameter expansion (VDE), which represents an established landmark of better prognosis when below 4 mm per year. 20 patients (42 ± 10 years, 10 female) with newly-diagnosed diffuse Grade II-III gliomas (17 with IDH mutation) were retrospectively included. All had a 18F-FDOPA PET, quantified with SUVmax ratio, along with a serial MRI enabling VDE determination. SUVmax ratio was above 1.8 in 5 patients (25%) all of whom had a VDE<4 mm/year (100%) and IDH mutation (100%). Moreover, a SUVmax ratio above 1.8 was associated with higher rates of VDE<4 mm/year in the overall population (45 vs 0%, p = 0.04) and also in the subgroup of patients with IDH mutation (45 vs 0%, p = 0.10). This pilot study shows that in diffuse GradeII-III gliomas, a high 18F-FDOPA uptake would be predictive of low tumour growth, with a different prognostic significance than IDH mutation. Advances in knowledge: 18F-FDOPA PET in a single session imaging could have prognostic value in initial diagnosis of diffuse Grade II-III gliomas.

TMOD-45. DEFINING THE ROLE OF MUTANT IDH IN GLIOMA INITIATION

Gliomas are the most common primary central nervous system tumor but the molecular mechanisms responsible for their development and progression are not completely understood. Genomic analyses identified a mutation at codon 132 in the isocitrate dehydrogenase 1 (IDH1) gene in ~80% of grade II-III gliomas. In patient tumors, IDH1R132H mutations co-exist with TP53 mutations and inactivating alterations of alpha thalassemia/mental retardation syndrome X-linked (ATRX). Some of these tumors also have amplification of loci encoding platelet-derived growth factor receptor A (PDGFRA), cyclin dependent kinase 4 (CDK4), and MYC. Loss of the chromosomal region surrounding phosphatase and tensin homolog deleted on chromosome ten (PTEN) is associated with the progression of low grade glioma to grade IV glioblastoma. The functional requirement of these alterations for glioma initiation has previously been hampered by difficulties in generating autochthonous mouse models harboring mutant IDH. In this study, we used the RCAS/TVA glioma mouse model to evaluate the effect of these clinically-relevant genetic alterations on the growth of astrocytes in vitro and glioma development in vivo. In the context of mutant IDH1 expression, increased proliferation and anchorage-independent growth was observed in astrocytes derived from these mice, relative to wild type IDH-expressing cells. Similar to patient tumors, mutant IDH elevated intracellular (R)-2-hydroxyglutarate (2-HG) levels and reduced NADPH, which results from the conversion of α-KG to 2-HG. Postnatal delivery of IDH1R132H to Nestin-expressing cells in vivo initiated neoplasms that resembled human gliomas harboring mutant IDH1, both genetically and histologically. These results functionally validate the genomic alterations observed in the human disease and suggest that mutant IDH is a bona fide glioma oncogene. This model will aid in furthering our understanding of the biology of mutant IDH1-driven gliomas and is ideally suited for assessing rational therapeutic strategies designed to combat this deadly disease.

Perfusion and diffusion MRI signatures in histologic and genetic subtypes of WHO grade II–III diffuse gliomas

The value of perfusion and diffusion-weighted MRI in differentiating histological subtypes according to the 2007 WHO glioma classification scheme (i.e. astrocytoma vs. oligodendroglioma) and genetic subtypes according to the 2016 WHO reclassification (e.g. 1p/19q co-deletion and IDH1 mutation status) in WHO grade II and III diffuse gliomas remains controversial. In the current study, we describe unique perfusion and diffusion MR signatures between histological and genetic glioma subtypes. Sixty-five patients with 2007 histological designations (astrocytomas and oligodendrogliomas), 1p/19q status (+ = intact/- = co-deleted), and IDH1 mutation status (MUT/WT) were included in this study. In all patients, median relative cerebral blood volume (rCBV) and apparent diffusion coefficient (ADC) were estimated within T2 hyperintense lesions. Bootstrap hypothesis testing was used to compare subpopulations of gliomas, separated by WHO grade and 2007 or 2016 glioma classification schemes. A multivariable logistic regression model was also used to differentiate between 1p19q+ and 1p19q- WHO II-III gliomas. Neither rCBV nor ADC differed significantly between histological subtypes of pure astrocytomas and pure oligodendrogliomas. ADC was significantly different between molecular subtypes (p = 0.0016), particularly between IDHWT and IDHMUT/1p19q+ (p = 0.0013). IDHMUT/1p19q+ grade III gliomas had higher median ADC; IDHWT grade III gliomas had higher rCBV with lower ADC; and IDHMUT/1p19q- had intermediate rCBV and ADC values, similar to their grade II counterparts. A multivariable logistic regression model was able to differentiate between IDHWT and IDHMUT WHO II and III gliomas with an AUC of 0.84 (p < 0.0001, 74% sensitivity, 79% specificity). Within IDHMUT WHO II-III gliomas, a separate multivariable logistic regression model was able to differentiate between 1p19q+ and 1p19q- WHO II-III gliomas with an AUC of 0.80 (p = 0.0015, 64% sensitivity, 82% specificity). ADC better differentiated between genetic subtypes of gliomas according to the 2016 WHO guidelines compared to the classification scheme outlined in the 2007 WHO guidelines based on histological features of the tissue. Results suggest a combination of rCBV, ADC, T2 hyperintense volume, and presence of contrast enhancement together may aid in non-invasively identifying genetic subtypes of diffuse gliomas.

Secondary Glioblastoma: Molecular and Clinical Factors That Affect Outcome After Malignant Progression of a Lower Grade Tumor

There is limited information on prognostic factors and outcomes in patients with secondary glioblastoma (sGBM). Herein we report on the outcomes of patients with sGBM and identify clinically relevant prognostic factors. We retrospectively analyzed our institutional database for patients with histologic evidence of World Health Organization (WHO) grade II-III gliomas that went on to develop WHO grade IV sGBM. The assessment of the isocitrate dehydrogenase-1 (IDH1) R132H mutation was performed by immunohistochemical staining. Forty-five patients with sGBM were included within our analysis (median age, 41 years). Mutated IDH1 (R132H) protein was present within the gliomas of 24 patients and was absent in 17. Immunohistochemistry assessment could not be performed for 4 patients. Themedian time between first diagnosis of glioma and sGBM was 158.9 weeks. Median overall survival (OS) after a diagnosis of sGBM was 63.6 weeks. When assessing patient-specific (i.e., therapy-independent) factors, mutated IDH1 (R132H) protein (P= 0.01; hazard ratio (HR), 0.54; confidence interval (CI) 0.33-0.87), WHO grade II tumor as precursor lesion (P= 0.05; HR, 0.49; CI 0.25-0.97), and a frontal tumor location (P= 0.04; HR, 0.48; CI 0.23-0.99) were found to be associated with better OS by multivariate analysis. Our data further indicate that complete tumor removal is associated with better patient survival in sGBM patients within certain risk groups (time period to development of sGBM, >104 weeks; initial WHO grade II tumor, IDH1 mutation, and time period to development of sGBM, >104 weeks; initial WHO grade II or III tumor, IDH1 wild type, frontal lobe localization). Our retrospective analysis suggested that the presence of an IDH1 (R132H) mutation, frontal tumor location, and WHO grade of the initial tumor are associated with OS after progression to sGBM. In addition, some patients with sGBM may benefit from complete tumor resection depending on these patient-specific parameters. This is a finding that will ultimately need prospective validation.

PLK1 inhibition enhances temozolomide efficacy in IDH1 mutant gliomas.

Despite multimodal therapy with radiation and the DNA alkylating agent temozolomide (TMZ), malignant gliomas remain incurable. Up to 90% of grades II-III gliomas contain a single mutant isocitrate dehydrogenase 1 (IDH1) allele. IDH1 mutant-mediated transformation is associated with TMZ resistance; however, there is no clinically available means of sensitizing IDH1 mutant tumors to TMZ. In this study we sought to identify a targetable mechanism of TMZ resistance in IDH1 mutant tumors to enhance TMZ efficacy. IDH1 mutant astrocytes rapidly bypassed the G2 checkpoint with unrepaired DNA damage following TMZ treatment. Checkpoint adaptation was accompanied by PLK1 activation and IDH1 mutant astrocytes were more sensitive to treatment with BI2536 and TMZ in combination (<20% clonogenic survival) than either TMZ (~60%) or BI2536 (~75%) as single agents. In vivo, TMZ or BI2536 alone had little effect on tumor size. Combination treatment caused marked tumor shrinkage in all mice and complete tumor regression in 5 of 8 mice. Mutant IDH1 promotes checkpoint adaptation which can be exploited therapeutically with the combination of TMZ and a PLK1 inhibitor, indicating PLK1 inhibitors may be clinically valuable in the treatment of IDH1 mutant gliomas.