MYC family amplification and clinical risk-factors interact to predict an extremely poor prognosis in childhood medulloblastoma.

The MYC oncogenes are the most commonly amplified loci in medulloblastoma, and have previously been proposed as biomarkers of adverse disease prognosis by us and others. Here, we report focussed and comprehensive investigations of MYCC, MYCN and MYCL in an extensive medulloblastoma cohort (n = 292), aimed to define more precisely their biological significance and optimal clinical application to direct improved disease risk-stratification and individualisation of therapy. MYCC and MYCN expression elevations were multifactorial, associated with high-risk (gene amplification, large-cell/anaplastic pathology (LCA)) and favourable-risk (WNT/SHH molecular subgroups) disease features.

RASSF1A and the BH3-only mimetic ABT-737 promote apoptosis in pediatric medulloblastoma cell lines.

The RASSF1A tumor suppressor is potentially the most important candidate gene identified in medulloblastoma to date, being epigenetically silenced in >79% of primary tumors. However, its functional role has not been previously addressed in this tumor type. Here, we demonstrate that expression of RASSF1A promotes the induction of cell death after activation of both the extrinsic and intrinsic apoptotic pathways in medulloblastoma cells.

Rapid diagnosis of medulloblastoma molecular subgroups.

Purpose: Microarray studies indicate medulloblastoma comprises distinct molecular disease subgroups, which offer potential for improved clinical management.

Experimental Design: Minimal mRNA expression signatures diagnostic for the Wnt/Wingless (WNT) and Sonic Hedgehog (SHH) subgroups were developed, validated, and used to assign subgroup affiliation in 173 tumors from four independent cohorts, alongside a systematic investigation of subgroup clinical and molecular characteristics.

Results: WNT tumors [12% (21/173)] were diagnosed >5 years of age (peak, 10 years), displayed classic histology, CTNNB1 mutation (19/20), and associated chromosome 6 loss, and have previously been associated with favorable prognosis.

Definition of disease-risk stratification groups in childhood medulloblastoma using combined clinical, pathologic, and molecular variables.

Purpose: Medulloblastomas are heterogeneous and include relatively good-prognosis tumors characterized by Wnt pathway activation, as well as those that cannot be successfully treated with conventional therapy. Developing a practical therapeutic stratification that allows accurate identification of disease risk offers the potential to individualize adjuvant therapy and to minimize long-term adverse effects in a subgroup of survivors.

Methods: Using formalin-fixed paraffin-embedded (FFPE) tissue for immunohistochemistry, fluorescent in situ hybridization, and direct sequencing to identify tumors with a Wnt pathway signature and those harboring copy number abnormalities (CNAs) of potential prognostic significance (MYC/MYCN amplification, CNAs of chromosome 6 and 17), we evaluated clinical, pathologic, and molecular outcome indicators and stratification models in a cohort (n = 207) of patients with medulloblastoma 3 to 16 years of age from the International Society of Pediatric Oncology CNS9102 (PNET3) trial.

Global analysis of the medulloblastoma epigenome identifies disease-subgroup-specific inactivation of COL1A2.

Candidate gene investigations have indicated a significant role for epigenetic events in the pathogenesis of medulloblastoma, the most common malignant brain tumor of childhood. To assess the medulloblastoma epigenome more comprehensively, we undertook a genomewide investigation to identify genes that display evidence of methylation-dependent regulation. Expression microarray analysis of medulloblastoma cell lines following treatment with a DNA methyltransferase inhibitor revealed deregulation of multiple transcripts (3%-6% of probes per cell line).

Wnt/Wingless pathway activation and chromosome 6 loss characterize a distinct molecular sub-group of medulloblastomas associated with a favorable prognosis.

The accurate assessment of disease risk remains a major goal in children with medulloblastoma. Activation of the canonical Wnt/Wingless (Wnt/Wg) signalling pathway occurs in up to 25% of cases and is associated with a favorable disease outcome. To explore the molecular pathogenesis of Wnt/Wg-active medulloblastomas, and to investigate any genetic basis for their observed clinical behavior, we assessed a series of primary medulloblastomas for evidence of Wnt/Wg pathway activation, alongside a genome-wide analysis of associated copy-number aberrations.

APC and CTNNB1 mutations are rare in sporadic ependymomas.

The ependymoma is the second most common malignant brain tumor of childhood; however, its molecular basis is poorly understood. The formation of multiple ependymomas has been reported as an occasional feature of Turcot syndrome type 2 (TS2), a familial cancer syndrome caused by inherited mutations of the APC tumor suppressor gene, and characterised by the concurrence of a primary CNS tumor (predominantly medulloblastoma) and multiple colorectal adenomas. APC is a critical component of the Wnt/Wingless signaling pathway, which is disrupted in sporadic cancers (e.

Epigenetic events in medulloblastoma development.

Over the last decade, the analysis of genetic defects in primary tumors has been central to the identification of molecular events and biological pathways involved in the pathogenesis of medulloblastoma, the most common malignant brain tumor of childhood. Despite this, understanding of the molecular basis of the majority of cases remains poor. In recent years, the emerging field of epigenetics, which describes heritable alterations in gene expression that occur in the absence of DNA sequence changes, has forced a revision of the understanding of the mechanisms of gene disruption in cancer.

beta-Catenin status predicts a favorable outcome in childhood medulloblastoma: the United Kingdom Children's Cancer Study Group Brain Tumour Committee.

Purpose: Identifying pathobiological correlates of clinical behavior or therapeutic response currently represents a key challenge for medulloblastoma research. Nuclear accumulation of the beta-catenin protein is associated with activation of the Wnt/Wg signaling pathway, and mutations affecting components of this pathway have been reported in approximately 15% of sporadic medulloblastomas. We tested the hypothesis that nuclear immunoreactivity for beta-catenin is a prognostic marker in medulloblastoma, and assessed the relationship between nuclear beta-catenin immunoreactivity and mutations of CTNNB1 and APC.

Epigenetic inactivation of the RASSF1A tumour suppressor gene in ependymoma.

To investigate the role of aberrant epigenetic events in ependymoma and identify critical genes in its pathogenesis, the methylation status of nine tumour suppressor genes (TSGs: p14(ARF), p15(INK4B), p16(INK4A), CASP8, MGMT, TIMP3, TP73, RB1 and RASSF1A) was assessed. Extensive hypermethylation across the RASSF1A CpG island was detected frequently in ependymomas of all clinical and pathological disease subtypes (86% of cases, n=35), but not in non-neoplastic brain tissues (n=6). Less frequent methylation was observed for CASP8, MGMT and TP73 (5-20%).

Epigenetic inactivation of MCJ (DNAJD1) in malignant paediatric brain tumours.

MCJ (DNAJD1) is a recently discovered member of the DNAJ protein family whose expression is controlled epigenetically by methylation of a CpG island located within the 5' transcribed region of its gene. Methylation-dependent transcriptional silencing of MCJ has been observed in ovarian cancers and associated with increased resistance to chemotherapeutic agents; however, its role in other cancer types has not been widely investigated. We examined the status of MCJ in intracranial primitive neuroectodermal tumours [PNETs, comprising cerebellar PNETs (medulloblastomas) and supratentorial PNETs (stPNETs)] and ependymomas, together representing the most common malignant brain tumours of childhood.

The TP53-ARF tumor suppressor pathway is frequently disrupted in large/cell anaplastic medulloblastoma.

We analyzed the TP53 and INK4A/ARF loci in 29 pediatric medulloblastomas. Mutually exclusive mutation in TP53, methylation of P14(ARF) or deletion of INK4A/ARF were identified in 21% (6/29) of tumors. Five of these alterations were detected in large cell/anaplastic medulloblastomas or tumors with significant anaplasia.

Identification of tumour-specific epigenetic events in medulloblastoma development by hypermethylation profiling.

Medulloblastoma arises in the cerebellum and is the most common malignant brain tumour of childhood, however its molecular basis is not well understood. To assess the role of aberrant epigenetic events in medulloblastoma and identify critical genes in its development, we profiled the promoter methylation status of 11 candidate tumour-suppressor genes (TSGs; p14(ARF), p15(INK4b), p16(INK4a), CASP8, HIC1, EDNRB, TIMP3, TP73, TSLC1, RIZ1 and RASSF1A) in medulloblastoma cell lines, primary tumours and the normal cerebellum. Gene-specific TSG methylation was a significant feature of both medulloblastomas and the cerebellum.

Biallelic epigenetic inactivation of the RASSF1A tumor suppressor gene in medulloblastoma development.

Epigenetic inactivation of the RASSF1A tumor suppressor gene (TSG) at chromosome 3p21.3 was examined in medulloblastoma, the most common malignant brain tumor of childhood. Seventy-nine % (27 of 34) of primary tumors and 100% (8 of 8) of medulloblastoma cell lines displayed extensive tumor-specific DNA hypermethylation across the RASSF1A promoter-associated CpG island.