The combination of IDH1 mutations and MGMT methylation status predicts survival in glioblastoma better than either IDH1 or MGMT alone.

BACKGROUND: Genetic and epigenetic profiling of glioblastomas has provided a comprehensive list of altered cancer genes of which only O(6)-methylguanine-methyltransferase (MGMT) methylation is used thus far as a predictive marker in a clinical setting. We investigated the prognostic significance of genetic and epigenetic alterations in glioblastoma patients. METHODS: We screened 98 human glioblastoma samples for genetic and epigenetic alterations in 10 genes and chromosomal loci by PCR and multiplex ligation-dependent probe amplification (MLPA). We tested the association between these genetic and epigenetic alterations and glioblastoma patient survival. Subsequently, we developed a 2-gene survival predictor. RESULTS: Multivariate analyses revealed that mutations in isocitrate dehydrogenase 1 (IDH1), promoter methylation of MGMT, irradiation dosage, and Karnofsky Performance Status (KFS) were independent prognostic factors. A 2-gene predictor for glioblastoma survival was generated. Based on the genetic and epigenetic status of IDH1 and MGMT, glioblastoma patients were stratified into 3 clinically different genotypes: glioblastoma patients with IDH1mt/MGMTmet had the longest survival, followed by patients with IDH1mt/MGMTunmet or IDH1wt/MGMTmet, and patients with IDH1wt/MGMTunmet had the shortest survival. This 2-gene predictor was an independent prognostic factor and performed significantly better in predicting survival than either IDH1 mutations or MGMT methylation alone. The predictor was validated in 3 external datasets. DISCUSSION: The combination of IDH1 mutations and MGMT methylation outperforms either IDH1 mutations or MGMT methylation alone in predicting survival of glioblastoma patients. This information will help to increase our understanding of glioblastoma biology, and it may be helpful for baseline comparisons in future clinical trials.

Significance of complete 1p/19q co-deletion, IDH1 mutation and MGMT promoter methylation in gliomas: use with caution.

The histopathological diagnosis of diffuse gliomas often lacks the precision that is needed for tailored treatment of individual patients. Assessment of the molecular aberrations will probably allow more robust and prognostically relevant classification of these tumors. Markers that have gained a lot of interest in this respect are co-deletion of complete chromosome arms 1p and 19q, (hyper)methylation of the MGMT promoter and IDH1 mutations. The aim of this study was to assess the prognostic significance of complete 1p/19q co-deletion, MGMT promoter methylation and IDH1 mutations in patients suffering from diffuse gliomas. The presence of these molecular aberrations was investigated in a series of 561 diffuse astrocytic and oligodendroglial tumors (low grade n=110, anaplastic n=118 and glioblastoma n=333) and correlated with age at diagnosis and overall survival. Complete 1p/19q co-deletion, MGMT promoter methylation and/or IDH1 mutation generally signified a better prognosis for patients with a diffuse glioma including glioblastoma. However, in all 10 patients with a histopathological diagnosis of glioblastoma included in this study complete 1p/19q co-deletion was not associated with improved survival. Furthermore, in glioblastoma patients >50 years of age the favorable prognostic significance of IDH1 mutation and MGMT promoter methylation was absent. In conclusion, molecular diagnostics is a powerful tool to obtain prognostically relevant information for glioma patients. However, for individual patients the molecular information should be interpreted with caution and weighed in the context of parameters such as age and histopathological diagnosis.

The nature and timing of specific copy number changes in the course of molecular progression in diffuse gliomas: further elucidation of their genetic "life story".

Up till now, typing and grading of diffuse gliomas is based on histopathological features. However, more objective tools are needed to improve reliable assessment of their biological behavior. We evaluated 331 diffuse gliomas for copy number changes involving 1p, 19q, CDKN2A, PTEN and EGFR(vIII) by Multiplex Ligation-dependent Probe Amplification (MLPA®, Amsterdam, The Netherlands). Specifically based on the co-occurrence of these aberrations we built a model for the timing of the different events and their exact nature (hemi- → homozygous loss; low-level gain → (high-copy) amplification) in the course of molecular progression. The mutation status of IDH1 and TP53 was also evaluated and shown to correlate with the level of molecular progression. The relevance of the proposed model was confirmed by analysis of 36 sets of gliomas and their 39 recurrence(s) whereas survival analysis for anaplastic gliomas confirmed the actual prognostic relevance of detecting molecular malignancy. Moreover, based on our results, molecular diagnostic analysis of 1p/19q can be further improved as different aberrations were identified, some of them being indicative for advanced molecular malignancy rather than for favorable tumor behavior. In conclusion, identification of molecular malignancy as proposed will aid in establishing a risk profile for individual patients and thereby in therapeutic decision making.

MS-MLPA: an attractive alternative laboratory assay for robust, reliable, and semiquantitative detection of MGMT promoter hypermethylation in gliomas.

Expression of the DNA repair protein O6-alkylguanine-DNA-alkyltransferase (AGT), encoded by the O6-methylguanine (O6-mG) -DNA-methyltransferase (MGMT) DNA repair gene, results in resistance to alkylating agents, and hypermethylation of the MGMT promoter is associated with chemosensitivity as it prevents AGT expression. As the interpretation of the results of immunohistochemistry to evaluate AGT expression proved to be difficult, the aim of our present study is to establish a feasible, reliable, and robust method for MGMT promoter hypermethylation testing that can be easily implemented in a diagnostic setting and is applicable to routinely processed tissue. MGMT hypermethylation analysis using methylation-specific (MS-) multiplex ligation-dependent probe amplification (MLPA) was performed on 62 glioma samples of 55 individual tumors (including 12 cell lines) and compared to the more conventionally used, but improved, MS-polymerase chain reaction (PCR). In contrast to MS-PCR, MS-MLPA (i) is not based on bisulfite conversion of unmethylated cytosines (a somewhat troublesome step in MS-PCR), (ii) provided methylation status of all samples, (iii) proved to be semiquantitative, (iv) can be used to evaluate methylation status of multiple sequences (CpG dinucleotides) simultaneously, and (v) allows for a combined copy number detection and methylation specific analysis. The potential therapeutic value of MGMT hypermethylation evaluation using MS-MLPA was shown in a group of 20 glioblastoma patients receiving temozolomide chemotherapy. We conclude that MS-MLPA is a robust and reliable method that can be easily applied to differently processed tissues, including those fixed in formalin and embedded in paraffin. The semiquantitative aspect of MS-MLPA may prove to be of great value, especially in predicting response to alkylating agents, not only for gliomas as evaluated in this study but also for tumors in general.

Cyclin D1 genotype and expression in sporadic hemangioblastomas.

Central nervous system (CNS) hemangioblastomas are highly-vascularized tumors occurring in sporadic form or as a manifestation of von Hippel-Lindau disease (VHL). The VHL protein (pVHL) regulates various target genes, one of which is the CCND1 gene, encoding cyclin D1, a protein that plays a critical role in the control of the cell cycle. Overexpression of cyclin D1 is found in many cancers. The CCND1 gene contains a common G --> A polymorphism (870G > A) that enhances alternative splicing of the gene. CCND1 genotype is associated with clinical outcome in a number of cancers although prognostic significance varies with tumor type. In VHL disease, CCND1 genotype has been suggested as a genetic modifier that influences susceptibility to hemangioblastomas. In order to analyze whether CCND1 genotype plays a role in sporadic CNS hemangioblastomas, we investigated CCND1 genotype in tumor tissue of 17 sporadic and also in five VHL-related CNS hemangioblastomas. In addition, in these tumors the extent and localization of cyclin D1 expression was investigated by immunohistochemistry. We found no deviation in CCND1 genotype distribution and allele frequencies from expected values. Also, there was no correlation between age at onset and CCND1 genotype. The expression of cyclin D1 as detected by immunohistochemistry was highly variable within and between tumors, without a clear correlation with CCND1 genotype. We conclude that, whereas variable but sometimes high cyclin D1 expression is a feature of sporadic hemangioblastomas, CCND1 genotype is unlikely to be an important genetic modifier in the oncogenesis of these tumors.

Comparative genomic hybridization: practical guidelines.

Comparative genomic hybridization (CGH) is a technique used to identify copy number changes throughout a genome. Until now, hundreds of CGH studies have been published reporting chromosomal imbalances in a large variety of human neoplasms. Additionally, technical improvements of specific steps in a CGH experiment and reviews on the technique have appeared. However, full CGH protocols are only occasionally published. In this paper a review of CGH is presented, including technique, pitfalls, and difficulties. Our own protocol is completely described and discussed, including the different optimization experiments used to establish this protocol and points requiring special attention. Although this protocol results in reliable and sensitive CGH experiments in our hands, readers should keep in mind that other laboratories may prefer other protocols. Testing different options, among others, as discussed in the current paper generates the most appropriate protocol. This paper shows the complexity of the CGH technique and may serve as a guideline for starting CGH or as a troubleshooting guide for those who perform CGH.

Analysis of von hippel-lindau mutations with comparative genomic hybridization in sporadic and hereditary hemangioblastomas: possible genetic heterogeneity.

OBJECT: Hemangioblastomas (HBs) occur sporadically or as a manifestation of von Hippel-Lindau (VHL) disease. In the majority of VHL-related HBs, inactivation of the VHL tumor suppressor gene (TSG), which is located on chromosome 3p25-26, is found. The VHL gene is assumed to be involved also in the development of sporadic HBs. In a previous study of chromosomal aberrations of sporadic HBs, multiple chromosomal imbalances were found in the majority of tumors. The aim of this study was to analyze further both sporadic HBs and VHL-related HBs to determine if these histopathologically identical tumors have a different genetic background. METHODS: Sixteen sporadic HBs and seven VHL-related HBs were identified by clinical criteria and analyzed. Comparative genomic hybridization was used to screen for chromosomal imbalances throughout the entire HB genome. Additionally, mutation analysis of the VHL gene was performed using direct sequencing. Loss of chromosome 3 and multiple other chromosomal imbalances were found in the sporadic HBs, although only one imbalance, a loss of chromosome 3, was detected in the seven VHL-related HBs. Somatic VHL gene mutations were found in one third of sporadic HBs, whereas a mutation of the VHL gene was detected in all VHL-related HBs. CONCLUSIONS: These results indicate that the molecular mechanisms underlying sporadic HBs and VHL-related HBs are different. Inactivation of the VHL gene is probably not the most important event in the tumorigenesis of sporadic HBs. Other mechanisms of inhibition of VHL protein function, or inactivation of other TSGs, on chromosome 3p or on other chromosomes, might be important in the development of sporadic HBs.

Correlation between localization, age, and chromosomal imbalances in ependymal tumours as detected by CGH.

Ependymal tumours (ETs) are gliomas that arise from the ependymal lining of the cerebral ventricles and from the remnants of the central canal of the spinal cord. Both clinical and genetic studies suggest that distinct genetic subtypes of ETs exist, the subtypes being correlated with patient age and/or tumour site. In the present study, the tumour genome of 20 ETs (15 adult and five paediatric cases) was screened for chromosomal imbalances by comparative genomic hybridization (CGH). The most frequently detected imbalances were -22q (75%), -10q (65%), -21 (50%), -16p (50%), -1p (45%), +4q (45%), -10p (45%), -2q (40%), -6 (40%), -19 (40%), -2p (35%), -3p (35%), and -16q (35%). Comparison of the chromosomal imbalances detected in ETs with those previously reported in oligodendroglial and astrocytic tumours revealed that in this respect ETs show similarities to these other gliomas. By combining these results with those of a recent study of Zheng et al. and Hirose et al., it was found that although ETs from different sites and from adult and paediatric patients show overlap at the CGH level, some chromosomal imbalances occur predominantly in a certain category. In adult patients, spinal ETs relatively often showed +2, +7, +12, and -14q; infratentorial ETs -22; and supratentorial ETs -9. In addition, in posterior fossa ETs, -6 and +9 were much more frequent in adults than in children. It is concluded that the genetic background of ETs is complex and partly determined by tumour site, histopathological subtype, and age of the patient.

Chromosomal imbalances in primary oligodendroglial tumors and their recurrences: clues about malignant progression detected using comparative genomic hybridization.

OBJECT: Despite the rapid increase in knowledge concerning the genetic basis of malignant progression in astrocytic tumors, progression of oligodendroglial tumors (including both pure oligodendrogliomas and mixed oligoastrocytomas) is still poorly understood. The aim of the present study is the elucidation of chromosomal imbalances involved in the progression of oligodendroglial tumors toward malignancy. METHODS: Using comparative genomic hybridization (CGH) on snap-frozen tumor tissue, the tumor genomes of five primary oligodendroglial tumors and associated recurrent tumors were screened for chromosomal imbalances. This information was correlated with clinical data (including follow-up data) and histopathological malignancy grade. In all cases an increase in chromosomal imbalances was detected in the recurrent tumor, indicating genetic progression. In three of the five cases this correlated with malignant progression detected at the histopathological level. The results indicate that, similar to what occurs in astrocytic tumors, chromosomal imbalances harboring genes involved in the cell proliferation control mechanism at the G1-S border are involved in the progression of oligodendroglial tumors. Additionally, although gains of genetic material on chromosome 7 and losses on chromosome 10 are most frequently detected in the course of malignant progression of astrocytic tumors, either or both of these can also occur during malignant progression of typical oligodendroglial tumors that contain losses involving chromosome 1p and/or chromosome 19q. CONCLUSIONS: When performed on optimally preserved material from a small set of primary oligodendroglial tumors and associated recurrent tumors, CGH detects chromosomal aberrations that potentially play a mechanistic role in the malignant progression of these tumors.