Dissecting the genomic complexity underlying medulloblastoma

Medulloblastoma is an aggressively growing tumour, arising in the cerebellum or medulla/brain stem. It is the most common malignant brain tumour in children, and shows tremendous biological and clinical heterogeneity. Despite recent treatment advances, approximately 40% of children experience tumour recurrence, and 30% will die from their disease. Those who survive often have a significantly reduced quality of life. Four tumour subgroups with distinct clinical, biological and genetic profiles are currently identified. WNT tumours, showing activated wingless pathway signalling, carry a favourable prognosis under current treatment regimens. SHH tumours show hedgehog pathway activation, and have an intermediate prognosis. Group 3 and 4 tumours are molecularly less well characterized, and also present the greatest clinical challenges. The full repertoire of genetic events driving this distinction, however, remains unclear. Here we describe an integrative deep-sequencing analysis of 125 tumour-normal pairs, conducted as part of the International Cancer Genome Consortium (ICGC) PedBrain Tumor Project. Tetraploidy was identified as a frequent early event in Group 3 and 4 tumours, and a positive correlation between patient age and mutation rate was observed. Several recurrent mutations were identified, both in known medulloblastoma-related genes (CTNNB1, PTCH1, MLL2, SMARCA4) and in genes not previously linked to this tumour (DDX3X, CTDNEP1, KDM6A, TBR1), often in subgroup-specific patterns. RNA sequencing confirmed these alterations, and revealed the expression of what are, to our knowledge, the first medulloblastoma fusion genes identified. Chromatin modifiers were frequently altered across all subgroups. These findings enhance our understanding of the genomic complexity and heterogeneity underlying medulloblastoma, and provide several potential targets for new therapeutics, especially for Group 3 and 4 patients.

Fluorescence-guided surgical sampling of glioblastoma identifies phenotypically distinct tumour-initiating cell populations in the tumour mass and margin

BACKGROUND

Acquiring clinically annotated, spatially stratified tissue samples from human glioblastoma (GBM) is compromised by haemorrhage, brain shift and subjective identification of 'normal' brain. We tested the use of 5-aminolevulinic acid (5-ALA) fluorescence to objective tissue sampling and to derive tumour-initiating cells (TICs) from mass and margin.

METHODS

The 5-ALA was administered to 30 GBM patients. Samples were taken from the non-fluorescent necrotic core, fluorescent tumour mass and non-fluorescent margin. We compared the efficiency of isolating TICs from these areas in 5-ALA versus control patients. HRMAS (1)H NMR was used to reveal metabolic alterations due to 5-ALA. We then characterised TICs for self-renewal in vitro and tumorigenicity in vivo.

RESULTS

The derivation of TICs was not compromised by 5-ALA and the metabolic profile was similar between tumours from 5-ALA patients and controls. The TICs from the fluorescent mass were self-renewing in vitro and tumour-forming in vivo, whereas TICs from non-fluorescent margin did not self-renew in vitro but did form tumours in vivo.

CONCLUSION

Our data show that 5-ALA does not compromise the derivation of TICs. It also reveals that the margin contains TICs, which are phenotypically different from those isolated from the corresponding mass.

Emerging findings in the Cancer Research UK stratified medicine program

TPS10633^

Background: Molecular analysis of tumours may be used to identify those predicted to benefit from novel targeted therapies. The Cancer Research UK programme is piloting plans to apply such testing broadly across the UK healthcare system, linking molecular phenotype to clinical outcomes. Methods: The Stratified Medicine Programme (SMP) aims to develop a model for high quality, large-scale molecular characterization of cancer specimens through an initiative developed in partnership with AstraZeneca, Pfizer, the UK Department of Health and academic researchers. Phase One of the SMP is a two year feasibility study. It aims to demonstrate the submission of consented blood samples and sections of surplus diagnostic formalin-fixed paraffin-embedded tumour tissue from 9,000 patients at centres across the UK to one of three ‘technology hubs’ for mutation testing of genes of potential clinical interest (KRAS, BRAF, NRAS, PIK3CA, TP53, PTEN, TMPRSS2-ERG, EGFR, EML4-ALK and KIT) in six selected tumour types. The tests are technically validated and will be completed in clinically relevant timescales. Data including pathological and treatment information and clinical outcome is also collected for the recruited patients, linked to the genetic data and stored in a central data repository hosted within the National Cancer Registration Service. The study opened in September 2011 at 7 sites across the UK and by the end of 2011, 760 patientswith breast, lung, prostate, colorectal, ovarian cancer or metastatic malignant melanoma had consented to participate. 142 sets of molecular results had been returned to clinical teams. Updated figures will be presented at the meeting, by which time the programme is projected to have accrued 4000 subjects. By 2013, we hope to have developed a scalable model for routine, high quality, prospective molecular characterisation of tumours for NHS cancer patients, with consent for the collection, storage and research use of population-scale genetic and clinical outcome data. We will report the emerging results from the Stratified Medicines Programme and early insights into implications for wider implementation across the UK healthcare system.

Genomic differences in benign and malignant follicular thyroid tumours using 1-Mb array-comparative genomic hybridisation

Currently there is a lack of objective markers that can reliably differentiate benign and malignant follicular thyroid tumours. Such markers are needed to avoid the morbidity and cost of diagnosing these lesions by a thyroid lobectomy and then a second operation to remove the remaining half of thyroid if cancer is found. The aim of this research was to look for genomic markers that might solve this important problem. Ethical approval for the project was obtained. DNA was extracted from formalin-fixed paraffin-embedded specimens and copy number analysed using an in-house produced 1-megabase genomic array by comparative genomic hybridization (1Mb-aCGH). Acceptable quality data were obtained in 25/26 (96 %) of adenomas and 17/28 (61 %) of carcinomas. Among the carcinomas, 11 were minimally invasive (MI), 5 widely invasive (WI) and there was one metastasis. Recurrent copy number changes distinguishing benign and malignant included +1p34.2-36.33, +1q, +13q12.11-14.3, +14q22.1-32.33, +20q and -22. +20q became more sensitive (36.4 %) for MI carcinomas, whereas +13q12.11-14.3 and +14q22.1-32.33 became more sensitive (66.7 %) for identifying WI cancers from adenomas. Only in the context of aneuploidy (3 adenomas, 3 MI, 3 WI) there were some specific copy number changes that could differentiate all aneuploid adenomas from carcinomas. This research is the first using 1Mb-aCGH to study benign and malignant follicular thyroid tumours. Overall, the incidence of any copy number changes is low, but there are a number of changes associated with different tumour types. Further research with a larger sample and better quality DNA will clarify these findings.

Clonal selection drives genetic divergence of metastatic medulloblastoma

Medulloblastoma, the most common malignant paediatric brain tumour, arises in the cerebellum and disseminates through the cerebrospinal fluid in the leptomeningeal space to coat the brain and spinal cord. Dissemination, a marker of poor prognosis, is found in up to 40% of children at diagnosis and in most children at the time of recurrence. Affected children therefore are treated with radiation to the entire developing brain and spinal cord, followed by high-dose chemotherapy, with the ensuing deleterious effects on the developing nervous system. The mechanisms of dissemination through the cerebrospinal fluid are poorly studied, and medulloblastoma metastases have been assumed to be biologically similar to the primary tumour. Here we show that in both mouse and human medulloblastoma, the metastases from an individual are extremely similar to each other but are divergent from the matched primary tumour. Clonal genetic events in the metastases can be demonstrated in a restricted subclone of the primary tumour, suggesting that only rare cells within the primary tumour have the ability to metastasize. Failure to account for the bicompartmental nature of metastatic medulloblastoma could be a major barrier to the development of effective targeted therapies.

Driver mutations in histone H3.3 and chromatin remodelling genes in paediatric glioblastoma

Glioblastoma multiforme (GBM) is a lethal brain tumour in adults and children. However, DNA copy number and gene expression signatures indicate differences between adult and paediatric cases. To explore the genetic events underlying this distinction, we sequenced the exomes of 48 paediatric GBM samples. Somatic mutations in the H3.3-ATRX-DAXX chromatin remodelling pathway were identified in 44% of tumours (21/48). Recurrent mutations in H3F3A, which encodes the replication-independent histone 3 variant H3.3, were observed in 31% of tumours, and led to amino acid substitutions at two critical positions within the histone tail (K27M, G34R/G34V) involved in key regulatory post-translational modifications. Mutations in ATRX (α-thalassaemia/mental retardation syndrome X-linked) and DAXX (death-domain associated protein), encoding two subunits of a chromatin remodelling complex required for H3.3 incorporation at pericentric heterochromatin and telomeres, were identified in 31% of samples overall, and in 100% of tumours harbouring a G34R or G34V H3.3 mutation. Somatic TP53 mutations were identified in 54% of all cases, and in 86% of samples with H3F3A and/or ATRX mutations. Screening of a large cohort of gliomas of various grades and histologies (n = 784) showed H3F3A mutations to be specific to GBM and highly prevalent in children and young adults. Furthermore, the presence of H3F3A/ATRX-DAXX/TP53 mutations was strongly associated with alternative lengthening of telomeres and specific gene expression profiles. This is, to our knowledge, the first report to highlight recurrent mutations in a regulatory histone in humans, and our data suggest that defects of the chromatin architecture underlie paediatric and young adult GBM pathogenesis.

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.

NG2 expression in glioblastoma identifies an actively proliferating population with an aggressive molecular signature

Glioblastoma multiforme (GBM) is the most common type of primary brain tumor and a highly malignant and heterogeneous cancer. Current conventional therapies fail to eradicate or curb GBM cell growth. Hence, exploring the cellular and molecular basis of GBM cell growth is vital to develop novel therapeutic approaches. Neuroglia (NG)-2 is a transmembrane proteoglycan expressed by NG2+ progenitors and is strongly linked to cell proliferation in the normal brain. By using NG2 as a biomarker we identify a GBM cell population (GBM NG2+ cells) with robust proliferative, clonogenic, and tumorigenic capacity. We show that a significant proportion (mean 83%) of cells proliferating in the tumor mass express NG2 and that over 50% of GBM NG2+ cells are proliferating. Compared with the GBM NG2- cells from the same tumor, the GBM of NG2+ cells overexpress genes associated with aggressive tumorigenicity, including overexpression of Mitosis and Cell Cycling Module genes (e.g., MELK, CDC, MCM, E2F), which have been previously shown to correlate with poor survival in GBM. We also show that the coexpression pattern of NG2 with other glial progenitor markers in GBM does not recapitulate that described in the normal brain. The expression of NG2 by such an aggressive and actively cycling GBM population combined with its location on the cell surface identifies this cell population as a potential therapeutic target in a subset of patients with GBM.

Oncogenic FAM131B-BRAF fusion resulting from 7q34 deletion comprises an alternative mechanism of MAPK pathway activation in pilocytic astrocytoma

Activation of the MAPK signaling pathway has been shown to be a unifying molecular feature in pilocytic astrocytoma (PA). Genetically, tandem duplications at chromosome 7q34 resulting in KIAA1549-BRAF fusion genes constitute the most common mechanism identified to date. To elucidate alternative mechanisms of aberrant MAPK activation in PA, we screened 125 primary tumors for RAF fusion genes and mutations in KRAS, NRAS, HRAS, PTPN11, BRAF and RAF1. Using microarray-based comparative genomic hybridization (aCGH), we identified in three cases an interstitial deletion of ~2.5 Mb as a novel recurrent mechanism forming BRAF gene fusions with FAM131B, a currently uncharacterized gene on chromosome 7q34. This deletion removes the BRAF N-terminal inhibitory domains, giving a constitutively active BRAF kinase. Functional characterization of the novel FAM131B-BRAF fusion demonstrated constitutive MEK phosphorylation potential and transforming activity in vitro. In addition, our study confirmed previously reported BRAF and RAF1 fusion variants in 72% (90/125) of PA. Mutations in BRAF (8/125), KRAS (2/125) and NF1 (4/125) and the rare RAF1 gene fusions (2/125) were mutually exclusive with BRAF rearrangements, with the exception of two cases in our series that concomitantly harbored more than one hit in the MAPK pathway. In summary, our findings further underline the fundamental role of RAF kinase fusion products as a tumor-specific marker and an ideally suited drug target for PA.

Adult grade II diffuse astrocytomas are genetically distinct from and more aggressive than their paediatric counterparts

Diffuse astrocytomas (WHO grade II) typically present as slow-growing tumours showing significant cellular differentiation, but possessing a tendency towards malignant progression. They account for ~10% of all astrocytic tumours, with a peak incidence between 30 and 40 years of age. Median survival is reported as around 6-8 years. Mutations of TP53 and IDH1 have been described as genetic hallmarks, while copy number alterations are also relatively common. However, there is some evidence to suggest that these characteristics may vary with age. Here, we present an integrated clinicopathologic, genomic and transcriptomic analysis suggesting that paediatric and adult tumours are associated with distinct genetic signatures. For example, no childhood tumour showed mutation of IDH1/2 or TP53, virtually no copy number changes were seen, and MGMT methylation was absent. In contrast, adult tumours showed IDH1/2 mutation in 94% and TP53 mutation in 69% of cases, with multiple copy number alterations per case and hypermethylation of MGMT in the majority of tumours. These differences were associated with a worse prognosis in the adult patients. The expression array data also revealed a significant difference in the expression of a number of genes putatively involved in neural stem cell maintenance and CNS development, including DLL3, HES5, BMP2, TIMP1 and BAMBI. Genes involved in DNA replication and the cell cycle were also enriched in the adult tumours, suggesting that their more aggressive behaviour may be due to derivation from a more rapidly dividing, less differentiated cell type.

Genetic aberrations leading to MAPK pathway activation mediate oncogene-induced senescence in sporadic pilocytic astrocytomas

PURPOSE

Oncogenic BRAF/Ras or NF1 loss can potentially trigger oncogene-induced senescence (OIS) through activation of the mitogen-activated protein kinase (MAPK) pathway. Somatic genetic abnormalities affecting this pathway occur in the majority of pilocytic astrocytomas (PA), the most prevalent brain neoplasm in children. We investigated whether OIS is induced in PA.

EXPERIMENTAL DESIGN

We tested expression of established senescence markers in three independent cohorts of sporadic PA. We also assessed for OIS in vitro, using forced expression of wild-type and V600E-mutant BRAF in two astrocytic cell lines: human telomerase reverse transcriptase (hTERT)-immortalized astrocytes and fetal astrocytes.

RESULTS

Our results indicate that PAs are senescent as evidenced by marked senescence-associated acidic β-galactosidase activity, low KI-67 index, and induction of p16(INK4a) but not p53 in the majority of 52 PA samples (46 of 52; 88.5%). Overexpression of a number of senescence-associated genes [CDKN2A (p16), CDKN1A (p21), CEBPB, GADD45A, and IGFBP7] was shown at the mRNA level in two independent PA tumor series. In vitro, sustained activation of wild-type or mutant BRAF induced OIS in both astrocytic cell lines. Loss of p16(INK4a) in immortalized astrocytes abrogated OIS, indicative of the role of this pathway in mediating this phenomenon in astrocytes. OIS is a mechanism of tumor suppression that restricts the progression of benign tumors. We show that it is triggered in PAs through p16(INK4a) pathway induction following aberrant MAPK activation.

CONCLUSIONS

OIS may account for the slow growth pattern in PA, the lack of progression to higher-grade astrocytomas, and the high overall survival of affected patients.

Abstract LB-181: Genome-wide DNA methylation analysis reveals novel hypermethylated genes in astrocytic tumors

Introduction:

Astrocytomas are the most common subtype of glioma, accounting for about 70% of all malignant tumors found in the central nervous system. Genetic alterations in gliomas have been extensively researched, but epigenetic changes are less well investigated. The aim of this study is to analyze genome-wide patterns of DNA methylation in a set of astrocytic tumors to identify aberrantly methylated genes, which could serve as candidates for new diagnostic markers and/or therapeutic targets.

Material & Methods:

DNA methylation was investigated genome-wide by methyl-DNA immunoprecipitation (MeDIP) and hybridization to customized Agilent Human CpG island (250K) oligonucleotide arrays. In total, 18 glioblastoma cell lines, 59 astrocytic tumor samples (4 diffuse astrocytomas WHO grade II, 17 anaplastic astrocytomas grade III and 38 glioblastomas grade IV) and 5 normal whole brain samples were analyzed. Data quality control, normalization and analysis was performed through the arrayQuality and LIMMA packages of R. Statistical comparisons were made between tumors grouped according to various parameters including tumor vs normal, malignancy grades and known genotypes such as IDH mutations using an empirical Bayes t-test. Methylation levels were validated by pyrosequencing and compared with mRNA expression measured by real-time-qPCR (RT-QPCR).

Results:

A number of differentially methylated genes (Log2 fold change > 1.5, adjusted p value < 0.001 after Benjamini & Hochberg multiple test correction) were identified in tumors as compared to normal brain samples. A selection of hypermethylated candidates were confirmed by pyrosequencing. The normalized array data significantly (p<0.0001) correlated to methylation (Pearson's correlation test) for SIM1 (r = 0.84), OTX2 (r = 0.78), NEFM (r = 0.88) and CDYL (r = 0.82). RT-QPCR was performed for NEFM and confirmed correlation between DNA methylation and mRNA expression (r = −0.76, p < 0.0001). SIM1 and OTX2 are transcription factors that play a key role in neurogenesis. NEFM encodes for a neurofilament and is expressed during neuronal differentiation. CDYL has recently been shown to be a REST/NRSF corepressor and key in the repression of the proto-oncogene TrkC. Functional annotation of the candidate gene lists indicated the significant (p<0.0001) enrichment of binding sites for the following transcription factors: E2F, PAX4, PAX5 and STAT5A.

Conclusion:

We have demonstrated the effectiveness of using MeDIP and the Agilent array platform to profile DNA methylation genome-wide in astrocytic tumors and identified a number of aberrantly hypermethylated genes in astrocytic tumors. Some of these genes are involved in transcriptional control of neuronal differentiation, suggesting that suppression of this pathway may be involved in the pathogenesis of these tumors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-181. doi:10.1158/1538-7445.AM2011-LB-181

Abstract 4699: Oncogenic fusion genes resulting from 7q34 deletions constitute a novel mechanism of MAPK pathway activation in pilocytic astrocytoma

Pilocytic astrocytoma (PA) is the most common brain tumor in children. Underlying genetic driver aberrations can currently be determined for 75-80% of cases. In particular, we and others have recently shown that tandem duplication at 7q34, resulting in BRAF fusion genes and constitutive activation of the MAPK signaling pathway, is a hallmark genetic lesion in PA development. Alternative mechanisms of MAPK activation include BRAF and KRAS point mutations, RAF1 fusions, and Neurofibromatosis-associated NF1 mutations.

In order to examine more precisely the spectrum of alterations in PA, we screened 79 tumor samples for RAF fusion genes and mutations in KRAS, NRAS, PTPN11, BRAF and RAF1. We used multiplex and long-distance inverse (LDI) PCR to identify BRAF and RAF1 fusion genes and direct sequencing for detailed breakpoint mapping.

Strikingly, LDI-PCR revealed a novel BRAF fusion gene with an uncharacterized gene, FAM131B, as a partner. Array-based comparative genomic hybridization (aCGH), revealed an interstitial deletion of ∼2.5 Mb as a novel mechanism forming the FAM131B-BRAF fusion. As with the more common duplication, this deletion removes the N-terminal auto-inhibitory domain of BRAF kinase, resulting in constitutive kinase activity. Functional characterization of the novel fusion gene demonstrated constitutive MEK phosphorylation potential and transforming activity in NIH 3T3 cells. The same fusion gene was also identified in one PA in an additional series from Cambridge, UK (n=7, with no previously identified alteration). Furthermore, we have detected a larger deletion at 7q in one additional case from our series, in which the alternative fusion partner is currently being identified.

Overall, gene fusions targeting RAF kinases were identified in 68% (54/79) of PA. Detailed analysis of genomic DNA mapped 96% (52/54) of the breakpoints to the same breakpoint cluster region in intron 8 of the BRAF gene. Moreover, we identified the first non-intronic breakpoint in exon 8 of BRAF and two novel SRGAP3-RAF1 fusion variants. BRAF, KRAS or NF1 mutations were observed as alternative mechanisms of MAPK activation in 9 tumors in which no RAF duplication was detected, as well as in two cases in our series which concomitantly harbored two or even three hits in the MAPK pathway.

In summary, we have identified a novel, recurrent BRAF fusion gene resulting in MAPK pathway activation in PA caused by a genomic deletion rather than amplification at 7q34, suggesting the possibility of further undiscovered fusion variants targeting RAF genes in this and other tumor types. Being a hallmark of PA tumorigenesis, these RAF fusion genes are expected to have clinical utility as both a specific marker for PA and a tumor-specific therapeutic target, which offers promise for applying novel treatment strategies in the near future.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4699. doi:10.1158/1538-7445.AM2011-4699

Chromosome 17 alterations identify good-risk and poor-risk tumors independently of clinical factors in medulloblastoma

Current risk stratification schemas for medulloblastoma, based on combinations of clinical variables and histotype, fail to accurately identify particularly good- and poor-risk tumors. Attempts have been made to improve discriminatory power by combining clinical variables with cytogenetic data. We report here a pooled analysis of all previous reports of chromosomal copy number related to survival data in medulloblastoma. We collated data from previous reports that explicitly quoted survival data and chromosomal copy number in medulloblastoma. We analyzed the relative prognostic significance of currently used clinical risk stratifiers and the chromosomal aberrations previously reported to correlate with survival. In the pooled dataset metastatic disease, incomplete tumor resection and severe anaplasia were associated with poor outcome, while young age at presentation was not prognostically significant. Of the chromosomal variables studied, isolated 17p loss and gain of 1q correlated with poor survival. Gain of 17q without associated loss of 17p showed a trend to improved outcome. The most commonly reported alteration, isodicentric chromosome 17, was not prognostically significant. Sequential multivariate models identified isolated 17p loss, isolated 17q gain, and 1q gain as independent prognostic factors. In a historical dataset, we have identified isolated 17p loss as a marker of poor outcome and 17q gain as a novel putative marker of good prognosis. Biological markers of poor-risk and good-risk tumors will be critical in stratifying treatment in future trials. Our findings should be prospectively validated independently in future clinical studies.

CpG island hypermethylation of the neurofibromatosis type 2 (NF2) gene is rare in sporadic vestibular schwannomas

AIMS

Loss of both wild-type copies of the neurofibromatosis type 2 (NF2) gene is found in both sporadic and neurofibromatosis type 2-associated vestibular schwannomas (VS). Previous studies have identified a subset of VS with no loss or mutation of NF2. We hypothesized that methylation of NF2 resulting in gene silencing may play a role in such tumours.

METHODS

Forty sporadic VS were analysed by array comparative genomic hybridization using 1 Mb whole genome and chromosome 22 tile path arrays. The NF2 genes were sequenced and methylation of NF2 examined by pyrosequencing.

RESULTS

Monosomy 22 was the only recurrent change found. Twelve tumours had NF2 mutations. Eight tumours had complete loss of wild-type NF2, four had one mutated and one wild-type allele, 11 had only one wild-type allele and 17 showed no abnormalities. Methylation analysis showed low-level methylation in four tumours at a limited number of CpGs. No high-level methylation was found.

CONCLUSIONS

This study shows that a significant proportion of sporadic VS (>40%) have unmethylated wild-type NF2 genes. This indicates that other mechanisms, yet to be identified, are operative in the oncogenesis of these VSs.

Temozolomide Versus Procarbazine, Lomustine, and Vincristine in Recurrent High-Grade Glioma

Purpose

Temozolomide (TMZ) is an alkylating agent licensed for treatment of high-grade glioma (HGG). No prospective comparison with nitrosourea-based chemotherapy exists. We report, to our knowledge, the first randomized trial of procarbazine, lomustine, and vincristine (PCV) versus TMZ in chemotherapy-naive patients with recurrent HGG.

Patients and Methods

Four hundred forty-seven patients were randomly assigned to PCV (224 patients) or TMZ (sub–random assignment: TMZ-5 [200 mg/m2 for 5 days, 112 patients] or TMZ-21 [100 mg/m2 for 21 days, 111 patients]) for up to 9 months or until progression. The primary outcomes were survival (PCV v TMZ) and 12-week progression-free survival (PFS; TMZ-5 v TMZ-21). This study is registered as ISRCTN83176944.

Results

Percentages of patients completing 9 months of treatment in the PCV, TMZ-5, and TMZ-21 arms were 17%, 26%, and 13%, respectively. Major toxicity was similar across all three groups. With a median follow-up time of 12 months and 382 deaths, there was no clear survival benefit when comparing PCV with TMZ (hazard ratio [HR], 0.91; 95% CI, 0.74 to 1.11; P = .350). For TMZ-5 versus TMZ-21, 12-week PFS rates were similar (63.6% and 65.7%, respectively; P = .745), but TMZ-5 improved overall PFS (HR, 1.38; 95% CI, 1.05 to 1.82; P = .023), survival (HR, 1.32; 95% CI, 0.99 to 1.75; P = .056), and global quality of life (49% v 19% improved > 10 points at 6 months, respectively; P = .005).

Conclusion

Although TMZ (both arms combined) did not show a clear benefit compared with PCV, comparison of the TMZ schedules demonstrated that the 21-day schedule was inferior to the 5-day schedule in this setting. This challenges the current understanding of increasing TMZ dose-intensity by prolonged scheduling.

Distinct patterns of 1p and 19q alterations identify subtypes of human gliomas that have different prognoses

We studied the status of chromosomes 1 and 19 in 363 astrocytic and oligodendroglial tumors. Whereas the predominant pattern of copy number abnormality was a concurrent loss of the entire 1p and 19q regions (total 1p/19q loss) among oligodendroglial tumors and partial deletions of 1p and/or 19q in astrocytic tumors, a subset of apparently astrocytic tumors also had total 1p/19q loss. The presence of total 1p/19q loss was associated with longer survival of patients with all types of adult gliomas independent of age and diagnosis (P = .041). The most commonly deleted region on 19q in astrocytic tumors spans 885 kb in 19q13.33-q13.41, which is telomeric to the previously proposed region. Novel regions of homozygous deletion, including a part of DPYD (1p21.3) or the KLK cluster (19q13.33), were observed in anaplastic oligodendrogliomas. Amplifications encompassing AKT2 (19q13.2) or CCNE1 (19q12) were identified in some glioblastomas. Deletion mapping of the centromeric regions of 1p and 19q in the tumors that had total 1p/19q loss, indicating that the breakpoints lie centromeric to NOTCH2 within the pericentromeric regions of 1p and 19q. Thus, we show that the copy number abnormalities of 1p and 19q in human gliomas are complex and have distinct patterns that are prognostically predictive independent of age and pathological diagnosis. An accurate identification of total 1p/19q loss and discriminating this from other 1p/19q changes is, however, critical when the 1p/19q copy number status is used to stratify patients in clinical trials.

Frequent amplification of a chr19q13.41 microRNA polycistron in aggressive primitive neuroectodermal brain tumors

We discovered a high-level amplicon involving the chr19q13.41 microRNA (miRNA) cluster (C19MC) in 11/45 ( approximately 25%) primary CNS-PNET, which results in striking overexpression of miR-517c and 520g. Constitutive expression of miR-517c or 520g promotes in vitro and in vivo oncogenicity, modulates cell survival, and robustly enhances growth of untransformed human neural stem cells (hNSCs) in part by upregulating WNT pathway signaling and restricting differentiation of hNSCs. Remarkably, the C19MC amplicon, which is very rare in other brain tumors (1/263), identifies an aggressive subgroup of CNS-PNET with distinct gene-expression profiles, characteristic histology, and dismal survival. Our data implicate miR-517c and 520g as oncogenes and promising biological markers for CNS-PNET and provide important insights into oncogenic properties of the C19MC locus.

IDH1 mutations are present in the majority of common adult gliomas but rare in primary glioblastomas

We screened exon 4 of the gene isocitrate dehydrogenase 1 (NADP+), soluble (IDH1) for mutations in 596 primary intracranial tumors of all major types. Codon 132 mutation was seen in 54% of astrocytomas and 65% of oligodendroglial tumors but in only 6% of glioblastomas (3% of primary and 50% of secondary glioblastomas). There were no mutations in any other type of tumor studied. While mutations in the tumor protein p53 gene (TP53) and total 1p/19q deletions were mutually exclusive, IDH1 mutations were strongly correlated with these genetic abnormalities. All four types of mutant IDH1 proteins showed decreased enzymatic activity. The data indicate that IDH1 mutation combined with either TP53 mutation or total 1p/19q loss is a frequent and early change in the majority of oligodendroglial tumors, diffuse astrocytomas, anaplastic astrocytomas, and secondary glioblastomas but not in primary glioblastomas.

Somatic mutations of the histone H3K27 demethylase gene UTX in human cancer

Somatically acquired epigenetic changes are present in many cancers. Epigenetic regulation is maintained via post-translational modifications of core histones. Here, we describe inactivating somatic mutations in the histone lysine demethylase gene UTX, pointing to histone H3 lysine methylation deregulation in multiple tumor types. UTX reintroduction into cancer cells with inactivating UTX mutations resulted in slowing of proliferation and marked transcriptional changes. These data identify UTX as a new human cancer gene.

A20 deletion is associated with copy number gain at the TNFA/B/C locus and occurs preferentially in translocation-negative MALT lymphoma of the ocular adnexa and salivary glands

The genetic basis of MALT lymphoma is largely unknown. Characteristic chromosomal translocations are frequently associated with gastric and pulmonary cases, but are rare at other sites. We compared the genetic profiles of 33 ocular adnexal and 25 pulmonary MALT lymphomas by 1 Mb array-comparative genomic hybridization (CGH) and revealed recurrent 6q23 losses and 6p21.2-6p22.1 gains exclusive to ocular cases. High-resolution chromosome 6 tile-path array-CGH identified NF-kappaB inhibitor A20 as the target of 6q23.3 deletion and TNFA/B/C locus as a putative target of 6p21.2-22.1 gain. Interphase fluorescence in situ hybridization showed that A20 deletion occurred in MALT lymphoma of the ocular adnexa (8/42=19%), salivary gland (2/24=8%), thyroid (1/9=11%) and liver (1/2), but not in the lung (26), stomach (45) and skin (13). Homozygous deletion was observed in three cases. A20 deletion and TNFA/B/C gain were significantly associated (p<0.001) and exclusively found in cases without characteristic translocation. In ocular cases, A20 deletion was associated with concurrent involvement of different adnexal tissues or extraocular sites at diagnosis (p=0.007), a higher proportion of relapse (67% versus 37%) and a shorter relapse-free survival (p=0.033). A20 deletion and gain at TNFA/B/C locus may thus play an important role in the development of translocation-negative MALT lymphoma.