A t(1;19)(q10;p10) mediates the combined deletions of 1p and 19q and predicts a better prognosis of patients with oligodendroglioma

Recent advances in the molecular understanding of glioblastoma

Glioblastoma is the most common and most aggressive primary brain tumor. Despite maximum treatment, patients only have a median survival time of 15 months, because of the tumor’s resistance to current therapeutic approaches. Thus far, methylation of the O⁶-methylguanine-DNA methyltransferase (MGMT) promoter has been the only confirmed molecular predictive factor in glioblastoma. Novel “genome-wide” techniques have identified additional important molecular alterations as mutations in isocitrate dehydrogenase 1 (IDH1) and its prognostic importance. This review summarizes findings and techniques of genetic, epigenetic, transcriptional, and proteomic studies of glioblastoma. It provides the clinician with an up-to-date overview of current identified molecular alterations that should ultimately lead to new therapeutic targets and more individualized treatment approaches in glioblastoma.

MGMT CpG island is invariably methylated in adult astrocytic and oligodendroglial tumors with IDH1 or IDH2 mutations

We have previously identified a region containing 16 CpGs within the MGMT CpG islands which is critical for the transcriptional control of MGMT (Malley, Acta Neuropathol 2011). To investigate the patterns and incidence of MGMT methylation in astrocytic and oligodendroglial tumors, we quantitatively assessed methylation at these 16 CpGs using bisulfite modification followed by pyrosequencing of 362 gliomas not treated with temozolomide, and correlated the findings with previously identified patterns of genetic abnormalities, patients' age and survival. The MGMT gene was considered to be methylated when the mean methylation of the 16 CpGs was 10% or higher. This cut-off value distinguished diffuse astrocytomas with high and low MGMT expression. Within each tumor type, the patterns of methylation were highly variable and also highly heterogeneous across the 16 CpGs. A high incidence of MGMT methylation was observed in all subtypes of gliomas included in this study. Among a subset of 97 tumors where conventional methylation-specific PCR (MSP) was also applied, methylation was detected by both methods in 54 tumors, while the pyrosequencing results identified a further 17 tumors. No additional cases were found using MSP alone, indicating that pyrosequencing is a robust method for methylation analysis. All tumors with IDH1/IDH2 mutations except two had MGMT methylation, while there were many tumors with MGMT methylation, particularly primary glioblastomas, which had no mutations of IDH1/2. We suggest that MGMT methylation may be one of the earliest events in the development of astrocytic and oligodendroglial tumors.

Low-grade gliomas in adults

In recent years, advances in the understanding of low-grade glioma (LGG) biology have driven new paradigms in molecular markers, diagnostic imaging, operative techniques and technologies, and adjuvant therapies. Taken together, these developments are collectively pushing the envelope toward improved quality of life and survival. In this article, the authors evaluate the recent literature to synthesize a comprehensive review of LGGs in the modern neurosurgical era.

Downregulation of PRDX1 by promoter hypermethylation is frequent in 1p/19q-deleted oligodendroglial tumours and increases radio- and chemosensitivity of Hs683 glioma cells in vitro

Deletions of chromosomal arms 1p and 19q are frequent in oligodendroglial tumours and linked to radio- and chemotherapy response as well as longer survival. The molecular mechanisms underlying this clinically important association are as yet unknown. Here, we studied the peroxiredoxin 1 (PRDX1) gene at 1p34.1 for promoter methylation and expression in primary gliomas and investigated its role in radio- and chemosensitivity of glioma cells in vitro. In total, we screened primary glioma tissues from 93 patients for methylation of the 5'-CpG island of PRDX1 by sodium bisulfite sequencing. PRDX1 mRNA and protein expression levels were determined in subsets of the tumours by quantitative PCR and western blot analysis, respectively. PRDX1 hypermethylation and reduced expression were frequently detected in oligodendroglial tumours and secondary glioblastomas, but not in primary glioblastomas. In oligodendroglial tumours, both PRDX1 hypermethylation and reduced mRNA expression were significantly associated with 1p/19q-deletion. Stable knockdown of PRDX1 by lentiviral transduction of short-hairpin (sh)RNA constructs significantly increased apoptosis and reduced cell viability of Hs683 glioma cells exposed to ionizing irradiation or temozolomide in vitro. Taken together, our findings indicate that epigenetic silencing of PRDX1 is frequent in 1p/19q-deleted oligodendroglial tumours and likely contributes to radio- and chemosensitivity of these tumours.

α-Internexin in the diagnosis of oligodendroglial tumors and association with 1p/19q status

α-Internexin (INA) has been proposed to be a surrogate marker for the 1p/19q codeletion in oligodendroglial tumors (OTs). We analyzed INA expression in 83 glioma and 21 oligodendroglial phenotype-mimicking tumors (OMT) to assess its usefulness in differential diagnosis and its correlation with 1p/19q status; in particular, INA expression in gliomas with isolated/partial 1p or 19q deletions was assessed. α-Internexin expression and 1p/19q codeletion were present in 92% (34/37) of codeleted tumors (p < 0.0001). By contrast, INA was found in only 20% of cases with isolated/partial 1p aberrations and 36% of cases without 1p/19q deletions; it was also foundin 63% (10/16) of cases with isolated/partial 19q aberrations. α-Internexin expression was more specific in high-grade than in low-grade gliomas (66% vs 31%). Notably, a subset of tumors (10/83) displayed a biphasic INA expression pattern that was significantly associated with proliferation rate, whereas all areas harbored the 1p/19q codeletion. Only no or weak INA expression was seen in OMTs. In summary, INA is a useful marker to differentiate OTs from astrocytic tumors and OMTs, but INA expression is not exclusively linked to OTs harboring the 1p/19q codeletion. Moreover, it can sometimes be heterogeneously distributed within tumors, which emphasizes the need for 1p/19q analysis by molecular genetic techniques for diagnosis.

Extracranial skeletal metastasis in anaplastic oligodendroglioma: case report and review of the literature

A case of anaplastic oligodendroglioma with femoral metastasis is presented in a 37-year old male with a 2-year history of progressive headaches and dizziness associated with a 2-month history of epilepsy and right hemiparesis. Magnetic resonance imaging (MRI) demonstrated a solid temporoparietal tumour and the patient underwent a left temporal craniotomy and subtotal resection followed by limited-field radiation therapy. The pathological diagnosis was anaplastic oligodendroglioma. The patient presented with left hip pain 3 years later. Radiography and computed tomography demonstrated osteosclerosis of the left proximal femur, and MRI revealed an intramedullary metastatic lesion. Total body (99m)Tc-methylene diphosphonate bone scan showed hyperactivity in the lesion and open biopsy confirmed it was a metastasis from the cerebral oligodendroglioma. The patient was treated with temozolomide and, to date, there is no sign of recurrence or progression in either the brain or the femur. Seven previously reported cases of extracranial skeletal metastasis from anaplastic oligodendroglioma are reviewed. Co-deletion of chromosome arms 1p and 19q and O(6)-methylguanine DNA methyltransferase status remain the most important prognostic and predictive markers.

Design of clinical trials for biomarker research in oncology

The developmental pathway from discovery to clinical practice for biomarkers and biomarker-directed therapies is complex. While several issues need careful consideration, two critical issues that surround the validation of biomarkers are the choice of clinical trial design (which is based on the strength of the preliminary evidence and marker prevalence) and the biomarker assay related issues surrounding the marker assessment methods such as the reliability and reproducibility of the assay. This review focuses on trial designs for marker validation, both in the setting of early phase trials for initial validation, as well as in the context of larger definitive trials. Designs for biomarker validation are broadly classified as retrospective (i.e., using data from previously well-conducted, randomized, controlled trials) or prospective (enrichment, allcomers or adaptive). We believe that the systematic evaluation and implementation of these design strategies are essential to accelerate the clinical validation of biomarker-guided therapy, thereby taking us a step closer to the goal of personalized medicine.

The role of glutathione in brain tumor drug resistance

Chemotherapy is central to the current treatment modality for primary human brain tumors, but despite high-dose and intensive treatment regimens there has been little improvement in patient outcome. The development of tumor chemoresistance has been proposed as a major contributor to this lack of response. While there have been some improvements in our understanding of the molecular mechanisms underlying brain tumor drug resistance over the past decade, the contribution of glutathione (GSH) and the GSH-related enzymes to drug resistance in brain tumors have been largely overlooked. GSH constitutes a major antioxidant defense system in the brain and together with the GSH-related enzymes plays an important role in protecting cells against free radical damage and dictating tumor cell response to adjuvant cancer therapies, including irradiation and chemotherapy. Glutamate cysteine ligase (GCL), glutathione synthetase (GS), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferases (GST), and GSH complex export transporters (GS-X pumps) are major components of the GSH-dependent enzyme system that function in a dynamic cascade to maintain redox homeostasis. In many tumors, the GSH system is often dysregulated, resulting in a more drug resistant phenotype. This is commonly associated with GST-mediated GSH conjugation of various anticancer agents leading to the formation of less toxic GSH-drug complexes, which can be readily exported from the cell. Advances in our understanding of the mechanisms of drug resistance and patient selection based on biomarker profiles will be crucial to adapt therapeutic strategies and improve outcomes for patients with primary malignant brain tumors.

Prognostic variables in oligodendroglial tumors: a single-institution study of 95 cases

We analyzed the relationships among clinical variables, histology, 1p/19q status, and outcome in 95 patients with oligodendroglial tumors. The study enrolled adult patients who underwent first-time surgery for a supratentorial oligodendroglial tumor at Oslo University Hospital, Rikshospitalet. Tumors were: 27 oligodendrogliomas, WHO grade II; 32 oligoastrocytomas, WHO grade II; 16 anaplastic oligodendrogliomas, WHO grade III; 14 anaplastic oligoastrocytomas, WHO grade III; and 6 glioblastomas with a major oligodendroglial component, WHO grade IV. The clinical files were reviewed. Three neuropathologists evaluated the histological slides independently. Loss-of-heterozygosity analysis for 1p and 19q was performed by PCR. Favorable prognostic factors from univariate analyses included seizures as presenting symptom, female sex, location in the frontal lobe, low WHO grade, classic histology, absence of gemistocytic cells, and combined 1p/19q loss. Solitary 19q loss was a negative prognostic marker. 1p/19q status was of prognostic significance in both tumors with classic and nonclassic oligodendroglial histology. In the multivariate analysis, WHO grade II (P< .001), frontal tumor location (P= .002), and combined 1p/19q loss (P< .001) remained favorable prognostic variables. Our results suggest that tumor location, WHO grade, and 1p/19q status are important independent variables associated with survival in oligodendroglial tumors. The study suggests that solitary 19q loss is a negative prognostic variable and that 1p/19q loss is associated with prolonged survival also in oligodendroglial tumors without classic histology.

Solid tumor cytogenetics: current perspectives

Conventional cytogenetics in conjunction with Fluorescence in Situ Hybridization (FISH) continues to remain an important and integral component in the diagnosis and management of solid tumors. The ability to effectively detect the vast majority of clinically relevant chromosomal aberrations with a rapid-to-acceptable turnaround time makes them the most cost-effective screening/detection tool currently available in modern pathology. In this review, we describe a representative set of solid tumors in which chromosomal analysis and/or FISH plays a significant role in the routine clinical management of solid tumors.

Outcome after bevacizumab clinical trial therapy among recurrent grade III malignant glioma patients

Although outcome following bevacizumab among recurrent grade IV malignant glioma patients is documented as poor by several analyses, outcome for recurrent grade III patients following bevacizumab therapy has not been specifically evaluated. We performed a pooled analysis of 96 recurrent grade III malignant glioma patients enrolled on three consecutive phase II bevacizumab salvage trials to evaluate overall outcome following bevacizumab trial discontinuation. Outcome on the three bevacizumab trials, which included similar eligibility, treatment and assessment criteria, was comparable. Forty-nine patients who progressed on bevacizumab trial therapy and remained alive for at least 30 days elected to receive additional therapy. These patients achieved a median PFS-6 and OS of 30.6% (95% CI: 18.4, 43.6) and 10.3 months (95% CI: 5.2, 11.7), respectively. Among patients who continued bevacizumab therapy (n = 23) after study progression, PFS-6 and median OS were 39.1% (95% CI: 19.9, 58.0) and 9.2 months (95% CI: 5.2, 13.6), respectively, compared to 23.1% (95% CI: 9.4, 40.3; P = 0.51) and 10.3 months (95% CI: 2.5, 14.4; P = 0.91) for patients who initiated non-bevacizumab containing therapy (n = 26). Outcome after discontinuation of bevacizumab therapy for recurrent grade III malignant glioma patients is associated with improved outcome compared to historical data for recurrent grade IV malignant glioma patients. Salvage therapies following bevacizumab failure have modest activity for grade III malignant glioma patients that is independent of further bevacizumab continuation.

Predictive and prognostic factors for gliomas

Despite recent therapeutic advances, gliomas, in particular the most frequent and malignant glioblastoma, remain devastating tumors and need a better molecular characterization to improve both classification and treatment. Currently, three molecular markers, related to better outcome, are particularly useful and complement the histological classification: the 1p/19q codeletion strongly predicts prolonged response to treatment and prolonged survival in oligodendroglial tumors; the O(6)-methylguanine-DNA methyltransferase promoter methylation, which is hypothesized to render the cell more vulnerable to alkylants, is associated with a stronger benefit of concomitant chemoradiotherapy in glioblastomas; mutations of the IDH1 (more rarely IDH2) gene affects 40% of gliomas (but 100% of the 1p/19q codeleted gliomas) and is inversely correlated to grade. IDH1 mutation is a strong and independent predictor of survival, whatever grade considered. The consequences of IDH1/IDH2 mutation (that results in a new enzymatic activity transforming alphacetoglutarate into 2-hydroxyglutarate) are currently under investigation. Recently, integrated genomic, transcriptomic and epigenetic studies have unraveled new glioblastoma subgroups that further refines the molecular classification of these tumors. Such an approach should be extended to lower grade gliomas.

Asymmetry-defective oligodendrocyte progenitors are glioma precursors

Postnatal oligodendrocyte progenitor cells (OPC) self-renew, generate mature oligodendrocytes, and are a cellular origin of oligodendrogliomas. We show that the proteoglycan NG2 segregates asymmetrically during mitosis to generate OPC cells of distinct fate. NG2 is required for asymmetric segregation of EGFR to the NG2(+) progeny, which consequently activates EGFR and undergoes EGF-dependent proliferation and self-renewal. In contrast, the NG2(-) progeny differentiates. In a mouse model, decreased NG2 asymmetry coincides with premalignant, abnormal self-renewal rather than differentiation and with tumor-initiating potential. Asymmetric division of human NG2(+) cells is prevalent in non-neoplastic tissue but is decreased in oligodendrogliomas. Regulators of asymmetric cell division are misexpressed in low-grade oligodendrogliomas. Our results identify loss of asymmetric division associated with the neoplastic transformation of OPC.

Mutations in CIC and FUBP1 contribute to human oligodendroglioma

Oligodendrogliomas are the second most common malignant brain tumor in adults and exhibit characteristic losses of chromosomes 1p and 19q. To identify the molecular genetic basis for this alteration, we performed exomic sequencing of seven tumors. Among other changes, we found that the CIC gene (homolog of the Drosophila gene capicua) on chromosome 19q was somatically mutated in six cases and that the FUBP1 gene [encoding far-upstream element (FUSE) binding protein] on chromosome 1p was somatically mutated in two tumors. Examination of 27 additional oligodendrogliomas revealed 12 and 3 more tumors with mutations of CIC and FUBP1, respectively, 58% of which were predicted to result in truncations of the encoded proteins. These results suggest a critical role for these genes in the biology and pathology of oligodendrocytes.

Histomolecular classification of adult diffuse gliomas: the diagnostic value of immunohistochemical markers

Adult gliomas are most often infiltrative. The World Health Organization (WHO) has classed them into three major groups according to the presomptive cell of origin: astrocytoma, oligodendroglioma and mixed oligoastrocytoma. Depending on the presence or absence of a small number of signs of anaplasia (mitosis, nuclear atypia, cell density, microvascular proliferation and necrosis) the WHO distinguishes grade II (LGG), III (anaplastic), and IV (glioblastomas, GBM). Mutation in the isocitrate deshydrogenase I and II (IDH1 and 2) genes distinguishes grade II, III and secondary GBM from primary GBM. Moreover two additional genetic alterations are recorded in grade II and III gliomas: TP53 mutations that characterize astrocytomas and 1p19q codeletion (as the result of t(1;19)(q10;p10) translocation) recorded in oligodendrogliomas. Mixed gliomas, the most non-reproducible category, share with astrocytomas and oligodendrogliomas the same genetic alterations. Interestingly TP53 mutation (p53+) and 1p19q codeletion (1p19q+) are mutually exclusive and involve IDH mutated (IDH+) glial precursor cells. According to IDH, TP53, and 1p19q status, four major subtypes of LGG are recorded: IDH+/p53-/1p19q-, IDH+/p53+/1p19q-, IDH+/p53-/1p19q+ and triple negative, this last subgroup having the worst prognosis. Interestingly, p53 expression and internexin alpha (INA) expression can replace to some extent TP53 mutation and 1p19 codeletion, respectively. Moreover the antibody directed against the IDH1R132H isoform is highly specific. Because this mutation is the most frequent it is sufficient to assess IDH status in more than 80% of grade II and III gliomas. Taken together these three immunohistochemical markers are contribute greatly to the classification of gliomas and should be tested routinely as diagnostic markers. Finally, although GBM are genetically heterogeneous, the vast majority display EGFR amplification, often associated with EGFR expression, which can be helpful for diagnosis in certain cases.

[OMICS and biomarkers of glial tumors]

INTRODUCTION

OMICS is the term used to designate new biological sciences investigating a large group of molecules in biological samples. For instance, genomics and transcriptomics study changes in genome and transcription expression respectively. Numerous others OMICS are emerging (e.g. epigen-, prote-, metabol-, lipid-, glucid-OMICS). Support from bioinformatics and biostatistics, together with new molecular biology technologies for screening these large molecular groups (i.e. high-throughput biological arrays), has led to the development of these scientific fields. They help to draw relevant molecular identity cards of tumors.

STATE OF THE ART

Glial tumors form a heterogeneous morphological and clinical tumor group including astrocytomas (from grade I to IV), oligodendrogliomas and oligoastrocytomas (grades II and III). OMICS has enabled a better understanding of clinical and biological behavior of these tumors identifying new molecular abnormalities and relevant biomarkers (i.e. diagnostic, prognostic, predictive of response to treatments and predisposing to gliomas). BRAF abnormalities are diagnostic markers in pilocytic astrocytomas and pleomorphic xanthoastrocytomas (duplication with rearrangement and V600E mutation, respectively). Translocation (1;19)(q10;p10) is associated with oligodendroglial phenotype and better prognosis in gliomas. MGMT promoter methylation is predictive of response to chemotherapy in grade IV astrocytomas (GBM). In GBM, high-throughput studies have discovered: genetic and genomic disruption of tyrosine kinase receptors, TP53 and RB signaling pathways in the vast majority of cases; several transcriptomic (e.g. neural, proneural, classic and mesenchymal), epigenomic (e.g. CpG Island Methylator phenotype versus non methylator phenotype) and proteomic (e.g. EGFR, PDGFR and NF1) patterns with biological and/or clinical impacts. Finally, OMICS have identified recurrent IDH1/IDH2 mutations with prognostic significance in glial tumors and five single nucleotide polymorphisms associated with susceptibility to gliomas (e.g. TERT, CCDC26, PHLDB1, RTEL1 and CDKN2A/CDKN2B). These latter data combined with already known inherited cancer syndromes (i.e. Turcot type 1, Cowden, melanoma-astrocytoma, Li-Fraumeni, tuberous sclerosis complex, type I and II neurofibromatosis) improve our knowledge of genetic predisposition to gliomas.

PERSPECTIVES

Data generated by OMICS are huge, multidimensional and promising. Bioinformatics and biostatistics will allow their integration (integromics) toward a precise dissection of their clinical of biological significance in neuro-oncology.

CONCLUSIONS

OMICS have a growing impact in neuro-oncology improving basic research in brain tumors and clinical management of patients through the discovery of biomarkers.

Low-grade gliomas in adults

In recent years, advances in the understanding of low-grade glioma (LGG) biology have driven new paradigms in molecular markers, diagnostic imaging, operative techniques and technologies, and adjuvant therapies. Taken together, these developments are collectively pushing the envelope toward improved quality of life and survival. In this article, the authors evaluate the recent literature to synthesize a comprehensive review of LGGs in the modern neurosurgical era.

Anaplastic oligodendroglioma

Although uncommon, anaplastic oligodendrogliomas (AODs) are important to recognize, as they have unique molecular, histologic, and clinical features. Patients with new seizures or new focal neurologic deficits should be referred for brain MRI with contrast. If the MRI suggests a malignant glioma, maximal feasible tumor resection is advised for accurate diagnosis and for relief of tumor-related neurologic symptoms. Radiation therapy (XRT) is the most commonly prescribed postsurgical therapy for patients with AODs. The role and timing of adjuvant chemotherapy are less clear. Tumor responses to PCV (the combination of procarbazine, lomustine, and vincristine) and to temozolomide have been documented in patients with AODs. However, two prospective phase 3 trials in patients with newly diagnosed AOD have shown no difference in overall survival when PCV is added to XRT. Ongoing trials investigating the benefit of temozolomide plus XRT in patients with newly diagnosed AOD will inform about the value of this common practice. The recognition that 1p19q codeletion is a marker of oligodendroglial differentiation and the subsequent prospective confirmation of this marker's importance in predicting better prognosis have been critical discoveries. Tumors with intermediate oligodendroglial features or mixed astrocytic features should be referred for 1p19q assessment. Identification of 1p19q status is also required in clinical trials for patients with AOD, given the association of 1p19q codeletion with improved response to therapies and overall prognosis. There are not yet sufficient data to guide individual treatment planning based on 1p19q status, but several planned and ongoing trials will address this issue. Unfortunately, AOD remains a terminal brain cancer even with maximal therapies. As more therapeutic options become available and the full significance of molecular markers is understood, 1p19q and other markers are expected to help guide optimal antitumor therapies, and it is hoped that survival and function will improve for all patients with AOD.

Low-grade gliomas in adults

Making treatment decisions for patients with infiltrating low-grade gliomas (LGGs) is challenging. Patients frequently present with seizures and usually have little or no neurologic deficit. In this younger and relatively well patient population, despite the potential for significant morbidity, we believe that surgical resection, radiation therapy, and chemotherapy each play an important role in the optimal management of these tumors. Randomized clinical trials have begun to address some of the many questions about prognosis, natural history, and treatment, but most questions have yet to be answered. We believe that, when possible, a maximal surgical resection consistent with preservation of neurologic function should be performed, even though it is likely that no randomized clinical trial will ever be done to demonstrate a survival advantage for this approach. External beam radiation therapy is most often given to a total dose of 50.4 or 54 Gy in 1.8-Gy fractions. The role of chemotherapy is less certain, but a growing body of evidence suggests that temozolomide, a generally well-tolerated drug, is active in the treatment of LGGs. In recent years, loss of heterozygosity of chromosome 1p and 19q, as well as silencing of the MGMT gene, have been identified as promising predictors of response to adjuvant therapy in gliomas. Although randomized trials have not yet shown a survival benefit for early radiation therapy or chemotherapy, one study by the European Organisation for Research and Treatment of Cancer did show an improvement in time to tumor progression with the earlier use of radiation therapy. In addition, a trial by the Radiation Therapy Oncology Group (soon to be analyzed and reported) is comparing radiation alone with radiation followed by a year (six cycles) of standard-dose PCV chemotherapy (procarbazine, CCNU, and vincristine); this trial may shed light on the use of chemotherapy in conjunction with radiation therapy for the initial treatment of LGGs. Because patients remain at risk for tumor progression for the remainder of their lives, we recommend lifelong follow-up with MRI scans, even for patients without documented tumor regrowth over long intervals. To give clinicians a more solid basis for guiding therapy recommendations, we encourage participation in large cooperative group clinical trials.

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.

Loss of heterozygosity analysis in malignant gliomas

Despite recent advances in the diagnosis and treatment of glioblastomas, patient outcomes for these highly malignant tumors remain poor. Research into the molecular pathology of glioblastoma has uncovered various genetic changes that contribute to malignancy. Some of the identified molecular markers--such as loss of heterozygosity (LOH) on chromosome 1p/19q and chromosome 10, O6-methylguanine methyltransferase promoter hypermethylation, and mutation of isocitrate dehydrogenase-1--may help to predict patient outcomes. Indeed, LOH analysis is an effective approach to classify malignant gliomas. Genome-wide analyses have revealed that the extent and pattern of LOH regions may have important implications for the clinical course of the disease. As the genetic underpinnings of malignant gliomas are complex and varied, careful selection of the methods for genetic analysis in the clinic is important. The fundamental principles of each assay need to be understood to allow careful selection of practically useful methods. This review summarizes recent developments in the molecular analysis of malignant glioma.

Molecular markers in low-grade gliomas: predictive or prognostic?

PURPOSE

To investigate whether TP53 mutation, 1p/19q codeletions, O(6)-methylguanylmethyltransferase (MGMT) promoter methylation, and isocitrate dehydrogenase 1 (IDH1) mutation predict natural course of disease or response to radiotherapy or chemotherapy or both in low-grade glioma patients.

EXPERIMENTAL DESIGN

Cohort A consisted of 89 patients with diffuse astrocytoma World Health Organization (WHO) grade II (n = 40), oligoastrocytoma (n = 23), or oligodendroglioma (n = 26) who did not receive radiotherapy or chemotherapy after first operation and were monitored until progression [progressive disease (PD); n = 59] and beyond or until the end of follow-up (n = 30). Cohort B consisted of 50 patients with WHO grade II gliomas who received radiotherapy or chemotherapy at diagnosis. Tumors were analyzed for TP53 mutations, 1p/19q codeletions, MGMT promoter methylation, and IDH1 mutations.

RESULTS

Median progression-free survival (PFS) in cohort A was 4.1 years (95% CI: 3.1-5.1). No molecular marker was prognostic for PFS after surgery alone, using multivariate adjustment for histology, age, and extent of resection. IDH1 mutations were associated with prolonged survival from the diagnosis of PD in oligoastrocytomas (OA II)/oligodendrogliomas (O II) and with overall survival (OS) in all tumors. 1p/19q codeletion and IDH1 mutation were prognostic for PFS and OS in cohort B.

CONCLUSIONS

None of the parameters are sensitive prognostic biomarkers in WHO grade II glioma patients who do not receive radiotherapy or chemotherapy after surgery. Limitations of this study include the selection of patients with favorable outcome, the nonrandomized allocation of treatment, and the insufficient sample size to distinguish between effects of radiotherapy versus chemotherapy. Regardless of histology, IDH1 mutation status is the strongest prognostic marker for OS.

Validation of EORTC prognostic factors for adults with low-grade glioma: a report using intergroup 86-72-51

PURPOSE

A prognostic index for survival was constructed and validated from patient data from two European Organisation for Research and Treatment of Cancer (EORTC) radiation trials for low-grade glioma (LGG). We sought to independently validate this prognostic index with a separate prospectively collected data set (Intergroup 86-72-51).

METHODS AND MATERIALS

Two hundred three patients were treated in a North Central Cancer Treatment Group-led trial that randomized patients with supratentorial LGG to 50.4 or 64.8 Gy. Risk factors from the EORTC prognostic index were analyzed for prognostic value: histology, tumor size, neurologic deficit, age, and tumor crossing the midline. The high-risk group was defined as patients with more than two risk factors. In addition, the Mini Mental Status Examination (MMSE) score, extent of surgical resection, and 1p19q status were also analyzed for prognostic value.

RESULTS

On univariate analysis, the following were statistically significant (p<0.05) detrimental factors for both progression-free survival (PFS) and overall survival (OS): astrocytoma histology, tumor size, and less than total resection. A Mini Mental Status Examination score of more than 26 was a favorable prognostic factor. Multivariate analysis showed that tumor size and MMSE score were significant predictors of OS whereas tumor size, astrocytoma histology, and MMSE score were significant predictors of PFS. Analyzing by the EORTC risk groups, we found that the low-risk group had significantly better median OS (10.8 years vs. 3.9 years, p<0.0001) and PFS (6.2 years vs. 1.9 years, p<0.0001) than the high-risk group. The 1p19q status was available in 66 patients. Co-deletion of 1p19q was a favorable prognostic factor for OS vs. one or no deletion (median OS, 12.6 years vs. 7.2 years; p=0.03).

CONCLUSIONS

Although the low-risk group as defined by EORTC criteria had a superior PFS and OS to the high-risk group, this is primarily because of the influence of histology and tumor size. Co-deletion of 1p19q is a prognostic factor. Future studies are needed to develop a more refined prognostic system that combines clinical prognostic features with more robust molecular and genetic data.

Glioblastomas with oligodendroglial component-common origin of the different histological parts and genetic subclassification

BACKGROUND

Glioblastomas are the most common and most malignant brain tumors in adults. A small subgroup of glioblastomas contains areas with histological features of oligodendroglial differentiation (GBMO). Our objective was to genetically characterize the oligodendroglial and the astrocytic parts of GBMOs and correlate morphologic and genetic features with clinical data.

METHODS

The oligodendroglial and the "classic" glioblastoma parts of 13 GBMO were analyzed separately by interphase fluoreszence in situ hybridization (FISH) on paraffin sections using a custom probe set (regions 1p, 1q, 7q, 10q, 17p, 19q, cen18, 21q) and by comparative genomic hybridization (CGH) of microdissected paraffin embedded tumor tissue.

RESULTS

We identified four distinct genetic subtypes in 13 GBMOs: an "astrocytic" subtype (9/13) characterized by +7/-10; an "oligodendroglial" subtype with -1p/-19q (1/13); an "intermediate" subtype showing +7/-1p (1/13), and an "other" subtype having none of the former aberrations typical for gliomas (2/13). The different histological tumor parts of GBMO revealed common genetic changes in all tumors and showed additional aberrations specific for each part.

CONCLUSION

Our findings demonstrate the monoclonal origin of GBMO followed by the development of the astrocytic and oligodendroglial components. The diagnostic determination of the genetic signatures may allow for a better prognostication of the patients.

Incorporation of biomarker assessment in novel clinical trial designs: personalizing brain tumor treatments

Advances in molecular genetics have aided the identification of potential biomarkers with significant clinical promise in neurooncology. These advances and the evolution of targeted therapeutics necessitate the development and incorporation of innovative clinical trial designs that can effectively validate and assess the clinical utility of biomarkers. In this article, we review the use and potential of several such designs in neurooncology trials in order to support the development of personalized treatment approaches for brain tumor patients.

Loss of chromosome 1p/19q in oligodendroglial tumors: refinement of chromosomal critical regions and evaluation of internexin immunostaining as a surrogate marker

Loss of chromosome 1p/19q in oligodendrogliomas represents a powerful predictor of good prognosis. Expression of internexin (INA), a neuronal specific intermediate filament protein, has recently been proposed as a surrogate marker for 1p/19q deletion based on the high degree of correlation between both parameters in oligodendrogliomas. The aim of this study was to assess further the diagnostic utility of INA expression in a set of genetically well-characterized oligodendrogliomas. On the basis of a conservative approach for copy number determination, using both comparative genomic hybridization and fluorescent in situ hybridization, INA expression as a surrogate marker for 1p/19q loss had both reduced specificity (80%) and sensitivity (79%) compared with respective values of 86% and 96% reported in the previous report. The histologic interpretation and diagnostic value of INA expression in oligodendrogliomas should therefore be assessed with greater caution when compared with 1p/19q DNA copy number analysis. In addition, DNA copy number aberrations of chromosomes 10, 16, and 17 were detected exclusively in 1p/19q codeleted samples, suggesting that other regions of the genome may contribute to the 1p/19q-deleted tumor phenotype inthese samples.

Response assessment in neuro-oncology (a report of the RANO group): assessment of outcome in trials of diffuse low-grade gliomas

Although low-grade gliomas (LGG) have a less aggressive course than do high-grade gliomas, the outcome of these tumours is ultimately fatal in most patients. Both the tumour and its treatment can cause disabling morbidity, particularly of cognitive functions. Because many patients present with seizures only, with no other signs and symptoms, maintenance of quality of life and function constitutes a particular challenge in LGG. The slow growth pattern of most LGG, and the rare radiological true responses despite a favourable clinical response to treatment, interferes with the use of progression-free survival as the primary endpoint in trials. Overall survival as an endpoint brings logistical challenges, and is sensitive to other non-investigational salvage therapies. Clinical trials for LGG need to consider other measures of patient benefit such as cognition, symptom burden, and seizure activity, to establish whether improved survival is reflected in prolonged wellbeing. This Review investigates clinical and imaging endpoints in trials of LGG, and provides response assessment in neuro-oncology (RANO) criteria for non-enhancing tumours. Additionally, other measures for patients with brain tumours that assess outcome are described. Similar considerations are relevant for trials of high-grade gliomas, although for these tumours survival is shorter and survival endpoints generally have more value than they do for LGG.

Leptomeningeal disease in oligodendroglial tumors: a population-based study

In this population-based study, we determined the frequency and clinical characteristics of leptomeningeal disease (LMD) developing in the context of oligodendroglial tumors (oligodendrogliomas and oligoastrocytomas). LMD occurred in only 3.9% (8/204) of oligodendroglial tumors and in patients with more recurrences [mean 2.88 vs. 1.27 in LMD and non-LMD, respectively (p = 0.001)]. In contrast to LMD from systemic solid tumors, the median survival following the diagnosis of LMD in oligodendroglial tumors was surprisingly long at 22 months (95% CI 11–33 months). Treatment with oral chemotherapy seemed as effective as more aggressive treatments (e.g. repeat RT or intrathecal chemotherapy) in these patients.

KIAA0495/PDAM is frequently downregulated in oligodendroglial tumors and its knockdown by siRNA induces cisplatin resistance in glioma cells

Co-deletion of chromosomes 1p and 19q is a common event in oligodendroglial tumors (OTs), suggesting the presence of OT-related genes. The aim of this study was to identify the target genes residing in the minimally deleted regions on chromosome 1p36.31-p36.32 that might be involved in OTs. A novel gene KIAA0495/p53-dependent apoptosis modulator (PDAM) was found frequently deregulated, with 37 of 58 (63.8%) OTs examined showing reduced expression compared with normal brain. Chromosome 1p loss and epigenetic modifications were the major mechanisms contributing to PDAM downregulation. The role of PDAM in chemosensitivity was also evaluated. PDAM knockdown had no effect on sensitivity to vincristine, lomustine, temozolomide and paclitaxel, but could induce cisplatin resistance in glioma cells harboring wild-type p53. B-cell CCL/lymphoma 2 (BCL2)-like 1 (BCL2L1) exhibited significant upregulation, while BCL2 showed partial derepression in PDAM-silenced cells after cisplatin treatment, suggesting that alteration of anti-apoptotic genes contributed in part to cisplatin resistance. Knockdown of BCL2L1 abrogated the induced cisplatin-resistant phenotype. Moreover, our data suggested that PDAM might function as a non-protein-coding RNA. Collectively, these findings suggest that PDAM deregulation may play a role in OT development and that PDAM may possess the capacity to modulate apoptosis via regulation of p53-dependent anti-apoptotic genes.

Should biomarkers be used to design personalized medicine for the treatment of glioblastoma?

Significant progress has been made in understanding the molecular pathogenesis of gliomas and in predicting general outcome depending on a limited set of clinical parameters and molecular markers. However, methylation of the O⁶-methylguanine DNA methyltransferase (MGMT) gene promoter is the only molecular marker linked to sensitivity of a specific treatment, that is, alkylating agent chemotherapy, and this predictive value may be limited to glioblastoma. Moreover, in the absence of potent alternative drugs, temozolomide chemotherapy should not be withheld from patients with newly diagnosed glioblastoma without MGMT promoter methylation in general practice. In the context of clinical trials, however, irrespective of whether classical cytotoxic drugs, tyrosine kinase inhibitors or antiangiogenic agents are used, tissue should be centrally collected. Appropriate research programs should seek to define enriched patient populations for future trials and ultimately facilitate individualized cancer treatments.

Classification and management of anaplastic gliomas

PURPOSE OF REVIEW

To summarize findings, discuss problems and define new questions from the past phase III trials in anaplastic gliomas.

RECENT FINDINGS

The current standard of care for first-line treatment in anaplastic gliomas is radiotherapy or chemotherapy. The next steps are to define the role and optimal sequencing of combined modality treatment focusing on radiotherapy and temozolomide and to develop trials with novel targeted treatments. The feature of necrosis in oligodendroglial tumors needs to be further studied, and molecular prognosticators will take more room. These include O⁶-methylguanylmethyltransferase promoter methylation, isocitrate dehydrogenase mutations and epidermal growth factor receptor amplification. Further, the notion that all anaplastic oligodendroglial tumors with or without a relevant astrocytic component fall into the same prognostic category and the obvious difficulties to type and to grade anaplastic gliomas pose an enormous burden on local diagnosis. The current and upcoming trials including the European Organization for Research and Treatment of Cancer 26053/22054 trial aim at solving some of these issues with an initial central pathology review.

SUMMARY

Anaplastic gliomas are an important group of brain tumors to develop future molecularly targeted therapies and should therefore be in the main focus of academic and industrial drug development, which aims at efficacy and avoiding long-term side effects.

Gone FISHing: clinical lessons learned in brain tumor molecular diagnostics over the last decade

Fluorescence in situ hybridization (FISH) is a powerful, morphology-based technique to assess targeted copy number alterations or gene rearrangements in formalin-fixed, paraffin-embedded tissues. It has a wide range of applications in routine clinical contexts to identify cytogenetic biomarkers for more accurate diagnosis and prognostic stratification. This review and update addresses practical uses of FISH as a molecular diagnostic tool in the setting of brain tumors, including gliomas, embryonal neoplasms, ependymomas and meningiomas, focusing on key genetic biomarkers, such as 1p19q codeletion, epidermal growth factor receptor (EGFR) gene amplification, BRAF rearrangement and many others. Also discussed are lessons learned over the past decade, including common technical issues to consider when implementing and interpreting FISH results in a clinical setting.

Diagnostic and prognostic value of alpha internexin expression in a series of 409 gliomas

The neuronal intermediate filament alpha internexin (INA) is expressed in most gliomas with 1p19q codeletion and could represent a valuable prognostic marker in clinical routine. INA expression was analysed on 409 gliomas and correlated with histology, progression free survival (PFS), overall survival (OS), genomic profile assessed by CGH-array, IDH1/IDH2 mutation and p53 expression. INA was expressed in 59% of grade II oligodendrogliomas (n=73), 45% of grade III oligodendrogliomas (n=133), 15% of grade II oligoastrocytomas (n=61), 12% of grade III oligoastrocytomas (n=41), 23% of glioblastomas with oligodendroglial component (n=31), 0% of grade I astrocytomas (n=3), 0% of grade II astrocytomas (n=14), 6% of grade III astrocytomas (n=17) and 0% of glioblastomas (n=36). INA expression was detected in 85% of gliomas with complete 1p19q codeletion ('true 1p19q signature') (n=85) versus 15% of gliomas without 1p19q codeletion (n=245), including 14% of gliomas with variable/partial 1p19q deletion ('false 1p19q signature') (n=72) (p<0.0001). INA was expressed by 43% of gliomas with IDH1 mutation (n=197) versus 12% of gliomas without IDH1 mutation (n=156) (p<0.0001). In oligodendroglial gliomas (n=240), INA expression specificity for 1p19q codeletion was 80%, sensitivity 85%, positive predictive value 70%, and negative predictive value was 91%. Combining INA and p53 expressions improved INA predictive accuracy for 1p19q codeletion. In grade III gliomas, INA expression was associated with longer PFS (42.1 versus 10.2 months, p=0.0007) and longer OS (124.6 versus 20.6 months, p=0.0001). In conclusion, INA expression is a fast, cheap and reliable prognostic marker, and represents a surrogate marker for 1p19q complete codeletion.

[Genetic and molecular abnormalities of glioblastomas (GBM)]

This presentation reports a series of data dealing with recurrent genetic abnormalities and gene expression profiles that characterize primary glioblastomas and secondary glioblastomas resulting from the transformation of low grade tumors (grade II and III astrocytomas and oligodendrogliomas). The most recent aspects of the concept of tumor stem cells that may explain the relentless growth of GBM will be reported. Molecular features of tumor neoangiogenesis will be described. Epigenetic alterations and deregulation of gene expression by microRNAs (miRs) will be also included. Some aspects of tumor predisposition will be also discussed. Finally, a short description of exosomes as vectors of tumor information will be presented.

Risk factors for oligodendroglial tumors: a pooled international study

Oligodendroglial tumors are rare subtypes of brain tumors and are often combined with other glial tumors in epidemiological analyses. However, different demographic associations and clinical characteristics suggest potentially different risk factors. The purpose of this study was to investigate possible risk factors for oligodendroglial tumors (including oligodendroglioma, anaplastic oligodendroglioma, and mixed glioma). Data from 7 case-control studies (5 US and 2 Scandinavian) were pooled. Unconditional logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs), adjusted for age group, gender, and study site. Data on 617 cases and 1260 controls were available for analyses. Using data from all 7 studies, history of allergies and/or asthma was associated with a decreased risk of anaplastic oligodendroglioma (OR = 0.6; 95% CI: 0.4-0.9), and history of asthma only was associated with a decreased risk of oligodendroglioma (OR = 0.5; 95% CI: 0.3-0.9) and anaplastic oligodendroglioma (OR = 0.3; 95% CI: 0.1-0.9). A family history of brain tumors was associated with an increased risk of anaplastic oligodendroglioma (OR = 2.2; 95% CI: 1.1-4.5). Having had chicken pox was associated with a decreased risk of oligodendroglioma (OR = 0.6; 95% CI: 0.4-0.9) and anaplastic oligodendroglioma (OR = 0.5; 95% CI: 0.3-0.9) in the US studies. Although there is some overlap in risk factors between oligodendroglial tumors and gliomas as a group, it is likely that additional factors specific to oligodendroglial tumors have yet to be identified. Large, multi-institution international studies will be necessary to better characterize these etiological risk factors.

Molecular classification of low-grade diffuse gliomas

The current World Health Organization classification recognizes three histological types of grade II low-grade diffuse glioma (diffuse astrocytoma, oligoastrocytoma, and oligodendroglioma). However, the diagnostic criteria, in particular for oligoastrocytoma, are highly subjective. The aim of our study was to establish genetic profiles for diffuse gliomas and to estimate their predictive impact. In this study, we screened 360 World Health Organization grade II gliomas for mutations in the IDH1, IDH2, and TP53 genes and for 1p/19q loss and correlated these with clinical outcome. Most tumors (86%) were characterized genetically by TP53 mutation plus IDH1/2 mutation (32%), 1p/19q loss plus IDH1/2 mutation (37%), or IDH1/2 mutation only (17%). TP53 mutations only or 1p/19q loss only was rare (2 and 3%, respectively). The median survival of patients with TP53 mutation ± IDH1/2 mutation was significantly shorter than that of patients with 1p/19q loss ± IDH1/2 mutation (51.8 months vs. 58.7 months, respectively; P = 0.0037). Multivariate analysis with adjustment for age and treatment confirmed these results (P = 0.0087) and also revealed that TP53 mutation is a significant prognostic marker for shorter survival (P = 0.0005) and 1p/19q loss for longer survival (P = 0.0002), while IDH1/2 mutations are not prognostic (P = 0.8737). The molecular classification on the basis of IDH1/2 mutation, TP53 mutation, and 1p/19q loss has power similar to histological classification and avoids the ambiguity inherent to the diagnosis of oligoastrocytoma.

Update on molecular findings, management and outcome in low-grade gliomas

Low-grade infiltrating gliomas in adults include diffuse astrocytoma, oligoastrocytoma and oligodendroglioma. The current gold standard diagnosis of these tumors relies on histological classification; however, emerging molecular abnormalities discovered in these tumors are playing an increasingly prominent part in the process of tumor diagnosis and, consequently, patient management. The frequency and clinical importance of tumor protein p53 (TP53) abnormalities, deletions involving chromosomes 1p and 19q, O(6)-methylguanine-DNA methyltransferase (MGMT) promoter methylation status, abnormalities in the PTEN tumor suppressor gene and the BRAF oncogene, and isocitrate dehydrogenase (IDH) mutations have become better defined. Molecular markers have not, historically, had an important role in determining the course of treatment for patients with low-grade gliomas, but ongoing phase III clinical trials incorporate 1p deletion or 1p19q codeletion status-and future trials plan to incorporate MGMT promoter methylation status-as stratification factors. Future trials will need to incorporate IDH mutational status in addition to these factors. Ultimately, molecular marker assessment will, hopefully, improve the accuracy of tumor diagnosis and enhance the effectiveness of treatment to achieve improved patient outcomes.

Molecular diagnostics of gliomas: state of the art

Modern neuropathology serves a key function in the multidisciplinary management of brain tumor patients. Owing to the recent advancements in molecular neurooncology, the neuropathological assessment of brain tumors is no longer restricted to provide information on a tumor's histological type and malignancy grade, but may be complemented by a growing number of molecular tests for clinically relevant tissue-based biomarkers. This article provides an overview and critical appraisal of the types of genetic and epigenetic aberrations that have gained significance in the molecular diagnostics of gliomas, namely deletions of chromosome arms 1p and 19q, promoter hypermethylation of the O6-methylguanine-methyl-transferase (MGMT) gene, and the mutation status of the IDH1 and IDH2 genes. In addition, the frequent oncogenic aberration of BRAF in pilocytic astrocytomas may serve as a novel diagnostic marker and therapeutic target. Finally, this review will summarize recent mechanistic insights into the molecular alterations underlying treatment resistance in malignant gliomas and outline the potential of genome-wide profiling approaches for increasing our repertoire of clinically useful glioma markers.

MR imaging characteristics of oligodendroglial tumors with assessment of 1p/19q deletion status

PURPOSE

Patients with oligodendrogliomas with allelic loss of chromosomal arm 1p and 19q have been shown, especially with anaplastic oligodendrogliomas, to have both a better initial and long-term response to chemotherapy as well as an improved overall survival. Effective treatment of patients with brain tumors requires accurate diagnostic techniques. MR imaging can be used to help differentiate between low- and high-grade tumors. We hypothesize that certain MR imaging characteristics can be used to differentiate between patients with and without 1p and 19q deletion.

METHODS

Using the clinical database at the University of Virginia Neuro-Oncology Center, we identified adult patients with grade II and III oligodendroglial tumors who underwent treatment from 2002 to 2007. Age at diagnosis, gender, tumor grade, chromosomal deletion status, duration of follow-up, and MR imaging characteristics were analyzed; the latter was read by a blinded neuroradiologist.

RESULTS

One hundred and four patients met the inclusion criteria. Of these patients, 44 manifested 1p/19q co-deletion and 60 patients lacked this deletion. The greatest cross-sectional area (mean) of the tumor measured 23.4 cm(2) for patients with the co-deletion and 31.7 cm(2) for patients with intact alleles (p = 0.008). In addition, inner table thinning was noted directly adjacent to seven tumors with intact 1p and 19q alleles and in no tumors with the 1p/19q co-deletion (p = 0.020). Amongst patients with pure oligodendrogliomas, those with 1p/19q co-deletion had tumors more often confined to a single lobe as compared with those patients without the co-deletion (p = 0.023). Finally, tumors with intact alleles were more often found in the temporal lobe (45.0%) as compared with co-deleted tumors (22.7%) (p = 0.011).

CONCLUSION

MR imaging is a valuable imaging modality for differentiating between oligodendrogliomas with or without the 1p/19q deletion. While imaging will never replace definitive tissue diagnosis, imaging characteristics such as tumor size, location, and overlying skull thinning can assist clinicians in assessing patients with oligodendroglial tumors prior to surgical or medical intervention.

Practical molecular diagnostics in neuropathology: making a tough job a little easier

Neuropathology is a challenging field, in large part because of the consequential decisions that must be made with small biopsy material. This is especially true concerning the most common primary brain tumor, the infiltrative glioma. Fortunately, abundant research has identified specific molecular alterations that are characteristic of gliomas, according to diagnostic class and tumor grade. Such alterations include 1p19q codeletion, EGFR amplification, p16 deletion, and IDH1/2 mutations. Using specific cases as examples, this review illustrates how molecular testing is of great help in avoiding misdiagnoses and enhancing the quality of information provided to clinicians.

Oligodendroglial tumors: diagnostic and molecular pathology

Oligodendroglial tumors, which encompass pure oligodendroglioma and mixed oligoastrocytoma, represent the second most common glioma in adults after glioblastoma. They remain controversial neoplasms in the realm of surgical neuropathology. The early recognition of their more favorable prognosis and responsiveness to treatment when compared with diffusely infiltrating astrocytomas has influenced the pathologic diagnostic interpretation, and resulted in a pervasive interobserver variability. The more recent finding of an increased frequency of 1p/19q deletion in these tumors by cytogenetic analysis, and the association of this molecular abnormality with a better prognosis has greatly impacted the field of neuro-oncology. In this review, we focus on important histopathologic aspects in the evaluation of oligodendroglial tumors, key differential diagnoses, and highlight particular clinical and molecular characteristics, as well as current diagnostic and conceptual controversies.

Genomic aberrations associated with outcome in anaplastic oligodendroglial tumors treated within the EORTC phase III trial 26951

Despite similar morphological aspects, anaplastic oligodendroglial tumors (AOTs) form a heterogeneous clinical subgroup of gliomas. The chromosome arms 1p/19q codeletion has been shown to be a relevant biomarker in AOTs and to be perfectly exclusive from EGFR amplification in gliomas. To identify new genomic regions associated with prognosis, 60 AOTs from the EORTC trial 26951 were analyzed retrospectively using BAC-array-based comparative genomic hybridization. The data were processed using a binary tree method. Thirty-three BACs with prognostic value were identified distinguishing four genomic subgroups of AOTs with different prognosis (p < 0.0001). Type I tumors (25%) were characterized by: (1) an EGFR amplification, (2) a poor prognosis, (3) a higher rate of necrosis, and (4) an older age of patients. Type II tumors (21.7%) had: (1) loss of prognostic BACs located on 1p tightly associated with 19q deletion, (2) a longer survival, (3) an oligodendroglioma phenotype, and (4) a frontal location in brain. Type III AOTs (11.7%) exhibited: (1) a deletion of prognostic BACs located on 21q, and (2) a short survival. Finally, type IV tumors (41.7%) had different genomic patterns and prognosis than type I, II and III AOTs. Multivariate analysis showed that genomic type provides additional prognostic data to clinical, imaging and pathological features. Similar results were obtained in the cohort of 45 centrally reviewed–validated cases of AOTs. Whole genome analysis appears useful to screen the numerous genomic abnormalities observed in AOTs and to propose new biomarkers particularly in the non-1p/19q codeleted AOTs.