Chromosome arm 17p deletion analysis reveals molecular genetic heterogeneity in supratentorial and infratentorial primitive neuroectodermal tumors of the central nervous system

Exploring the role and clinical implications of proteasome inhibition in medulloblastoma

Ubiquitin proteasome-mediated protein degradation has been implicated in posttranslational oncogenesis in medulloblastoma. Current research is evaluating the clinical implications of proteasome inhibition as a therapeutic target. In medulloblastoma cell lines, proteasome inhibitors induce apoptosis and inhibit cell proliferation via multiple pathways involving activation of caspase pathways, NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells) pathway inhibition, reduced AKT/mTOR pathway activity, and pro-apoptotic protein expression. Second-generation proteasome inhibitors demonstrate blood-brain barrier penetration while maintaining antitumor effect. This review summarizes the ubiquitin-proteasome system in the pathogenesis of medulloblastoma and the potential clinical implications.

The ubiquitin-proteasome system and chromosome 17 in cerebellar granule cells and medulloblastoma subgroups

Chromosome 17 abnormalities are often observed in medulloblastomas (MBs), particularly those classified in the consensus Groups 3 and 4. Herein we review MB signature genes associated with chromosome 17 and the relationship of these signature genes to the ubiquitin-proteasome system. While clinical investigators have not focused on the ubiquitin-proteasome system in relation to MB, a substantial amount of data on the topic has been hidden in the form of supplemental datasets of gene expression. A supplemental dataset associated with the Thompson classification of MBs shows that a subgroup of MB with 17p deletions is characterized by reduced expression of genes for several core particle subunits of the beta ring of the proteasome (β1, β4, β5, β7). One of these genes (PSMB6, the gene for the β1 subunit) is located on chromosome 17, near the telomeric end of 17p. By comparison, in the WNT group of MBs only one core proteasome subunit, β6, associated with loss of a gene (PSMB1) on chromosome 6, was down-regulated in this dataset. The MB subgroups with the worst prognosis have a significant association with chromosome 17 abnormalities and irregularities of APC/C cyclosome genes. We conclude that the expression of proteasome subunit genes and genes for ubiquitin ligases can contribute to prognostic classification of MBs. The therapeutic value of targeting proteasome subunits and ubiquitin ligases in the various subgroups of MB remains to be determined separately for each classification of MB.

WIP1 modulates responsiveness to Sonic Hedgehog signaling in neuronal precursor cells and medulloblastoma

High-level amplification of the protein phosphatase PPM1D (WIP1) is present in a subset of medulloblastomas (MBs) that have an expression profile consistent with active Sonic Hedgehog (SHH) signaling. We found that WIP1 overexpression increased expression of Shh target genes and cell proliferation in response to Shh stimulation in NIH3T3 and cerebellar granule neuron precursor cells in a p53-independent manner. Thus, we developed a mouse in which WIP1 is expressed in the developing brain under control of the Neurod2 promoter (ND2:WIP1). The external granule layer (EGL) in early postnatal ND2:WIP1 mice exhibited increased proliferation and expression of Shh downstream targets. MB incidence increased and survival decreased when ND2:WIP1 mice were crossed with an Shh-activated MB mouse model. Conversely, Wip1 knockout significantly suppressed MB formation in two independent mouse models of Shh-activated MB. Furthermore, Wip1 knockdown or treatment with a WIP1 inhibitor suppressed the effects of Shh stimulation and potentiated the growth inhibitory effects of SHH pathway-inhibiting drugs in Shh-activated MB cells in vitro. This suggests an important cross-talk between SHH and WIP1 pathways that accelerates tumorigenesis and supports WIP1 inhibition as a potential treatment strategy for MB.

Treatment Outcome and Prognostic Molecular Markers of Supratentorial Primitive Neuroectodermal Tumors

Background

To identify prognostic factors and define the optimal management of patients with supratentorial primitive neuroectodermal tumors (sPNETs), we investigated treatment outcomes and explored the prognostic value of specific molecular markers.

Methods

A total of 47 consecutive patients with pathologically confirmed sPNETs between May 1985 and June 2012 were included. Immunohistochemical analysis of LIN28, OLIG2, and Rad51 expression was performed and correlated with clinical outcome.

Results

With a median follow-up of 70 months, 5-year overall survival (OS) and progression-free survival (PFS) was 55.5% and 40%, respectively, for all patients. Age, surgical extent, and radiotherapy were significant prognostic factors for OS and PFS. Patients who received initially planned multimodal treatment without interruption (i.e., radiotherapy and surgery (≥subtotal resection), with or without chemotherapy) showed significantly higher 5-year OS (71.2%) and PFS (63.1%). In 29 patients with available tumor specimens, tumors with high expression of either LIN28 or OLIG2 or elevated level of Rad51 were significantly associated with poorer prognosis.

Conclusions

We found that multimodal treatment improved outcomes for sPNET patients, especially when radiotherapy and ≥subtotal resection were part of the treatment regimen. Furthermore, we confirmed the prognostic significance of LIN28 and OLIG2 and revealed the potential role of Rad51 in sPNETs.

Cytogenetic landscape of paired neurospheres and traditional monolayer cultures in pediatric malignant brain tumors

BACKGROUND

New therapeutic targets are needed to eliminate cancer stem cells (CSCs). We hypothesize that direct comparison of paired CSCs and nonstem tumor cells (NSTCs) will facilitate identification of primary "driver" chromosomal aberrations that can serve as diagnostic markers and/or therapeutic targets.

METHODS

We applied spectral karyotyping and G-banding to matched pairs of neurospheres (CSC-enriched cultures) and fetal bovine serum-based monolayer cultures (enriched with NSTCs) from 16 patient-derived orthotopic xenograft mouse models, including 9 medulloblastomas (MBs) and 7 high-grade gliomas (HGGs), followed by direct comparison of their numerical and structural abnormalities.

RESULTS

Chromosomal aberrations were detected in neurospheres of all 16 models, and 82.0% numerical and 82.4% structural abnormalities were maintained in their matching monolayer cultures. Among the shared abnormalities, recurrent clonal changes were identified including gain of chromosomes 18 and 7 and loss of chromosome 10/10q (5/16 models), isochromosome 17q in 2 MBs, and a new breakpoint of 13q14 in 3 HGGs. Chromothripsis-like evidence was also observed in 3 HGG pairs. Additionally, we noted 20 numerical and 15 structural aberrations that were lost from the neurospheres and found 26 numerical and 23 structural aberrations that were only present in the NSTCs. Compared with MBs, the neurosphere karyotypes of HGG were more complex, with fewer chromosomal aberrations preserved in their matching NSTCs.

CONCLUSION

Self-renewing CSCs in MBs and pediatric HGGs harbor recurrent numerical and structural aberrations that were maintained in the matching monolayer cultures. These primary chromosomal changes may represent new markers for anti-CSC therapies.

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.

HDM2 promotes WIP1-mediated medulloblastoma growth

Medulloblastoma is the most common malignant childhood brain tumor. The protein phosphatase and oncogene WIP1 is over-expressed or amplified in a significant number of primary human medulloblastomas and cell lines. In the present study, we examine an important mechanism by which WIP1 promotes medulloblastoma growth using in vitro and in vivo models. Human cell lines and intracerebellar xenografted animal models were used to study the role of WIP1 and the major TP53 regulator, HDM2, in medulloblastoma growth. Stable expression of WIP1 enhances growth of TP53 wild-type medulloblastoma cells, compared with cells with stable expression of an empty-vector or mutant WIP1. In an animal model, WIP1 enhances proliferation and reduces the survival of immunodeficient mice bearing intracerebellar xenografted human medulloblastoma cells. Cells with increased WIP1 expression also exhibit increased expression of HDM2. HDM2 knockdown or treatment with the HDM2 inhibitor Nutlin-3a, the active enantomer of Nutlin-3, specifically inhibits the growth of medulloblastoma cells with increased WIP1 expression. Nutlin-3a does not affect growth of medulloblastoma cells with stable expression of an empty vector or of mutant WIP1. Knockdown of WIP1 or treatment with the WIP1 inhibitor CCT007093 results in increased phosphorylation of known WIP1 targets, reduced HDM2 expression, and reduced growth specifically in WIP1 wild-type and high-expressing medulloblastoma cells. Combined WIP1 and HDM2 inhibition is more effective than WIP1 inhibition alone in blocking growth of WIP1 high-expressing medulloblastoma cells. Our preclinical study supports a role for therapies that target WIP1 and HDM2 in the treatment of medulloblastoma.

Genome-wide molecular characterization of central nervous system primitive neuroectodermal tumor and pineoblastoma

Central nervous system primitive neuroectodermal tumor (CNS PNET) and pineoblastoma are highly malignant embryonal brain tumors with poor prognoses. Current therapies are based on the treatment of pediatric medulloblastoma, even though these tumors are distinct at both the anatomical and molecular level. CNS PNET and pineoblastoma have a worse clinical outcome than medulloblastoma; thus, improved therapies based on an understanding of the underlying biology of CNS PNET and pineoblastoma are needed. To this end, we characterized the genomic alterations of 36 pediatric CNS PNETs and 8 pineoblastomas using Affymetrix single nucleotide polymorphism arrays. Overall, the majority of CNS PNETs contained a greater degree of genomic imbalance than pineoblastomas, with gain of 19p (8 [27.6%] of 29), 2p (7 [24.1%] of 29), and 1q (6 [20.7%] of 29) common events in primary CNS PNETs. Novel gene copy number alterations were identified and corroborated by Genomic Identification of Significant Targets In Cancer (GISTIC) analysis: gain of PCDHGA3, 5q31.3 in 62.1% of primary CNS PNETs and all primary pineoblastomas and FAM129A, 1q25 in 55.2% of primary CNS PNETs and 50% of primary pineoblastomas. Comparison of our GISTIC data with publically available data for medulloblastoma confirmed these CNS PNET-specific copy number alterations. With use of the collection of 5 primary and recurrent CNS PNET pairs, we found that gain of 2p21 was maintained at relapse in 80% of cases. Novel gene copy number losses included OR4C12, 11p11.12 in 48.2% of primary CNS PNETs and 50% of primary pineoblastomas. Loss of CDKN2A/B (9p21.3) was identified in 14% of primary CNS PNETs and was significantly associated with older age among children (P = .05). CADPS, 3p14.2 was lost in 27.6% of primary CNS PNETs and was associated with poor prognosis (P = .043). This genome-wide analysis revealed the marked molecular heterogeneity of CNS PNETs and enabled the identification of novel genes and clinical associations potentially involved in the pathogenesis of these tumors.

Molecular diagnostics of CNS embryonal tumors

Tremendous progress has recently been made in both molecular subgrouping, and the establishment of prognostic biomarkers for embryonal brain tumors, particularly medulloblastoma. Several prognostic biomarkers that were initially identified in retrospective cohorts of medulloblastoma, including MYC and MYCN amplification, nuclear β-catenin accumulation, and chromosome 17 aberrations have now been validated in clinical trials. Moreover, molecular subgroups based on distinct transcriptome profiles have been consistently reported from various groups on different platforms demonstrating that the concept of distinct medulloblastoma subgroups is very robust. Well-described subgroups of medulloblastomas include tumors showing wingless signaling pathway (Wnt) activation, and another characterized by sonic hedgehog pathway activity. Two or more additional subgroups were consistently reported to contain the vast majority of high-risk tumors, including most tumors with metastatic disease at diagnosis and/or large cell/anaplastic histology. Several years ago, atypical teratoid rhabdoid tumor (AT/RT) was recognized as a separate entity based on its distinct biology and particularly aggressive clinical behavior. These tumors may occur supra or infratentorially and are usually found to have genetic alterations of SMARCB1 (INI1/hSNF5), a tumor suppressor gene located on chromosome 22q. Subsequent loss of SMARCB1 protein expression comprises a relatively specific and sensitive diagnostic marker for AT/RT. For CNS primitive neuroectodermal tumors (CNS PNETs), a consistent finding has been that they are molecularly distinct from medulloblastoma. Furthermore, a distinct fraction of CNS PNETs with particularly poor prognosis only occurring in young children was delineated, which was previously labeled ependymoblastoma or embryonal tumor with abundant neuropil and true rosettes (ETANTR) and which is morphologically characterized by the presence of multilayered "ependymoblastic" rosettes. This group of tumors shows a unique cytogenetic abnormality not seen in other brain tumors: focal amplification of a micro-RNA cluster at chromosome 19q13.42, which has never been found to be amplified in other CNS PNETs, medulloblastoma or AT/RT. In summary, these consistent findings have significantly contributed to our ability to sub-classify embryonal brain tumors into clinically and biologically meaningful strata and, for some of the subgroups, have led to the identification of specific targets for future development of molecularly targeted therapies.

Detection of genetic and chromosomal aberrations in medulloblastomas and primitive neuroectodermal tumors with DNA microarrays

Medulloblastoma (MB) is the most frequent infratentorial malignant brain tumor in children. In contrast, primitive neuroectodermal tumor (PNET) is defined as a supratentorial malignant tumor generated from the cerebral hemisphere. These tumors have considerable histological overlap but have different clinical outcomes including overall survival period, recurrence rate, and chemosensitivity. We investigated the amplification and/or deletion of genes and the chromosomal gain and/or loss in 10 MBs and 3 PNETs with a genomic DNA microarray system. Genes that are frequently amplified in these both these tumors include MSH2, N-myc, AKT3, and EGFR. Amplifications of SNRPN, MYB, and PTEN are observed only in MB. The genes associated with Wnt/APC and Shh/PTCH pathways also have some aberrations. Common chromosomal aberrations include gains at 17q and 7q and losses at 17p. Minor chromosomal losses were also detected at 1p, 8p + q, 11p, 10p + q, 13q, 16q, and Xp + q in MB. SPNETs tend to contain fewer chromosomal and genetic abnormalities than MBs. In conclusion, there are gene expression and chromosomal differences between MBs and SPNETs. These differences may correlate with the prognosis.

Mouse models of CNS embryonal tumors

Central nervous system (CNS) embryonal tumors are devastating cancers in children, consisting of medulloblastomas, CNS primitive neuroectodermal tumors, and atypical teratoid/rhabdoid tumors. One of the reasons that CNS embryonal tumors remain difficult to treat is their rarity, which makes conducting clinical trials for these tumors difficult. Recent advances of molecular biology have led us to identify molecular and genetic causality of brain tumors. Based on the genetic alterations found in humans, multiple models of human CNS embryonal tumors have been generated in genetically engineered mice. These mouse models are valuable tools for understanding brain tumor biology and discovering novel therapeutic targets and drugs. In this article, we review molecular and cytogenetic characteristics of human CNS embryonal tumors and corresponding mouse models that have been developed. These findings indicate that common genetic abnormalities are seen in variants of human CNS embryonal tumors, and multiple histological variants of these tumors can be generated from a single set of genetic abnormalities in mice. These data provide insight into the biology and classification of CNS embryonal tumors.

Amplification and overexpression of KIT, PDGFRA, and VEGFR2 in medulloblastomas and primitive neuroectodermal tumors

Medulloblastomas (MB) and primitive neuroectodermal tumors (PNET) are the most common malignant brain tumors in children. These two tumor types are histologically similar, but have different genetic backgrounds and clinical outcomes. Other brain tumors, such as gliomas, frequently have coamplification and overexpression of receptor tyrosine kinases KIT, platelet-derived growth factor receptor alpha (PDGFRA), and vascular endothelial growth factor receptor 2 (VEGFR2). We investigated protein expression and gene copy numbers of KIT, PDGFRA, and VEGFR2 in 41 MB and 11 PNET samples by immunohistochemistry (IHC) and chromogenic in situ hybridization (CISH). KIT and PDGFRA expression was detected in both MBs and PNETs, whereas VEGFR2 expression was weak in these tumors. KIT, PDGFRA, and VEGFR2 amplifications were all present in 4% of MBs/PNETs, and KIT amplification was associated with concurrent PDGFRA and VEGFR2 amplifications (P <or= 0.001). Most strikingly, increased gene copy number of PDGFRA was associated with poor overall survival (P = 0.027). We suggest that coamplification of PDGFRA or VEGFR2 with KIT may be clinically useful novel molecular markers in MBs and PNETs.

Central nervous system primitive neuroectodermal tumors: a clinicopathologic and genetic study of 33 cases

Central nervous system (CNS) primitive neuroectodermal tumors (PNETs) include supratentorial, brain stem, and spinal cord tumors with medulloblastoma-like histopathology. The prognostic impact of various pathologic and genetic features has not been thoroughly investigated. After re-diagnosis of three infantile cases as atypical teratoid/rhabdoid tumor (AT/RT), 33 remaining CNS PNETs were retrieved for clinicopathologic and fluorescence in situ hybridization studies. Anaplastic and/or large cell features were seen in 18 of 33 (55%) examples and survival was decreased in these patients (P = 0.036). MYCN or MYCC gene amplifications were noted in about half, with a trend towards decreased survival (P = 0.112). Polysomies of chromosomes 2 and 8 were each individually associated with decreased survival in children, with an even stronger association when combined (P = 0.013). Neither EWS gene rearrangements, nor AT/RT-like 22q deletions were encountered. We conclude that in CNS PNET: (i) routine application of INI1 immunohistochemistry helps rule out AT/RT, particularly in infants; (ii) MYC gene amplifications (especially MYCN) are common; (iii) involvement of CNS parenchyma by Ewing sarcoma/peripheral PNET is rare enough that EWS gene testing is not necessary unless significant dural involvement is present; and (iv) both anaplastic/large cell features and polysomies of 2 and 8 are associated with more aggressive clinical behavior.

Embryonal neural tumours and cell death

Medulloblastoma and neuroblastoma are malignant embryonal childhood tumours of the central and peripheral nervous systems, respectively, which often show poor clinical prognosis due to resistance to current chemotherapy. Both these tumours have deficient apoptotic machineries adopted from their respective progenitor cells. This review focuses on the specific background for tumour development, and highlights biological pathways that present potential targets for novel therapeutic approaches.

A pilot study of risk-adapted radiotherapy and chemotherapy in patients with supratentorial PNET

We undertook this study to estimate the event-free survival (EFS) of patients with newly diagnosed supratentorial primitive neuroectodermal tumor (SPNET) treated with risk-adapted craniospinal irradiation (CSI) with additional radiation to the primary tumor site and subsequent high-dose chemotherapy supported by stem cell rescue. Between 1996 and 2003, 16 patients with SPNET were enrolled. High-risk (HR) disease was differentiated from average-risk (AR) disease by the presence of residual tumor (M(0) and tumor size > 1.5 cm(2)) or disseminated disease in the neuraxis (M(1)-M(3)). Patients received risk-adapted CSI: those with AR disease received 23.4 Gy; those with HR disease, 36-39.6 Gy. The tumor bed received a total of 55.8 Gy. Subsequently, all patients received four cycles of high-dose cyclophosphamide, cisplatin, and vincristine with stem cell support. The median age at diagnosis was 7.9 years; eight patients were female. Seven patients had pineal PNET. Twelve patients are alive at a median follow-up of 5.4 years. The 5-year EFS and overall survival (OS) estimates for all patients were 68% +/- 14% and 73% +/- 13%. The 5-year EFS and OS estimates were 75% +/- 17% and 88% +/- 13%, respectively, for the eight patients with AR disease and 60% +/- 19% and 58% +/- 19%, respectively, for the eight with HR disease. No deaths were due to toxicity. High-dose cyclophosphamide-based chemotherapy with stem cell support after risk-adapted CSI results in excellent EFS estimates for patients with newly diagnosed AR SPNET. Further, this chemotherapy allows for a reduction in the dose of CSI used to treat AR SPNET without compromising EFS.

Biological background of pediatric medulloblastoma and ependymoma: a review from a translational research perspective

Survival rates of pediatric brain tumor patients have significantly improved over the years due to developments in diagnostic techniques, neurosurgery, chemotherapy, radiotherapy, and supportive care. However, brain tumors are still an important cause of cancer-related deaths in children. Prognosis is still highly dependent on clinical characteristics, such as the age of the patient, tumor type, stage, and localization, but increased knowledge about the genetic and biological features of these tumors is being obtained and might be useful to further improve outcome for these patients. It has become clear that the deregulation of signaling pathways essential in brain development, for example, sonic hedgehog (SHH), Wnt, and Notch pathways, plays an important role in pathogenesis and biological behavior, especially for medulloblastomas. More recently, data have become available about the cells of origin of brain tumors and the possible existence of brain tumor stem cells. Newly developed array-based techniques for studying gene expression, protein expression, copy number aberrations, and epigenetic events have led to the identification of other potentially important biological abnormalities in pediatric medulloblastomas and ependymomas.

An update on mouse brain tumor models in cancer drug discovery

Gliomas and medulloblastomas are the most common primary brain tumors in adults and children, respectively. Although the standard of care for gliomas may have evolved slightly over the last 50 years, the clinical outcome of this disease remains unchanged. Therefore, further research to improve the treatment modalities is urgently needed. An important step forward is the use of genetically and histologically accurate mouse glioma models that mimic the human tumors in their native microenvironment in order to fully understand the biology and mechanistic causes of this disease. Such strategy will help us to identify novel targets for therapies and use these models for preclinical testing.

Type I collagen is overexpressed in medulloblastoma as a component of tumor microenvironment

Medulloblastoma is the most common malignant brain tumor of children, and more specific and effective therapeutic management needs to be developed to improve upon existing survival rates and to avoid side-effects from current treatment. Gain of chromosome seven is the most frequent chromosome copy number aberration in medulloblastoma, suggesting that overexpression of genes on chromosome seven might be important for the pathogenesis of medulloblastoma. We used microarrays to identify chromosome seven genes overexpressed in medulloblastoma specimens, and validated using data from published gene expression datasets. The gene encoding the alpha 2 subunit of type I collagen, COL1A2, was overexpressed in all three datasets. Immunohistochemistry of tumor tissues revealed type I collagen in the leptomeninges, and in the extracellular matrix surrounding blood vessels and medulloblastoma cells. Expression of both type I collagen and the beta1 subunit of integrin, a subunit of a known type I collagen receptor, localized to the same area of medulloblastoma. Adherence of D283 medulloblastoma cells to type I collagen matrix in vitro depends on the beta1 subunit of integrin. Because medulloblastoma is characteristic of high vascularity, and because inhibition of type I collagen synthesis has been shown to suppress angiogenesis and tumor growth, our data suggest that type I collagen might be a potential therapeutic target for treating medulloblastoma.

Primary spinal primitive neuroectodermal tumor: case series and review of the literature

Primary spinal primitive neuroectodermal tumor (PSPNET) is extremely rare and only 25 cases have been reported in the world literature so far. Three patients of 8, 9 and 18 years of age, who presented with variable grades of neurological deficit were diagnosed as having a dorsal intramedullary lesion, a holocord lesion and cervical extradural tumor with extraspinal extension, respectively, and were operated at our institute. The histopathology of all 3 children revealed PNET. The clinical course, image characteristics and outcome of the 3 children are described, and the relevant literature is reviewed. The following conclusions were drawn from the present study and review of the literature. PNET may manifest itself as a primary lesion of the spine unlike the more common drop metastases from an intracranial lesion. PSPNET may be intramedullary, intradural and extradural with variable extraspinal extension. PSPNET may present as holocord intramedullary lesion, an entity which has not been described earlier. These lesions have a short history, significant neurological deficits and rapid course of illness. PSPNET, though an established entity, did not find a place in the WHO 2000 classification of CNS tumors. Hence its status has to be defined.

Supratentorial primitive neuroectodermal tumors of the central nervous system frequently harbor deletions of theCDKN2A locus and other genomic aberrations distinct from medulloblastomas

Supratentorial primitive neuroectodermal tumors (stPNETs) and medulloblastomas have long been thought to arise from a common cell type in the subventricular germinal matrix. Because of the infrequent occurrence of stPNETs, little is known about their genetic background. Here, we performed a genome-wide screening for DNA copy-number aberrations in 10 supratentorial PNETs using array-based comparative genomic hybridization (array-CGH). Comparing our findings with data from a previous array-CGH study on 47 medulloblastomas, we identified differences in the frequency of copy-number losses at chromosome regions 1p12-22.1 and 9p, and gains at 19p, all of them more frequently occurring in stPNETs. In contrast to previous reports, we detected chromosome 17 aberrations by array-CGH in 2/10 stPNETs. To validate our findings obtained by array-CGH, we analyzed the loci of interest by fluorescence in situ hybridization in an independent set of 11 stPNETs and found deletions of 9p21 in 5/11 tumors of the second set, three of them being homozygous. All 9p21 deletions were associated with loss of CDKN2A protein expression. Altogether, CDKN2A deletions were detected in 7/21 stPNETs including four homozygous deletions, whereas such deletions were only found in 4/112 medulloblastomas, all of these being heterozygous (P < 0.001). Gains of 19p (14% vs. 0% in medulloblastomas, P = 0.02) were found to be significantly more frequent in stPNETs, whereas gains of 17q (14% vs. 45% in medulloblastomas, P = 0.02) were confirmed to be more frequent in medulloblastomas. These data further support the hypothesis of two different tumor entities of embryonal neuroepithelial tumors with characteristic genetic aberrations. (c) 2007 Wiley-Liss, Inc.

Metaphase and array comparative genomic hybridization: unique copy number changes and gene amplification of medulloblastomas in South America

Tumors of the central nervous system are the second most frequent malignancy of childhood, accounting for the majority of cancer-related deaths in this age group. Among these tumors, medulloblastomas (MB) remain in need of further genomic characterization toward understanding of pathogenesis and outcome predictors. Eight pediatric embryonal brain tumors were analyzed: five MB (one being desmoplastic), one PNET, one medulloepithelioma, and one ependymoblastoma. Analyses identified genomic imbalances, including the gain of 16p and the nonsyntenic coamplification of MYCN and TERT loci. More detailed FISH analysis showed that coamplification of MYCN and TERT in one of the MBs manifested as dispersed nuclear speckling, consistent with the presence of double minute chromosomes. There was considerable cell-to-cell copy number heterogeneity present, but it was clear that both genes were amplified concordantly. The amplification of oncogenes seems to play an important role in the pathogenesis of MB, and the association between MYCN and TERT amplifications and poor prognosis has not been well recognized. The uncharacteristic pattern of genomic imbalances detected in MB tumors may be a reflection of the characteristics of these tumors occurring in South America.

Childhood pineoblastoma: experiences from the prospective multicenter trials HIT-SKK87, HIT-SKK92 and HIT91

OBJECTIVE

To analyze the outcome of children with pineoblastoma (PB), treated within the prospective multicenter trials HIT-SKK87, HIT-SKK92 and HIT91 of German-speaking countries.

PATIENTS

We report on 11 children suffering from PB. Five children younger than 3 years of age received chemotherapy after surgery until eligible for radiotherapy (HIT-SKK87 and HIT-SKK92). Five of six children older than 3 years were treated after surgery with immediate chemotherapy and craniospinal irradiation, and one child received maintenance chemotherapy after postoperative radiotherapy (HIT91).

RESULTS

Five of the six older children are still alive in continuous complete remission (CCR) with a median overall survival (OS) and progression free survival (PFS) of 7.9 years. Five of these six HIT91 patients responded to postoperative chemotherapy and radiotherapy. The only patient with tumor progression during initial chemotherapy achieved complete remission with radiotherapy and is alive. In contrast, all five young children died of tumor progression after a median OS of 0.9 years (PFS 0.6 years). They had either metastatic disease (M1) and/or postoperative residual tumor. Response to postoperative chemotherapy was lower than in the older age group, and only one of these children received radiotherapy.

CONCLUSIONS

Combined chemotherapy and radiotherapy were feasible and effective in the older age group, leading to prolonged remissions in five of six children. Tumor biology may be more aggressive in younger children with PB, who presented more frequently with high-risk features at diagnosis and had poorer response rates to neoadjuvant postoperative chemotherapy. More intensified treatment regimens may be needed for young children with PB.

High-resolution array-based comparative genomic hybridization of medulloblastomas and supratentorial primitive neuroectodermal tumors

Medulloblastomas and supratentorial primitive neuroectodermal tumors are aggressive childhood tumors. We report our findings using array comparative genomic hybridization (CGH) on a whole-genome BAC/PAC/cosmid array with a median clone separation of 0.97 Mb to study 34 medulloblastomas and 7 supratentorial primitive neuroectodermal tumors. Array CGH allowed identification and mapping of numerous novel, small regions of copy number change to genomic sequence in addition to the large regions already known from previous studies. Novel amplifications were identified, some encompassing oncogenes MYCL1, PDGFRA, KIT, and MYB not previously reported to show amplification in these tumors. In addition, one supratentorial primitive neuroectodermal tumor had lost both copies of the tumor-suppressor genes CDKN2A and CDKN2B. Ten medulloblastomas had findings suggestive of isochromosome 17q. In contrast to previous reports using conventional CGH, array CGH identified 3 distinct breakpoints in these cases: Ch 17: 17940393-19251679 (17p11.2, n = 6), Ch 17: 20111990-23308272 (17p11.2-17q11.2, n = 4), and Ch 17: 38425359-39091575 (17q21.31, n = 1). Significant differences were found in the patterns of copy number change between medulloblastomas and supratentorial primitive neuroectodermal tumors, providing further evidence that these tumors are genetically distinct despite their morphologic and behavioral similarities.

High promoter hypermethylation frequency of p14/ARF in supratentorial PNET but not in medulloblastoma

AIMS

Medulloblastoma (MB) is the most common primitive neuroectodermal tumour (PNET) of the central nervous system. Although supratentorial PNET (sPNET) and MB are histologically similar, their clinical behaviour differs, sPNET being more aggressive than MB. The aim of this study was to determine whether sPNET and MB are genetically different entities.

METHODS AND RESULTS

We investigated 32 PNET primary tumour samples (23 MB and nine sPNET) and four PNET cell lines, for the presence of CDKN2A homozygous deletions at exon 1-alpha of p16/INK4 and exon 1-beta of p14/ARF, and promoter hypermethylation of both genes. No homozygous deletion of either p16/INK4 or p14/ARF was demonstrated in any of the PNET primary tumour samples. Methylation of p16/INK4 was found in one of six sPNET and in one of 23 MB, while p14/ARF methylation was observed in three of six sPNET and in three of 21 MB. No methylation of p16/INK4 or p14/ARF was found in any of the PNET cell lines analysed. The three MB cell lines did not show p16/INK4 expression, and only the MB Daoy cell line (homozygously deleted at CDKN2A) presented loss of p14/ARF expression.

CONCLUSIONS

Our results in this limited series of central PNET show that p14/ARF is frequently involved in PNET carcinogenesis, with a higher frequency, but not statistically significant, for sPNET than for MB.

Fluorescence in situ hybridization (FISH) in diagnostic and investigative neuropathology

Over the last decade, fluorescence in situ hybridization (FISH) has emerged as a powerful clinical and research tool for the assessment of target DNA dosages within interphase nuclei. Detectable alterations include aneusomies, deletions, gene amplifications, and translocations, with primary advantages to the pathologist including its basis in morphology, its applicability to archival, formalin-fixed paraffin-embedded (FFPE) material, and its similarities to immunohistochemistry. Recent technical advances such as improved hybridization protocols, markedly expanded probe availability resulting from the human genome sequencing initiative, and the advent of high-throughput assays such as gene chip and tissue microarrays have greatly enhanced the applicability of FISH. In our lab, we currently utilize only a limited battery of DNA probes for routine diagnostic purposes, with determination of chromosome 1p and 19q dosage in oligodendroglial neoplasms representing the most common application. However, research applications are numerous and will likely translate into a growing list of clinically useful markers in the near future. In this review, we highlight the advantages and disadvantages of FISH and familiarize the reader with current applications in diagnostic and investigative neuropathology.

Genetic heterogeneity in supratentorial and infratentorial primitive neuroectodermal tumours of the central nervous system

AIMS

Medulloblastoma (MB), a kind of infratentorial primitive neuroectodermal tumour (PNET), is the most frequent malignant brain tumour in childhood. In contrast, supratentorial PNET (sPNET) are very infrequent tumours, but they are histologically similar to MB, although they present a worse clinical outcome. We investigated the differences in genetic abnormalities between sPNET and MB.

METHODS AND RESULTS

We analysed 20 central PNET (14 MB and six sPNET) by conventional comparative genomic hybridization (CGH) in order to determine whether a different genetic profile for each tumour exists. Isochromosome 17q was detected in four of the 14 MB cases, but not in any sPNET. Gains at 17q and 7 happened more frequently in MB, and those at 1q in sPNET. Losses at chromosome 10 were detected only in MB, while losses at 16p and 19p happened more frequently in sPNET. A new amplification site, on 4q12, was detected in two MB.

CONCLUSIONS

Central PNET are a heterogeneous group of tumours from the genetic point of view. The present and previous data, together with further results from larger series, might contribute to the establishment of specific treatments for supratentorial and infratentorial PNET.

Supratentorial primitive neuroectodermal tumors (S-PNET) in children: A prospective experience with adjuvant intensive chemotherapy and hyperfractionated accelerated radiotherapy

PURPOSE

Supratentorial primitive neuroectodermal tumors (S-PNET) are rare and have a grim prognosis, frequently taking an aggressive course with local relapse and metastatic spread. We report the results of a mono-institutional therapeutic trial.

METHODS AND MATERIALS

We enrolled 15 consecutive patients to preradiation chemotherapy (CT) consisting of high-dose methotrexate, high-dose etoposide, high-dose cyclophosphamide, and high-dose carboplatin, craniospinal irradiation (CSI) with hyperfractionated accelerated radiotherapy (HART) plus focal boost, maintenance with vincristine/lomustine or consolidation with high-dose thiotepa followed by autologous stem-cell rescue.

RESULTS

Median age was 9 years; 7 were male, 8 female. Site of disease was pineal in 3, elsewhere in 12. Six patients were had no evidence of disease after surgery (NED). Of those with evidence of disease after surgery (ED), 2 had central nervous system spread. Of the 9 ED patients, 2 had complete response (CR) and 2 partial response (PR) after CT, 4 stable disease, and 1 progressive disease. Of the 7 ED patients before radiotherapy, 1 had CR, 4 PR, and 2 minor response, thus obtaining a 44% CR + PR after CT and 71% after HART. Because of rapid progression in 2 of the first 5 patients, high-dose thiotepa was systematically adopted after HART in the subsequent 10 patients. Six of 15 patients relapsed (4 locally, 1 locally with dissemination, 1 with dissemination) a mean of 6 months after starting CT, 2 developed second tumors; 5 of 6 relapsers died at a median of 13 months. Three-year progression-free survival, event-free survival, and overall survival were 54%, 34%, and 61%, respectively.

CONCLUSION

Hyperfractionated accelerated RT was the main tool in obtaining responses in S-PNET; introducing the myeloablative phase improved the prognosis (3/10 vs. 3/5 relapses), though the outcome remained unsatisfactory despite the adoption of this intensive treatment.

Molecular cytogenetic analysis in the study of brain tumors: findings and applications

Classic cytogenetics has evolved from black and white to technicolor images of chromosomes as a result of advances in fluorescence in situ hybridization (FISH) techniques, and is now called molecular cytogenetics. Improvements in the quality and diversity of probes suitable for FISH, coupled with advances in computerized image analysis, now permit the genome or tissue of interest to be analyzed in detail on a glass slide. It is evident that the growing list of options for cytogenetic analysis has improved the understanding of chromosomal changes in disease initiation, progression, and response to treatment. The contributions of classic and molecular cytogenetics to the study of brain tumors have provided scientists and clinicians alike with new avenues for investigation. In this review the authors summarize the contributions of molecular cytogenetics to the study of brain tumors, encompassing the findings of classic cytogenetics, interphase- and metaphase-based FISH studies, spectral karyotyping, and metaphase- and array-based comparative genomic hybridization. In addition, this review also details the role of molecular cytogenetic techniques in other aspects of understanding the pathogenesis of brain tumors, including xenograft, cancer stem cell, and telomere length studies.

Molecular genetics of supratentorial primitive neuroectodermal tumors and pineoblastoma

The supratentorial primitive neuroectodermal tumors (PNETs) are a group of highly malignant lesions primarily affecting young children. Although these tumors are histologically indistinguishable from infratentorial medulloblastoma, they often respond poorly to medulloblastoma-specific therapy. Indeed, existing molecular genetic studies indicate that supratentorial PNETs have transcriptional and cytogenetic profiles that are different from those of medullo-blastomas, thus pointing to unique biological derivation for the supratentorial PNET. Due to the rarity of these tumors and disagreement about their histopathological diagnoses, very little is known about the molecular characteristics of the supratentorial PNET. Clearly, future concerted efforts to characterize the molecular features of these rare tumors will be necessary for development of more effective supratentorial PNET treatment protocols and appropriate disease models. In this article the authors review existing molecular genetic data derived from human and mouse studies, with the aim of providing some insight into the putative histogenesis of these rare tumors and the underlying transforming pathways that drive their development. Studies of the related but distinct pineoblastoma PNET are also reviewed.

Genomic deletions in cell lines derived from primitive neuroectodermal tumors of the central nervous system

Extensive genomic deletions affecting a variety of chromosomes are a common finding in primitive neuroectodermal tumors of the central nervous system (CNS-PNETs), implicating the loss of multiple tumor suppressor genes in the pathogenesis of these tumors. We have used representational difference analysis, microsatellite mapping, and quantitative polymerase chain reaction to identify and verify the presence of genomic deletions on a number of chromosomes in CNS-PNET cell lines. This systematic approach has confirmed the importance of deletions at 10q, 16q, and 17p in PNET pathology and has revealed other regions of deletion not commonly described (e.g., Xq, 1p, 7p, and 13q). These data highlight the prevalence of hemizygous loss in CNS-PNET cells, suggesting that haploinsufficiency affecting multiple tumor suppressor genes may play a fundamental role in CNS-PNET pathogenesis. The identification of specific genes and signaling pathways that are compromised in CNS-PNET cells is crucial for development of more efficacious and less invasive treatments, as are urgently needed.

Molecular diagnostics in central nervous system tumors

Central nervous system (CNS) neoplasms can be diagnostically challenging, due to remarkably wide ranges in histologic appearance, biologic behavior, and therapeutic approach. Nevertheless, accurate diagnosis is the critical first step in providing optimal patient care. As with other oncology-based specialties, there is a rapidly expanding interest and enthusiasm for identifying and utilizing new biomarkers to enhance the day-to-day practice of surgical neuropathology. In this regard, the field is primed by recent advances in basic research, elucidating the molecular mechanisms of tumorigenesis and progression in the most common adult and pediatric brain tumors. Thus far, few have made the transition into routine clinical practice, the most notable example being 1p and 19q testing in oligodendroglial tumors. However, the field is rapidly evolving and many other biomarkers are likely to emerge as useful ancillary diagnostic, prognostic, or therapeutic aids. The goal of this article is to highlight the most common genetic alterations currently implicated in CNS tumors, focusing most on those that are either already in common use in ancillary molecular diagnostics testing or are likely to become so in the near future.

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.

Pediatric surgical neuro-oncology: current best care practices and strategies

Significant advances have been made in the diagnosis and treatment of childhood brain tumors. Gross total surgical resection combined with appropriate adjuvant therapies can achieve a high rate of disease control for low grade gliomas, ependymomas and medulloblastomas. High grade gliomas, tumors involving the optic apparatus or diencepahalic structures, diffuse brainstem lesions, and recurrent or metastatic disease still pose considerable therapeutic challenges. We review the current treatment strategies of the three most common types of pediatric brain tumors: gliomas, medulloblastomas and ependymomas, and discuss current and future diagnostic and therapeutic modalities.

Genetic and expression profiles of cerebellar liponeurocytomas

Cerebellar liponeurocytoma, a rare, newly identified CNS neoplasm of adults, is characterized by advanced neuronal/neurocytic and focal lipomatous differentiation, low proliferative potential and a favorable clinical prognosis. Despite the different age distribution and benign biological behavior, the cerebellar liponeurocytoma shares several features with the cerebellar medulloblastoma, which may include an origin from the periventricular matrix of the fourth ventricle or the external granular layer of the cerebellum. To establish the genetic profile of cerebellar liponeurocytomas, we have formed an international consortium and collected tumor samples from 20 patients. DNA sequencing revealed TP53 missense mutations in 4 (20%) of 20 cerebellar liponeurocytomas, a frequency higher than in medulloblastomas. There was no case with PTCH, APC, or beta-catenin mutations, each of which may be present in subsets of medulloblastomas. Isochromosome 17q, a genetic hallmark of classic medulloblastomas, was not observed in any of the cases investigated by FISH analysis. cDNA array analyses were carried out on 4 cerebellar liponeurocytomas, 4 central neurocytomas, and 4 classic medulloblastomas. Cluster analysis of the cDNA expression data of 1176 genes grouped cerebellar liponeurocytomas close to central neurocytomas, but distinct from medulloblastomas. These results suggest cerebellar liponeurocytoma as a distinct tumor entity that is genetically different from medulloblastoma. Furthermore, the cDNA expression array data suggest a relationship to central neurocytomas, but the presence of TP53 mutations, which are absent in central neurocytomas, suggests that their genetic pathways are different.

Medullomyoblastoma: a radiographic and clinicopathologic analysis of six cases and review of the literature

BACKGROUND

Medullomyoblastoma (MMB) is a rare cerebellar embryonal neoplasm that occurs almost exclusively in children. It is biphasic by microscopy, containing myoblastic and primitive neuroectodermal components.

METHODS

The authors conducted a retrospective review of the radiographic and pathologic characteristics, treatment, and clinical outcomes of six children with MMB who were treated at St. Jude Children's Research Hospital (Memphis, TN) between 1984 and 2003. Fluorescence in situ hybridization (FISH) data were available for four children. A literature review also was conducted and focused on imaging and pathologic findings.

RESULTS

The median age at diagnosis was 4.5 years (range, 0.83-7.5 years). Radiographically, all tumors were cerebellar and exhibited variable enhancement, and 50% of tumors had necrotic foci. Three tumors contained discrete, magnetic resonance imaging (MRI) T2-weighted-hypointense/computed tomography (CT)-hyperdense enhancing regions and separate hyperintense/hypodense nonenhancing regions, which correlated microscopically with geographic islands of primitive neuroectodermal and rhabdomyoblastic cells. Large cell/anaplastic (five tumors), nodular/desmoplastic (two tumors), and classic (two tumors) medulloblastoma histologies were encountered either alone (five tumors) or in combination with each other (two tumors). All 4 tumors that were tested exhibited alterations in chromosome 17 or c-myc amplification. All patients underwent macroscopic total resection and subsequently received chemotherapy and craniospinal (five patients) or local conformal (one patient) radiotherapy. At a median follow-up of 92 months (range, 23-187 months), 3 patients remain alive with no evidence of disease, 2 patients have died of disease, and 1 patient has died of secondary acute lymphocytic leukemia.

CONCLUSIONS

The results of the current study demonstrated the frequent correlation of biphasic nodularity (as determined by MRI or CT) with discrete rhabdomyoblastic and primitive neuroectodermal islands (as revealed by microscopy) in MMB. These results also support the view that MMB and medulloblastoma may have common tumorigenic origins, given their similar histologic and molecular features.

Advances in the diagnosis, molecular genetics, and treatment of pediatric embryonal CNS tumors

Embryonal central nervous system (CNS) tumors are the most common group of malignant brain tumors in children. The diagnosis and classification of tumors belonging to this family have been controversial; however, utilization of molecular genetics is helping to refine traditional histopathologic and clinical classification schemes. Currently, this group of tumors includes medulloblastomas, supratentorial primitive neuroectodermal tumors, atypical teratoid/rhabdoid tumors, ependymoblastomas, and medulloepitheliomas. While the survival of older children with nonmetastatic medulloblastomas has improved considerably within the past two decades, the outcomes for infants and for those with metastatic medulloblastomas or other high-risk embryonal CNS tumors remain poor. It is anticipated that the emerging field of molecular biology will greatly aid in the future stratification and therapy for pediatric patients with malignant embryonal tumors. In this review, recent advances in the diagnosis, molecular genetics, and treatment of the most common pediatric embryonal CNS tumors are discussed.

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.

A unique occurrence of a cerebral atypical teratoid/rhabdoid tumor in an infant and a spinal canal primitive neuroectodermal tumor in her father

This report describes the clinical, pathological, immunohistochemical and genetic data of two rare malignant neoplasms of the central nervous system (CNS)--a cerebral atypical teratoid/rhabdoid tumor (AT/RT) in a 5-month-old girl and a spinal canal primitive neuroectodermal tumor (PNET) in her father. Despite aggressive treatment, both tumors were fatal, displaying extensive local recurrence and diffuse neoplastic dissemination. The paraffin-embedded tumor tissue samples were analyzed using a dual-color FISH with a locus specific LSI22q (BCR) probe. In the AT/RT tissue, a loss of BCR locus was observed in a significant proportion of the cells in contrast to the PNET specimen where the majority of nuclei did not reveal any loss of the BCR region. No mutations in exon 5 and no changes in SNP of intron 5 of hSNF/INI1 gene were found. In addition, analysis of loss of heterozygosity (LOH) was performed using a panel of 15 microsatellite markers of chromosome 22. No LOH were found in both tumor tissues. In both cases no constitutional mutations of gene TP53 were found. Analysis of the TP53 mutations in the tumor tissues revealed that the PNET, not the AT/RT tumor, was homozygous for a missense mutation at codon 175 (CGC ==> CAC). Thus, our findings emphasize the genetic differences between the two specimens and suggest that the occurrence of these two aggressive tumors of CNS in one family could be coincidental.

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.

Molecular genetic analysis of the TP53, PTEN, CDKN2A, EGFR, CDK4 and MDM2 tumour-associated genes in supratentorial primitive neuroectodermal tumours and glioblastomas of childhood

Supratentorial primitive neuroectodermal tumours (sPNETs) are malignant central nervous system tumours of childhood which are histologically characterized by poorly differentiated neuroepithelial cells with the capacity for divergent differentiation into glial, neuronal, myogenic or melanotic lines. The histological differential diagnosis between sPNET and glioblastoma multiforme (GBM) may be difficult, particularly as GBMs can sometimes demonstrate a poorly differentiated PNET-like phenotype. To identify molecular genetic markers that may distinguish sPNET and GBM, we investigated 12 cerebral sPNETs and six GBMs from paediatric patients for genetic alterations of the TP53, PTEN, CDKN2A, EGFR, CDK4 and MDM2 genes, as well as for allelic loss on chromosome arms 10q and 17p. Mutations of the TP53 tumour suppressor gene were found in one of 12 sPNETs (8%) and two of six GBMs (33%). None of the sPNETs but two of six GBMs (33%, including one GBM with a TP53 mutation) showed allelic losses on chromosome arm 17p. PTEN mutations were detected in one of 12 sPNET (8%) and one of six GBMs (17%). None of the sPNETs and GBMs carried a homozygous deletion involving the CDKN2A tumour suppressor gene. No amplification of the EGFR, CDK4 or MDM2 proto-oncogenes was detected. Taken together, our results indicate that paediatric GBMs differ from sPNETs by a higher incidence of allelic losses on 17p and TP53 mutations. In addition, the patterns of genetic alterations in sPNETs and paediatric GBMs appear to be distinct from those in cerebellar medulloblastomas and adult GBMs, respectively.

Primary peripheral PNET/Ewing's sarcoma of the dura: a clinicopathologic entity distinct from central PNET

We describe two cases of peripheral primitive neuroectodermal tumor-Ewing's sarcoma (PNET-ES) arising intracranially in the leptomeninges. Both tumors exhibited a primitive undifferentiated round-cell morphology. Immunohistochemical stains revealed strong membrane expression of CD99 in both cases. A t(11;22)(q24;q12) could be demonstrated with reverse transcriptase-polymerase chain reaction in one case, whereas fluorescence in situ hybridization analysis performed in the second case showed a rearrangement of the EWS gene. The occurrence of PNET-ES at this site is very unusual. Immunophenotypical as well as genetic analysis play a key role in the diagnosis and the distinction from central PNET.

Human medulloblastomas lack point mutations and homozygous deletions of the hSNF5/INI1 tumour suppressor gene

Medulloblastomas (MBs) are malignant primitive neuroectodermal tumours (PNETs) of the cerebellum occurring predominantly in childhood. The association of monosomy of chromosome 22 with MB is controversial. Atypical teratoid/rhabdoid tumours (AT/RTs) of the brain share clinical and histological features with MBs and supratentorial PNETs (sPNETs). In particular, AT/RTs can be misdiagnosed as MBs and sPNETs because AT/RTs frequently contain areas of primitive neuroepithelial cells similar to PNETs. Recently, mutations of the tumour suppressor gene hSNF5/INI1, located on 22q11.23, have been described in AT/RTs, MBs and sPNETs, with conflicting data on the prevalence of hSNF5/INI1 mutations in the latter entities. Therefore, we screened MBs for point mutations and homozygous deletions of the hSNF5/INI1 tumour suppressor gene. In 90 MBs, no mutations of the hSNF5/INI1 gene were identified. Thus, our study virtually rules out hSNF5/INI1 as a tumour suppressor gene involved in the pathogenesis of medulloblastoma.

Role of radiotherapy in the treatment of supratentorial primitive neuroectodermal tumors in childhood: results of the prospective German brain tumor trials HIT 88/89 and 91

PURPOSE

To evaluate the outcome of children with supratentorial primitive neuroectodermal tumors after surgery, irradiation, and chemotherapy and to identify factors predictive for survival.

PATIENTS AND METHODS

Sixty-three children in the prospective trials HIT 88/89 and HIT 91 were eligible. Complete resection was performed in 21 patients. Patients were randomized for preirradiation chemotherapy, consisting of two cycles of ifosfamide, etoposide, methotrexate, cisplatin, and cytarabine (n = 40), or chemotherapy after irradiation, consisting of eight cycles with cisplatin, vincristine, and lomustine (n = 23). Irradiation volume was recommended to encompass the neuraxis with 35.2-Gy total dose followed by a boost (20.0 Gy) to the primary tumor site (n = 54). Seven patients were irradiated to the tumor region only with a total dose of 54.0 Gy.

RESULTS

Overall survival at 3 years was 48.4%. Progression occurred in 38 children, with local recurrences in 27 patients. The only significant prognostic factor was dose and volume of radiotherapy (progression-free survival after 3 years was 49.3% with correct treatment compared with 6.7% for 15 children with major violations of radiotherapy). Ten early progressions occurred during adjuvant therapy (eight before and two during radiotherapy), nine of them treated with preirradiation chemotherapy. There was a positive trend in outcome for nonmetastatic and pineal tumors.

CONCLUSION

Significant predictive factors were dose and volume of radiotherapy. Volume of irradiation should encompass the whole CNS with additional boost to the tumor region. Local doses of at least 54 Gy and a craniospinal dose of 35 Gy are necessary. Preirradiation chemotherapy seems to increase risk of early progression.

Expression of a human polyomavirus oncoprotein and tumour suppressor proteins in medulloblastomas

AIMS

Although the aetiology of medulloblastoma remains elusive, several lines of evidence suggest an association with the human neurotropic polyomavirus JC and its oncoprotein T antigen. The tumour forming properties of JC virus T antigen are the result, at least in part, of its ability to bind and inactivate tumour suppressor/cell cycle regulatory proteins, such as p53 and the retinoblastoma family of proteins.

METHODS

To examine potential relations between these factors, immunohistochemistry was used to determine associations between the T antigen and the expression of p53 and the retinoblastoma proteins pRb, p107, and Rb2/p130 in eight medulloblastomas.

RESULTS

Only the three medulloblastomas with T antigen expression also showed nuclear positivity with antibodies to p53. Although immunohistochemistry detected nuclear labelling for pRb in five of the cases, the three that were positive for T antigen showed the highest pRb labelling. The retinoblastoma related proteins p107 and Rb2/p130 were also immunopositive in most T antigen positive medulloblastomas. Double label immunohistochemistry also demonstrated p53 and pRb positivity in the same cells that were T antigen positive.

CONCLUSIONS

These correlations suggest that associations between T antigen and p53 and/or T antigen and pRb occur in some of these tumours. These data provide indirect evidence that JC virus, acting through T antigen, might be involved in the formation and progression of medulloblastoma.

The developmental biology of brain tumors

Tumors of the central nervous system (CNS) can be devastating because they often affect children, are difficult to treat, and frequently cause mental impairment or death. New insights into the causes and potential treatment of CNS tumors have come from discovering connections with genes that control cell growth, differentiation, and death during normal development. Links between tumorigenesis and normal development are illustrated by three common CNS tumors: retinoblastoma, glioblastoma, and medulloblastoma. For example, the retinoblastoma (Rb) tumor suppressor protein is crucial for control of normal neuronal differentiation and apoptosis. Excessive activity of the epidermal growth factor receptor and loss of the phosphatase PTEN are associated with glioblastoma, and both genes are required for normal growth and development. The membrane protein Patched1 (Ptc1), which controls cell fate in many tissues, regulates cell growth in the cerebellum, and reduced Ptc1 function contributes to medulloblastoma. Just as elucidating the mechanisms that control normal development can lead to the identification of new cancer-related genes and signaling pathways, studies of tumor biology can increase our understanding of normal development. Learning that Ptc1 is a medulloblastoma tumor suppressor led directly to the identification of the Ptc1 ligand, Sonic hedgehog, as a powerful mitogen for cerebellar granule cell precursors. Much remains to be learned about the genetic events that lead to brain tumors and how each event regulates cell cycle progression, apoptosis, and differentiation. The prospects for beneficial work at the boundary between oncology and developmental biology are great.

Aberrant promoter methylation of previously unidentified target genes is a common abnormality in medulloblastomas--implications for tumor biology and potential clinical utility

Medulloblastomas exhibit an array of diverse cytogenetic abnormalities. To evaluate the significance of epigenetic rather than genetic lesions in medulloblastomas and other primitive neuroectodermal tumors (PNETs) of the childhood CNS we performed a systematic analysis of gene specific and global methylation. Methylation-specific PCR detected no methylation for p15(INK4B), von Hippel Lindau and TP53 and only limited methylation for E-Cadherin and p16(INK4A) in tumors. The cell lines Daoy and MHH-PNET-5 in which the p16(INK4A) promoter was methylated did not express the gene, but demonstrated abnormalities by SSCP. Immunohistochemistry for p16 was negative in all examined normal cerebella and medulloblastomas. Using the technique of Restriction Landmark Genomic Scanning we detected methylation affecting up to 1% of all CpG islands in primary MB/PNETs and 6% in MB cell lines. Methylation patterns differed between medulloblastomas and PNETs. Examination of several methylated sequences revealed homologies to known genes and expressed sequences. Analysis of survival data identified seven of 30 hypermethylated sequences significantly correlating with poor prognosis. We suggest that DNA hypermethylation has an outstanding potential for the identification of novel tumor suppressors as well as diagnostic and therapeutic targets in MBs and other PNETs of the CNS.

Gene amplification in PNETs/medulloblastomas: mapping of a novel amplified gene within the MYCN amplicon

OBJECTIVES

The pathological entity of primitive neuroectodermal tumour/medulloblastoma (PNET/MB) comprises a very heterogeneous group of neoplasms on a clinical as well as on a molecular level. We evaluated the importance of DNA amplification in medulloblastomas and other primitive neuroectodermal tumours (PNETs) of the CNS.

METHOD

Restriction landmark genomic scanning (RLGS), a method that allows the detection of low level amplification, was used. RLGS provides direct access to DNA sequences circumventing positional cloning efforts. Furthermore, we analysed several samples by CGH.

DESIGN

Twenty primary medulloblastomas, five supratentorial PNETs, and five medulloblastoma cell lines were studied.

RESULTS

Although our analysis confirms that gene amplification is generally a rare event in childhood PNET/MB, we found a total of 17 DNA fragments that were amplified in seven different tumours. Cloning and sequencing of several of these fragments confirmed the previous finding of MYC amplification in the cell line D341 Med and identified novel DNA sequences amplified in PNET/MB. We describe for the first time amplification of the novel gene, NAG, in a subset of PNET/MB. Despite genomic amplification, NAG was not overexpressed in the tumours studied. We have determined that NAG maps less than 50 kb 5' of DDX1 and approximately 400 kb telomeric of MYCN on chromosome 2p24.

CONCLUSION

We found a similar but slightly higher frequency of amplification than previously reported. We present several DNA fragments that may belong to the CpG islands of novel genes amplified in a small subset of PNET/MB. As an example we describe for the first time the amplification of NAG in the MYCN amplicon in PNET/MB.