Germ-line and somatic mutations of the APC gene in patients with Turcot syndrome and analysis of APC mutations in brain tumors

Haploinsufficiency of Adenomatous Polyposis Coli Coupled with Kirsten Rat Sarcoma Viral Oncogene Homologue Activation and P53 Loss Provokes High-Grade Glioblastoma Formation in Mice

Glioblastoma multiforme (GBM) is the most common and deadly type of brain tumor originating from glial cells. Despite decades of clinical trials and research, there has been limited success in improving survival rates. However, molecular pathology studies have provided a detailed understanding of the genetic alterations associated with the formation and progression of glioblastoma-such as Kirsten rat sarcoma viral oncogene homolog (KRAS) signaling activation (5%), P53 mutations (25%), and adenomatous polyposis coli (APC) alterations (2%)-laying the groundwork for further investigation into the biological and biochemical basis of this malignancy. These analyses have been crucial in revealing the sequential appearance of specific genetic lesions at distinct histopathological stages during the development of GBM. To further explore the pathogenesis and progression of glioblastoma, here, we developed the glial-fibrillary-acidic-protein (GFAP)-Cre-driven mouse model and demonstrated that activated KRAS and p53 deficiencies play distinct and cooperative roles in initiating glioma tumorigenesis. Additionally, the combination of APC haploinsufficiency with mutant Kras activation and p53 deletion resulted in the rapid progression of GBM, characterized by perivascular inflammation, large necrotic areas, and multinucleated giant cells. Consequently, our GBM models have proven to be invaluable resources for identifying early disease biomarkers in glioblastoma, as they closely mimic the human disease. The insights gained from these models may pave the way for potential advancements in the diagnosis and treatment of this challenging brain tumor.

Adenomatous polyposis coli in cancer and therapeutic implications

Inactivating mutations of the adenomatous polyposis coli (APC) gene and consequential upregulation of the Wnt signaling pathway are critical initiators in the development of colorectal cancer (CRC), the third most common cancer in the United States for both men and women. Emerging evidence suggests APCmutations are also found in gastric, breast and other cancers. The APC gene, located on chromosome 5q, is responsible for negatively regulating the b-catenin/Wnt pathway by creating a destruction complex with Axin/Axin2, GSK-3b, and CK1. In the event of an APC mutation, b-catenin accumulates, translocates to the cell nucleus and increases the transcription of Wnt target genes that have carcinogenic consequences in gastrointestinal epithelial stem cells. A literature review was conducted to highlight carcinogenesis related to APC mutations, as well as preclinical and clinical studies for potential therapies that target steps in inflammatory pathways, including IL-6 transduction, and Wnt pathway signaling regulation. Although a range of molecular targets have been explored in murine models, relatively few pharmacological agents have led to substantial increases in survival for patients with colorectal cancer clinically. This article reviews a range of molecular targets that may be efficacious targets for tumors with APC mutations.

Medulloblastomas associated with an APC germline pathogenic variant share the good prognosis of CTNNB1-mutated medulloblastomas

BACKGROUND

Medulloblastomas may occur in a predisposition context, including familial adenomatosis polyposis. Medulloblastomas related to a germline pathogenic variant of adenomatous polyposis coli (APC) remain rare and poorly described. Their similarities with sporadic WNT medulloblastomas still require description.

METHODS

We performed a multicentric retrospective review of 12 patients treated between 1988 and 2018 for medulloblastoma with an identified or highly suspected (personal or familial history) APC germline pathogenic variant. We report personal and familial history APC gene pathogenic variants whenever available: clinical and histologic characteristics of the medulloblastoma, treatments, and long-term outcome, including second tumor and late sequelae.

RESULTS

Medulloblastomas associated with APC pathogenic variants are mainly classic (11/11 patients, 1 not available), nonmetastatic (10/12 patients) medulloblastomas, with nuclear immunoreactivity for ß-catenin (9/9 tested cases). Ten of 11 assessable patients are disease free with a median follow-up of 10.7 years (range, 1-28 y). Secondary tumors included desmoid tumors in 7 patients (9 tumors), 1 thyroid carcinoma, 2 pilomatricomas, 1 osteoma, 1 vertebral hemangioma, and 1 malignant triton in the radiation field, which caused the only cancer-related death in our series.

CONCLUSIONS

Medulloblastomas associated with an APC pathogenic variant have an overall favorable outcome, even for metastatic tumors. Yet, long-term survival is clouded by second tumor occurrence; treatment may play some role in some of these second malignancies. Our findings raise the question of applying a de-escalation therapeutic protocol to treat patients with APC germline pathogenic variants given the excellent outcome, and reduced intensity of craniospinal irradiation may be further evaluated.

Possible Considerations for the Management of Turcot’s Syndrome?

Background:

Turcot’s syndrome (TS) is a rare disease with known incidence of about 1-2 cases per year. It is, however, linked to high mortality due to the brain cancer. And because of this, we propose recommendations, aimed at preventing the mortality of the patients and to minimize the risk of undiagnosed Turcot’s syndrome.

Methods:

The authors collected the worldwide published data on TS, from the year of its definition till 2018, all of which was published on the search engines, such as Medline, Medknow, Cohraine and Wiley.

Results:

We included 97 patients, 57 from which are females and 40 males with median age of 22 years. The most common type of cancer is medulloblastoma, followed by glioblastoma and astrocytoma. We further divided the patients into two categories based on the first symptom of the disease and we made an algorithm of approaching these patients.

Conclusion:

TS is a disease that affects mostly members of families with multiple genetic mutations and types of cancers. And because of the unknown mechanisms of inheritance, it is useful to establish guidelines for the approach of those patients, in order to minimize the high mortality rate.

Genetic and epigenetic contribution to astrocytic gliomas pathogenesis

Astrocytic gliomas are the most common and lethal form of intracranial tumors. These tumors are characterized by a significant heterogeneity in terms of cytopathological, transcriptional, and (epi)genomic features. This heterogeneity has made these cancers one of the most challenging types of cancers to study and treat. To uncover these complexities and to have better understanding of the disease initiation and progression, identification, and characterization of underlying cellular and molecular pathways related to (epi)genetics of astrocytic gliomas is crucial. Here, we discuss and summarize molecular and (epi)genetic mechanisms that provide clues as to the pathogenesis of astrocytic gliomas.

Aberrant Activation of β-Catenin Signaling Drives Glioma Tumorigenesis via USP1-Mediated Stabilization of EZH2

Aberrant activation of β-catenin signaling is a critical driver for tumorigenesis, but the mechanism underlying this activation is not completely understood. In this study, we demonstrate a critical role of β-catenin signaling in stabilization of enhancer of zeste homolog 2 (EZH2) and control of EZH2-mediated gene repression in oncogenesis. β-Catenin/TCF4 activated the transcription of the deubiquitinase USP1, which then interacted with and deubiquitinated EZH2 directly. USP1-mediated stabilization of EZH2 promoted its recruitment to the promoters of CDKN1B, RUNX3, and HOXA5, resulting in enhanced enrichment of histone H3K27me3 and repression of target gene expression. In human glioma specimens, expression levels of nuclear β-catenin, USP1, and EZH2 correlated with one another. Depletion of β-catenin/USP1/EZH2 repressed glioma cell proliferation in vitro and tumor formation in vivo. Our findings indicate that a β-catenin-USP1-EZH2 axis orchestrates the interplay between dysregulated β-catenin signaling and EZH2-mediated gene epigenetic silencing during glioma tumorigenesis. SIGNIFICANCE: These findings identify the β-catenin-USP1-EZH2 signaling axis as a critical mechanism for glioma tumorigenesis that may serve as a new therapeutic target in glioblastoma.

The whole-genome landscape of medulloblastoma subtypes

Current therapies for medulloblastoma, a highly malignant childhood brain tumour, impose debilitating effects on the developing child, and highlight the need for molecularly targeted treatments with reduced toxicity. Previous studies have been unable to identify the full spectrum of driver genes and molecular processes that operate in medulloblastoma subgroups. Here we analyse the somatic landscape across 491 sequenced medulloblastoma samples and the molecular heterogeneity among 1,256 epigenetically analysed cases, and identify subgroup-specific driver alterations that include previously undiscovered actionable targets. Driver mutations were confidently assigned to most patients belonging to Group 3 and Group 4 medulloblastoma subgroups, greatly enhancing previous knowledge. New molecular subtypes were differentially enriched for specific driver events, including hotspot in-frame insertions that target KBTBD4 and ‘enhancer hijacking’ events that activate PRDM6. Thus, the application of integrative genomics to an extensive cohort of clinical samples derived from a single childhood cancer entity revealed a series of cancer genes and biologically relevant subtype diversity that represent attractive therapeutic targets for the treatment of patients with medulloblastoma.

Genomic analysis of 491 medulloblastoma samples, including methylation profiling of 1,256 cases, effectively assigns candidate drivers to most tumours across all molecular subgroups.

Medulloblastomas are highly malignant brain tumours that develop during childhood. Paul Northcott and colleagues analysed the whole-genome sequences of 491 medulloblastomas in order to characterize the genomic landscape across tumours and identify new drivers and mutational signatures. Their integrative genomic analyses, including methylation profiling of 1,256 medulloblastomas, identifies subgroup-specific driver mutations and suggests additional tumour subtypes. The authors assign driver mutations to a high proportion of the less well characterized Group 3 and Group 4, which together contribute to more than 60% of all medulloblastomas.

EGFR and EGFRvIII Promote Angiogenesis and Cell Invasion in Glioblastoma: Combination Therapies for an Effective Treatment

Epidermal growth factor receptor (EGFR) and the mutant EGFRvIII are major focal points in current concepts of targeted cancer therapy for glioblastoma multiforme (GBM), the most malignant primary brain tumor. The receptors participate in the key processes of tumor cell invasion and tumor-related angiogenesis and their upregulation correlates with the poor prognosis of glioma patients. Glioma cell invasion and increased angiogenesis share mechanisms of the degradation of the extracellular matrix (ECM) through upregulation of ECM-degrading proteases as well as the activation of aberrant signaling pathways. This review describes the role of EGFR and EGFRvIII in those mechanisms which might offer new combined therapeutic approaches targeting EGFR or EGFRvIII together with drug treatments against proteases of the ECM or downstream signaling to increase the inhibitory effects of mono-therapies.

[Muir-Torre syndrome and Turcot syndrome]

INTRODUCTION

Lynch syndrome (LS) is a syndrome that carries a genetic predisposition to certain cancers associating, either in a single individual or in a family, a visceral tumour, mainly colorectal, with a high risk of other synchronous or metachronous cancers. LS is linked with mutations in the genes coding for proteins in the DNA repair system. Phenotypic variants of SL exist, including Muir-Torre syndrome (MTS) and Turcot syndrome (TS), both of which predispose to colorectal cancer. They may be distinguished by the presence of benign or malignant sebaceous tumours in MTS, and tumours of the central nervous system in TS.

PATIENTS AND METHODS

A 59-year-old man, with a history of right colon cancer at the age of 36 years, consulted for a nose lesion shown by histopathological examination to be a sebaceous tumour. Immunohistochemistry revealed loss of expression of proteins MSH2 and MSH6, strongly suggesting a diagnosis of MTS. Eight years earlier, the man's son had developed a fatal glioblastoma; given the paternal phenotype of MTS, the hypothesis of TS in the son is probable.

DISCUSSION

This case suggests that several variants of Lynch syndrome may be seen within the same family. It raises the issue of screening for cerebral tumours in patients with MTS and in their family members, even though such a recommendation does not exist; current recommendations in fact consist primarily of gastrointestinal and gynaecological monitoring.

Current Understanding on EGFR and Wnt/β-Catenin Signaling in Glioma and Their Possible Crosstalk

Glioblastoma multiformes (GBMs) are extensively heterogeneous at both cellular and molecular levels. Current therapeutic strategies include targeting of key signaling molecules using pharmacological inhibitors in combination with genotoxic agents such as temozolomide. In spite of all efforts, the prognosis of glioma patients remains dismal. Therefore, a proper understanding of individual molecular pathways responsible for the progression of GBM is necessary. The epidermal growth factor receptor (EGFR) pathway is probably the most significant signaling pathway clinically implicated in glioma. Not surprisingly, anti-EGFR therapies mostly prevail for therapeutic purposes. The Wnt/β-catenin pathway is well implicated in multiple tumors; however, its role in glioma has only recently started to emerge. We give a concise account of the current understanding of the role of both these pathways in glioma. Last, taking evidences from a limited literature, we outline a number of points where these pathways intersect each other and put forward the possibility of combinatorially targeting them for treatment of glioma.

Diagnostic application of high resolution single nucleotide polymorphism array analysis for children with brain tumors

Single nucleotide polymorphism (SNP) array analysis is currently used as a first tier test for pediatric brain tumors at The Children's Hospital of Philadelphia. The results from 100 consecutive patients are summarized in the present report. Eighty-seven percent of the tumors had at least one pathogenic copy number alteration. Nineteen of 56 low grade gliomas (LGGs) demonstrated a duplication in 7q34, which resulted in a KIAA1549-BRAF fusion. Chromosome band 7q34 deletions, which resulted in a FAM131B-BRAF fusion, were identified in one pilocytic astrocytoma (PA) and one dysembryoplastic neuroepithelial tumor (DNT). One ganglioglioma (GG) demonstrated a 6q23.3q26 deletion that was predicted to result in a MYB-QKI fusion. Gains of chromosomes 5, 6, 7, 11, and 20 were seen in a subset of LGGs. Monosomy 6, deletion of 9q and 10q, and an i(17)(q10) were each detected in the medulloblastomas (MBs). Deletions and regions of loss of heterozygosity that encompassed TP53, RB1, CDKN2A/B, CHEK2, NF1, and NF2 were identified in a variety of tumors, which led to a recommendation for germline testing. A BRAF p.Thr599dup or p.V600E mutation was identified by Sanger sequencing in one and five gliomas, respectively, and a somatic TP53 mutation was identified in a fibrillary astrocytoma. No TP53 hot-spot mutations were detected in the MBs. SNP array analysis of pediatric brain tumors can be combined with pathologic examination and molecular analyses to further refine diagnoses, offer more accurate prognostic assessments, and identify patients who should be referred for cancer risk assessment.

Turcot syndrome: a synchronous clinical presentation of glioblastoma multiforme and adenocarcinoma of the colon

Turcot syndrome (TS) is a rare hereditary disorder clinically characterized by the occurrence of primary tumors of the colon and the central nervous system (CNS). Here we present the case of an 11-year-old boy with a synchronous clinical presentation of both glioblastoma multiforme (GBM) and colonic adenocarcinoma. A molecular genetic study revealed microsatellite instability in the DNA mismatch repair (MMR) gene. This patient ultimately survived for 13 months after clinical presentation. Based on this case study, the synchronous presentation of glioblastoma multiforme and adenocarcinoma of the colon might suggest a shorter survival rate for patients with Turcot syndrome. A literature review complements this paper.

An epigenetic genome-wide screen identifies SPINT2 as a novel tumor suppressor gene in pediatric medulloblastoma

Medulloblastoma (MB) is a malignant cerebellar tumor that occurs primarily in children. The hepatocyte growth factor (HGF)/MET pathway has an established role in both normal cerebellar development as well as the development and progression of human brain tumors, including MB. To identify novel tumor suppressor genes involved in MB pathogenesis, we performed an epigenome-wide screen in MB cell lines, using 5-aza-2'deoxycytidine to identify genes aberrantly silenced by promoter hypermethylation. Using this technique, we identified an inhibitor of HGF/MET signaling, serine protease inhibitor kunitz-type 2 (SPINT2/HAI-2), as a putative tumor suppressor silenced by promoter methylation in MB. In addition, based on single nucleotide polymorphism array analysis in primary MB samples, we identified hemizygous deletions targeting the SPINT2 locus in addition to gains on chromosome 7 encompassing the HGF and MET loci. SPINT2 gene expression was down-regulated and MET expression was up-regulated in 73.2% and 45.5% of tumors, respectively, by quantitative real-time PCR. SPINT2 promoter methylation was detected in 34.3% of primary MBs examined by methylation-specific PCR. SPINT2 reexpression in MB cell lines reduced proliferative capacity, anchorage independent growth, cell motility in vitro, and increased overall survival times in vivo in a xenograft model (P<0.0001). Taken together, these data support the role of SPINT2 as a putative tumor suppressor gene in MB, and further implicate dysregulation of the HGF/MET signaling pathway in the pathogenesis of MB.

Meningiomas exhibit loss of heterozygosity of the APC gene

The molecular mechanisms and candidate genes involved in development of meningiomas still need investigation and elucidation. In the present study 33 meningiomas were analyzed regarding genetic changes of tumor suppressor gene Adenomatous polyposis coli (APC), a component of the wnt signaling. Gene instability was tested by polymerase chain reaction/loss of heterozygosity (LOH) using Restriction Fragment Length Polymorphism (RFLP) method. RFLP was performed by two genetic markers, Rsa I in APC's exon 11 and Msp I in its exon 15. The results of our analysis showed altogether 15 samples with LOH of the APC gene out of 32 heterozygous patients (47%). Seven patients had LOHs at both exons, while four LOHs were exclusive for exon 11 and four for exon 15. The changes were distributed according to pathohistological grade as follows: 46% of meningothelial meningioma showed LOH; 33% of fibrous; 75% of mixed (transitional); 75% of angiomatous, and one LOH was found in a single case of psammomatous meningioma. None of the LOHs were found in atypical and anaplastic cases. Immunostaining showed that samples with LOHs were accompanied with the absence of APC protein expression or presence of mutant APC proteins (chi(2 )= 13.81, df = 2, P < 0.001). We also showed that nuclear localization of beta-catenin correlates to APC genetic changes (chi(2 )= 21.96, df = 2, P < 0.0001). The results of this investigation suggest that genetic changes of APC gene play a role in meningioma formation.

Turcot syndrome confirmed with molecular analysis

Turcot syndrome is clinically characterized by the occurrence of primary brain tumor and colorectal tumor and has, in previous reports, been shown associated with germline mutations in the genes APC, MLH1, MHS6, and PMS2. To date, only few families have been documented by molecular analysis. We report two new families with Turcot syndrome to illustrate and review its characteristics and facilitate diagnosis. Molecular analysis revealed two germline mutations, one in the MLH1 gene and one in MSH2. The latter has never been describe in the literature. Personal and familial relevant anamnestic data from patients with glioma might aid in the diagnosis of genetic disorders. The subsequent molecular characterization may contribute to the appropriate care of affected patients and asymptomatic gene carriers.

Brain tumors in individuals with familial adenomatous polyposis: a cancer registry experience and pooled case report analysis

BACKGROUND

Most individuals with Familial Adenomatous Polyposis (FAP) harbor mutations in the APC gene on chromosome 5q21. They are at an increased risk of brain tumors, including cerebellar medulloblastoma, when compared with the general population (Brain Tumor Polyposis-BTP Type 2). Genotype-phenotype correlations between APC gene mutations and central nervous system (CNS) tumors have, thus far not been successful. Herein the authors have pooled their registry experience in BTP type 2 with the published reports.

METHODS

The authors analyzed their established hereditary CRC Registry for brain tumors in FAP pedigrees (56 families, 213 individuals), pooled their patients with BTP and known APC mutations with those reported thus far elsewhere, and compared the resulting mutation distribution of FAP-BTP with the mutation distribution for APC mutations in the US.

RESULTS

Twenty-eight patients from 24 families were accrued, the most common brain tumor in BTP was medulloblastoma (60%) predominantly in females (12:5) under the age of 20 (mean age 14.7 SD 9.2). Other histologic subtypes included astrocytoma and ependymoma. Analysis of the pooled APC mutation data by Chi-square test of association shows an odds ratio of 3.7 (P < .005) for all brain tumor subtypes and 13.1 (P < .001) for medulloblastoma in patients harboring segment 2 APC mutation (codons 679-1224) compared to nonsegment 2 mutation.

CONCLUSIONS

In patients with FAP and identifiable APC gene mutation, CNS tumors, especially medulloblastoma which developed in most cases during childhood, are more common in females with FAP and APC gene mutation in codons 686-1217. Further studies are necessary to determine if this observation and the natural history of medulloblastoma in children justifies novel, aggressive, targeted screening of at-risk individuals.

Oligonucleotide DNA chips are useful adjuncts in epigenetic studies of glioblastomas

Several studies have suggested that hypermethylation and hypomethylation of CpG islands within the promoters and 5' exons of tumor-related genes are closely associated with carcinogenesis. However, large-scale analysis of candidate genes has been hampered by the lack of a high throughput approach for analyzing methylation patterns. Using methylation-specific oligonucleotide (MSO) chips, we evaluated the methylation patterns of eight samples of fresh frozen glioblastoma tissue. The MSO chip used contained DNA probes with the CpG sites of p16 (p16INK4A, CDKN2A), MGMT (O6-Methylguanine-DNA-methyltransferase), APC (adenomatous polyposis coil), RASSF1A (human RAS effect homolog), which are usually hypermethylated in cancer cells and MAGE (melanoma antigen), which is usually hypomethylated in cancer cells. We selected CpG sites for analysis; 28 CpG sites (263 bp) for p16, 26 CpG sites (249 bp) for MGMT, 16 CpG sites (195 bp) for APC, 22 CpG sites (262 bp) for RASSF1A and 18 CpG sites (235 bp) for MAGE. We then constructed primer sets not including CpG sites. Bisulfite modification of genomic DNA, methylation specific PCR, hybridization and image scan with data analysis and sequencing of the bisulfite modified DNA were carried out. Of the eight glioblastomas, hypermethylation of the 5'-CpG sites of the MGMT were found in two, RASSF1A were found in five, and p16 and APC genes were not found in any cases and hypomethylation of that of the MAGE was found in eight cases. These results obtained from the oligo DNA chip study were correlated well with the sequencing data of bisulfite modified genomic DNA except in regard to the RASSF1A and MAGE genes. The devised MSO DNA chip is a useful tool for studies on methylation.

Genetic testing for colon cancer

Colon cancer remains the third leading cause of death due to cancer in the US, where it affected more than 145,000 individuals in 2005. Up to 30% of these cases exhibit familial clustering, which means that tens of thousands of individuals have a disease with a potentially definable genetic component. Approximately 3-5% of colon cancers are associated with high-risk, inherited colon cancer syndromes. Identification of the genes that cause these colon cancer syndromes, coupled with additional insights into their clinical course, has led to the development of specific management guidelines--and genetic tests--that can diagnose these familial disorders. These guidelines can be life-saving, not only for the affected patient, but also for their family members.

The genetics of HNPCC: application to diagnosis and screening

Hereditary nonpolyposis colorectal cancer syndrome (HNPCC; Lynch Syndrome) is the most common form of hereditary colorectal cancers. Predisposed individuals have increased lifetime risk of developing colorectal, endometrial and other cancers. The syndrome is primarily due to heterozygous germline mutations in one of the mismatch repair genes; mainly MLH1, MSH2, MSH6 and PMS2. The resulting mismatch repair deficiency leads to microsatellite instability which is the hallmark of tumors arising within this syndrome, as well as a variable proportion of sporadic tumors. Diagnostic guidelines and criteria for molecular testing of suspected families have been proposed and are continuously updated. However, not all families fulfilling these criteria show mutations in mismatch repair genes and/or microsatellite instability implicating other, as yet unknown, carcinogenic mechanisms and predisposition genes. This subset of tumors is the focus of current clinical and molecular research. This review addresses recent advances in the field of HNPCC research and their applications in the management of affected individuals and families.

A homozygous mutation in MSH6 causes Turcot syndrome

Heterozygous mutations in one of the DNA mismatch repair genes cause hereditary nonpolyposis colorectal cancer (MIM114500). Turcot syndrome (MIM276300) has been described as the association of central nervous system malignant tumors and familial colorectal cancer and has been reported to be both a dominant and recessive disorder. Homozygous and compound heterozygous mutations in APC, MLH1, MSH2, and PMS2 genes have been reported in five families. Here we describe a nonconsanguineous Pakistani family, including a son with lymphoma and colorectal cancer diagnosed at ages 5 and 8, respectively, and an 8-year-old daughter with glioblastoma multiforme. Both children had features of neurofibromatosis type 1 including atypical café au lait spots and axillary freckling without a family history consistent with neurofibromatosis type 1, familial adenomatous polyposis, or hereditary nonpolyposis colorectal cancer. Mutational analysis was done for MLH1, MSH2, and MSH6 using denaturing high-performance liquid chromatography and sequencing of a blood sample from the daughter. A novel homozygous single base insertion mutation was identified (3634insT) resulting in a premature stop at codon 1,223 in exon 7 of the MSH6 gene. Both parents were found to be heterozygous for the 3634insT mutation. Microsatellite instability testing showed instability in the glioblastoma sample. We report here the first identification of a homozygous mutation in MSH6 in a family with childhood-onset brain tumor, lymphoma, colorectal cancer, and neurofibromatosis type 1 phenotype. Our findings support a role for MSH6 in Turcot syndrome and are consistent with an autosomal recessive mode of inheritance.

An unusual case of Turcot’s syndrome associated with ileal adenocarcinoma, intestinal non-Hodgkin’s lymphoma, and duodenal adenocarcinoma. Review of the classification and genetic basis of Turcot’s syndrome

A 38-year-old man with a history of colonic and small bowel polyposis and glioblastoma was investigated for dyspepsia. Upper GI endoscopy identified an abnormal area in the duodenum, confirmed by histology as high grade non-Hodgkin's B cell MALT lymphoma. Although cases of Turcot's syndrome (TS) (colonic polyposis and primary brain tumour occurring in the same patient) have been previously described, association with haematological malignancy is rare. This is the first report of intestinal lymphoma occurring in an adult with TS.

Medulloblastoma: molecular genetics and animal models

Medulloblastoma is a primary brain tumor found in the cerebellum of children. The tumor occurs in association with two inherited cancer syndromes: Turcot syndrome and Gorlin syndrome. Insights into the molecular biology of the tumor have come from looking at alterations in the genes altered in these syndromes, PTC and APC, respectively. Murine models of medulloblastoma have been constructed based on these alterations. Additional murine models that, while mimicking the appearance of the human tumor, seem unrelated to the human tumor's molecular alterations have been made. In this review, the clinical picture, origin, molecular biology, and murine models of medulloblastoma are discussed. Although a great deal has been discovered about this tumor, the genetic alterations responsible for tumor development in a majority of patients have yet to be described.

Recent advances in embryonal tumours of the central nervous system

INTRODUCTION

Embryonal tumours of the central nervous system (CNS) are the commonest malignant paediatric brain tumours. This group includes medulloblastomas, supratentorial primitive neuroectodermal tumours, atypical teratoid/rhabdoid tumours, ependymoblastomas, and medulloepitheliomas. Earlier, all these tumours were grouped under a broad category of primitive neuroectodermal tumours (PNETs). However, the current WHO classification (2000) separates them into individual types based on significant progress in the understanding of their distinctive clinical, pathological, molecular genetic, histogenetic, and behavioural characteristics. Furthermore, advances in histopathology and molecular genetics have shown great promise for refining risk assessment in these tumours, especially medulloblastomas, thus providing a more accurate basis for tailoring therapies to individual patients. Correlation of histological changes with genetic events has also led to a new model of medulloblastoma tumorigenesis.

REVIEW

This review presents an updated comparative profile of these tumours, highlighting the clinical and biological relevance of the recent advances.

Molecular pathogenesis of childhood brain tumors

In the last decade, the molecular biology revolution has advanced considerably. These advances have enhanced our understanding of the genetic underpinnings of human brain tumors in general, and pediatric brain tumors in particular. We now know that many pediatric brain tumors arise from disturbances in developmentally regulated signaling pathways. The medulloblastoma, a tumor in which the developmental Hedgehog and WNT pathways have gone awry, is a prime example of this. New techniques in genetic engineering have allowed for the creation of sophisticated mouse models of brain tumors that recapitulate the human disease. Many laboratories are now using cDNA microarrays to study the expression level of thousands of genes that may be aberrantly expressed in brain tumors when compared to normal control cells. In the next decade, the use of several new molecular techniques to establish brain tumor diagnoses will likely become standard tools in the diagnostics and treatment stratification of children with central nervous system tumors.

Failure of a medulloblastoma-derived mutant of SUFU to suppress WNT signaling

Germline mutations of APC in patients with Turcot syndrome (colon cancer and medulloblastoma), was well as somatic mutations of APC, beta-catenin, and Axin in sporadic medulloblastomas (MBs) have shown the importance of WNT signaling in the pathogenesis of MB. A subset of children with MB have germline mutations of SUFU, a known inhibitor of Hedgehog signal transduction. A recent report suggested that murine Sufu can bind beta-catenin, export it from the nucleus, and thereby repress beta-catenin/T-cell factor (Tcf)-mediated transcription. We show that an MB-derived mutant of SUFU has lost the ability to decrease nuclear levels of beta-catenin, and cannot inhibit beta-catenin/Tcf-mediated transcription as compared to wild type SUFU. Our results suggest that loss of function of SUFU results in overactivity of both the Sonic Hedgehog, and the WNT signaling pathways, leading to excessive proliferation and failure to differentiate resulting in MB.

Molecular basis and diagnostics of hereditary colorectal cancers

Hereditary colorectal cancer syndromes are classified according to the presence of unusually large number of adenomatous or hamartomatous polyps, or their absence. The latter category includes hereditary non-polyposis colorectal cancer (Lynch syndrome) and its variants Muir-Torre and Turcot's syndromes. Adenomatous polyposis syndromes include familial adenomatous polyposis (FAP) and its variants, and the recently identified MYH- (mutY homolog)-associated polyposis. Hamartomatous polyposis syndromes include juvenile polyposis, Peutz-Jeghers syndrome, and Cowden syndrome, which is now included within the broader category 'PTEN (phosphatase and tensin homolog) hamartoma tumour syndrome'. Other syndromes such as the 'hereditary breast and colon cancer' and 'familial colorectal cancer' are not yet fully characterized. This review addresses the molecular basis of these syndromes with particular reference to the recent advances in this rapidly progressive field and the applications of such knowledge in diagnosis and management.

The Wnt signaling pathway in solid childhood tumors

The Wnt signaling pathway has long been known to direct growth and patterning during embryonic development. Recent evidence also implicates this pathway in the development of childhood tumors of the liver, the kidney, the brain, and the pancreas. Here, we review the current evidence on how constitutive activation of the Wnt signaling pathway may occur in hepato-, nephro-, medullo- and pancreatoblastomas. With particular emphasis the mutational activation of CTNNB1, an emerging major oncogene in solid childhood tumors, is discussed.

Genetic testing for high-risk colon cancer patients

Colorectal cancer is the third leading cause of cancer-related deaths in both men and women in the United States and is estimated to have affected 148,000 people in 2002. The cumulative lifetime risk for colon cancer is approximately 5%-6%, and this risk is influenced by hereditary and lifestyle factors. In fact, 20%-30% of all colon cancer cases have a potentially definable inherited cause, and 3%-5% of colon cancers occur in genetically defined high-risk colon cancer family syndromes. Although the genes responsible for the cases of moderate-risk colon cancer remain to be characterized, many of the genes responsible for the high-risk colon cancer cases have already been determined. These genetic discoveries have been translated into clinical practice and have led to improved risk assessment through the use of genetic testing. The introduction into clinical practice of genetic testing for the assessment of colon cancer risk has led to more effective management strategies for patients with potentially high-risk colon cancer and has presented new challenges to the clinician because of the unique issues involved with genetic testing. In this review, an overview of the colon cancer high-risk syndromes, with a focus on the availability and indications for genetic testing, is presented.

Classifying the medulloblastoma: insights from morphology and molecular genetics

Significant advances in the treatment of the medulloblastoma (MB) have been made in the last 30 years, reducing mortality by 2-fold. Further improvements in the cure rate require an increased understanding of the biology of MBs, and this will translate into refinements in their classification. Scrutiny of the cytological variation found among MBs has recently led to the concept of the anaplastic MB, which overlaps the large-cell variant and appears to share its poor prognosis. In contrast, the MB with extensive nodularity, a distinctive nodular/desmoplastic variant occurring in infants, has a better outcome than most MBs in these young patients. Building on cytogenetic studies that have drawn attention to abnormalities on chromosome 17 in over a third of MBs, research shows non-random losses on chromosomes 8, 9, 10, 11 and 16, and gains on chromosomes 1, 7 and 9. Overexpression of ErbB2 receptors and losses on chromosome 17p have been proposed as independent indicators of aggressive behaviour, while high TrkC receptor expression indicates a favourable outcome. There is a strong association between anaplastic/large-cell tumours and MYC amplification, which has previously been linked with aggressive disease, but associations between abnormalities on chromosome 17 and anaplastic/large-cell MBs and between abnormalities in the shh/PTCH pathway and the desmoplastic variant are more controversial. Classification of the MB histopathologically and according to profiles of molecular abnormalities will help both to rationalize approaches to therapy, increasing the cure rate and reducing long-term side-effects, and to suggest novel treatments.

Paediatric embryonic brain tumours. biological and clinical relevance of molecular genetic abnormalities

Embryonal tumours constitute the largest group of malignant paediatric brain tumours. Their origin and histological classification remain somewhat controversial. However, in recent years real progress has been made in our understanding of the molecular genetic abnormalities that govern the initiation and/or progression of these tumours. A number of these abnormalities appear to involve alterations in signalling systems that control normal cerebellar development. Increasing our understanding of both the biology and clinical relevance of these molecular defects is a major challenge to the field of paediatric neuro-oncology. However, it likely represents the only means by which we will advance the management of these tumours, significantly reducing disease-related morbidity and mortality. This review focuses on the principal molecular genetic abnormalities so far identified in embryonal brain tumours and discusses their biological and clinical relevance.

Familial neurogenic tumor syndromes

Cancer caused more than 0.5 million deaths in the United States in 2000. This estimate includes patients who have a genetic predisposition to neoplastic disease, including brain neoplasms. Familial tumor syndromes are important to identify clinically because family members require high degrees of monitoring and genetic counseling. Study of these individuals and families has led to the discovery of genes that are an intrinsic aspect of cell regulation and will continue to be relevant in defining mechanisms of neoplastic development in brain and other tissues.

Somatic mutations of WNT/wingless signaling pathway components in primitive neuroectodermal tumors

Primitive neuroectodermal tumors (PNETs) represent the most frequent malignant brain tumors in childhood. The majority of these neoplasms occur in the cerebellum and are classified as medulloblastomas (MB). Most PNETs develop sporadically; however, their incidence is highly elevated in patients carrying germline APC gene mutations. The APC gene encodes a central component of the WNT/wingless developmental signaling pathway. It regulates the levels of cytoplasmic beta-catenin protein that plays a central role in neural development and cell proliferation. We analyzed 87 sporadic PNETs and 10 PNET cell lines for mutations of the APC gene and beta-catenin (CTNNB1) gene using single strand conformational polymorphism (SSCP) and sequencing analysis. We examined the mutation cluster region of APC (codons 1255--1641) for germline variants and somatic mutations. The medulloblastoma cell line MHH-MED-2 carried a Glu1317Gln missense germline variant and a sporadic MB sample showed a somatic Pro1319Leu substitution. Mutational analysis of exon 3 of CTNNB1 uncovered 4 PNETs (4.8%) with somatic missense mutations. These mutations caused amino acid substitutions in 3 of 80 medulloblastomas (Ser33Phe, Ser33Cys and Ser37Cys) and 1 of 4 supratentorial PNETs (Gly34Val). All mutations affected GSK-3 beta phosphorylation sites of the degradation targeting box of beta-catenin and resulted in nuclear beta-catenin protein accumulation. Deletions of CTNNB1 were not detected by PCR amplification with primers spanning exons 1--5. Our data indicate that inappropriate activation of the WNT/wingless signaling pathway by mutations of its components may contribute to the pathogenesis of a subset of PNETs.

A mouse model for medulloblastoma and basal cell nevus syndrome

Medulloblastoma (MB), a tumor of the cerebellum, is the most frequent type of malignant childhood brain tumor. Multiple genes are causally involved in medulloblastoma including PATCHED1 (PTCH). The Patchedl (Ptc1) protein is a receptor for Sonic hedgehog (Shh), a secreted protein ligand. Shh is involved in many signaling processes that control cell fate and growth, among which is its emission from Purkinje cells in the developing cerebellum. Purkinje cell-derived Shh stimulates mitosis of the granule cell precursors that may be the cell type of origin in medulloblastoma. Ptc1 limits the effects of the Shh signal, so mutations in PTCH may lead to persistent granule cell precursors susceptible to further genetic or environmental events that cause medulloblastoma. Mice heterozygous for patched (ptc1) mutations, like heterozygous PTCH humans, have a high rate of medulloblastoma as well as other tumors. We discuss features of the mouse model and how it is contributing to understanding the process of brain tumorigenesis.

Oral trofosfamide and etoposide in pediatric patients with glioblastoma multiforme

BACKGROUND

Glioblastoma multiforme in childhood is rare, and the prognosis for patients with the disease is poor. The Pediatric Oncology Society of the Germanic language group (GPOH) enrolls patients in a series of pilot trials, the first of which is reported here (HIT-GBM-A).

METHODS

Twenty-two patients with glioblastoma multiforme, World Health Organization Grade 4, between the ages of 3-15 years (45% male) were enrolled during the period 1995-1997. There were 13 supratentorial tumors, 8 brainstem tumors, and 1 cerebellar tumor. The patients underwent the following procedures: stereotactic biopsy (n = 3 patients), open biopsy (n = 1 patient), partial resection (n = 6 patients), subtotal resection (n = 4 patients), and macroscopic total resection (n = 8 patients). Adjuvant treatment consisted of oral chemotherapy with trofosfamide, 100 mg/m(2), and etoposide, 25 mg/m(2), daily or for 21-day cycles interrupted by 1-week rests. Standard fractionated radiation (54 grays) was started concurrently with the first cycle.

RESULTS

The chemotherapy was well tolerated, with no treatment-related deaths and only minor side effects. The responses in 12 evaluable patients after two cycles were as follows: 1 complete response, 1 partial response, 3 patients with stable disease, and 7 patients with progressive disease. The median overall survival was 12 months. The 1-year, 2-year, and 4-year overall survival rates were 52%, 26%, and 22%, respectively, and the event free survival rates were 26%, 22%, and 4%, respectively. None of the four surviving patients (3.2 years, 3.4 years, 4.0 years, and 4.2 years after diagnosis) is event free. Two patients are alive after tumor progression: One patient was diagnosed with a medulloblastoma, and one patient was diagnosed with an osteosarcoma as second malignancies. A control group extracted from the Surveillance, Epidemiology, and End Results data had lower survival rates: the difference between the groups was not statistically significant (P = 0.26).

CONCLUSIONS

This chemotherapy will not be used in a randomized trial of patients with glioblastoma; however, it may be evaluated for patients with tumors that have more chemoresponsive histologies.

Molecular insight into medulloblastoma and central nervous system primitive neuroectodermal tumor biology from hereditary syndromes: a review

Through the study of uncommon familial syndromes, physicians and scientists have been able to illuminate the underlying mechanisms of some of the more common sporadic diseases; this is illustrated best by studies of familial retinoblastoma. A number of rare familial syndromes have been described in which affected individuals are at increased risk of developing medulloblastoma and/or supratentorial primitive neuroectodermal tumors. The descriptions of many of these syndromes are based on patients observed by clinicians in their clinical practice. Determination of the underlying genetic defects in these patients with uncommon syndromes has led to identification of a number of genes subsequently found to be mutated in sporadic medulloblastomas (tumor suppressor genes). Associated genes in the same signaling pathways have also been found to be abnormal in sporadic medulloblastoma. Identification of patients with these rare syndromes is important, as they are often at increased risk for additional neoplasms, as are family members and future children. We review the published literature describing hereditary syndromes that have been associated with an increased incidence of medulloblastoma and/or central nervous system primitive neuroectodermal tumor. Review of the underlying molecular abnormalities in comparison to changes found in sporadic neoplasms suggests pathways important for tumorigenesis.

Nuclear localization and mutation of beta-catenin in medulloblastomas

The adenomatous polyposis coli (APC) gene, a member of the Wingless/Wnt signal transduction pathway, has been implicated in the development of medulloblastomas in Turcot's syndrome. beta-catenin also functions in this highly conserved signaling pathway and is instrumental in growth and development. Mutations in either APC or beta-catenin can stabilize beta-catenin protein. Stabilized beta-catenin complexes with Tcf/Lef transcription factors and moves from the cytoplasm into the nucleus where it regulates the transcription of c-Myc and other genes. Nuclear localization of beta-catenin therefore implies activation of the signaling pathway. We have analyzed the subcellular localization of beta-catenin in 51 sporadic medulloblastomas and in 1 medulloblastoma arising in a patient with Turcot's syndrome. Nuclear beta-catenin staining was present in 9 of the sporadic tumors (18%) and in the 1 medulloblastoma from a Turcot's patient. The remaining 41 cases did not show nuclear staining. This confirms earlier observations that Wingless/Wnt signaling is involved in a subset of sporadic medulloblastomas. We also examined 48 glial and meningeal CNS tumors, all of which were negative for nuclear beta-catenin. Exon 3 of beta-catenin was sequenced in 6 of the 9 sporadic medulloblastomas with nuclear beta-catenin staining. Five of the 6 tumors sequenced had mutations affecting highly conserved beta-catenin phosphorylation sites involved in protein stability. These data suggest a simple immunohistochemical method to screen for beta-catenin mutations in medulloblastomas.

Evidence for a recessive inheritance of Turcot's syndrome caused by compound heterozygous mutations within the PMS2 gene

Turcot's syndrome is a genetic disease characterized by the concurrence of primary brain tumors and colon cancers and/or multiple colorectal adenomas. We report a Turcot family with no parental consanguinity, in which two affected sisters, with no history of tumors in their parents, died of a brain tumor and of a colorectal tumor, respectively, at a very early age. The proband had a severe microsatellite instability (MIN) phenotype in both tumor and normal colon mucosa, and mutations in the TGFbeta-RII and APC genes in the colorectal tumor. We identified two germline mutations within the PMS2 gene: a G deletion (1221delG) in exon 11 and a four-base-pair deletion (2361delCTTC) in exon 14, both of which were inherited from the patient's unaffected parents. These results represent the first evidence that two germline frameshift mutations in PMS2, an MMR gene which is only rarely involved in HNPCC, are not pathogenic per se, but become so when occurring together in a compound heterozygote. The compound heterozygosity for two mutations in the PMS2 gene has implications for the role of protein PMS2 in the mismatch repair mechanism, as well as for the presymptomatic molecular diagnosis of at-risk family members. Furthermore, our data support and enlarge the notion that high DNA instability in normal tissues might trigger the development of cancer in this syndrome.

APC mutations in sporadic medulloblastomas

The cerebellar medulloblastoma (WHO Grade IV) is a highly malignant, invasive embryonal tumor with preferential manifestation in children. Several molecular alterations appear to be involved, including isochromosome 17q and the p53, PTCH, and beta-catenin gene mutations. In this study, 46 sporadic medulloblastomas were screened for the presence of mutations in genes of the Wnt signaling pathway (APC and beta-catenin). Single-strand conformational polymorphism (SSCP) analysis followed by direct DNA sequencing revealed 3 miscoding APC mutations in 2 (4.3%) medulloblastomas. One case contained a GCA-->GTA mutation at codon 1296 (Ala-->Val), and another case had double point mutations at codons 1472 (GTA-->ATA, Val-->Ile) and 1495 (AGT-->GGT, Ser-->Gly). Miscoding beta-catenin mutations were detected in 4 tumors (8.7%). Three of these were located at codon 33 (TCT -->TTT, Ser-->Phe) and another at codon 37 (TCT-->GCT, Ser-->Ala). Adenomatous polyposis coli (APC) gene and beta-catenin mutations were mutually exclusive and occurred in a total of 6 of 46 cases (13%). Although germline APC mutations are a well established cause of familial colon and brain tumors (Turcot syndrome), this study provides the first evidence that APC mutations are also operative in a subset of sporadic medulloblastomas.

Ganglioglioma in a patient with Turcot syndrome. Case report

A 33-year-old woman with Turcot syndrome harbored a brain tumor and colon cancer and had a familial history of this syndrome. On histological examination, the brain tumor was found to have large and diffusely scattered ganglion cells within a diffuse background of astrocytic cells in a fibrillary matrix. The tumor was diagnosed as a ganglioglioma. No germline mutation in the adenomatous polyposis coli gene was detected using a protein truncation assay. These findings indicate that this patient had brain tumor-polyposis syndrome Type 1 of Turcot syndrome. This is the first report of a ganglioglioma related to Turcot syndrome.

Germline mutations of p53 but not p16/CDKN2 or PTEN/MMAC1 tumor suppressor genes predispose to gliomas. The ANOCEF Group. Association des NeuroOncologues d'Expression Française

Constitutional DNA from 44 selected patients suspected of being genetically predisposed to develop astrocytic tumors was analyzed for germline mutations of the p53, p16, and PTEN genes. Six constitutional missense mutations of the p53 gene were identified (13.6%), but no mutations of the p16 and PTEN genes were found, suggesting that (1) germline p53 mutations contribute to a small portion of astrocytic tumors, (2) inherited mutations of the p16 and PTEN gene do not predispose to the development of gliomas, and (3) other genes are involved in glioma predisposition.

Turcot syndrome with colonic obstruction and small intestinal invagination: report of a case

We report herein the case of a 16-year-old boy diagnosed as having Turcot syndrome, otherwise known as glioma-polyposis syndrome. The patient was transferred from the Department of Neurosurgery where he was undergoing investigation of a brain tumor, to the Department of Medicine for investigation of gastrointestinal symptoms. The patient was diagnosed as having Turcot syndrome, and was then transferred to the Department of Surgery for treatment of an obstruction in the sigmoid colon and small intestinal invagination. A subtotal colectomy with side-to-end ileoproctostomy and release of the invaginations was carried out. Multiple polyps were found in the colon, two of which, including a large polyp that obstructed the colonic lumen, were confirmed histologically to be adenocarcinoma. The remaining polyps were adenomas. A biopsy of the brain tumor confirmed a diagnosis of astrocytoma (WHO grade II). This case report describes the characteristic features of Turcot syndrome presented by this patient.

Analysis of APCL, a brain-specific adenomatous polyposis coli homologue, for mutations and expression in brain tumors

We recently identified a novel homologue of the adenomatous polyposis coli (APC) tumor suppressor gene, APCL, whose abundant and specific expression in the central nervous system indicated an important role in neuronal proliferation and differentiation. To investigate possible involvement of APCL alterations in brain tumors, we first analyzed the expression of APCL mRNA in seven glioma tissues by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis, and in nine glioma cell lines by northern blotting. APCL expression was reduced significantly in most of the glioma tissues and all nine cell lines in comparison with normal brain tissue. However, single-strand conformation polymorphism (SSCP) analysis and DNA sequencing of the entire coding region of APCL detected no mutations in any of the glioma cell lines, or in any of the 35 astrocytic gliomas and five medulloblastomas examined. Our results suggested that some epigenetic mechanism is responsible for the decrease in APCL expression in our panel of brain tumors.

Molecular heterogeneity in medulloblastoma with implications for differing tumor biology

Medulloblastomas and related primitive neuroectodermal tumors are the second most common malignant tumors of childhood. In spite of improvements in cancer therapy, these tumors are still associated with significant morbidity and mortality. Although these tumors share similar histologic features, recent molecular studies suggest that they could represent a genetically mixed group of tumors. The genetic events that might play a role in the biology of these tumors also could allow a molecular subtyping of medulloblastomas. Such molecular subtyping of medulloblastomas could allow for the use of newer therapeutic techniques, such as gene therapy, for selective targeting of critical genetic events in subsets of medulloblastomas. It is becoming increasingly clear that in medulloblastomas, the morphologic similarity of "small blue" cells does not imply similar or shared molecular characteristics, with implications for differing tumor biology.

The hPMS2 exon 5 mutation and malignant glioma. Case report

Patients with Turcot syndrome (TS) are predisposed to colon tumors and primary brain tumors, typically glioblastomas or medulloblastomas. The authors describe a patient with TS featuring a known germline mutation of exon 5 of the hPMS2 mismatch repair gene who developed two metachronous glioblastomas, both with distinct oligodendroglial features. Molecular genetic analysis revealed allelic loss of chromosome 19q in the patient's second tumor but no allelic loss of chromosome 1p. Prominent microsatellite instability was also found in this tumor, consistent with a germline mismatch repair defect. Because this patient had an unusual underlying condition and his tumor had a unique histological appearance for TS, it was hypothesized that this genetic defect may predispose to malignant gliomas with oligodendroglial features. The authors therefore evaluated whether sporadic glioblastomas and oligodendrogliomas undergo mutations of this region of the hPMS2 gene. However, single-strand conformation polymorphism analysis of hPMS2 exon 5 failed to reveal mutations in 20 sporadic glioblastomas and 16 sporadic oligodendroglial gliomas. Thus, although it is possible that the germline hPMS2 exon 5 mutation may predispose to glioblastomas with an oligodendroglial component, the same genetic defect is not commonly involved in sporadic oligodendrogliomas or glioblastomas.