Application of Mutant IDH1 Antibody to Differentiate Diffuse Glioma From Nonneoplastic Central Nervous System Lesions and Therapy-induced Changes

The role of neuropathology in the management of progressive glioblastoma : a systematic review and evidence-based clinical practice guideline

QUESTION

1. What are the most important diagnostic considerations in reporting progressive glioblastoma?

TARGET POPULATION

These recommendations apply to adults with progressive glioblastoma

RECOMMENDATIONS

LEVEL III

For patients who undergo biopsy or neurosurgical resection at the time of radiologic or clinical progression, it is recommended that the pathologist report the presence and extent of progressive neoplasm as well as the presence and extent of necrosis within the pathologic material examined. Furthermore, to ensure the proper interpretation of progressive glioblastoma, it is recommended that the pathologist take into account the patient's previous diagnosis and treatment, as well as the current clinical and neuroimaging features that have led to a second biopsy or resection.

QUESTION

2. What techniques and ancillary studies are most useful in separating malignant progression from treatment effect?

TARGET POPULATION

These recommendations apply to adults with progressive glioblastoma

RECOMMENDATIONS

LEVEL III

In the setting of prior radiation and chemotherapy, it is recommended to adhere to strict histologic criteria for microvascular proliferation and necrosis in order to establish a diagnosis of a glioblastoma. Immunohistochemistry and genetic studies are selectively recommended for distinguishing neoplastic cells from atypical reactive cells in progressive glioblastoma.

Can diffusion tensor imaging noninvasively detect IDH1 gene mutations in astrogliomas? A retrospective study of 112 cases

BACKGROUND AND PURPOSE

IDH1 mutational status probably plays an important role in the predictive response for patients with astroglioma. This study explores whether DTI metrics are able to noninvasively detect IDH1 status in astrogliomas.

MATERIALS AND METHODS

The DTI data of 112 patients with pathologically proven astroglioma (including 25, 12, and 10 cases with IDH1 mutation and 11, 11, and 43 cases without mutation in grades II, III, and IV, respectively) were retrospectively reviewed. The maximal fractional anisotropy, minimal ADC, ratio of maximal fractional anisotropy, and ratio of minimal ADC in the tumor body were measured. In the same World Health Organization grading, the imaging parameters of patients with and without IDH1 R132H mutation were compared by means of optimal metrics for detecting mutations. Receiver operating characteristic curve analysis was performed.

RESULTS

The maximal fractional anisotropy and ratio of maximal fractional anisotropy values had statistical significance between patients with IDH1 R132H mutation and those without mutation in astrogliomas of grades II and III. The areas under the curve for maximal fractional anisotropy and ratio of maximal fractional anisotropy were both 0.92 in grade II and 0.80 and 0.82 in grade III. The minimal ADC value and ratio of minimal ADC value also demonstrated statistical significance between patients with mutation and those without mutation in all astroglioma grades. The areas under the curve for minimal ADC were 0.94 (II), 0.76 (III), and 0.66 (IV), and the areas under the curve for ratio of minimal ADC were 0.93 (II), 0.83 (III), and 0.70 (IV).

CONCLUSIONS

Fractional anisotropy and ADC from DTI can noninvasively detect IDH1 R132H mutation in astrogliomas.

Oligodendrocyte progenitor cells promote neovascularization in glioma by disrupting the blood-brain barrier

Enhanced platelet-derived growth factor (PDGF) signaling in glioma drives its development and progression. In this study, we define a unique role for stroma-derived PDGF signaling in maintaining tumor homeostasis within the glioma microenvironment. Large numbers of PDGF receptor-α (PDGFRα)-expressing stromal cells derived from oligodendrocytes progenitor cells (OPC) were discovered at the invasive front of high-grade gliomas, in which they exhibited a unique perivascular distribution. In PDGFRα-deficient host mice, in which orthotopic Gl261 tumors displayed reduced outgrowth, we found that tumor-associated blood vessels displayed smaller lumens and normalized vascular morphology, with tumors in host animals injected with the vascular imaging agent gadolinium also being enhanced less avidly by MRI. Notably, glioma-associated OPC promoted endothelial sprouting and tubule formation, in part by abrogating the inhibitory effect that perivascular astrocytes exert on vascular endothelial conjunctions. Stromal-derived PDGF-CC was crucial for the recruitment and activation of OPC, insofar as mice genetically deficient in PDGF-CC phenocopied the glioma/vascular defects observed in PDGFRα-deficient mice. Clinically, we showed that higher levels of PDGF-CC in glioma specimens were associated with more rapid disease recurrence and poorer overall survival. Our findings define a PDGFRα/PDGF-CC signaling axis within the glioma stromal microenvironment that contributes to vascular remodeling and aberrant tumor angiogenesis in the brain.

Correlation of IDH1/2 mutation with clinicopathologic factors and prognosis in anaplastic gliomas: a report of 203 patients from China

PURPOSE

Isocitrate dehydrogenase (IDH) gene mutation is one of the most exciting new advances in these years. It has been reported that IDH gene frequently altered in grade II and grade III gliomas. We aimed to identify the mutation frequency of IDH genes in Chinese anaplastic glioma patients, the association of IDH gene mutation with other clinical and molecular pathological features and the prognostic value of it.

METHODS

We performed polymerase chain reaction-based IDH gene mutation detection in 203 anaplastic glioma patients from China.

RESULTS

A total of 108 and 3 patients harbored IDH1 and IDH2 gene mutation, respectively. And there was a higher proportion of MGMT promoter methylation, frontal lobe location, and better outcome and lower proportion of temporal location in IDH-mutated samples. There were hardly any significant association between protein expression level of well-known markers and IDH mutation. Anaplastic oligoastrocytoma and anaplastic astrocytoma patients with IDH gene mutation showed similar prognosis with anaplastic oligodendroglioma patients with wild-type IDH gene.

CONCLUSIONS

IDH gene mutation is a good prognostic marker and a potential substratification factor for anaplastic glioma patients.

The Utility of Immunohistochemistry for Providing Genetic Information on Tumors

With advances in immunohistochemical technology and growing knowledge of the molecular genetics of tumors, immunohistochemistry is playing an increasingly important role in providing genetic information for tumors. Specific chromosomal translocations can be demonstrated through detection of the protein product of one of the genes involved in gene fusion (such as BCL2, cyclin D, and ALK). Some mutations can be detected by (1) aberrant localization of the protein product (such as β-catenin and nucleophosmin), (2) abnormal accumulation of the protein product as a result of stabilization of the protein (such as p53), and (3) mutation-specific antibodies directed against the mutant protein (such as isocitrate dehydrogenase gene R132H mutation, epidermal growth factor receptor gene L858R and exon 19 deletion mutations, and BRAF gene V600E mutation). Gene deletion or loss of function can be demonstrated by the loss of immunostaining for the protein product (such as mismatch repair proteins in microsatellite-unstable tumors, E-cadherin in lobular carcinoma of the breast, and INI1 in rhabdoid tumors, atypical teratoid/rhabdoid tumors, and epithelioid sarcomas). Gene amplification can be demonstrated by overexpression of the protein product (such as HER2 in breast and gastric cancers, and MDM2 or CDK4 in well-differentiated/dedifferentiated liposarcomas). Viruses associated with tumors can be demonstrated directly (such as Epstein-Barr virus latent membrane protein-1 in Hodgkin lymphomas, human herpesvirus 8 in Kaposi sarcomas, and Merkel cell polyomavirus in Merkel cell carcinomas) or by a surrogate marker (such as p16 in human papillomavirus infection). In this review, examples are given to illustrate the principles and pitfalls of these applications.

Extraventricular neurocytoma in pediatric populations: A case report and review of the literature

Extraventricular neurocytomas (EVNs) are rare neuronal tumors included in the definition of neoplasms in the 2007 World Health Organization classification of tumors of the central nervous system. Although a small case series of EVNs in adults has been previously reported, EVNs in pediatric populations are extremely rare. The current case report presents the clinicopathological features of an EVN in a 2-year-old female who presented with nausea and vomiting that had lasted for five days. In addition, an analysis of the imaging features, histology, treatment and prognosis of these reported rare lesions is presented. Immunohistochemically, EVNs are characterized by the robust expression of synaptophysin, but with a lack of oligodendrocyte transcription factor 2, isocitrate dehydrogenase enzyme isoform 1 (IDH1) R132/IDH2 R172 mutations and p53 immunoexpression. The treatment for EVNs in pediatric and adult populations is gross total resection, with post-operative radiation reserved for subtotal resection or recurrent disease. In addition, drop metastasis must be carefully avoided.

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.

Clinical neuropathology practice guide 3-2013: levels of evidence and clinical utility of prognostic and predictive candidate brain tumor biomarkers

A large number of potential tissue biomarkers has been proposed for brain tumors. However, hardly any have been adopted for routine clinical use, so far. For most candidate biomarkers substantial controversy exists with regard to their usefulness in clinical practice. The multidisciplinary neurooncology taskforce of the Vienna Comprehensive Cancer Center Central Nervous System Unit (CCC-CNS) addressed this issue and elaborated a four-tiered levels-of-evidence system for assessing analytical performance (reliability of test result) and clinical performance (prognostic or predictive) based on consensually defined criteria. The taskforce also consensually agreed that only biomarker candidates should be considered as ready for clinical use, which meet defined quality standards for both, analytical and clinical performance. Applying this levels-of-evidence system to MGMT, IDH1, 1p19q, Ki67, MYCC, MYCN and β-catenin, only immunohistochemical IDH1 mutation testing in patients with diffuse gliomas is supported by sufficient evidence in order to be unequivocally qualified for clinical use. For the other candidate biomarkers lack of published evidence of sufficiently high analytical test performance and, in some cases, also of clinical performance limits evidence-based confirmation of their clinical utility. For most of the markers, no common standard of laboratory testing exists. We conclude that, at present, there is a strong need for studies that specifically address the analytical performance of candidate brain tumor biomarkers. In addition, standardization of laboratory testing is needed. We aim to regularly challenge and update the present classification in order to systematically clarify the current translational status of candidate brain tumor biomarkers and to identify specific research needs for accelerating the translational pace.

Clinical neuropathology practice news 2-2013: immunohistochemistry pins IDH in glioma - molecular testing procedures under scrutiny

Isocitrate dehydrogenase 1 (IDH1) gene mutations occur in ~ 60 – 90% of diffuse and anaplastic gliomas and secondary glioblastomas. IDH status is strongly associated with patient survival times and IDH testing is relevant for clinical patient management and for stratification in clinical trials. A recent interlaboratory ring trial shows that immunohistochemistry is a highly reliable method to detect the most common IDH mutation (R132H), while IDH gene sequencing is less robust. These results support initial immunohistochemistry and subsequent gene sequencing in cases with negative or inconclusive immunostaining result as valid algorithm for IDH testing. Furthermore, they highlight the need for strict quality control of DNA-based biomarker analyses on formalin-fixed and paraffin-embedded tumor samples.

Accumulation of 2-hydroxyglutarate is not a biomarker for malignant progression in IDH-mutated low-grade gliomas

OBJECTIVES

To determine whether accumulation of 2-hydroxyglutarate in IDH-mutated low-grade gliomas (LGG; WHO grade II) correlates with their malignant transformation and to evaluate changes in metabolite levels during malignant progression.

METHODS

Samples from 54 patients were screened for IDH mutations: 17 patients with LGG without malignant transformation, 18 patients with both LGG and their consecutive secondary glioblastomas (sGBM; n = 36), 2 additional patients with sGBM, 10 patients with primary glioblastomas (pGBM), and 7 patients without gliomas. The cellular tricarboxylic acid cycle metabolites, citrate, isocitrate, 2-hydroxyglutarate, α-ketoglutarate, fumarate, and succinate were profiled by liquid chromatography-tandem mass spectrometry. Ratios of 2-hydroxyglutarate/isocitrate were used to evaluate differences in 2-hydroxyglutarate accumulation in tumors from LGG and sGBM groups, compared with pGBM and nonglioma groups.

RESULTS

IDH1 mutations were detected in 27 (77.1%) of 37 patients with LGG. In addition, in patients with LGG with malignant progression (n = 18), 17 patients were IDH1 mutated with a stable mutation status during their malignant progression. None of the patients with pGBM or nonglioma tumors had an IDH mutation. Increased 2-hydroxyglutarate/isocitrate ratios were seen in patients with IDH1-mutated LGG and sGBM, in comparison with those with IDH1-nonmutated LGG, pGBM, and nonglioma groups. However, no differences in intratumoral 2-hydroxyglutarate/isocitrate ratios were found between patients with LGG with and without malignant transformation. Furthermore, in patients with paired samples of LGG and their consecutive sGBM, the 2-hydroxyglutarate/isocitrate ratios did not differ between both tumor stages.

CONCLUSION

Although intratumoral 2-hydroxyglutarate accumulation provides a marker for the presence of IDH mutations, the metabolite is not a useful biomarker for identifying malignant transformation or evaluating malignant progression.

Progress on molecular biomarkers and classification of malignant gliomas

Gliomas are the most common primary intracranial tumors in adults. Anaplastic gliomas (WHO grade III) and glioblastomas (WHO grade IV) represent the major groups of malignant gliomas in the brain. Several diagnostic, predictive, and prognostic biomarkers for malignant gliomas have been reported over the last few decades, and these markers have made great contributions to the accuracy of diagnosis, therapeutic decision making, and prognosis of patients. However, heterogeneity in patient outcomes may still be observed, which highlights the insufficiency of a classification system based purely on histopathology. Great efforts have been made to incorporate new information about the molecular landscape of gliomas into novel classifications that may potentially guide treatment. In this review, we summarize three distinctive biomarkers, three most commonly altered pathways, and three classifications based on microarray data in malignant gliomas.

Histone 3 lysine 9 trimethylation is differentially associated with isocitrate dehydrogenase mutations in oligodendrogliomas and high-grade astrocytomas

Trimethylation of histone 3 lysine 9 (H3K9me3) is a marker of repressed transcription. Cells transfected with mutant isocitrate dehydrogenase (IDH) show increased methylation of histone lysine residues, including H3K9me3, because of inhibition of histone demethylases by 2-hydroxyglutarate. Here, we evaluated H3K9me3 and its association with IDH mutations in 284 gliomas. Trimethylation of H3K9 was significantly associated with IDH mutations in oligodendrogliomas. Moreover, 72% of World Health Organization grade II and 65% of grade III oligodendrogliomas showed combined H3K9me3 positivity and 1p19q codeletion. In astrocytic tumors, H3K9me3 positivity was found in all grades of tumors; it showed a significant relationship with IDH mutational status in grade II astrocytomas but not in grade III astrocytomas or glioblastomas. Finally, H3K9me3-positive grade II oligodendrogliomas, but not other tumor subtypes, showed improved overall survival compared with H3K9me3-negative cases. These results suggest that repressive trimethylation of H3K9 in gliomas may occur in a context-dependent manner and is associated with IDH mutations in oligodendrogliomas but may be differently regulated in high-grade astrocytic tumors. Furthermore, H3K9me3 may define a subset of grade II oligodendrogliomas with better overall survival. Our results suggest variable roles for IDH mutations in the pathogenesis of oligodendrogliomas versus astrocytic tumors.

Longitudinal expression analysis of αv integrins in human gliomas reveals upregulation of integrin αvβ3 as a negative prognostic factor

Integrin inhibitors targeting αv series integrins are being tested for their therapeutic potential in patients with brain tumors, but pathologic studies have been limited by lack of antibodies suitable for immunohistochemistry (IHC) on formalin-fixed, paraffin-embedded specimens. We compared the expression of αv integrins by IHC in brain tumor and normal human brain samples with gene expression data in a public database using new rabbit monoclonal antibodies against αvβ3, αvβ5, αvβ6, and αvβ8 complexes using both manual and automated microscopy analyses. Glial tumors usually shared an αvβ3-positive/αvβ5-positive/αvβ8-positive/αvβ6-negative phenotype. In 94 WHO (World Health Organization) grade II astrocytomas, 85 anaplastic astrocytomas WHO grade III, and 324 glioblastomas from archival sources, expression of integrins generally increased with grade of malignancy. Integrins αvβ3 and αvβ5 were expressed in many glioma vessels; the intensity of vascular expression of αvβ3 increased with grade of malignancy, whereas αvβ8 was absent. Analysis of gene expression in an independent cohort showed a similar increase in integrin expression with tumor grade, particularly of ITGB3 and ITGB8; ITGB6 was not expressed, consistent with the IHC data. Parenchymal αvβ3 expression and ITGB3 gene overexpression in glioblastomas were associated with a poor prognosis, as revealed by survival analysis (Kaplan-Meier logrank, p = 0.016). Together, these data strengthen the rationale for anti-integrin treatment of glial tumors.

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.

Diagnostic implications of IDH1-R132H and OLIG2 expression patterns in rare and challenging glioblastoma variants

Recent work has demonstrated that nearly all diffuse gliomas display nuclear immunoreactivity for the bHLH transcription factor OLIG2, and the R132H mutant isocitrate dehydrogenase 1 (IDH1) protein is expressed in the majority of diffuse gliomas other than primary glioblastoma. However, these antibodies have not been widely applied to rarer glioblastoma variants, which can be diagnostically challenging when the astrocytic features are subtle. We therefore surveyed the expression patterns of OLIG2 and IDH1 in 167 non-conventional glioblastomas, including 45 small cell glioblastomas, 45 gliosarcomas, 34 glioblastomas with primitive neuroectodermal tumor-like foci (PNET-like foci), 23 with an oligodendroglial component, 11 granular cell glioblastomas, and 9 giant cell glioblastomas. OLIG2 was strongly expressed in all glioblastomas with oligodendroglial component, 98% of small cell glioblastomas, and all granular cell glioblastomas, the latter being particularly helpful in ruling out macrophage-rich lesions. In 74% of glioblastomas with PNET-like foci, OLIG2 expression was retained in the PNET-like foci, providing a useful distinction from central nervous system PNETs. The glial component of gliosarcomas was OLIG2 positive in 93% of cases, but only 14% retained focal expression in the sarcomatous component; as such this marker would not reliably distinguish these from pure sarcoma in most cases. OLIG2 was expressed in 67% of giant cell glioblastomas. IDH1 was expressed in 55% of glioblastomas with oligodendroglial component, 15% of glioblastomas with PNET-like foci, 7% of gliosarcomas, and none of the small cell, granular cell, or giant cell glioblastomas. This provides further support for the notion that most glioblastomas with oligodendroglial component are secondary, while small cell glioblastomas, granular cell glioblastomas, and giant cell glioblastomas are primary variants. Therefore, in one of the most challenging differential diagnoses, IDH1 positivity could provide strong support for glioblastoma with oligodendroglial component, while essentially excluding small cell glioblastoma.

Relationship between SATB1 expression and prognosis in astrocytoma

Special AT-rich-sequence-binding protein 1 (SATB1), a new type of gene regulator, has been reported to be expressed in various human cancers and may be associated with malignancy. The aim of this study was to investigate the expression of SATB1 in astrocytoma and to determine its prognostic value for the overall survival of patients with astrocytoma. The expression of SATB1 protein and messenger RNA (mRNA) in human astrocytoma specimens was examined using immunohistochemistry and semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). The relationship between SATB1 expression and O-6-methylguanine-DNA methyltransferase (MGMT) promoter methylation status was also investigated. Spearman's correlation coefficient was used to describe the association between SATB1 expression and the clinical parameters of astrocytoma patients. SATB1 protein and mRNA were expressed at significant levels in astrocytoma specimens. SATB1 expression was positively correlated with astrocytoma pathological grade but negatively correlated with the life span of astrocytoma patients. SATB1 expression was also significantly lower in astrocytoma specimens with MGMT promoter methylation than in those without MGMT promoter methylation. Our findings suggest that SATB1 may have an important role as a positive regulator of astrocytoma development and progression and that SATB1 might be a useful molecular marker for predicting the prognosis of patients with astrocytoma and could be a novel target for treating astrocytoma.

Clear cell tumors of the central nervous system: a case-based review

Clear cell tumors of the central nervous system (CNS) encompass a variety of tumor subtypes that are challenging to diagnose given their similar morphologic features. Here, I use a case-based approach to review the clinicopathologic and radiologic features to help guide the general pathologist in the diagnosis of clear cell tumors of the CNS. First, the reader is invited to study 6 images of different CNS tumors with clear cell morphology. Then, each case is expanded in light of clinical and radiologic data and includes a histopathologic description of the tumor. A brief discussion follows with up-to-date diagnostic tools. Finally, I propose an immunohistochemical algorithm to navigate through the complex features that characterize clear cell tumors of the CNS. This review aims to provide a comprehensive approach to diagnosing clear cell neoplasms of the CNS based on improved assessment of the clinicopathologic and radiologic features of each entity.

IDH1 and IDH2 mutations in tumorigenesis: mechanistic insights and clinical perspectives

Genes encoding for isocitrate dehydrogenases 1 and 2, IDH1 and IDH2, are frequently mutated in multiple types of human cancer. Mutations targeting IDH1 and IDH2 result in simultaneous loss of their normal catalytic activity, the production of α-ketoglutarate (α-KG), and gain of a new function, the production of 2-hydroxyglutarate (2-HG). 2-HG is structurally similar to α-KG, and acts as an α-KG antagonist to competitively inhibit multiple α-KG-dependent dioxygenases, including both lysine histone demethylases and the ten-eleven translocation family of DNA hydroxylases. Abnormal histone and DNA methylation are emerging as a common feature of tumors with IDH1 and IDH2 mutations and may cause altered stem cell differentiation and eventual tumorigenesis. Therapeutically, unique features of IDH1 and IDH2 mutations make them good biomarkers and potential drug targets.

IDH mutations in acute myeloid leukemia

Acute myeloid leukemia is a heterogeneous group of diseases. Mutations of the isocitrate dehydrogenase (IDH) genes represent a novel class of point mutations in acute myeloid leukemia. These mutations prevent oxidative decarboxylation of isocitrate to α-ketoglutarate and confer novel enzymatic activity, facilitating the reduction of α-ketoglutarate to d-2-hydroxyglutarate, a putative oncometabolite. IDH1/IDH2 mutations are heterozygous, and their combined frequency is approximately 17% in unselected acute myeloid leukemia cases, 27% in cytogenetically normal acute myeloid leukemia cases, and up to 67% in acute myeloid leukemia cases with cuplike nuclei. These mutations are largely mutually exclusive. Despite many similarities of IDH1 and IDH2 mutations, it is possible that they represent distinct molecular or clinical subgroups of acute myeloid leukemia. All known mutations involve arginine (R), in codon 132 of IDH1 or codon 140 or 172 of IDH2. IDH1(R132) and IDH2(R140) mutations are frequently accompanied by normal cytogenetics and NPM1 mutation, whereas IDH2(R172) is frequently the only mutation detected in acute myeloid leukemia. There is increasing evidence that the prognostic impact of IDH1/2 mutations varies according to the specific mutation and also depends on the context of concurrent mutations of other genes. IDH1(R132) mutation may predict poor outcome in a subset of patients with molecular low-risk acute myeloid leukemia, whereas IDH2(R172) mutations confer a poor prognosis in patients with acute myeloid leukemia. Expression of IDH1/2 mutants induces an increase in global DNA hypermethylation and inhibits TET2-induced cytosine 5-hydroxymethylation, DNA demethylation. These data suggest that IDH1/2 mutations constitute a distinct mutational class in acute myeloid leukemia, which affects the epigenetic state, an important consideration for the development of therapeutic agents.

Diagnostic segregation of human brain tumours using Fourier-transform infrared and/or Raman spectroscopy coupled with discriminant analysis

The most common initial treatment received by patients with a brain tumour is surgical removal of the growth. Precise histopathological diagnosis of brain tumours is to some extent subjective. Furthermore, currently available diagnostic imaging techniques to delineate the excision border during cytoreductive surgery lack the required spatial precision to aid surgeons. We set out to determine whether infrared (IR) and/or Raman spectroscopy combined with multivariate analysis could be applied to discriminate between normal brain tissue and different tumour types (meningioma, glioma and brain metastasis) based on the unique spectral "fingerprints" of their biochemical composition. Formalin-fixed paraffin-embedded tissue blocks of normal brain and different brain tumours were de-waxed, mounted on low-E slides and desiccated before being analyzed using attenuated total reflection Fourier-transform IR (ATR-FTIR) and Raman spectroscopy. ATR-FTIR spectroscopy showed a clear segregation between normal and different tumour subtypes. Discrimination of tumour classes was also apparent with Raman spectroscopy. Further analysis of spectral data revealed changes in brain biochemical structure associated with different tumours. Decreased tentatively-assigned lipid-to-protein ratio was associated with increased tumour progression. Alteration in cholesterol esters-to-phenylalanine ratio was evident in grade IV glioma and metastatic tumours. The current study indicates that IR and/or Raman spectroscopy have the potential to provide a novel diagnostic approach in the accurate diagnosis of brain tumours and have potential for application in intra-operative diagnosis.

The relationship between Cho/NAA and glioma metabolism: implementation for margin delineation of cerebral gliomas

Background

The marginal delineation of gliomas cannot be defined by conventional imaging due to their infiltrative growth pattern. Here we investigate the relationship between changes in glioma metabolism by proton magnetic resonance spectroscopic imaging (¹H-MRSI) and histopathological findings in order to determine an optimal threshold value of choline/N-acetyl-aspartate (Cho/NAA) that can be used to define the extent of glioma spread.

Method

Eighteen patients with different grades of glioma were examined using ¹H-MRSI. Needle biopsies were performed under the guidance of neuronavigation prior to craniotomy. Intraoperative magnetic resonance imaging (MRI) was performed to evaluate the accuracy of sampling. Haematoxylin and eosin, and immunohistochemical staining with IDH1, MIB-1, p53, CD34 and glial fibrillary acidic protein (GFAP) antibodies were performed on all samples. Logistic regression analysis was used to determine the relationship between Cho/NAA and MIB-1, p53, CD34, and the degree of tumour infiltration. The clinical threshold ratio distinguishing tumour tissue in high-grade (grades III and IV) glioma (HGG) and low-grade (grade II) glioma (LGG) was calculated.

Results

In HGG, higher Cho/NAA ratios were associated with a greater probability of higher MIB-1 counts, stronger CD34 expression, and tumour infiltration. Ratio threshold values of 0.5, 1.0, 1.5 and 2.0 appeared to predict the specimens containing the tumour with respective probabilities of 0.38, 0.60, 0.79, 0.90 in HGG and 0.16, 0.39, 0.67, 0.87 in LGG.

Conclusions

HGG and LGG exhibit different spectroscopic patterns. Using ¹H-MRSI to guide the extent of resection has the potential to improve the clinical outcome of glioma surgery.

Gliosis versus glioma?: don't grade until you know

A major challenge in the routine practice of surgical neuropathology is the distinction between reactive astrocytosis, which may be because of non-neoplastic and neoplastic conditions, and a low-grade infiltrating diffuse astrocytoma [World Health Organization (WHO) grade II]. This can be particularly challenging with small biopsies that often yield limited amounts of tissue for pathologic study, especially considering the marked differences in prognosis and therapy after a pathologic diagnosis. This paper will review some basic principles of gliosis as an astrocytic reaction to a wide range of central nervous system insults and focus on some common diagnostic pitfalls such as (1) gliosis associated with brain tumor mimics, including demyelinating disease and infections, (2) gliosis associated with nonglial tumors such as craniopharyngioma, hemangioblastoma, metastases, and central nervous system lymphoma. New diagnostic methods have facilitated the differentiation between reactive astrocytosis and the diffuse gliomas. Of these, the use of mutated isocitrate dehydrogenase-1 (IDH-1) as a marker of diffuse infiltrating astroctomas, oligodendrogliomas, and a subset of glioblastomas (secondary glioblastomas) is particularly exciting for tissue diagnosis and patient prognosis. In addition IDH-1 may be useful to distinguish a diffuse infiltrating glioma from low-grade "focal" neoplasms such as the pilocytic astocytoma in histologically ambiguous cases. The discovery of BRAF mutations as molecular signatures of some pilocytic astrocytomas, gangliogliomas, and pleomorphic xanthoastrocytomas has provided another diagnostic tool for the pathologist. Only after a definitive diagnosis of a diffuse infiltrating glioma or a focal glioma is made should a tumor grade be applied and some practical issues in current glioma grading are provided.

Pathologic diagnosis of recurrent glioblastoma: morphologic, immunohistochemical, and molecular analysis of 20 paired cases

To evaluate the prognostic value of the volume of residual viable tumor versus therapy-induced necrosis in resection material and the diagnostic value of ancillary tests in recurrent glioblastoma (GBM), we conducted a retrospective review of 20 patients whose initial and recurrent specimens were available. Recurrent GBMs were graded according to the extent of histopathologic parameters: recurrent tumor with high-grade, non-high-grade, and pure high-grade tumor components and therapy-related necrosis. We also examined MIB-1 labeling, isocitrate dehydrogenase 1 mutation, and epidermal growth factor receptor amplification in primary and recurrent GBMs. To evaluate patient outcomes according to clinical and pathologic parameters, a survival analysis was performed, and correlations between histopathologic parameters and each ancillary test were assessed. Among clinical parameters, age above 60 years was associated with decreased survival (P=0.022), but other clinical parameters showed no significant association with overall survival. Among the 3 histopathologic parameters, the extent of recurrent tumor, including high-grade and non-high-grade components, revealed a significant association with overall survival (P=0.042), but neither the extent of pure high-grade components nor therapy-related necrosis showed any prognostic value. MIB-1 labeling, isocitrate dehydrogenase 1 mutation, and epidermal growth factor receptor amplification were useful for the diagnosis of recurrent GBMs but showed no prognostic value. Our data suggest that histopathologic evaluation on the basis of tumor extent in resected recurrent GBM specimens may provide additional prognostic information on the survival of patients with recurrent GBM.

IDH mutation detection in formalin-fixed paraffin-embedded gliomas using multiplex PCR and single-base extension

Isocitrate dehydrogenase (IDH) genes are mutated in a significant portion of gliomas, myeloid leukemias and chondroid neoplasms. In gliomas, IDH mutations are prognostic, as those tumors with the mutation are associated with a proneural subclass and have longer survival compared with those without the mutation. We developed a simple, PCR-based SNaPshot® assay (Life Technologies, Carlsbad, CA, USA) to detect IDH1/2 mutations. This protocol combines a single, multiplexed PCR reaction using gene specific primers followed by a single, multiplexed SNaPshot reaction and detection by capillary electrophoresis. In a blinded study of 32 paraffin-embedded glioma specimens previously screened for IDH mutations by a PCR/direct sequencing method, concordance of our IDH SNaPshot test with sequencing was 100%. We performed the assay on an additional 57 specimens submitted for diagnostic IDH mutation evaluation. Data analysis was much faster and easier to perform than analysis of the sequencing data, and results could be obtained in 1 day from DNA extraction to analysis. Furthermore, we could readily identify a mixture of 5% mutant allele vs. 95% wild-type allele in our SNaPshot assay, in comparison to approximately 20% mutant allele in our PCR-sequencing assay. Our assay represents a fast, sensitive, straightforward method of reliably detecting common mutations of IDH genes in glial neoplasms, or other tumors.

Isocitrate dehydrogenase mutations in gliomas: mechanisms, biomarkers and therapeutic target

PURPOSE OF REVIEW

Isocitrate dehydrogenases, IDH1 and IDH2, decarboxylate isocitrate to α-ketoglutarate (α-KG) and reduce NADP to NADPH. Point mutations of IDH1 and IDH2 have been discovered in gliomas. IDH mutations cause loss of native enzymatic activities and confer novel activity of converting α-KG to 2-hydroxyglutarate (2-HG). The mechanisms of IDH mutations in gliomagenesis, and their value as diagnostic, prognostic marker and therapeutic target have been extensively studied. This review is to summarize the findings of these studies.

RECENT FINDINGS

Crystal structural studies revealed conformation changes in mutant IDHs, which may explain the gain of function by mutant IDHs. The product of mutant IDHs, 2-HG, is an inhibitor of α-KG-dependent dioxygenases, which may cause genome-wide epigenetic changes in human gliomas. IDH mutations are a favorable prognostic factor for human glioma and can be used as biomarker for differential diagnosis and subclassification rather than predictor of response to treatment. Preliminary data suggested that inhibiting production of the substrate of mutant IDH enzymes caused slow-down of glioma cell growth.

SUMMARY

As valuable diagnostic and prognostic markers of human gliomas, there is still a lack of knowledge on biological functions of mutant IDHs, making targeting IDHs in glioma both difficult and unsecured.

Immunohistochemical analysis of 1844 human epithelial and haematopoietic tumours and sarcomas for IDH1R132H mutation

AIMS

Mutations in the isocitrate dehydrogenase 1 gene have been identified recently to play a key role in diffuse astrocytoma and oligodendroglioma as well as in acute myeloid leukaemia. In glioma, IDH1R132H is the most common mutation type, which is associated with younger patient age and longer patient survival compared to wild-type status. Sequencing analyses of carcinomas and lymphomas have detected IDH1 mutations in only a small fraction of cases. In those studies, IDH1R132H was also the most frequent mutation. The aim of the present study was to analyse a comprehensive series of human tumours for IDH1R132H mutation.

METHODS AND RESULTS

A total of 1844 formalin-fixed paraffin-embedded tumours, including carcinomas, sarcomas and haematopoietic tumours were investigated immunohistochemically using a mutation-specific antibody for IDH1(R132H). Our positive control series consisted of a collection of diffuse astrocytomas and oligodendrogliomas. No IDH1R132H mutation was found in this series.

CONCLUSIONS

IDH1R132H mutations occur almost exclusively in glioma and acute myeloid leukaemia.

Value and limitations of immunohistochemistry and gene sequencing for detection of the IDH1-R132H mutation in diffuse glioma biopsy specimens

To assess the value of anti-isocitrate dehydrogenase 1 (IDH1) immunohistochemistry for evaluating diffuse gliomas, we analyzed anti-IDH1-R132H immunohistochemistry using monoclonal antibodies DIA-H09 and IMab-1 and IDH1 gene sequencing in formalin-fixed and paraffin-embedded biopsy samples of 95 diffuse gliomas. We found concordant immunostaining results using the 2 antibodies in 94 (98.9%) of the 95 cases, but DIA-H09 generally showed a higher signal-to-background ratio than IMab-1 did. Fifty-five percent of cases showed anti-IDH1-R132H immunostaining of virtually all tumor cells and 15% of only a fraction of tumor cells. All cases with complete or partial immunostaining of the tumor tissue carried the IDH1-R132H mutation. In all cases with negative immunostaining results (approximately 30%), genetic analysis showed IDH1 wild-type or non-R132H-IDH1 mutations. In a single tiny biopsy, both anti-IDH1-R132H antibodies showed immunoreactivity, but genetic testing was inconclusive. Our data confirm anti-IDH1-R132H immunostaining as a reliable method for evaluation of IDH1 gene mutation status. They also suggest the following: (i) in some cases, nonspecific background staining or regional heterogeneity of IDH1-R132H protein expression may necessitate confirmatory genetic analysis; (ii) for individual cases, anti-IDH1-R132H immunostaining may not reliably identify infiltrating tumor cells admixed with preexisting or reactive glial cells; and (iii) in tiny biopsies, immunohistochemistry may be more sensitive for detection of IDH1-R132H mutation than genetic analysis.

Detection of 2-hydroxyglutarate in formalin-fixed paraffin-embedded glioma specimens by gas chromatography/mass spectrometry

Mutations in the isocitrate dehydrogenase (IDH) 1 and 2 genes occur frequently in diffuse astrocytoma and oligodendroglioma. The consecutive amino acid substitutions in the mutant proteins result in a gain of the function to catalyze the reduction of alpha-ketoglutarate to 2-hydroxyglutarate (2HG). So far, all investigated IDH mutations share this gain of function. We here describe a method to detect 2HG levels in archival formalin-fixed paraffin-embedded tumor specimens by stable isotope dilution using gas chromatography followed by mass spectrometry (GC/MS). While 2HG levels are notably decreased during the routine embedding process, preserved amounts are still sufficient to indicate a mutation. Detection of 2HG in archival specimens could make routinely processed tissue accessible for research on 2HG accumulation and may allow studies on correlation with clinical data.

The neurobiology of gliomas: from cell biology to the development of therapeutic approaches

Gliomas are the most common type of primary brain tumour and are often fast growing with a poor prognosis for the patient. Their complex cellular composition, diffuse invasiveness and capacity to escape therapies has challenged researchers for decades and hampered progress towards an effective treatment. Recent molecular characterization of tumour cells combined with new insights into cellular diversification that occurs during development, and the modelling of these processes in transgenic animals have enabled a more detailed understanding of the events that underlie gliomagenesis. Combining this enhanced understanding of the relationship between neural stem cell biology and the cell lineage relationships of tumour cells with model systems offers new opportunities to develop specific and effective therapies.

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.

Assessment of BRAF V600E mutation status by immunohistochemistry with a mutation-specific monoclonal antibody

Activating mutations of the serine threonine kinase v-RAF murine sarcoma viral oncogene homolog B1 (BRAF) are frequent in benign and malignant human tumors and are emerging as an important biomarker. Over 95% of BRAF mutations are of the V600E type and specific small molecular inhibitors are currently under pre-clinical or clinical investigation. BRAF mutation status is determined by DNA-based methods, most commonly by sequencing. Here we describe the development of a monoclonal BRAF V600E mutation-specific antibody that can differentiate BRAF V600E and wild type protein in routinely processed formalin-fixed and paraffin-embedded tissue. A total of 47 intracerebral melanoma metastases and 21 primary papillary thyroid carcinomas were evaluated by direct sequencing of BRAF and by immunohistochemistry using the BRAF V600E mutation-specific antibody clone VE1. Correlation of VE1 immunohistochemistry and BRAF sequencing revealed a perfect match for both papillary thyroid carcinomas and melanoma metastases. The staining intensity in BRAF V600E mutated tumor samples ranged from weak to strong. The generally homogenous VE1 staining patterns argue against a clonal heterogeneity of the tumors investigated. Caution is essential when only poorly preserved tissue is available for VE1 immunohistochemical analysis or when tissues with only little total BRAF protein are analyzed. Immunohistochemistry using antibody VE1 may substantially facilitate molecular analysis of BRAF V600E status for diagnostic, prognostic, and predictive purposes.

Molecular diagnostics of gliomas

CONTEXT

Gliomas are the most common primary brain tumors of adults and include a variety of histologic types and morphologies. Histologic evaluation remains the gold standard for glioma diagnosis; however, diagnostic difficulty may arise from tumor heterogeneity, overlapping morphologic features, and tumor sampling. Recently, our knowledge about the genetics of these tumors has expanded, and new molecular markers have been developed. Some of these markers have shown diagnostic value, whereas others are useful prognosticators for patient survival and therapeutic response.

OBJECTIVE

To review the most clinically useful molecular markers and their detection techniques in gliomas.

DATA SOURCES

Review of the pertinent literature and personal experience with the molecular testing in gliomas.

CONCLUSIONS

This article provides an overview of the most common molecular markers in neurooncology, including 1p/19q codeletion in oligodendroglial tumors, mutations in the isocitrate dehydrogenase 1 and 2 genes in diffuse gliomas, hypermethylation of the O(6)-methylguanine-DNA methyltransferase gene promoter in glioblastomas and anaplastic gliomas, alterations in the epidermal growth factor receptor and phosphatase and tensin homolog genes in high-grade gliomas, as well as BRAF alterations in pilocytic astrocytomas. Molecular testing of gliomas is increasingly used in routine clinical practice and requires that neuropathologists be familiar with these genetic markers and the molecular diagnostic techniques for their detection.

Overview and recent advances in neuropathology. Part 1: Central nervous system tumours

This review highlights the recent changes to the World Health Organization (WHO) 4th edition of the classification of central nervous system tumours. The mixed glial and neuronal tumour group continues to expand to encompass three new subtypes of glioneuronal tumours. The main diagnostic points differentiating these tumours are covered. Also covered is an update on issues relating to grading of astrocytic, oligodendroglial and pineal tumours and the recent molecular subtypes observed in medulloblastomas. The theme of molecular genetics is continued in the following section where the four subtypes in the molecular subclassification of glioblastoma; classical, mesenchymal, proneural and neural are outlined. The genetic profile of these subtypes is highlighted as is their varying biological responses to adjuvant therapies. The relationship between chromosome 1p and 19q deletions and treatment responsive oligodendrogliomas is discussed, as are the newer advances relating to silencing of the MGMT gene in astrocytomas and mutations in the IDH-1 gene in both astrocytomas and oligodendrogliomas. The final section in this article provides an update on the concept of glioma stem cells.

Isocitrate dehydrogenase mutations: a challenge to traditional views on the genesis and malignant progression of gliomas

Isocitrate dehydrogenases (IDHs) convert isocitrate to α-ketoglutarate by oxidative decarboxylation and are thereby involved in multiple metabolic processes. Mutations in the genes encoding IDH1 and IDH2 were first reported in human gliomas in 2008 and later on also identified in a minority of patients with acute myeloid leukemia. The mutations universally affect codons 132 in IDH1 and 172 in IDH2 and result in decreased enzymatic activity. The oncogenic pathway triggered by IDH mutations may involve the activation of hypoxia-inducible factor pathway as well as the acquisition of a novel (gain of enzymatic) function consuming NADPH and generating α-hydroxyglutarate. Most intriguingly, IDH mutations are observed in ∼70-80% of grade II/III gliomas and the majority of secondary glioblastomas, but only 10% of primary glioblastomas, suggesting a different cellular origin of the gliomas, which had previously been viewed as a multistep process of malignant progression. Understanding the oncogenic pathway mediated by mutant IDH might result in the development of novel, tailored pharmacological therapies for human glioma patients.