Frequent promoter hypermethylation and low expression of the MGMT gene in oligodendroglial tumors

Methylation profiling identifies 2 groups of gliomas according to their tumorigenesis

Extensive genomic and gene expression studies have been performed in gliomas, but the epigenetic alterations that characterize different subtypes of gliomas remain largely unknown. Here, we analyzed the methylation patterns of 807 genes (1536 CpGs) in a series of 33 low-grade gliomas (LGGs), 36 glioblastomas (GBMs), 8 paired initial and recurrent gliomas, and 9 controls. This analysis was performed with Illumina's Golden Gate Bead methylation arrays and was correlated with clinical, histological, genomic, gene expression, and genotyping data, including IDH1 mutations. Unsupervised hierarchical clustering resulted in 2 groups of gliomas: a group corresponding to de novo GBMs and a group consisting of LGGs, recurrent anaplastic gliomas, and secondary GBMs. When compared with de novo GBMs and controls, this latter group was characterized by a very high frequency of IDH1 mutations and by a hypermethylated profile similar to the recently described glioma CpG island methylator phenotype. MGMT methylation was more frequent in this group. Among the LGG cluster, 1p19q codeleted LGG displayed a distinct methylation profile. A study of paired initial and recurrent gliomas demonstrated that methylation profiles were remarkably stable across glioma evolution, even during anaplastic transformation, suggesting that epigenetic alterations occur early during gliomagenesis. Using the Cancer Genome Atlas data set, we demonstrated that GBM samples that had an LGG-like hypermethylated profile had a high rate of IDH1 mutations and a better outcome. Finally, we identified several hypermethylated and downregulated genes that may be associated with LGG and GBM oncogenesis, LGG oncogenesis, 1p19q codeleted LGG oncogenesis, and GBM oncogenesis.

Quantitative analysis of O6-methylguanine DNA methyltransferase (MGMT) promoter methylation in patients with low-grade gliomas

Methylation of the MGMT promoter is supposed to be a predictive and prognostic factor in glioblastoma. Whether MGMT promoter methylation correlates with tumor response to temozolomide in low-grade gliomas is less clear. Therefore, we analyzed MGMT promoter methylation by a quantitative methylation-specific PCR in 22 patients with histologically verified low-grade gliomas (WHO grade II) who were treated with temozolomide (TMZ) for tumor progression. Objective tumor response, toxicity, and LOH of microsatellite markers on chromosomes 1p and 19q were analyzed. Histological classification revealed ten oligodendrogliomas, seven oligoastrocytomas, and five astrocytomas. All patients were treated with TMZ 200 mg/m2 on days 1-5 in a 4 week cycle. The median progression-free survival was 32 months. Combined LOH 1p and 19q was found in 14 patients; one patient had LOH 1p alone and one patient LOH 19q alone. The LOH status could not be determined in two patients and was normal in the remaining four. LOH 1p and/or 19q correlated with longer time to progression but not with radiological response to TMZ. MGMT promoter methylation was detectable in 20 patients by conventional PCR and quantitative analysis revealed the methylation status was between 12 and 100%. The volumetric response to chemotherapy analyzed by MRI and time to progression correlated with the level of MGMT promoter methylation. Therefore, our retrospective case series suggests that quantitative methylation-specific PCR of the MGMT promoter predicts radiological response to chemotherapy with TMZ in WHO grade II gliomas.

MGMT activity, promoter methylation and immunohistochemistry of pretreatment and recurrent malignant gliomas: a comparative study on astrocytoma and glioblastoma

The DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT) is a key player in tumor cell resistance. Promoter methylation, MGMT activity and immunohistochemistry are used for determining the MGMT status. However, it is unclear whether MGMT promoter methylation correlates with MGMT activity and whether MGMT promoter methylation of the pretreatment tumor predicts the MGMT status of recurrences. To address these questions, we determined MGMT activity promoter methylation and immunoreactivity in pretreatment and recurrent glioblastomas (GB, WHO Grade IV), and in astrocytomas (WHO Grade III). We show that GB that were promoter methylated display a range of 0-62 fmol/mg MGMT and tumors that were nonmethylated 0-423 fmol/mg protein. For astrocytomas, promoter-methylated samples displayed 0-28 fmol/mg and, nonmethylated samples, 23-107 fmol/mg. No correlation was found between the intensity of promoter methylation and MGMT activity. Given a threshold level of 30 fmol/mg of protein, we found a correlation between promoter methylation and no/low MGMT activity in 82.4% of the tumors. This high correlation level was only observed when tumors were excluded showing a hemimethylated promoter (20%). Therefore, classification of hemimethylated tumors remains questionable. Further, we show that 39.1% of pretreatment GB and 5.3% of recurrences were promoter methylated, which is in line with the observed increase of MGMT activity in recurrences. Although individual exceptions were found, the data show an overall correlation between promoter methylation and lack/low MGMT activity in GB and astrocytomas. We also show that promoter methylation assay is superior over immunohistochemistry in determining the MGMT status defined by a given MGMT activity level.

Prognosis of oligodendroglial tumor with ring enhancement showing central necrotic portion

Oligodendroglial tumors sometimes show heterogeneous ring enhancement with a central necrotic portion. We aimed to reveal the prognosis of such tumors based on such radiologic findings and compare them to other prognostic factors. Participants were 32 patients with oligodendroglioma (17 oligodendrogliomas, 15 anaplastic oligodendrogliomas) who underwent surgery from 2004 to 2008. We investigated tumor radiologic findings, locations, calcification, whether localized or diffuse type, and enhancement patterns. Of other prognostic factors, we analyzed age, sex, pathology, extent of removal, adjuvant therapy, genetic change in 1p and 19q, and MGMT methylation status. We checked for genetic abnormality in 1p and 19q using the FISH method. To investigate MGMT methylation, we performed methylation-specific PCR (MSP). Mean follow-up duration was 3.2 years. Median age was 42.4 years, and the male:female ratio was 21:11. Out of 17 oligodendrogliomas, 14 (82.4%) showed combined 1p/19q deletion, and 14 (82.4%), methylated MGMT. Among 15 anaplastic oligodendrogliomas, there were 7 (46.6%) with combined 1p/19q deletion and 11 (73.3%) with methylated MGMT. The 4-year recurrence-free survival and overall survival were 77.6 and 100% in oligodendrogliomas and 59.1 and 71.6% in anaplastic oligodendrogliomas, respectively. On univariate analysis, radiologic variable of ring enhancement pattern was statistically significant related with recurrence-free survival (P = 0.003). Variables such as sex (P = 0.03), combined 1p/19q loss (P = 0.04), tumor location (P = 0.02), and anaplastic pathology (P = 0.04) were significantly correlated with overall survival. Cox's regression model revealed that ring enhancement pattern was associated with frequent recurrence (ring enhancement, hazard ratio = 8.281, P = 0.04), and these showed 1p deletion only. Anaplastic oligodendrogliomas with ring enhancement like glioblastomas and without combined 1p/19q loss should receive close follow-up after treatment because of frequent recurrences.

WHO grade-specific comparative genomic hybridization pattern of astrocytoma - a meta-analysis

To detect novel genetic alterations, many astrocytomas have been investigated by comparative genomic hybridization (CGH). To identify aberration profiles characteristic of World Health Organization (WHO) grade I, II, III, and IV astrocytoma, we performed a meta-analysis of detailed genome wide CGH data of all 467 cases published so far. After expansion of all given aberrations to the maximum of 850 GTG-band resolution, the frequencies of genetic imbalances were calculated for each chromosomal band, separately for all four WHO grades. Low-grade astrocytoma has already demonstrated one characteristic of glioblastoma multiforme, gain of chromosome 7 with a hot spot at 7q32, but without loss of chromosome 10. In anaplastic astrocytoma, a more complex aberration pattern emerges from diffuse genetic imbalances. Gains of 7q32-q36 and 7p12 become the most frequent aberrations at chromosome 7. In glioblastoma multiforme, coarse aberrations like +7, -9p, -10, and -13 represent the most frequent aberrations as a characteristic pattern. In contrast to lower tumor grades, glioblastoma multiforme demonstrates +7p12 as the most frequently affected band on chromosome 7. To quantify the gradual transition from WHO grade II-IV astrocytoma, we calculated the relative increase and decrease in frequency for each detected aberration of the tumor genome. The most pronounced and diverse changes of genetic material occur at the virtual transition from low-grade to anaplastic astrocytoma. Further transition to glioblastoma multiforme is characterized by gain of 1p, chromosome 7, and loss of chromosome 10. Summing up, the expansion of the CGH results to the 850 GTG-band resolution enabled a meta-analysis to visualize WHO grade-specific aberration profiles in astrocytoma.

Prognostic markers in gliomas

In recent years, extensive molecular studies have identified diagnostic and prognostic markers in gliomas that reinforce the WHO histological classification. 1p19q codeletion, O6-methylguanine DNA methyltransferase (MGMT) status, and mutations of isocitrate dehydrogenases 1 and 2 (IDH1/IDH2) are currently the three most pertinent markers in diffuse gliomas. Ongoing clinical trials already stratify or select patients according to their 1p19q codeletion or MGMT status. Mutations of IDH1 have been recently identified as a major prognostic factor in diffuse gliomas. Future studies should determine whether IDH1/IDH2 mutations are predictive of response to treatments. Routine use of these markers considerably contributes to a more objective classification of gliomas based on both histological and molecular features.

Rapid and sensitive assessment of the IDH1 and IDH2 mutation status in cerebral gliomas based on DNA pyrosequencing

Diffusely infiltrating cerebral gliomas frequently carry point mutations in codon 132 of the isocitrate dehydrogenase 1 (IDH1) gene or in codon 172 of the IDH2 gene, which are both clinically important as diagnostic and prognostic markers. Here, we report on a method that allows for the rapid detection of IDH1 and IDH2 mutations based on pyrosequencing. The method is applicable to routinely processed tissue specimens and provides quantitative mutation data within less than one working day. Due to its high sensitivity, the technique may also be used for the diagnostic assessment of IDH1 or IDH2 mutation in tissue samples with low tumor cell content, such as the infiltration zone of diffuse gliomas. Using pyrosequencing and/or conventional cycle sequencing of IDH1 and IDH2 in 262 gliomas, we confirm frequent mutations in diffuse astrocytic and oligodendroglial gliomas, corroborate a prognostic role for IDH1 mutation in primary glioblastomas and show that pleomorphic xanthoastrocytomas generally lack mutations in these genes.

Multiplex detection of CpG methylation using microarray combining with target-selection-padlock probe

BACKGROUND

Microarray technology combining with bisulfite-PCR offers a high-throughput approach for detection of DNA methylation. However, the use of microarray-based DNA methylation analysis has been limited by the low throughput of sample preparation due to the difficulty in simultaneous amplification of multiple targets.

METHODS

A set of target-selection-padlock probes was designed to capture the target sequences containing the queried CpG sites from bisulfite-treated genomic DNA. Then all targets were simultaneously amplified by a pair of common primers. The methylation status of multiple targets was detected by single base extension (SBE) on oligonucleotide microarray based on polyacrylic acid-covered surface.

RESULTS

This assay has been successfully applied to analyze promoter methylation of 8 tumor suppressor genes in 12 colorectal cancer samples and 2 normal control samples. The target-selection-padlock probe exhibited both high specificity and high efficiency for the parallel amplification of multiple genes. The accurate and high-throughput detection for DNA methylation was achieved by a combination of target-selection-padlock probes and microarray.

CONCLUSIONS

The present study provides a robust and accurate assay for DNA methylation status of multiple genes. This method may be useful for a large-scale screen of DNA methylation in cancer cell lines and clinical samples.

IDH1 and IDH2 mutations are prognostic but not predictive for outcome in anaplastic oligodendroglial tumors: a report of the European Organization for Research and Treatment of Cancer Brain Tumor Group

PURPOSE

Recent studies have shown the prognostic significance of IDH1 mutations in glioma. It is yet unclear if IDH1 mutations are predictive for outcome to chemotherapy. We determined the effect of IDH1 mutations on progression-free survival and overall survival (OS), and its correlation with other clinical and molecular features in the prospective randomized European Organization for Research and Treatment of Cancer study 26951 on adjuvant procarbazine, 1-(2-chloroethyl)-3-cyclohexyl-l-nitrosourea, and vincristine (PCV) in anaplastic oligodendroglioma.

EXPERIMENTAL DESIGN

IDH1 and IDH2 alterations of the mutational hotspot codons R132 and R172 were assessed by the bidirectional cycle sequencing of PCR-amplified fragments. MGMT promoter methylation was assessed using methylation-specific multiplex ligation-dependant probe amplification based on methylation-sensitive restriction analysis. Loss of chromosomes 1p, 19q, 10, and 10q and the gain of 7 and the EGFR gene were assessed with fluorescence in situ hybridization.

RESULTS

From 159 patients, sufficient material was available for IDH1 analysis. In 151 and 118 of these patients, respectively, the 1p/19q status and the MGMT promoter methylation status were known. In 73 cases (46%), an IDH1 mutation was found and only one IDH2 mutation was identified. The presence of IDH1 mutations correlated with 1p/19q codeletion and MGMT promoter methylation, and inversely correlated with loss of chromosome 10, EGFR amplification, polysomy of chromosome 7, and the presence of necrosis. IDH1 mutations were found to be prognostic in the radiotherapy- and the radiotherapy/PCV-treated patients, for both progression-free survival and OS. With Cox proportional hazard modeling for OS with stepwise selection, IDH1 mutations and 1p/19q codeletion but not MGMT promoter methylation were independent prognostic factors.

CONCLUSION

In this homogeneously treated group of anaplastic oligodendroglioma patients, the presence of IDH1 mutations was found to carry a very strong prognostic significance for OS but without evidence of a predictive significance for outcome to PCV chemotherapy. IDH1 mutations were strongly associated with 1p/19q codeletion and MGMT promoter methylation.

A phase II trial of primary temozolomide in patients with grade III oligodendroglial brain tumors

Glial tumors with oligodendroglial components are considered chemo-responsive. Forty newly diagnosed patients (11 anaplastic oligodendrogliomas [OD] and 29 anaplastic oligoastrocytomas [OA]) were enrolled into this multicenter, open-label, single-arm Phase II trial of first-line temozolomide (200 mg/m(2) on days 1-5 every 4 weeks for 6 cycles). The primary endpoint was 6-month progression-free survival (PFS) with response rate (RR), median PFS, and median overall survival (OS) as secondary endpoints. Of 39 evaluable patients at the 6-month time point (median follow-up, 34 months), 6-month PFS was 77% (95% confidence interval [CI], 74.5%-79.3%). There were 15 complete responses (CRs, 38%), 6 partial responses (PRs, 15%), and 9 disease stabilization (23%). The median PFS was 21 months (95% CI, 3-39 months), and the median OS was 43 months (95% CI, 20-66 months). Chromosome 1p/19q codeletions were seen in 47% (18 of 38) of the patients, and O-6-methylguanine-DNA-methyltransferase (MGMT) methylation was seen in 48% (10 of 21) of the patients. All patients with OD showed MGMT methylation and most (71%) had chromosome 1p/19q codeletions. Conversely, fewer patients with OA showed MGMT methylation (23%) or had chromosome 1p/19q codeletions (31%). The presence of either 1p/19q codeletion or MGMT methylation was associated with increased RR at 6 months but not with improved PFS or OS. Only 18% of the patients (7 of 40) experienced treatment-related grade 3/4 toxicities. This regimen was active and well tolerated. These data add to the growing body of data showing that primary chemotherapy may be an acceptable alternative to radiotherapy for patients with gliomas containing oligodendroglial histology.

Epigenetic downregulation of mitogen-activated protein kinase phosphatase MKP-2 relieves its growth suppressive activity in glioma cells

Critical tumor suppression pathways in brain tumors have yet to be fully defined. Along with mutational analyses, genome-wide epigenetic investigations may reveal novel suppressor elements. Using differential methylation hybridization, we identified a CpG-rich region of the promoter of the dual-specificity mitogen-activated protein kinase phosphatase-2 gene (DUSP4/MKP-2) that is hypermethylated in gliomas. In 83 astrocytic gliomas and 5 glioma cell lines examined, hypermethylation of the MKP-2 promoter was found to occur relatively more frequently in diffuse or anaplastic astrocytomas and secondary glioblastomas relative to primary glioblastomas. MKP-2 hypermethylation was associated with mutations in TP53 and IDH1, exclusive of EGFR amplification, and with prolonged survival of patients with primary glioblastoma. Expression analysis established that promoter hypermethylation correlated with reduced expression of MKP-2 mRNA and protein. Consistent with a regulatory role, reversing promoter hypermethylation by treating cells with 5-aza-2'-deoxycytidine increased MKP-2 mRNA levels. Furthermore, we found that glioblastoma cell growth was inhibited by overexpression of exogenous MKP-2. Our findings reveal MKP-2 as a common epigenetically silenced gene in glioma, the inactivation of which may play a significant role in glioma development.

Diagnostic and prognostic markers in gliomas

PURPOSE OF REVIEW

This review summarizes recent studies on diagnostic and prognostic markers in gliomas such as the BRAF fusion gene in pilocytic astrocytomas and 1p/19q codeletion, O-6-methylguanine-DNA methyltransferase status and isocitrate dehydrogenase 1 (IDH1)/IDH2 mutations in diffuse gliomas.

RECENT FINDINGS

In pilocytic astrocytomas, the BRAF fusion gene has been recently identified as a specific and frequent event leading to potentially targetable mitogen-activated protein kinase pathway activation. In grade II/III gliomas and in glioblastomas, chromosome 1p/19q codeletion and O-6-methylguanine-DNA methyltransferase status remain the most important prognostic and predictive markers. Recently identified mutations in IDH1/IDH2, however, are specific for diffuse gliomas, occur frequently in grade II/III gliomas and are of prognostic value in grade III gliomas, as well in glioblastomas in which they characterize secondary glioblastomas.

SUMMARY

Extensive molecular studies have enabled the discovery of new diagnostic and prognostic markers that are refining the histomolecular classification of gliomas.

Up-front temozolomide in elderly patients with glioblastoma

Upfront temozolomide (TMZ) is often proposed for elderly patients with malignant gliomas as an alternative to radiotherapy (RT). A recent randomized trial showed that RT provides a survival benefit in elderly glioblastoma patients (>or=70 years) with good performance status (KPS >or= 70) compared with supportive care alone (median survival (MS) = 29.1 vs. 16.9 weeks). We retrospectively analyzed all patients who were eligible for this trial, but who refused to participate and were finally treated with TMZ alone. Thirty-nine eligible patients (median age: 75 years (range 70-83), median KPS: 70 (range 70-80), histologically proven glioblastomas) were treated up-front with oral TMZ for 1-12 cycles (mean = 5). One complete response and 10 partial responses were observed. Overall median survival (MS) was 36 weeks and median progression-free survival (PFS) was 20 weeks for the whole group. MS was 27.4 weeks and PFS was 19.5 weeks for the 27 patients that did not receive second-line treatment at progression. Eight grade III/IV toxicities (seven hematologic, one gastro-intestinal) were seen, but no treatment-related deaths were observed. These preliminary results support further randomized studies comparing TMZ with RT.

Molecular neuropathology of low-grade gliomas and its clinical impact

The term "low-grade glioma" refers to a heterogeneous group of slowly growing glial tumors corresponding histologically to World Health Organization (WHO) grade I or II. This group includes astrocytic, oligodendroglial, oligoastrocytic and ependymal tumor entities, most of which preferentially manifest in children and young adults. Depending on histological type and WHO grade, growth patterns of low-grade gliomas are quite variable, with some tumors diffusely infiltrating the surrounding central nervous system tissue and others showing well demarcated growth. Furthermore, some entities tend to recur and show spontaneous malignant progression while others remain stable for many years. This review provides a condensed overview concerning the molecular genetics of different glioma entities subsumed under the umbrella of low-grade glioma. For a better understanding the cardinal epidemiological, histological and immunohistochemical features of each entity are shortly outlined. Multiple cytogenetic, chromosomal and genetic alterations have been identified in low-grade gliomas to date, with distinct genetic patterns being associated with the individual tumor subtypes. Some of these molecular alterations may serve as a diagnostic adjunct for tumor classification in cases with ambiguous histological features. However, to date only few molecular changes have been associated with clinical outcome, such as the combined losses of chromosome arms 1p and 19q as a favorable prognostic marker in patients with oligodendroglial tumors.

Selection of chemotherapy for glioblastoma expressing O(6)-methylguanine-DNA methyltransferase

The therapeutic benefit of nitrosoureas or temozolomide for glioblastoma is limited mainly by O(6)-methylguanine-DNA methyltransferase (MGMT) expression. The aim of this study was to evaluate the effectiveness of various anticancer drugs for MGMT-positive glioblastoma. Seventy-four glioblastoma patients were administered various anticancer drugs according to drug sensitivity testing. For the individualization, drug-induced apoptosis was quantified by flow cytometry in the primary culture of surgically resected tumor cells. The MGMT protein expression was analyzed by immunohistochemistry. The median survival of the patients receiving the individualized chemotherapy was 19.4 months (95% CI, 15.9-22.1). The patients with negative MGMT immunostaining had significantly longer survival than those with positive MGMT immunostaining [median survival, 22.3 months (95% CI, 17.6-27.0) vs. 15.1 months (95% CI, 13.4-16.8); p=0.0188]. For MGMT-positive tumors, the platinum agents and the taxanes were more frequently selected for administration than the other categories of anticancer agents. The patient survival period of MGMT-positive glioblastomas treated with the platinum agents or the taxanes [median survival, 20.1 months (95% CI, 18.0-22.7)] was significantly longer than that of MGMT-positive tumors treated with nitrosoureas (p=0.0026), and was equivalent to that of MGMT-negative glioblastomas (p=0.3047). These results suggest that the platinum agents and the taxanes offer the best probability to be effective against immunohistochemically MGMT-positive glioblastomas.

Genetic signature of adult gliomas and correlation with MRI features

In recent years the amount of information concerning the genetics and the biology of gliomas, and particularly of glioblastoma multiforme, increased steadily. Such an increase has been paralleled by the technological progress of MRI. The merging of these scientific areas, as summarized in this review, is helping the stratification of glioma patients for clinical trials and their clinical follow-up. Although available therapeutic options appear limited in number, it is likely that in the next 5 years, both as a consequence of the increased knowledge due to genomic sequencing of hundreds of glioblastoma specimens and to continuous improvements of MRI, new perspectives will be available for these patients, with a sizable impact on their prognosis.

MGMT promoter methylation in malignant gliomas: ready for personalized medicine?

The DNA repair enzyme O(6)-methylguanine-DNA methyltransferase (MGMT) antagonizes the genotoxic effects of alkylating agents. MGMT promoter methylation is the key mechanism of MGMT gene silencing and predicts a favorable outcome in patients with glioblastoma who are exposed to alkylating agent chemotherapy. This biomarker is on the verge of entering clinical decision-making and is currently used to stratify or even select glioblastoma patients for clinical trials. In other subtypes of glioma, such as anaplastic gliomas, the relevance of MGMT promoter methylation might extend beyond the prediction of chemosensitivity, and could reflect a distinct molecular profile. Here, we review the most commonly used assays for evaluation of MGMT status, outline the prerequisites for standardized tests, and evaluate reasons for difficulties in reproducibility. We critically discuss the prognostic and predictive value of MGMT silencing, reviewing trials in which patients with different types of glioma were treated with various chemotherapy schedules, either up-front or at recurrence. Standardization of MGMT testing requires comparison of different technologies across laboratories and prospectively validated cut-off values for prognostic or predictive effects. Moreover, future clinical trials will need to determine, for each subtype of glioma, the degree to which MGMT promoter methylation is predictive or prognostic, and whether testing should become routine clinical practice.

NOA-04 randomized phase III trial of sequential radiochemotherapy of anaplastic glioma with procarbazine, lomustine, and vincristine or temozolomide

PURPOSE

The standard of care for anaplastic gliomas is surgery followed by radiotherapy. The NOA-04 phase III trial compared efficacy and safety of radiotherapy followed by chemotherapy at progression with the reverse sequence in patients with newly diagnosed anaplastic gliomas.

PATIENTS AND METHODS

Patients (N = 318) were randomly assigned 2:1:1 (A:B1:B2) to receive conventional radiotherapy (arm A); procarbazine, lomustine (CCNU), and vincristine (PCV; arm B1); or temozolomide (arm B2) at diagnosis. At occurrence of unacceptable toxicity or disease progression, patients in arm A were treated with PCV or temozolomide (1:1 random assignment), whereas patients in arms B1 or B2 received radiotherapy. The primary end point was time to treatment failure (TTF), defined as progression after radiotherapy and one chemotherapy in either sequence.

RESULTS

Patient characteristics in the intention-to-treat population (n = 274) were balanced between arms. All histologic diagnoses were centrally confirmed. Median TTF (hazard ratio [HR] = 1.2; 95% CI, 0.8 to 1.8), progression-free survival (PFS; HR = 1.0; 95% CI, 0.7 to 1.3, and overall survival (HR = 1.2; 95% CI, 0.8 to 1.9) were similar for arms A and B1/B2. Extent of resection was an important prognosticator. Anaplastic oligodendrogliomas and oligoastrocytomas share the same, better prognosis than anaplastic astrocytomas. Hypermethylation of the O(6)-methylguanine DNA-methyltransferase (MGMT) promoter (HR = 0.59; 95% CI, 0.36 to 1.0), mutations of the isocitrate dehydrogenase (IDH1) gene (HR = 0.48; 95% CI, 0.29 to 0.77), and oligodendroglial histology (HR = 0.33; 95% CI, 0.2 to 0.55) reduced the risk of progression. Hypermethylation of the MGMT promoter was associated with prolonged PFS in the chemotherapy and radiotherapy arm.

CONCLUSION

Initial radiotherapy or chemotherapy achieved comparable results in patients with anaplastic gliomas. IDH1 mutations are a novel positive prognostic factor in anaplastic gliomas, with a favorable impact stronger than that of 1p/19q codeletion or MGMT promoter methylation.

MGMT promoter methylation is prognostic but not predictive for outcome to adjuvant PCV chemotherapy in anaplastic oligodendroglial tumors: a report from EORTC Brain Tumor Group Study 26951

PURPOSE

O6-methylguanine-methyltransferase (MGMT) promoter methylation has been shown to predict survival of patients with glioblastomas if temozolomide is added to radiotherapy (RT). It is unknown if MGMT promoter methylation is also predictive to outcome to RT followed by adjuvant procarbazine, lomustine, and vincristine (PCV) chemotherapy in patients with anaplastic oligodendroglial tumors (AOT).

PATIENTS AND METHODS

In the European Organisation for the Research and Treatment of Cancer study 26951, 368 patients with AOT were randomly assigned to either RT alone or to RT followed by adjuvant PCV. From 165 patients of this study, formalin-fixed, paraffin-embedded tumor tissue was available for MGMT promoter methylation analysis. This was investigated with methylation specific multiplex ligation-dependent probe amplification.

RESULTS

In 152 cases, an MGMT result was obtained, in 121 (80%) cases MGMT promoter methylation was observed. Methylation strongly correlated with combined loss of chromosome 1p and 19q loss (P = .00043). In multivariate analysis, MGMT promoter methylation, 1p/19q codeletion, tumor necrosis, and extent of resection were independent prognostic factors. The prognostic significance of MGMT promoter methylation was equally strong in the RT arm and the RT/PCV arm for both progression-free survival and overall survival. In tumors diagnosed at central pathology review as glioblastoma, no prognostic effect of MGMT promoter methylation was observed.

CONCLUSION

In this study, on patients with AOT MGMT promoter methylation was of prognostic significance and did not have predictive significance for outcome to adjuvant PCV chemotherapy. The biologic effect of MGMT promoter methylation or pathogenetic features associated with MGMT promoter methylation may be different for AOT compared with glioblastoma.

Methylation Status of the O6-Methylguanine-Deoxyribonucleic Acid Methyltransferase Gene Promoter in World Health Organization Grade III Gliomas

OBJECTIVE

We analyzed the methylation status of the O6-methylguanine-DNA methyltransferase (MGMT) gene promoter in World Health Organization (WHO) grade III gliomas in association with other molecular markers to evaluate their prevalence.

METHODS

The samples of a total of 36 newly WHO grade III glioma patients including 19 anaplastic oligodendrogliomas (AO), 7 anaplastic oligoastrocytomas (AOA), and 10 anaplastic astrocytomas (AA) were analyzed. The methylation status of the MGMT gene promoter was confirmed by methylation-specific polymerase chain reaction. The 1p/19q chromosomal deletion status and EGFR amplification were assessed by Fluorescence In-Situ Hybridization. MGMT, EGFR, EGFRvIII, and p53 expression were analyzed by immunohistochemical staining.

RESULTS

The MGMT gene promoter was methylated in 32 (88.9%) and unmethylated in 4 (11.2%). Among them, all of the AO and AOA had methylated MGMT gene promoter without exception. Significant associations between MGMT gene promoter hypermethylation and 1p/19q deletion was observed (p = 0.003). Other molecular markers failed to show significant associations between MGMT gene promoter statuses.

CONCLUSION

There was extensive epigenetic silencing of MGMT gene in high grade gliomas with oligodendroglial component. Together with frequent 1p/19q co-deletion in oligodendroglial tumors, this may add plausible explanations supporting the relative favorable prognosis in oligodendroglial tumors compared with pure astrocytic tumors.

Prognostic significance of molecular markers and extent of resection in primary glioblastoma patients

PURPOSE

Despite multimodal aggressive treatment glioblastoma patients still face a rather poor prognosis. Recent data indicate that certain molecular markers, in particular MGMT promoter hypermethylation, are associated with response to alkylating chemotherapy and longer survival. The clinical significance of other glioblastoma-associated molecular aberrations and their relationship to MGMT promoter hypermethylation is still poorly understood.

EXPERIMENTAL DESIGN

We conducted a translational study involving 67 newly diagnosed glioblastoma patients treated at our institution from 1998 to 2004. All patients were treated by open resection, followed by radiotherapy and adjuvant temozolomide chemotherapy. The tumors were investigated for MGMT promoter methylation, mRNA and protein expression, as well as presence of MGMT sequence polymorphisms. In addition, we screened for genetic aberrations of the EGFR, TP53, CDK4, MDM2, and PDGFRA genes as well as allelic losses on chromosomal arms 1p, 10q, and 19q.

RESULTS

Correlation of molecular findings with clinical data revealed significantly longer time to progression after onset of chemotherapy and longer overall survival of patients with MGMT-hypermethylated tumors. In contrast, MGMT protein expression, MGMT polymorphisms, and aberrations in any of the other genes and chromosomes were not significantly linked to patient outcome. Multivariate analysis identified MGMT promoter hypermethylation and near-complete tumor resection as the most important parameters associated with better prognosis.

CONCLUSION

Our study provides novel insights into the significance of molecular and clinical markers in predicting the prognosis of glioblastoma patients, which may improve stratification of patients into distinct prognostic subgroups.

Primary CNS lymphoma in the elderly: temozolomide therapy and MGMT status

This retrospective series explores temozolomide monotherapy in elderly patients with primary CNS lymphoma (PCNSL) and severe comorbidities. In 17 patients (62-90 years old), the complete response rate was 47%, median progression-free survival was 5 months, and median overall survival was 21 months. Five of 17 patients (29.4%) had prolonged responses for at least 12 months and survived for more than 24 months. Three of these patients had a methylated O(6)-methylguanine-DNA methyltransferase (MGMT) promoter, while the MGMT status was not assessable in the remaining two patients. Temozolomide monotherapy appears to be effective in a subgroup of elderly PCNSL patients and deserves further evaluation.

Molecular predictors of progression-free and overall survival in patients with newly diagnosed glioblastoma: a prospective translational study of the German Glioma Network

PURPOSE

The prognostic value of genetic alterations characteristic of glioblastoma in patients treated according to present standards of care is unclear.

PATIENTS AND METHODS

Three hundred one patients with glioblastoma were prospectively recruited between October 2004 and December 2006 at the clinical centers of the German Glioma Network. Two hundred fifty-eight patients had radiotherapy, 199 patients had temozolomide, 189 had both, and seven had another chemotherapy as the initial treatment. The tumors were investigated for TP53 mutation, p53 immunoreactivity, epidermal growth factor receptor, cyclin-dependent kinase CDK 4 or murine double minute 2 amplification, CDKN2A homozygous deletion, allelic losses on chromosome arms 1p, 9p, 10q, and 19q, O(6)-methylguanine methyltransferase (MGMT) promoter methylation, and isocitrate dehydrogenase 1 (IDH1) mutations.

RESULTS

Median progression-free (PFS) and overall survival (OS) were 6.8 and 12.5 months. Multivariate analysis revealed younger age, higher performance score, MGMT promoter methylation, and temozolomide radiochemotherapy as independent factors associated with longer OS. MGMT promoter methylation was associated with longer PFS (relative risk [RR], 0.5; 95% CI, 0.38 to 0.68; P < .001) and OS (RR, 0.39; 95% CI, 0.28 to 0.54; P < .001) in patients receiving temozolomide. IDH1 mutations were associated with prolonged PFS (RR, 0.42; 95% CI, 0.19 to 0.91; P = .028) and a trend for prolonged OS (RR, 0.43; 95% CI, 0.15 to 1.19; P = .10). No other molecular factor was associated with outcome.

CONCLUSION

Molecular changes associated with gliomagenesis do not predict response to therapy in glioblastoma patients managed according to current standards of care. MGMT promoter methylation and IDH1 mutational status allow for stratification into prognostically distinct subgroups.

Low-grade oligodendroglioma: an indolent but incurable disease? Clinical article

OBJECT

The authors reviewed their institutional experience with pure low-grade oligodendroglioma (LGO), correlating outcomes with several variables of possible prognostic values.

METHODS

Sixty-nine patients with WHO-classified LGOs were treated between 1992 and 2006 at the McGill University Health Center. Clinical, pathological, and radiological records were carefully reviewed. Demographic characteristics; the nature and duration of presenting symptoms; baseline neurological function; extent of resection; Karnofsky Performance Scale score; preoperative radiological findings including tumor size, location, and absence/presence of enhancement; and pathological data including chromosome arms 1p/19q codeletion and O-methylguanine-DNA methyltransferase promoter gene methylation status were all compiled. The timing and dose of radio- and/or chemotherapy, date of tumor progression, pathological finding at disease progression, treatment at time of disease progression, and status at the last follow-up were also recorded.

RESULTS

The median follow-up period was 6.1 years (range 1.3-16.3 years). The majority (78%) of patients presented with seizures; contrast enhancement was initially seen in 16 patients (25%). All patients had undergone an initial surgical procedure: gross-total resection in 27%, partial resection in 59%, and biopsy only in the remaining 13%. Fifteen patients received adjuvant radiotherapy. Data on O-methylguanine-DNA methyltransferase promoter gene methylation status was available in 47 patients (68%) and in all but 1 patient for 1p/19q status. Survival at 5, 10, and 15 years was 83, 63, and 29%, respectively. Multivariate analysis showed that seizures at presentation and the absence of contrast enhancement were the only independent favorable prognostic factors for survival. The 5-, 10-, and 15-year progression-free survival rates were 46, 7.7, and 0%, respectively.

CONCLUSIONS

This retrospective review confirms the indolent but progressively fatal nature of LGOs. Contrast enhancement was the most evident single prognostic factor. New treatment strategies are clearly needed in the management of this disease.

Activation of PI3K/mTOR pathway occurs in most adult low-grade gliomas and predicts patient survival

Recent evidence suggests the Akt-mTOR pathway may play a role in development of low-grade gliomas (LGG). We sought to evaluate whether activation of this pathway correlates with survival in LGG by examining expression patterns of proteins within this pathway. Forty-five LGG tumor specimens from newly diagnosed patients were analyzed for methylation of the putative 5′-promoter region of PTEN using methylation-specific PCR as well as phosphorylation of S6 and PRAS40 and expression of PTEN protein using immunohistochemistry. Relationships between molecular markers and overall survival (OS) were assessed using Kaplan-Meier methods and exact log-rank test. Correlation between molecular markers was determined using the Mann-Whitney U and Spearman Rank Correlation tests. Eight of the 26 patients with methylated PTEN died, as compared to 1 of 19 without methylation. There was a trend towards statistical significance, with PTEN methylated patients having decreased survival (P = 0.128). Eight of 29 patients that expressed phospho-S6 died, whereas all 9 patients lacking p-S6 expression were alive at last follow-up. There was an inverse relationship between expression of phospho-S6 and survival (P = 0.029). There was a trend towards decreased survival in patients expressing phospho-PRAS40 (P = 0.077). Analyses of relationships between molecular markers demonstrated a statistically significant positive correlation between expression of p-S6(235) and p-PRAS40 (P = 0.04); expression of p-S6(240) correlated positively with PTEN methylation (P = 0.04) and negatively with PTEN expression (P = 0.03). Survival of LGG patients correlates with phosphorylation of S6 protein. This relationship supports the use of selective mTOR inhibitors in the treatment of low grade glioma.

Low O6-methylguanine-DNA methyltransferase (MGMT) expression and response to temozolomide in aggressive pituitary tumours

CONTEXT

Recent case reports detail the successful use of temozolomide in the management of aggressive pituitary tumours. O(6)-methylguanine-DNA methyltransferase (MGMT) is a DNA repair protein that counteracts the effect of temozolomide.

OBJECTIVE

To study MGMT expression in pituitary tumours and consider whether MGMT expression is associated with response to temozolomide therapy in aggressive pituitary tumours.

PATIENTS

We report two patients with aggressive pituitary tumours treated with temozolomide, one who responded to temozolomide and the other who did not. MGMT expression was assessed in a further 88 archived pituitary tumour samples.

DESIGN

MGMT expression was assessed by immunohistochemistry. MGMT promoter methylation was studied by methylation-specific polymerase chain reaction (MSP), sequencing of MGMT was performed and loss of heterozygosity (LOH) analysis undertaken.

RESULTS

Low MGMT expression and MGMT promoter methylation were found in the pituitary tumour of the patient who responded to temozolomide. Conversely, high MGMT expression was seen in the patient demonstrating a poor response to temozolomide. Eleven out of 88 archived tumour samples (13%) had low MGMT expression. Prolactinomas were more likely to have low MGMT expression compared with other pituitary tumour subtypes (P < 0.001). There was no significant difference in MGMT expression between invasive and noninvasive tumours, or between recurrent and nonrecurrent tumours. A significant inverse correlation was found between MGMT expression and promoter methylation (P = 0.012).

CONCLUSION

MGMT expression as assessed by immunohistochemistry may predict response to temozolomide therapy in patients with aggressive pituitary tumours. MGMT promoter methylation is likely to explain low MGMT expression in some, but not all, pituitary tumours.

Correlation among pathology, genetic and epigenetic profiles, and clinical outcome in oligodendroglial tumors

Recent studies have revealed a correlation between specific genetic changes, such as loss of chromosome 1p and 19q, and sensitivity of oligodendroglial neoplasm to radiotherapy and chemotherapy; epigenetic changes also play an important role in some tumors. In this retrospective study, we analyzed chromosomal alterations in 17 loci and promoter methylation status of 8 tumor-related genes in 49 oligodendroglial tumors (29 WHO grade II and 11 WHO grade III oligodendrogliomas; 7 WHO grade II and 2 WHO grade III oligoastrocytomas) using quantitative microsatellite analysis and methylation-specific polymerase chain reaction and correlated this information with clinical data. We also performed immunohistochemical stains for Ki-67 and O (6)-methyl guanine-DNA methyl transferase. Our results showed that the frequency of deletions in regions on 1p, 9p, 10q, 17p and 19q were 71.4%, 26.5%, 6.1%, 69.4% and 89.8%, respectively. Promoter methylation was detected in p14, p15, p16, p53, p73, PTEN, MGMT and RASSF1A genes in 24.5%, 6.1%, 46.9%, 0%, 6.1%, 42.9%, 53.1% and 77.6% of tumors, respectively. Statistical analysis identified that 9p22 loss, p73 methylation and p15 methylation were independently associated with reduced overall survival, and Ki-67 labeling index (LI) > or = 5%, 9p22 loss, no loss of 19q, p73 methylation, p14 methylation and unmethylated MGMT predicted shorter progression-free survival. Our findings suggest that the frequent deletion and hypermethylation of tumor-related genes may represent a mechanism of tumor development and progression and emphasize the importance of defining new molecular markers for predicting prognosis, tumor recurrence and therapeutic response in cancer management.

The role of chemotherapy for pure and mixed anaplastic oligodendroglial tumors

Pure and mixed anaplastic oligodendrogliomas (AO/mixed-AOs) remain terminal primary brain tumors, without a defined optimal initial therapy, and without sufficiently active and tolerable therapies at recurrence/progression (R/P). Very heterogeneous international therapy recommendations remain. Historical advances have resulted in only modest improvements in outcome. AO/mixed-AOs with 1p/19q co-deletion are prognostically favorable, regardless of therapy, and must be identified as early as possible. Following resection, outcome data on initial therapy with radiation (RT) remain the most mature, although controversies regarding its true toxicities and optimal timing continue. Recently, the landmark RTOG 9402 and EORTC 26951 trials showed that the addition of Procarbazine, CCNU, Vincristine chemotherapy to RT, at anytime during initial therapy, prolongs progression-free survival, but not survival, and not without moderate toxicity. Despite a lack of definitive evidence, this strategy has commonly been extrapolated to Temozolomide. Chemo-sensitivity of AO/mixed-AOs provides the rationale for the chemotherapy-only strategies being explored. In the setting of recurrence/progression (R/P), chemotherapy, small molecule (targeted), biologic, and other strategies have been relatively disappointing, toxic, and cumbersome. Partly secondary to biases regarding the relative toxicities of tumor burden vs. treatment effect, therapy remains highly individualized. Future international research must prospectively evaluate health-related quality of life, toxicity, and molecular genetic markers.

Molecular profiling of oligodendrogliomas: impact on prognosis, treatment, and future directions

Oligodendrogliomas account for a small subset of all gliomas, but they often are more sensitive to treatment than other glioma subtypes. In addition, oligodendrogliomas are the first central nervous system neoplasm for which a specific molecular abnormality, allelic loss of 1p/19q (1p/19q loss), correlates with patient outcome in large-scale prospective clinical trials. However, the incorporation of 1p/19q status into clinical practice remains controversial. Other molecular alterations found in oligodendrogliomas include hypermethylation of the promoter for the MGMT gene, TP53 mutations, EGFR and platelet-derived growth factor/PDGFR alterations, and 9p and 10q loss.

Long-Term Survival of Patients With Glioblastoma Treated With Radiotherapy and Lomustine Plus Temozolomide

Purpose

To evaluate long-term survival in a prospective series of patients newly diagnosed with glioblastoma and treated with a combination of lomustine (CCNU), temozolomide (TMZ), and radiotherapy.

Patients and Methods

Thirty-nine patients received radiotherapy of the tumor site only (60 Gy) and CCNU/TMZ chemotherapy (n = 31 received standard-dose CCNU, 100 mg/m2 on day 1 and TMZ 100 mg/m2/d on days 2 to 6; n = 8 received intensified-dose CCNU 110 mg/m2 on day 1 and TMZ 150 mg/m2 on days 2 to 6) for up to six courses.

Results

In the whole cohort, the median overall survival (mOS) was 23.1 months; 47.4% survived for 2 years, and 18.5% survived for 4 years. After a median follow-up of 41.5 months, mOS had not been reached in the intensified group and was significantly higher than in the standard group (22.6 months; P = .024). In the intensified group, four of eight patients survived for at least 56 months, two of them without recurrence. O6-methylguanine–DNA methyltransferase (MGMT) gene promotor methylation in the tumor tissue was associated with significantly longer mOS (methylated, 34.3 months v nonmethylated, 12.5 months). A multivariate Cox proportional hazard model revealed MGMT status (methylated v nonmethylated; relative risk [RR] of death, 0.43; P = .003) and chemotherapy dose (intensified v standard; RR, 0.37; P = .012) as independent prognostic factors. WHO grade 4 hematoxicity was observed more frequently in the intensified group (57% v 16%).

Conclusion

The combination of radiotherapy, CCNU, and TMZ yielded promising long-term survival data in patients with newly diagnosed glioblastoma. Intensification of CCNU/TMZ chemotherapy may add an additional survival benefit, albeit with greater acute toxicity.

Identification of regions correlating MGMT promoter methylation and gene expression in glioblastomas

The O(6)-methylguanine-DNA methyltransferase gene (MGMT) is methylated in several cancers, including gliomas. However, the functional role of cysteine-phosphate-guanine (CpG) island (CGI) methylation in MGMT silencing is still controversial. The aim of this study was to investigate whether MGMT CGI methylation correlates inversely with RNA expression of MGMT in glioblastomas and to determine the CpG region whose methylation best reflects the level of expression. The methylation level of CpG sites that are potentially related to expression was investigated in 54 glioblastomas by pyrosequencing, a highly quantitative method, and analyzed with respect to their MGMT mRNA expression status. Three groups of patients were identified according to the methylation pattern of all 52 analyzed CpG sites. Overall, an 85% rate of concordance was observed between methylation and expression (p < 0.0001). When analyzing each CpG separately, six CpG sites were highly correlated with expression (p < 0.0001), and two CpG regions could be used as surrogate markers for RNA expression in 81.5% of the patients. This study indicates that there is good statistical agreement between MGMT methylation and expression, and that some CpG regions better reflect MGMT expression than do others. However, if transcriptional repression is the key mechanism in explaining the higher chemosensitivity of MGMT-methylated tumors, a substantial rate of discordance should lead clinicians to be cautious when deciding on a therapeutic strategy based on MGMT methylation status alone.

Gliomas with 1p/19q codeletion: a.k.a. oligodendroglioma

Today, treatment recommendations for patients with all types of gliomas are based on light microscopic evaluation of tumor tissue with no allowance for genetic variability. Oligodendrogliomas are treated in a uniform manner with, as yet, no unique therapeutic approach or targeted therapy for those harboring a codeletion of chromosomes 1p and 19q. Surgical resection and radiotherapy are the standards-of-care for patients with oligodendrogliomas. Surgery improves symptoms, especially headache or seizures, and radiotherapy controls tumor growth for most patients. By extrapolation from randomized trials of glioblastoma, radiotherapy likely prolongs survival. Uncertainties persist about the timing of radiotherapy in the management of patients with low-grade oligodendrogliomas, but a superior antitumor treatment has yet to emerge. That said, the recognition that oligodendrogliomas with 1p/19q loss are sensitive to current therapies and slowly growing is already influencing our management of patients with this type of glioma, spawning trials in which patients are selected by molecular signature.

Oligodendrogliomas: molecular biology and treatment

Oligodendroglial tumors continue to receive much attention because of their relative sensitivity to chemotherapy. The histological diagnosis of oligodendroglial tumors is subject to considerable interobserver variation. The revised 2007 World Health Organization classification of brain tumors no longer accepts the diagnosis "mixed anaplastic oligoastrocytoma" if necrosis is present; these tumors should be considered glioblastomas (perhaps with oligodendroglial features). The 1p/19q codeletion that is associated with sensitivity to chemotherapy is mediated by an unbalanced translocation of 19p to 1q. Randomized studies have shown that patients with 1p/19q codeleted tumors also have a better outcome with radiotherapy. Histologically more atypical tumors are less likely to have this 1p/19q codeletion; here, other alterations usually associated with astrocytic tumors are often found. Some patients with tumors with classic histological features but no 1p/19q codeletion still have a very favorable prognosis. Currently, the best approach for newly diagnosed anaplastic oligodendroglial tumors is unclear. Early adjuvant chemotherapy does not provide a better outcome than chemotherapy at the time of progression. The value of combined chemoirradiation with temozolomide has not been proven in these tumors, and could at least theoretically be associated with greater neurotoxicity. Tumors with 1p and 19q loss can also be managed with early chemotherapy, while deferring radiotherapy to the time of further progression. The presently available second-line chemotherapy results are modest, and better salvage treatments are necessary. The molecular explanation for the greater sensitivity of 1p/19q codeleted tumors is still unclear, and this could, in part, be explained by more frequent MGMT promoter gene methylation.

Molecular neuropathology of gliomas

Gliomas are the most common primary human brain tumors. They comprise a heterogeneous group of benign and malignant neoplasms that are histologically classified according to the World Health Organization (WHO) classification of tumors of the nervous system. Over the past 20 years the cytogenetic and molecular genetic alterations associated with glioma formation and progression have been intensely studied and genetic profiles as additional aids to the definition of brain tumors have been incorporated in the WHO classification. In fact, first steps have been undertaken in supplementing classical histopathological diagnosis by the use of molecular tests, such as MGMT promoter hypermethylation in glioblastomas or detection of losses of chromosome arms 1p and 19q in oligodendroglial tumors. The tremendous progress that has been made in the use of array-based profiling techniques will likely contribute to a further molecular refinement of glioma classification and lead to the identification of glioma core pathways that can be specifically targeted by more individualized glioma therapies.

Gene regulation by methylation

Epigenetic gene regulation of specific genes strongly affects clinical outcome of malignant glioma. MGMT is the best studied gene for the connection of promoter methylation and clinical course in glioblastoma. While MGMT promoter methylation analysis currently does not alter treatment of glioblastoma patients, mainly because of a lack of convincing therapy to radiotherapy and concomitant administration of alkylating drugs, there is increasing interest on the part of patients and physicians in having this molecular parameter assessed. This chapter gives a short overview of the physiological characteristics of the epigenome in normal cells and tissues and the changes in epigenetic gene regulation following malignant transformation. It discusses the technical aspects, advantages, and shortcomings of currently used approaches for single-gene and genome-wide methylation analyses. Finally, an outlook is given on potential therapeutic avenues and targets to overcome tumor-suppressor gene silencing by aberrant promoter methylation in gliomas.

Epigenetic markers in human gliomas: prospects for therapeutic intervention

Gliomas represent the most common CNS cancers in adults. Prognosis for patients harboring malignant gliomas is particularly dismal and, despite current treatment strategies comprising surgery, radiotherapy and chemotherapy, the median survival time after diagnosis is still in the range of just 12 months. In recent years, there has been an increased effort to identify tumor biomarkers that can be used as diagnostic tools, or markers for predicting therapeutic response and prognosis. Investigation of genetic changes has identified several such markers that have shown some success in predicting the most effective therapy. In recent years, however, it has become apparent that the biology of many cancers of the CNS is determined not only by their genetic profile but also their epigenetic profile. Epigenetic biomarkers show great potential in effectively predicting patient prognosis and response to therapy. The eventual application of epigenetic profiling of tumors may help to indicate the most effective tailored therapy for individual patients.

Correlation of chromosomes 1p and 19q status and expressions of O6-methylguanine DNA methyltransferase (MGMT), p53 and Ki-67 in diffuse gliomas of World Health Organization (WHO) grades II and III: a clinicopathological study

AIMS

The objective of the present study was to verify the correlation of chromosomes 1p and 19q status and expressions of O(6)-methylguanine DNA methyltransferase (MGMT), p53 and Ki-67 in diffuse gliomas of World Health Organization grades II and III.

METHODS

A series of 146 diffuse gliomas, including 45 oligodendrogliomas, 42 oligoastrocytomas and 59 astrocytomas, were analysed by denaturing high-performance liquid chromatography for 1p and 19q status and by immunohistochemistry for MGMT, p53 and Ki-67 expression patterns. The molecular alterations were then correlated with clinicopathological characteristics and with each other.

RESULTS

Loss of heterozygosity (LOH) on 1p, combined LOH on 1p and 19q, low MGMT expression and high Ki-67 expression were associated with oligodendroglial tumours, whereas high p53 expression was associated with astrocytic and mixed tumours. LOH on 1p and low MGMT expression were associated with grade II oligodendroglial tumours, whereas high expressions of p53 and Ki-67 were associated with grade III oligodendroglial tumours. In addition, high Ki-67 expression was associated with grade III astrocytomas. LOH on 1p and LOH on 19q were associated with nontemporal oligodendroglial tumours. Nonrandom associations were found between LOH on 1p and LOH on 19q, MGMT expression and p53 expression, and MGMT expression and Ki-67 expression, whereas mutual exclusions were found between LOH on 1p and 19q and p53 expression, and LOH on 1p and Ki-67 expression.

CONCLUSIONS

The present study revealed significant interrelationships of the investigated molecular alterations and clinicopathological characteristics in diffuse gliomas of World Health Organization grades II and III, which support a promising role of molecular markers in the diagnostic assessment of these neoplasms.

Correlation of O6-methylguanine methyltransferase (MGMT) promoter methylation with clinical outcomes in glioblastoma and clinical strategies to modulate MGMT activity

Resistance to alkylating agents via direct DNA repair by O(6)-methylguanine methyltransferase (MGMT) remains a significant barrier to the successful treatment of patients with malignant glioma. The relative expression of MGMT in the tumor may determine response to alkylating agents, and epigenetic silencing of the MGMT gene by promoter methylation plays an important role in regulating MGMT expression in gliomas. MGMT promoter methylation is correlated with improved progression-free and overall survival in patients treated with alkylating agents. Strategies to overcome MGMT-mediated chemoresistance are being actively investigated. These include treatment with nontoxic pseudosubstrate inhibitors of MGMT, such as O(6)-benzylguanine, or RNA interference-mediated gene silencing of MGMT. However, systemic application of MGMT inhibitors is limited by an increase in hematologic toxicity. Another strategy is to deplete MGMT activity in tumor tissue using a dose-dense temozolomide schedule. These alternative schedules are well tolerated; however, it remains unclear whether they are more effective than the standard dosing regimen or whether they effectively deplete MGMT activity in tumor tissue. Of note, not all patients with glioblastoma having MGMT promoter methylation respond to alkylating agents, and even those who respond will inevitably experience relapse. Herein we review the data supporting MGMT as a major mechanism of chemotherapy resistance in malignant gliomas and describe ongoing studies that are testing resistance-modulating strategies.

[Molecular diagnostic testing in gliomas]

Glial tumours represent the majority of central nervous system tumours. Even though current therapy guidelines do not advocate the routine use of molecular markers for treatment decisions, the identification of prognostic markers and patient subgroups that may especially benefit from novel therapeutic options becomes increasingly important also outside the setting of clinical trials. This review summarizes methods and rationale for the use of the determination of 1p/19q loss, MGMT promoter methylation and tyrosine kinase receptor expression as diagnostic, prognostic and predictive markers in gliomas.