IDH1 mutations in gliomas: First series from a tertiary care centre in India with comprehensive review of literature

Pathological Evaluation of Diffuse Gliomas Using IDH1 and ATRX in a Resource-Limited Setting

INTRODUCTION

Classification of gliomas based on tumor histology remains the gold standard in the diagnosis and prognosis of gliomas. However, the recent World Health Organization (WHO) classification has included molecular studies for diagnosis and prognostication. Immunohistochemical markers such as isocitrate dehydrogenase 1 (IDH1) and alpha thalassemia/mental retardation syndrome X-linked (ATRX) can be used for the diagnosis and prognosis of the majority of gliomas.

OBJECTIVES

We aim to study the frequencies of IDH1 and ATRX mutations in diffuse gliomas using surrogate immunohistochemical markers and correlate histopathological findings of gliomas with immunohistochemical findings.

MATERIAL AND METHODS

This was a retrospective study of one-year duration from January 2022 to December 2022, conducted in the department of pathology. Relevant data was retrieved from medical records. Histopathology blocks were collected and sent for immunohistochemical studies using tissue microarray for IDH1 and ATRX.

STATISTICAL ANALYSIS

Qualitative data were expressed in percentages and proportions. The difference in proportion was calculated using the chi-square test, and a p-value of <0.005 was taken as significant.

RESULTS

A total of 51 cases of diffuse gliomas were included in the study. The frequency of IDH1-positive diffuse astrocytomas was 33 (64.7%), and loss of ATRX was seen in 12 (23.5%) cases.

CONCLUSION

Immunohistochemistry serves as a surrogate marker to detect molecular alterations in diffuse gliomas.

Diagnostic algorithm for pathological evaluation of gliomas in a resource-constrained setting

Introduction

Gliomas are the most common primary intracranial tumors. The current World Health Organization (WHO) classification of central nervous system tumors recommends integrated histo-molecular diagnosis of gliomas. However, molecular testing is not available in even most of the advanced centers of our country, and histopathology aided with immunohistochemistry (IHC) is still widely used for diagnosis. Immunohistochemical markers such as iso-citrate dehydrogenase1 (IDH1) and Alpha Thalassemia/Mental Retardation Syndrome X-linked (ATRX) can be reliably used for the correct diagnosis, prognosis, and treatment of gliomas.

Aim

We aimed to develop a diagnostic algorithm by integrating morphology, IDH1, and ATRX status of gliomas seen in our institute for 1 year.

Settings and Design

Analytical cross-sectional study.

Materials and Methods

This study included 60 histopathologically confirmed cases of astrocytic (n = 51) and oligodendroglial tumors (n = 9). Clinical, radiological, and histopathological features were noted and tumor grades assigned according to the WHO recommendations. IDH1 and ATRX mutation status was evaluated using IHC. The tumors were divided into three molecular groups on the basis of their IDH1 and ATRX mutation status: (1) Group 1: IDH1 negative and ATRX positive, (2) Group 2: IDH1 positive and ATRX positive, (3) Group 3: IDH1 positive and ATRX negative.

Results

The mean age of presentation was 45.0 ± 15.8 years with a male-to-female ratio of 2:1. Seizures, headache, and hemiparesis were the most common modes of presentation. The tumor subtypes studied were glioblastoma (n = 32), anaplastic astrocytoma (n = 7), diffuse astrocytoma (n = 6), oligodendroglioma (n = 6), pilocytic astrocytoma (n = 6), and anaplastic oligodendroglioma (n = 3). IDH1 mutation was present in 26 cases including anaplastic astrocytoma (n = 7), diffuse astrocytoma (n = 6), oligodendroglioma (n = 5), secondary glioblastoma (n = 5), and anaplastic oligodendroglioma (n = 3). ATRX mutation, i. e., loss of ATRX was observed in 17 cases including diffuse astrocytoma (n = 5), anaplastic astocytoma (n = 5), anaplastic oligodendroglioma (n = 3), oligodendroglioma (n = 3), and secondary glioblastoma (n = 1). All six cases of pilocytic astrocytoma were negative for IDH1 and ATRX mutation. There were 34 patients in Group 1 (IDH1- and ATRX +), nine cases in Group 2 (IDH1 + and ATRX +), and 17 patients in Group 3 (IDH1 + and ATRX-).

Conclusion

Diagnosis of gliomas should be based on a detailed clinicoradiological and histopathological assessment, followed by genotypic characterization. Evaluation for IDH1and ATRX status has both diagnostic and prognostic value as it helps in differentiating gliomas from reactive gliosis, primary glioblastoma from secondary glioblastoma, and pilocytic astrocytoma (WHO grade I) from diffuse astrocytoma (WHO grade II). Tumors with IDH1 mutations have a better outcome than those with wild-type IDH. IHC can serve as a useful surrogate to conventional molecular tests in resource-constrained settings. By devising an algorithm based on morphological and IHC features, we were able to stratify gliomas into three prognostic subgroups.

Epidermal Growth Factor Receptor Variant III Mutation, an Emerging Molecular Marker in Glioblastoma Multiforme Patients: A Single Institution Study on the Indian Population

Background

Glioblastoma is the most frequent and the most aggressive primary malignant brain tumor in adults. Standard treatment includes surgical removal of the tumor followed by concomitant chemotherapy and radiotherapy. Temozolomide, an oral alkylating agent, is currently the most commonly used chemotherapy. However, the median survival of glioblastoma multiforme (GBM) patients remains very low. Epidermal growth factor receptor variant III (EGFRvIII) is a novel marker for GBM patients of Indian origin as very few studies have been done on this molecular marker in our country. This is the first study utilizing this molecular marker among GBM patients in Rajasthan, India. This was a single institutional study that aimed to estimate the proportion of EGFRvIII mutation in GBM patients of Indian origin.

Methodology

This was a non-randomized, ambispective, single institutional observational study done on 35 brain tissue biopsies of histopathologically diagnosed and confirmed cases of GBM based on the World Health Organization 2007 Classification received in the pathology department of Dr. Sampurnanand Medical College, Jodhpur from 2015 to 2020 after applying inclusion and exclusion criteria. Molecular study of the EGFRvIII marker was conducted in all cases of GBM in the same institution on the RNA extracted from selected biopsy samples. Statistical analysis was performed using the SPSS version 22.0 software package (IBM Corp., Armonk, NY USA). The correlation between age and gender with EGFR-positive cases was analyzed, and EGFR positivity compared with previous studies.

Results

The occurrence of the EGFRvIII mutation was found to be 17.4% (6/35 cases). The mean age of presentation of a tumor with this mutation was estimated to be 54.3 years. Males were more commonly found to be affected (66.6%, 4/6 cases).

Conclusions

Thus, the identification of this mutation would segregate patients who may benefit from newer therapeutic approaches. In the future, personalized treatment may be advised for GBM patients depending on the presence of the EGFRvIII mutation.

Study of Surrogate Immunohistochemical Markers IDH1, ATRX, BRAF V600E, and p53 Mutation in Astrocytic and Oligodendroglial Tumors

Introduction In consonance with current the World Health Organization (WHO) classification of the central nervous system (CNS) tumors (2016), histological diagnosis of gliomas should be reinforced by molecular information. This study was performed to determine the frequency of isocitrate dehydrogenase 1 (IDH1), α thalassemia/intellectual disability syndrome X-linked (ATRX), p53, and BRAF V600E mutations in different grade astrocytomas and oligodendrogliomas.

Methods Seventy-seven cases of astrocytoma and oligodendroglioma (7 pilocytic astrocytomas, 15 diffuse astrocytomas [DA], 4 anaplastic astrocytomas [AA], 29 glioblastomas [GBM], and 22 oligodendrogliomas) were analyzed using immunohistochemistry for IDH1 mutant protein, ATRX, p53, and BRAF as well as their clinicopathological features assessed.

Results All pilocytic astrocytoma and primary glioblastoma cases were negative for an IDH1 mutation. IDH1 mutation was detected in 66.7% (10/15) of DA, 50% (2/4) of AA, 20.7% (6/29) of glioblastomas, and 81.8% (18/22) of oligodendroglioma cases. Loss of nuclear ATRX expression was found in 86.7% (13/15), 75% (3/4), and 34.5% (10/29) of DA, AA, and GBM cases, respectively. All oligodendroglioma cases showed retained ATRX expression. Both markers were found statistically significant in the above tumors (p <0.05). BRAF V600E mutation was detected in a single case of pilocytic astrocytoma and pleomorphic xanthoastrocytoma as well as both cases of epithelioid glioblastoma.

Conclusions IDH1 and ATRX mutations are very common in diffuse astrocytoma and anaplastic astrocytoma, while they are rare in pilocytic astrocytoma and glioblastoma. Immunohistochemistry for IDH1 and ATRX can successfully characterize the diffuse gliomas into molecularly defined groups in the majority of the cases. BRAF V600E mutation is rare in astrocytic tumors in the Indian population.

Molecular Biomarker Testing for the Diagnosis of Diffuse Gliomas

CONTEXT.—

The diagnosis and clinical management of patients with diffuse gliomas (DGs) have evolved rapidly over the past decade with the emergence of molecular biomarkers that are used to classify, stratify risk, and predict treatment response for optimal clinical care.

OBJECTIVE.—

To develop evidence-based recommendations for informing molecular biomarker testing for pediatric and adult patients with DGs and provide guidance for appropriate laboratory test and biomarker selection for optimal diagnosis, risk stratification, and prediction.

DESIGN.—

The College of American Pathologists convened an expert panel to perform a systematic review of the literature and develop recommendations. A systematic review of literature was conducted to address the overarching question, "What ancillary tests are needed to classify DGs and sufficiently inform the clinical management of patients?" Recommendations were derived from quality of evidence, open comment feedback, and expert panel consensus.

RESULTS.—

Thirteen recommendations and 3 good practice statements were established to guide pathologists and treating physicians on the most appropriate methods and molecular biomarkers to include in laboratory testing to inform clinical management of patients with DGs.

CONCLUSIONS.—

Evidence-based incorporation of laboratory results from molecular biomarker testing into integrated diagnoses of DGs provides reproducible and clinically meaningful information for patient management.

Evaluating Quality Indicators of Glioblastoma Care: Audit Results From an Indian Tertiary Care Cancer Center

PURPOSE

There are limited reports of quality metrics in glioblastoma. We audited our adherence to quality indicators as proposed in the PRIME Quality Improvement study.

METHODS

This is a retrospective audit of patients treated between 2017 and 2020. After postsurgical integrated diagnosis, patients received radiotherapy (RT) with concurrent and adjuvant temozolomide (TMZ). Multiparametric magnetic resonance imaging at predefined times guided management. Numbers with proportions for indices were calculated. Survival was estimated using the Kaplan-Meier method.

RESULTS

One hundred six patients were consecutively treated. The median age was 55 years (interquartile range of 47-61 years) with a male preponderance (68%). Ninety-six (90.6%) patients underwent subtotal resection, and 10 (9.4%) biopsy alone. Isocitrate dehydrogenase was wild-type in 96 (91%), and O⁶-methylguanine-DNA methyltransferase was unmethylated in 70 (66.0%) patients. Telomerase reverse transcriptase promoter was mutated in 64 (60.4%), and TP53 was mutated in 22 (20.8%). Concurrent radiation and TMZ were planned for 104 (98.1%), and radiation alone for 2 (1.9%). The median time to concurrent RT-TMZ was 36 days (interquartile range 30-44 days). All patients planned for RT-TMZ completed treatment, but only 81 (76%) completed adjuvant TMZ. Sixty-three (59%) completed six cycles, 18 (17%) received less than six cycles, and 25 (24%) did not receive adjuvant TMZ. At a median follow-up of 24 months (range 21-31 months), the median (95% CI) progression-free survival and overall survival were 11 (95% CI, 9.4 to 13.0) and 20.0 (95% CI, 15 to 26) months, respectively.

CONCLUSION

Our patients met quality indices in most domains; outcomes are comparable with global results. Metrics will be periodically evaluated to include new standards and assess continuous service appropriateness.

IDH1, ATRX, and BRAFV600E mutation in astrocytic tumors and their significance in patient outcome in north Indian population

Background:

According to the current World Health Organization (WHO) classification of central nervous system (CNS) tumors (2016), histological diagnosis of gliomas should be supplemented by molecular information. This study was carried out to determine the frequency of isocitrate dehydrogenase 1 (IDH1), ATRX, and BRAF V600E mutations in different grade astrocytomas and their prognostic value.

Methods:

Eighty cases of astrocytoma (15 pilocytic astrocytoma, 25 diffuse astrocytoma, 15 anaplastic astrocytoma, and 25 glioblastoma) with follow-up information were analyzed using immunohistochemistry for IDH1 mutant protein, ATRX, p53, and BRAF. Sanger sequencing was carried out for IDH1 exon 4 and BRAF exon 15.

Results:

All pilocytic astrocytoma and primary glioblastoma cases were negative for IDH1 mutation. IDH1 mutation was detected in 80% (20/25) DA and 87% (13/15) AA cases. IDH1 R132H was the commonest IDH1 mutation (94.1%) and immunohistochemistry showed 100% sensitivity and specificity to detect this mutation. Loss of nuclear ATRX expression was found in 87% (20/23) and 100% (14/14) DA and AA cases, respectively. IDH1 mutant DA patients had longer overall survival than IDH1 wild cases, although this difference was not significant (79.5 months vs. 42.5 months, P value 0.417). BRAF V600E mutation was not detected in any astrocytic tumor.

Conclusions:

IDH1 and ATRX mutations are very common in diffuse astrocytoma and anaplastic astrocytoma, while they are rare in pilocytic astrocytoma and glioblastoma. Immunohistochemistry for IDH1 and ATRX can successfully characterize the diffuse gliomas into molecularly defined groups in majority of the cases. BRAF V600E mutation is rare in astrocytic tumors in Indian population.

Shedding Light on the 2016 World Health Organization Classification of Tumors of the Central Nervous System in the Era of Radiomics and Radiogenomics

The new World Health Organization classification of brain tumors depends on combining the histologic light microscopy features of central nervous system (CNS) tumors with canonical genetic alterations. This integrated diagnosis is redrawing the pedigree chart of brain tumors with rearrangement of tumor groups on the basis of geno-phenotypical behaviors into meaningful groups. Multiple radiogenomic studies provide a bridge between imaging features and tumor microenvironment. An overlap that can be integrated within the genophenotypical classification of CNS tumors for a better understanding of different clinically relevant entities.

Association of The IDH1 C.395G>A (R132H) Mutation with Histological Type in Malay Brain Tumors

Background:

Brain tumors, constituting one of the most deadly forms of cancer worldwide, result from the accumulation of multiple genetic and epigenetic alterations in genes and signaling pathways. Isocitrate dehydrogenase enzyme isoform 1 (IDH1) mutations are frequently identified in primary brain tumors and acute myeloid leukemia. Studies on IDH1 gene mutations have been extensively performed in various populations worldwide but not in Malaysia. This work was conducted to study the prevalence of IDH1 c.395G>A (R132H) hotspot mutations in a group of Malaysian patients with brain tumors in order to gain local data for the IDH1 mutation profile in our population.

Methods:

Mutation analysis of c.395G>A (R132H) of IDH1 was performed in 40 brain tumor specimens by the polymerase chain reaction-restriction fragment length polymorphism method (PCR-RFLP) and then verified by direct sequencing. Associations between the IDH1 c.395G>A (R132H) mutation and clinicopathologic characteristics were also analyzed.

Results:

The IDH1 c.395G>A (R132H) mutation was detected in 14/40 patients (35%). A significant association was found with histological tumor types, but not with age, gender and race.

Conclusions:

IDH1 is frequently mutated and associated with histological subtypes in Malay brain tumors.

ATRX loss in glioneuronal tumors with neuropil-like islands indicates similarity to diffuse astrocytic tumors

Glioneuronal tumor with neuropil-like islands (GTNI) is a rare, recently described neoplasm, whose pathogenesis has not been studied extensively. The role of ATRX mutations, a class-defining alteration in diffuse astrocytic neoplasms, has not been assessed in GTNIs previously. We therefore aimed to assess the status of ATRX, along with IDH1, 1p/19q and p53, in cases of GTNI in order to evaluate the molecular profile of these tumors. All cases of GTNI diagnosed at our Institute were retrieved and clinicopathological features were reviewed. Immunohistochemistry for ATRX, IDH1 and p53 was performed. We identified four cases of GTNI, majority of which occurred in young adults. Loss of ATRX immunoexpression, a surrogate marker for ATRX mutation, was seen in all four cases. All cases were immunopositive for p53, while IDH1 positivity was seen in all three cases assessed. 1p/19q codeletion was absent in the three cases analyzed. These results indicate that the molecular pathogenesis of GTNIs similar to that of diffuse astrocytic tumors. Further, the loss of ATRX expression is seen in both the glial as well as neuronal components, indicating that both arise from the same tumor stem/progenitor cell and that the latter may be a metaplastic change. Thus, loss of ATRX immunoexpression, shown for the first time in these tumors, along with immunopositivity for p53 and IDH1, indicates that these tumors are molecular astrocytomas, and their clinical behaviour is likely to recapitulate that of ATRX-mutant and IDH-mutant diffuse astrocytomas of the same grade.

An analysis of 170 glioma patients and systematic review to investigate the association between IDH-1 mutations and preoperative glioma-related epilepsy

Seizure is a common presenting symptom of glioma, and many biomarkers have been suggested to be associated with preoperative seizure; however, the relationships between IDH (isocitrate dehydrogenase) mutations and glioma-related epilepsy only recently been studied. The authors aimed to examine the correlations between IDH mutations in glioma patients with preoperative seizures and tumor location. A series of 170 glioma samples were analyzed for IDH1 R132H mutations (amino acid change from arginine to histidine at codon 132) with immunohistochemistry (IHC) staining and for IDH mutations with direct DNA sequencing when the IHC results were negative. If either the IHC or direct DNA sequencing result was positive, the IDH status was defined as mutated. The results of the IDH mutation examinations were used to analyze the relationship between mutations and glioma-related epilepsy. The study population consisted of 64 (37.6%) World Health Organization (WHO) grade II gliomas, 58 (34.1%) grade III, and 48 (28.3%) grade IV gliomas. A total of 84 samples with IDH1 mutations were observed in our study, and 54 of these presented with seizures as the initial symptoms, whereas 28 of the patients with wild-type IDH status presented with seizures (p=0.043 for the WHO grade II gliomas, p=0.002 for the grade III gliomas and p=0.942 for the grade IV gliomas, chi-squared tests). Among the WHO grade II and III gliomas, IDH1 mutations were significantly associated with preoperative seizures, but no significant relationship between IDH mutations and preoperative seizures was found with glioblastoma multiforme.

Indian data on central nervous tumors: A summary of published work

Tumors of the central nervous system (CNS) constitute approximately 2% of all malignancies. Although relatively rare, the associated morbidity and mortality and the significant proportion of affected young and middle-aged individuals has a major bearing on the death-adjusted life years compared to other malignancies. CNS tumors encompass a very broad spectrum with regards to age, location, histology, and clinical outcomes. Advances in diagnostic imaging, surgical techniques, radiotherapy equipment, and generation of newer chemotherapeutic and targeted agents over the past few years have helped improving treatment outcome. Further insights into the molecular pathways leading to the development of tumors made in the past decade are being incorporated into routine clinical practice. Several focused groups within India have been working on a range of topics related to CNS tumors, and a significant body of work from India, in the recent years, is being increasingly recognized throughout the world. The present article summarizes key published work with particular emphasis on gliomas and medulloblastoma, the two commonly encountered tumors.

Mutational status of IDH1 in uveal melanoma

Uveal (intraocular) melanoma is an uncommon malignancy that comprises a small percentage of all melanoma cases. While many uveal melanomas harbor mutations in the BRCA-Associated Protein 1 (BAP1) gene, the genetics of non-BAP1 associated tumors are not completely understood. Recent studies have shown that a small subset of non-uveal melanomas hold mutations in isocitrate dehydrogenase (IDH), but the mutational status of IDH in uveal melanoma is unclear. Mutations in IDH are strongly prognostic and predictive of tumor behavior in other cancers, mainly diffuse gliomas, which commonly contain the IDH1-R132H mutation. For this study, we hypothesized that uveal melanoma may contain the IDH1-R132H mutation, similar to non-uveal melanoma and other cancers. A search of our institutional pathology files identified 50 consecutive cases of uveal melanoma with additional material utilized for retrospective IDH1-R132H immunohistochemical testing. The demographics of these patients included similar ages, gender distributions, and other clinical characteristics as described in previous studies. Similarly, histological subtype distributions and the presence of high risk pathologic features were consistent with other reports. All 50 of the uveal melanoma cases demonstrated negativity for IDH1-R132H by immunohistochemistry. This rate is unlike that of non-uveal melanoma and further supports their distinct molecular oncogenic profile.

Expression of DNA methyltransferases 1 and 3B correlates with EZH2 and this 3-marker epigenetic signature predicts outcome in glioblastomas

This study aims to analyze expression of EZH2 and DNA-methyltransferases (DNMT1, 3A and 3B) in astrocytic tumors and investigate their link as well as their correlation with survival, especially in GBMs. Expression of EZH2 and DNMTs (DNMT1, DNMT3A and DNMT3B) in different grades of astrocytomas (n=93) was assessed by qRT-PCR and immunohistochemistry. GBM-U87MG cell line was used for functional studies. Strong immunopositivity (LI≥25%) for EZH2, DNMT1 and DNMT3B was detected in 52%, 56% and 64% cases of GBMs respectively, which was significantly higher as compared to Grade II/III cases. Similarly, their median fold change of mRNA expression was also significantly higher in GBMs. There was also a significant positive correlation between DNMT1/DNMT3B and EZH2 mRNA and protein expression, which was in concordance with TCGA data set. Inhibition of DNMTs in cell line by Azacytidine resulted in down-regulation of EZH2, while knock-down of EZH2 by siRNA was not associated with any significant alteration of DNMTs, indicating that EZH2 expression in GBMs is possibly regulated by DNMTs, but not the reverse. Strong immunopositivity for EZH2, DNMT1 and DNMT3B were individually associated with significantly shorter survival and showed no correlation with IDH1 mutation status. In addition, the combination of these 3 markers represented an independent prognostic signature with cases having weak/negative expression of all 3 markers being associated with best prognosis. For the first time, the present study describes an epigenetic prognostic signature in GBMs based on immunohistochemical expression of EZH2, DNMT1 and 3B which can be used easily in routine neuropathology practice.

IDH1 Mutation in Gliomas in Mosul City - Iraq

BACKGROUND:

IDH1 (isocitrate dehydrogenase 1) mutation might be encounter in the low grade glioma and directs the progression of the tumor to a higher grade.

OBJECTIVE:

To assess the frequency of IDH1 mutations in gliomas and to correlate the IDH1 positivity with the type and grade of tumors, the age and sex of the patients.

MATERIAL AND METHODS:

A retro– and prospective case series study. One hundred and nine cases of intracranial gliomas were collected between 2008 and 2014 from Mosul Private Laboratories and Al-Jamboree Teaching Hospitals in Mosul. IDH1 mutations were assessed immunohistochemically using anti-IDH1 R132H mouse monoclonal antibody.

RESULTS:

IDH1 mutation was perceived in 34.86% of gliomas. In adult gliomas, the secondary glioblastoma and the low-grade astrocytoma had the greatest values of IDH1 positivity (88.88% and 62.5% respectively), followed by oligoastrocytoma/oligodendroglioma (50.0%), and anaplastic astrocytoma (47.36%). The primary glioblastomsa showed 17.64% IDH1 positivity. Males and females expressed the IDH1 equally. While, there was no role of IDH1 in pediatric gliomas.

CONCLUSION:

IDH1 mutation is commonly present in adult gliomas particularly in low-grade gliomas, and secondary glioblastoma, with equal sex distribution, but it has no role in pediatric gliomas.

Molecular investigation of isocitrate dehydrogenase gene (IDH) mutations in gliomas: first report of IDH2 mutations in Indian patients

Recent genome wide sequencing has identified mutations in IDH1/IDH2 predominantly in grade II-III gliomas and secondary glioblastomas which are associated with favorable clinical outcome. These mutations have become molecular markers of significant diagnostic and prognostic relevance in the assessment of human gliomas. In the current study we evaluated IDH1 (R132) and IDH2 (R172) in 32 gliomas of various grades and tumor subtypes. Sequencing analysis revealed R132H mutations in 18.7% tumors, while none of the cases showed IDH2 (R172) mutations. The frequency of IDH1 mutations was higher in females (21.4%) than males (11.1%), and it was significantly higher in younger patients. Histological analyses demonstrated presence of necrosis and micro vascular proliferation in 69% and 75% respectively. Interestingly, IDH1 mutations were predominantly present in non-necrotic tumors as well as in cases showing microvascular proliferation. Of the six IDH1 positive cases, three were glioblastomas (IV), and one each were anaplastic oligoastrocytoma (III), anaplastic oligodendroglioma III (n=1) and diffuse astrocytoma. In conclusion, IDH1 mutations are quite frequent in Indian glioma patients while IDH2 mutations are not observed. Since IDH mutations are associated with good prognosis, their use in routine clinical practice will enable better risk stratification and management of glioma patients.

Altered global histone-trimethylation code and H3F3A-ATRX mutation in pediatric GBM

Mutations in H3.3-ATRX-DAXX chromatin remodeling pathway have been reported in pediatric GBMs. H3.3 (H3F3A) mutations may affect transcriptional regulation by altered global histone-methylation. Therefore, we analyzed yet partly understood global histone code (H3K-4/9/27/36) trimethylation pattern in H3F3A-ATRX mutants and wild-type. H3F3A, HIST1H3B, IDH1, ATRX, DAXX and Tp53 mutations were identified by sequencing/immunohistochemistry in 27 pediatric GBMs. Global histone-methylation H3K-4/9/27/36me3 and Polycomb-protein EZH2 expression were evaluated by immunohistochemistry. H3F3A-ATRX mutation was observed in 66.7 % (18/27) of pediatric GBMs. K27M and G34R-H3F3A mutations were found in 37 % (10/27) and 14.8 % (4/27) patients respectively. G34V-H3F3A, HIST1H3B and IDH1 mutations were absent. Notably, commonest global histone-methylation mark lost was H3K27me3 (17/25, 68 %) followed by H3K4me3 (45.5 %, 10/22) and H3K9me3 (18.2 %, 4/22). Global H3K36me3 showed no loss. Most significant observation was loss of one or more histone-trimethylation mark in 80 % (20/25) pediatric GBMs. Notably, simultaneous loss of H3K27me3 and H3K4me3 were present in 7/22 (31.8 %) of pediatric GBMs. Low expression of EZH2 was found in 12/24 (50 %) of cases. However no significant correlation of loss of histone-marks or EZH2 expression with H3F3A-ATRX mutants (loss of at least one histone-marks in 87.5 % (14/16) cases) versus wild-types (loss of at least one histone-marks in 75 % (6/8) cases) was seen. The present study highlights for the first time combinatorial loss of one or more histone-trimethylation marks associated with majority of pediatric GBMs and the finding suggests significant role of histone-code in the molecular biology that underlies pediatric GBMs. Hence therapies for patients with particular combinations of histone modifications present opportunity to design innovative patient-tailored treatment protocols.

IDH1/2 mutations target a key hallmark of cancer by deregulating cellular metabolism in glioma

Isocitrate dehydrogenase (IDH) enzymes have recently become a focal point for research aimed at understanding the biology of glioma. IDH1 and IDH2 are mutated in 50%-80% of astrocytomas, oligodendrogliomas, oligoastrocytomas, and secondary glioblastomas but are seldom mutated in primary glioblastomas. Gliomas with IDH1/2 mutations always harbor other molecular aberrations, such as TP53 mutation or 1p/19q loss. IDH1 and IDH2 mutations may serve as prognostic factors because patients with an IDH-mutated glioma survive significantly longer than those with an IDH-wild-type tumor. However, the molecular pathogenic role of IDH1/2 mutations in the development of gliomas is unclear. The production of 2-hydroxyglutarate and enhanced NADP+ levels in tumor cells with mutant IDH1/2 suggest mechanisms through which these mutations contribute to tumorigenesis. Elucidating the pathogenesis of IDH mutations will improve understanding of the molecular mechanisms of gliomagenesis and may lead to development of a new molecular classification system and novel therapies.

The emerging role of d-2-hydroxyglutarate as an oncometabolite in hematolymphoid and central nervous system neoplasms

Approximately 20% of unselected cases and 30% cytogenetically diploid cases of acute myeloid leukemia (AML) and 80% of grade II–III gliomas and secondary glioblastomas carry mutations in the isocitrate dehydrogenase (IDH) 1 and 2 genes. IDH1/2 mutations prevent oxidative decarboxylation of isocitrate to α-ketoglutarate (α-KG) and modulate the function of IDH (neomorphic activity) thereby facilitating reduction of α-KG to D-2-hydroxyglutarate (D-2HG), a putative oncometabolite. D-2HG is thought to act as a competitive inhibitor of α-KG-dependent dioxygenases that include prolyl hydroxylases and chromatin-modifying enzymes. The end result is a global increase of cellular DNA hypermethylation and alterations of the cellular epigenetic state, which has been proposed to play a role in the development of a variety of tumors. In this review, we provide an update on potential molecular mechanisms linking IDH1/2 mutations and the resulting oncometabolite, D-2HG, with malignant transformation. In addition, in patients with AML and glioma we focus on the associations between IDH1/2 mutations and clinical, morphologic, cytogenetic, and molecular characteristics.

Expanding the spectrum of IDH1 mutations in gliomas

Mutations in isocitrate dehydrogenase -1 or -2 (IDH1 or IDH2) are found in the majority of WHO grade II and III diffuse gliomas and secondary glioblastomas. IDH mutation screening is rapidly becoming part of the routine pathological work up of human brain tumors, providing both diagnostic and prognostic information. Here, we characterize four rare and novel IDH1 mutations identified in surgical human glioma samples: two instances of an IDH1 p.R132S mutation caused by a previously undescribed dinucleotide deletion/insertion mutation, a novel homozygous somatic IDH1 p.R132L mutation, and an IDH1 p.R100Q mutation. Characterization of novel and rare IDH mutations may provide additional insight into the mechanisms of mutant IDH in neoplasia. Furthermore, given the clinical import of IDH status, these results highlight the need for comprehensive mutation screening, beyond the targeted identification of common pathogenic variants.

Comparative study of IDH1 mutations in gliomas by immunohistochemistry and DNA sequencing

BACKGROUND

Mutations involving isocitrate dehydrogenase 1 (IDH 1) occur in a high proportion of diffuse gliomas, with implications on diagnosis and prognosis. About 90% involve exon 4 at codon 132, replacing amino acid arginine with histidine (R132H). Rarer ones include R132C, R132S, R132G, R132L, R132V, and R132P. Most authors have used DNA-based methods to assess IDH1 status. Preliminary studies comparing imunohistochemistry (IHC) with IDH1-R132H mutation-specific antibodies have shown concordance with DNA sequencing and no cross-reactivity with wild-type IDH1 or other mutant proteins. The present study compares results of IHC with DNA sequencing in diffuse gliomas.

MATERIALS AND METHODS

Fifty diffuse gliomas with frozen tissue samples for DNA sequencing and adequate tissue in paraffin blocks for IHC using IDH1-R132H specific antibody were assessed for IDH1 mutations.

RESULTS

Concordance of findings between IHC and DNA sequencing was noted in 88% (44/50) cases. All 6 cases with discrepancy were immunopositive with DIA-H09 antibody. While in 3 of these 6 cases, DNA sequencing failed to reveal any mutations, R132L (arginine replaced by leucine) mutation was found in the rest 3 cases. Interestingly, of the immunopositive cases, 46.6% (14/30) showed immunostaining in only a fraction of tumor cells.

CONCLUSIONS

IHC is an easy and quick method of detecting IDH1-R132H mutations, but there may be some discrepancies between IHC and DNA sequencing. Although there were no false-negative cases, cross-reactivity with IDH1-R132L was seen in 3, a finding not reported thus far. Because of more universal availability of IHC over genetic testing, cross-reactivity and staining heterogeneity may have bearing over its use in detecting IDH1-R132H mutation in gliomas.

IDH mutations in human glioma

A novel mutation of isocitrate dehydrogenase-1 (IDH1) was recently found in a large percentage of secondary human gliomas. Unlike previously discovered prognostic molecular characteristics, IDH1 mutations were found across gliomas of many different grades and histologies. Further studies have illuminated its utility as a prognostic marker in low-grade and high-grade gliomas and its ability to aid the differentiation and diagnosis of various tumors with histologic ambiguity. As a metabolic enzyme, its inhibitory actions and neomorphic activity present a unique avenue in the understanding of these tumors and potentially a novel mechanism through which they may be treated.

Molecular profile of oligodendrogliomas in young patients

Several studies on molecular profiling of oligodendrogliomas (OGs) in adults have shown a distinctive genetic pattern characterized by combined deletions of chromosome arms 1p and 19q, O6-methylguanine-methyltransferase (MGMT) methylation, and isocitrate dehydrogenase 1 (IDH1) mutation, which have potential diagnostic, prognostic, and even therapeutic relevance. OGs in pediatric and young adult patients are rare and have been poorly characterized on a molecular and biological basis, and it remains uncertain whether markers with prognostic significance in adults also have predictive value in these patients. Fourteen cases of OGs in young patients (age, ≤ 25 years) who received a diagnosis over 7 years were selected (7 pediatric patients age ≤ 18 years and 7 young adults aged 19-25 years). The cases were evaluated for 1p/19q status, MGMT promoter methylation, p53 mutation, and IDH1 mutation. None of the pediatric cases showed 1p/19q deletion. In young adults, combined 1p/19q loss was observed in 57% and isolated 1p loss in 14% of cases. The majority of cases in both subgroups (71% in each) harbored MGMT gene promoter methylation. TP53 and IDH1 mutations were not seen in any of the cases in both the groups. To our knowledge, this is the first study to show that molecular profile of OGs in pediatric and young adult patients is distinct. Further large-scale studies are required to identify additional clinically relevant genetic alterations in this group of patients.

Significance of IDH mutations varies with tumor histology, grade, and genetics in Japanese glioma patients

Mutations in isocitrate dehydrogenase 1 (IDH1) and IDH2 are found frequently in malignant gliomas and are likely involved in early gliomagenesis. To understand the prevalence of these mutations and their relationship to other genetic alterations and impact on prognosis for Japanese glioma patients, we analyzed 250 glioma cases. Mutations of IDH1 and IDH2 were found in 73 (29%) and 2 (1%) cases, respectively. All detected mutations were heterozygous, and most mutations were an Arg132His (G395A) substitution. IDH mutations were frequent in oligodendroglial tumors (37/52, 71%) and diffuse astrocytomas (17/29, 59%), and were less frequent in anaplastic astrocytomas (8/29, 28%) and glioblastomas (13/125, 10%). The pilocytic astrocytomas and gangliogliomas did not have either mutation. Notably, 28 of 30 oligodendroglial tumors harboring the 1p/19q co-deletion also had an IDH mutation, and these alterations were significantly correlated (P < 0.001). The association between TP53 and IDH mutation was significant in diffuse astrocytomas (P = 0.0018). MGMT promoter methylation was significantly associated with IDH mutation in grade 2 (P < 0.001) and grade 3 (P = 0.02) gliomas. IDH mutation and 1p/19q co-deletion were independent favorable prognostic factors for patients with grade 3 gliomas. For patients with grade 3 gliomas and without 1p/19q co-deletion, IDH mutation was strongly associated with increased progression-free survival (P < 0.0001) and overall survival (P < 0.0001), but no such marked correlation was observed with grade 2 gliomas or glioblastomas. Therefore, IDH mutation would be most useful when assessing prognosis of patients with grade 3 glioma with intact 1p/19q; anaplastic astrocytomas account for most of these grade 3 gliomas.

Isocitrate dehydrogenase mutations in diffuse gliomas: clinical and aetiological implications

The discovery of isocitrate dehydrogenase (IDH) mutations in gliomas is one example of the large impact that next-generation sequencing is having on the understanding of tumour biology and human disease in general. IDH mutations are early and common events in the development of astrocytomas, oligodendrogliomas and oligoastrocytomas. IDH mutations are also found in some myeloid malignancies and soft tissue tumours, but are rare in other malignancies. IDH mutation detection can be incorporated into routine pathology practice via immunohistochemistry and/or standard sequencing techniques and has great diagnostic value. An emerging theme is that IDH mutation status in gliomas is of great prognostic relevance, and there are proposals to include IDH mutation status in the next iteration of the WHO classification of gliomas. The mechanisms of action(s) of mutant IDH are not fully understood, but the understanding is progressing rapidly, and may provide a mechanism to link diverse proneoplastic processes such as oxidative damage and epigenetic dysregulation. There are exciting prospects of novel therapies for glioma patients emerging from the elucidation of these mechanisms. Given the diagnostic and prognostic implications of IDH mutation, and the potential for new therapies, all gliomas should be assessed for IDH mutation status in the future.