TrkC expression predicts good clinical outcome in primitive neuroectodermal brain tumors

Transformation of breast cells by truncated neurokinin-1 receptor is secondary to activation by preprotachykinin-A peptides

Breast cancer remains the cancer with the highest mortality among women in the United States. Peptides derived from the oncogenic Tac1 gene (full transcript: betaPPT-A) stimulate the proliferation of breast cancer cells (BCCs) via seven-transmembrane G protein-coupled neurokinin 1 (NK1) and NK2 receptors. The NK1 gene could generate full-length (NK1-FL) and truncated (NK1-Tr) transcripts. NK1-Tr lacks 100 residues in their cytoplasmic end, could couple to G proteins, and shows reduced efficiency with respect to internalization and desensitization. This study reports on a role of NK1-Tr in the transformation of nontumorigenic breast cells, and investigates whether Tac1 expression is linked to the generation of NK1-Tr. Western blots and Northern analyses showed coexpressions of NK1-Tr and NK1-FL in BCCs (cell lines and primary cells from patients with different stages of breast cancer). Stable transfections of betaPPT-A or NK1-Tr expression vectors in nontumorigenic cells showed each induces the expression of the other, consequently resulting in a transformed phenotype. Analyses with microarrays indicate similar patterns of cytokine production by NK1-Tr transfectants and BCCs, but not NK1-FL transfectants. These observations indicate tumor-promoting properties by NK1-Tr, but not NK1-FL. Overall, the oncogenic property of Tac1 in breast cells involves concomitant expression of NK1-Tr and vice versa, consequently leading to the production of cytokines with growth promoting functions.

β-Catenin Status Predicts a Favorable Outcome in Childhood Medulloblastoma: The United Kingdom Children's Cancer Study Group Brain Tumour Committee

Purpose

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

Patients and Methods

Medulloblastomas from children entered onto the International Society for Pediatric Oncology (SIOP)/United Kingdom Children's Cancer Study Group (UKCCSG) PNET3 trial (n = 109) were examined for β-catenin immunoreactivity, and where tissue was available, evidence of CTNNB1 and APC mutations. The results were correlated with clinicopathologic variables, principally outcome.

Results

Children with medulloblastomas that showed a nucleopositive β-catenin immunophenotype (27 of 109; 25%) had significantly better overall (OS) and event-free (EFS) survivals than children with tumors that showed either membranous/cytoplasmic β-catenin immunoreactivity or no immunoreactivity (P = .0015 and P = .0026, respectively). For β-catenin nucleopositive and nucleonegative medulloblastomas, 5-year OS was 92.3% (95% CI, 82% to 100%) versus 65.3% (95% CI, 54.8 to 75.7%), and 5-year EFS was 88.9% (95% CI, 77% to 100%) versus 59.5% (95% CI, 48.8 to 70.2%), respectively. Mutations in CTNNB1 were found exclusively among medulloblastomas that demonstrated nuclear β-catenin immunoreactivity, but no evidence of APC mutation was found in these cases. All children with β-catenin nucleopositive large cell/anaplastic medulloblastomas and β-catenin nucleopositive medulloblastomas presenting with metastatic disease are alive at least 5 years postdiagnosis.

Conclusion

Nuclear accumulation of β-catenin appears to be a marker of favorable outcome in medulloblastoma, and should be investigated further in large group-wide trials.

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.

Multiagent chemotherapy and deferred radiotherapy in infants with malignant brain tumors: a report from the Children's Cancer Group

PURPOSE

To evaluate response rate, event-free survival (EFS), and toxicity of two chemotherapeutic regimens for treatment of children younger than 36 months with malignant brain tumors and to estimate control intervals without irradiation in children with no residual tumor after initial surgery and induction chemotherapy and with delayed irradiation in patients with residual tumor or metastatic disease at diagnosis.

PATIENTS AND METHODS

Patients were randomly assigned to one of two regimens of induction chemotherapy (vincristine, cisplatin, cyclophosphamide, and etoposide v vincristine, carboplatin, ifosfamide, and etoposide). Maintenance chemotherapy began after induction in children without progressive disease. Children with no residual tumors after induction therapy and no metastatic disease at diagnosis were not to receive radiation therapy unless their tumors progressed.

RESULTS

Two hundred ninety-nine infants were enrolled. Forty-two percent of patients responded to induction chemotherapy. At 5 years from study entry, the EFS rate was 27% +/- 3%, and the survival rate was 43% +/- 3%. There was no significant difference between the two arms in terms of response rate or EFS. For medulloblastoma, supratentorial primitive neuroectodermal tumor, ependymoma, and rhabdoid tumors, 5-year EFS rates were 32% +/- 5%, 17% +/- 6%, and 32% +/- 6%, and 14% +/- 7%, respectively. Fifty-eight percent of patients who were alive 5 years after study entry had not received radiation therapy.

CONCLUSION

Intensified induction chemotherapy resulted in a high response rate of malignant brain tumors in infants. Survival was comparable to that of previous studies, and most patients who survived did not receive radiation therapy.

Correlation of gamma-catenin expression with good prognosis in medulloblastomas

OBJECT

Medulloblastoma is a malignant cerebellar tumor of childhood and is difficult to cure due to frequent cerebrospinal fluid dissemination. Amplification of the c-myc gene (4%) and messenger (mRNA) overexpression (50%) are known to be adverse prognostic indicators. Because mRNA overexpression cannot be explained by gene amplification alone, mechanisms other than gene amplification are postulated. Molecules on the Wnt signal pathway in primary tumors were examined.

METHODS

Immunohistochemical and cytogenetic examinations of beta- and gamma-catenin, c-myc, N-myc, and cyclin D1 in 24 primary medulloblastomas were conducted, and their clinical relevance was evaluated. Cytoplasmic/membranous staining of beta- and gamma-catenin was detected in 19 (79%) and nine (37%) cases, respectively, and nuclear expression of cyclin D1 and c-myc was detected in six (25%) and 21 (83%) cases, respectively. The expression levels of gamma-catenin in Western blot analysis and immunohistochemistry were similar. By differential polymerase chain reaction, c-myc and N-myc were amplified separately in two large cell/anaplastic medulloblastomas. No cyclin D1 amplification, or beta- or gamma-catenin mutations were found. Kaplan-Meier analysis revealed no dissemination at diagnosis (Chang Grade M0) and gamma-catenin expression was correlated with good prognosis (p = 0.0002 and 0.003, respectively). Expression of gamma-catenin was also significant in the M0 group (p = 0.022). Expression of cyclin D1 showed a trend toward adverse outcome (p = 0.057) and all patients in whom cyclin D1 expression was found died of disease.

CONCLUSIONS

Expression of gamma-catenin is of great prognostic value and its immunohistochemistry may be useful for further stratification of treatment. Cyclin D expression may have the potential to be an adverse prognostic indicator.

Epigenetic repression of RASSF1A but not CASP8 in supratentorial PNET (sPNET) and atypical teratoid/rhabdoid tumors (AT/RT) of childhood

Supratentorial primitive neuroectodermal tumors (sPNET) and atypical teratoid/rhabdoid tumors (AT/RT) of the CNS represent a biological and clinical enigma, despite advances in both molecular techniques and clinical management for these two rare embryonal brain tumors of childhood. Epigenetic changes hold great potential as possible disease mechanisms and may be manipulated therapeutically. We thus studied aberrant methylation of the genes RASSF1A and CASP8 and its consequence on expression in cell lines and primary tumors using a combination of semiquantitative methylation specific PCR (MSP), bisulfite sequencing and RT-PCR. In all, 17 samples of autopsy-derived normal appearing brain served as controls. Opposed to control tissues 19/24 sPNET and 4/6 AT/RT demonstrated aberrant methylation for the RASSF1A promoter region. Treatment of cell lines using 5-Aza-2'-deoxycytidine (5AZA) alone or in combination with trichostatin A (TSA) succeeded in re-establishing expression of RASSF1A in cell lines derived from a renal rhabdoid, an AT/RT and a medulloblastoma. A 5' CpG-rich region of CASP8 was methylated in normal tissues and in tumors. However, CASP8 showed inconsistent expression patterns in normal and tumor tissues. Our results indicate that aberrant methylation of the RASSF1A promoter region may be of importance in the origin and progression of sPNET and AT/RT while the analysed 5'-CpG rich region of the CASP8 gene does not seem to play an important role in these tumors. Further studies of epigenetic changes in these rare tumors are warranted as their biology remains obscure and treatment efforts have been rather unsuccessfull.

A novel role for extracellular signal-regulated kinase 5 and myocyte enhancer factor 2 in medulloblastoma cell death

Expression of the neurotrophin-3 receptor, tyrosine kinase C (TrkC), is associated with favorable prognosis in medulloblastoma patients. This may be due to increased tumor apoptosis induced by TrkC activation. Neurotrophin-3/TrkC-induced apoptosis is inhibited by the mitogen-activated protein (MAP) kinase (MAPK) pharmacologic antagonists SB203580 and PD98059. In addition to extracellular signal-regulated kinase (ERK)-1/2, PD98059 also inhibits the more recently identified neurotrophin-responsive MAPK, ERK5 (big MAPK 1). In the present study, we investigate the contribution of ERK5 and its target myocyte enhancer factor 2 (MEF2) to neurotrophin-3/TrkC-induced medulloblastoma cell death. Neurotrophin-3 not only enhanced ERK5 phosphorylation but also significantly enhanced the transcriptional activity of MEF2, a specific target of ERK5. Overexpression of both ERK5 and MEF2 induced a statistically significant increase in cell death of neurotrophin-3-responsive and nonresponsive medulloblastoma cell lines (Daoy-trkC and Daoy) and primary cultures of patched heterozygous mouse medulloblastomas. Only those cells expressing MAP/ERK kinase 5 (MEK5) plus ERK5 or MEF2 constructs underwent apoptosis, indicating that overexpression of either is sufficient to induce medulloblastoma cell death. Expression of a dominant-negative MEF2 or small interfering RNA for the ERK5 activator, MEK5, significantly inhibited neurotrophin-3-induced cell death. The dominant-negative MEF2 construct also blocked MEK5/ERK5-induced cell death, supporting a role for MEF2 downstream of ERK5. Co-immunoprecipitation studies revealed direct interaction of phosphorylated ERK5 with MEF2 in response to neurotrophin-3. Our investigation of the mechanism of neurotrophin-3/TrkC-induced apoptosis has identified a novel role for both MEK5/ERK5 and MEF2 in cell death, suggesting that these molecules can be exploited to induce apoptosis in both TrkC-expressing and non-expressing medulloblastoma cells.

Role of NRSF/REST in the molecular mechanisms regulating neural-specific expression of trkC/neurotrophin-3 receptor gene

The processes of differentiation and development of neurons involve the induction of neuron-specific genes by instructive signals with subsequent neurotrophic factor-driven survival and functional maturation. We have previously shown that bone morphogenetic protein-2 (BMP2) and retinoic acid synergistically induce the responsiveness of developing sympathetic neurons to neurotrophic factors, neurotrophin 3 (NT-3), and GDNF by upregulating corresponding receptors concomitantly with the induction of other neuron-specific genes including BRINP1, a neuron-specific cell-cycle regulatory protein. In the present study, we analyzed transcriptional mechanisms regulating the neuron-specific expression of TrkC/NT-3 receptor gene. TrkC gene contains at least four NRSE/RE-1 (neuron-restrictive silencing element/repressor element 1)-like elements (TrkC-NRSE A-D). Consequently, we found that in non-neuronal cells, neuron-restrictive silencing factor (NRSF) acts on TrkC-NRSE D located at the downstream of exon 3 to suppress the promoter activity of TrkC gene in a manner similar to the mechanism of NRSF suppressing BRINP1 transcription. In contrast, in neuronal cells, the biological activity of NRSF on TrkC was suppressed. From these observations, molecular mechanisms regulating the expression of neuron-specific genes via NRSE during neuronal differentiation are discussed.

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.

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.

Combined histopathological and molecular cytogenetic stratification of medulloblastoma patients

This study examined the utility of stratifying children with medulloblastomas by a combination of refined histopathological classification and molecular cytogenetic evaluation. Detailed histopathological classification of tumors from a cohort of patients (n = 87) composed mainly of children entered into the International Society of Pediatric Oncology (SIOP)/United Kingdom Children's Cancer Study Group PNET3 trial (n = 65), included identification of the large cell/anaplastic phenotype. Fluorescence in situ hybridization was used to detect chromosome 17 abnormalities, losses of 9q22 and 10q24, and amplification of the MYCC and MYCN oncogenes. The large cell/anaplastic phenotype, which was present in 20% of medulloblastomas, emerged as an independent prognostic indicator. Loss of 17p13.3 (38% of medulloblastomas) was found across all of the histopathological variants, whereas MYCC/MYCN amplification (6%/8% of medulloblastomas) was significantly associated with the large cell/anaplastic phenotype. Both of these genetic abnormalities emerged as prognostic indicators. Loss of 9q22 was associated with the nodular/desmoplastic medulloblastoma variant, whereas loss of 10q24 was found in all of the variants. Together with metastatic tumor at presentation, the large cell/anaplastic phenotype, 17p13.3 loss, or high-frequency MYC amplification defined a high-risk group of children whose outcome was significantly (P = 0.0002) poorer than a low-risk group without these tumor characteristics. Combined evaluation of novel histopathological features and molecular cytogenetic abnormalities promises to allow stratification of patients with medulloblastoma, such that those likely to be cured will be spared the side effects of maximal therapy, which can be targeted at those with aggressive disease.

Expression of MATH1, a marker of cerebellar granule cell progenitors, identifies different medulloblastoma sub-types

In order to look for genetic markers helpful for the biological risk stratification of medulloblastomas (MBs) we assayed by real-time PCR expression levels of the following genes: MATH1, encoding a critical transcription factor for the differentiation of cerebellar granular cells (CGCs); PEDF, that encodes a trophic factor for CGCs and is located in a region of frequent allelic imbalance in MBs; and BIRC5, encoding the antiapoptotic protein survivin, usually overexpressed in malignancies. Expression levels of TRKC, higher in MBs with a more favorable prognosis, were also studied. Twenty-three patients were considered: MATH1 expression was strong in 14/23 and undetectable in the others. PEDF was up-regulated in 8/23, TRKC in 9/23, and BIRC5 in 23/23. MATH1 expression was significantly correlated with adult age (p < 0.0001), tumor location in hemispheres rather than the vermis (p < 0.0004), and PEDF and TRKC up-regulation (p < 0.008 and p < 0.04, respectively). During development MATH1 is selectively expressed in the external germinal layer (EGL) of the cerebellum. Thus, MATH1 expression identifies a subgroup of MBs that derive from the EGL and arise during adult age into cerebellar hemispheres. MATH1 mRNA-positive MBs express high levels of PEDF and show a trend towards longer survival, in agreement with increased expression of TRKC. BIRC5 expression, which is strong in all MBs and absent in normal cerebellum, lacks any prognostic value but could be explored for selective targeting of therapeutic factors to MBs.

Expression of matrix metalloproteinases and their inhibitors in medulloblastomas and their prognostic relevance

PURPOSE AND EXPERIMENTAL DESIGN

The cellular mechanisms leading to metastatic disease in medulloblastoma (MB), the most common malignant brain tumor in childhood, are mainly unknown. Recently, however, the involvement of matrix metalloproteinases (MMPs) has been suggested. We examined the expression and localization of four MMPs-MMP-2 and -9, membrane-type 1 and 2 MMP (MT1- and MT2-MMP)-and correlated the data with those for their main inhibitors, tissue inhibitors of metalloproteinases (TIMP-1, -2, and -3), in 83 classical and 18 desmoplastic MBs.

RESULTS

Independent of the histological subtype, MMP-2 expression was found in a small percentage of tumors, whereas MMP-9 and MT1- or MT2-MMP were expressed in >75% of tumor samples. The expression of TIMP-1, -2, and -3, on the other hand, was found to depend on the histological subtype: TIMP-3 was often found in classical MB, whereas TIMP-2 was often expressed in desmoplastic MB (P = 0.007-0.001). In addition, both TIMP-3 and -2 correlated significantly with the expression of all studied metalloproteinases except MMP-2. TIMP-1, detected only in classical MB in a low percentage, was the only TIMP that correlated with the expression of MMP-2. Kaplan-Meier estimation revealed significantly reduced long-term survival of patients with strong MMP expression in tumor samples. In multivariate logistic regression analysis, however, the prognosis was significantly determined only by clinical parameters.

CONCLUSIONS

TIMP-3 and -2 expression is highly correlated with histological subtypes of MBs and strongly associated with the expression of certain MMPs. The expression of TIMPs and MMPs, however, does not determine prognosis independently of clinical parameters.

Prognosis-related histomorphological and immunohistochemical markers in central nervous system tumors of childhood and adolescence

Brain tumors account for approximately 20% of all childhood cancers, and are the leading cause of cancer morbidity and mortality among children. Although numerous demographic, clinical and therapeutic parameters have been identified over the past few years that have significant prognostic bearing for some pediatric brain tumors, predicting the clinical course and outcome among children with central nervous system tumors is still difficult. A survey of publications on prognosis-related histopathological and immunohistochemical features among pediatric brain tumors revealed 172 series, of which 91 presented statistically significant outcome-associated parameters as defined by a P value of less than 0.05. Most investigations revealing significant prognosis-related markers were performed on medulloblastomas (30 publications), ependymomas (25) and astrocytic tumors (18). In total, 16 cohorts consisted of more than 100 cases (5 on ependymomas, 3 each on medulloblastomas and astrocytic tumors). On the other hand, there were also 13 series with fewer than 20 cases (5 on medulloblastomas). Potentially prognostic histopathological markers vary among different entities and consist of assessment of necroses, mitoses, differentiation, vascular proliferation, and growth pattern, whereas immunohistochemical features include proliferation markers (Ki-67, MIB-1), expression of oncogenes/tumor suppressor genes and their proteins (TP53, c-erbB2), growth factor and hormonal receptors (VEGF, EGFR, HER2, HER4, ErbB-2), cell cycle genes (p27, p14ARF) and cell adhesion molecules, as well as factors potentially related to therapeutic resistance (DNA topoisomerase IIalpha, metallothionein, P-glycoprotein, tenascin). This review discusses the prognostic potential of histopathological and immunohistochemical markers that can be investigated by the practicing neuropathologist as part of the routine diagnostic workload, and scrutinizes their benefit for predicting therapy response and patient outcome among children with brain tumors.

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.

Prognosis-Related Molecular Markers in Pediatric Central Nervous System Tumors

In the wake of recent progress in understanding the genetic pathways involved in the development of brain tumors, a major goal is to correlate molecular data with clinical outcome, survival, and response to treatment modalities. This is of particular importance among the pediatric population. Reliable prognostic factors could potentially permit a tailoring of therapy in that only patients with the most aggressive tumors would receive the most intense treatments. A survey of publications about prognosis-related molecular features among pediatric brain tumors revealed 74 series, of which 46 presented statistically significant outcome-associated parameters as defined by a p value <0.05. Most investigations revealing significant prognosis-related features were performed on medulloblastomas (34 publications), followed by astrocytic tumors (6 publications) and ependymomas (5 publications). Promising approaches and molecular markers include gene expression profiles, DNA ploidy, loss of heterozygosity and chromosomal aberrations as detected by CGH and FISH (1q, 17p, 17q), as well as oncogenes/ tumor suppressor genes and their proteins (TP53, PTEN, c-erbB2, N-myc, c-myc), growth factor and hormonal receptors (PDGFRA, VEGF, EGFR, HER2, HER4, ErbB-2, hTERT, TrkC), cell cycle genes (p27) and cell adhesion molecules, as well as factors potentially related to therapeutic resistance (multi-drug resistance, DNA topoisomerase IIalpha, metallothionein, P-glycoprotein, tenascin). This review discusses the predictive potential of molecular markers for clinical outcome and their influence on therapeutic decision-making among children with brain tumors.

A Clinicobiological Model Predicting Survival in Medulloblastoma

PURPOSE

The purpose of this study was to determine the relative contributions of biological and clinical predictors of survival in patients with medulloblastoma (MB).

EXPERIMENTAL DESIGN

Clinical presentation and survival information were obtained for 119 patients who had undergone surgery for MB at the Hospital for Sick Children (Toronto, Ontario, Canada) between 1985 and 2001. A tissue microarray was constructed from the tumor samples. The arrays were assayed for immunohistochemical expression of MYC, p53, platelet-derived growth factor receptor-alpha, ErbB2, MIB-1, and TrkC and for apoptosis (terminal deoxynucleotidyl transferase-mediated nick end labeling). Both univariable and multivariable analyses were conducted to characterize the association between survival and both clinical and biological markers. For the strongest predictors of survival, a weighted predictive score was calculated based on their hazard ratios (HRs). The sum of these scores was then used to give an overall prediction of survival using a nomogram.

RESULTS

The four strongest predictors of survival in the final multivariable model were the presence of metastatic disease at presentation (HR, 2.02; P=0.01) and p53 (HR, 2.29; P=0.02), TrkC (HR, 0.65; P=0.14), and ErbB2 (HR, 1.51; P=0.21) immunopositivity. A linear prognostic index was derived, with coefficients equal to the logarithm of these HRs. The 5-year survival rate for patients at the 10th, 50th, and 90th percentiles of the score distribution was 80.0%, 71.0%, and 35.7%, respectively, with radiation therapy and 70.5%, 58.5%, and 20.0%, respectively, without radiation therapy.

CONCLUSIONS

In this study, we demonstrate an approach to combining both clinical and biological markers to quantify risk in MB patients. This provides further prognostic information than can be obtained when either clinical factors or biological markers are studied separately and establishes a framework for comparing prognostic markers in future clinical studies.

Current treatment of medulloblastoma: recent advances and future challenges

Medulloblastoma (MB) is the most common malignant brain tumor of childhood, yet it makes up only 1% of adult brain tumors. MB is uniquely sensitive to chemotherapy and radiation, but successful surgical resection continues to be an important component of therapeutic success. Progress in the treatment of MB has occurred in multiple areas from improved neurosurgical techniques, refined dosing and delivery of radiation, and optimized chemotherapy. Tumors are currently risk-stratified as average risk or high risk depending on clinical factors such as age, extent of resection, and presence of metastases. Molecular biology is beginning to improve upon clinical prognostication and may soon provide the means to accurately predict response to therapy. Treatment for average-risk MB has achieved a level of success that allows efforts to be focused on the limitation of adverse treatment effects. Therapy for high-risk and relapsed MB has been positively affected by the advent of high-dose chemotherapy with stem cell rescue. In addition, molecular targets are being elucidated and new therapeutic agents are being tested for safety and efficacy. Treatment for this disease has evolved a great deal over the preceding decades, but a great deal of work remains to be done to effect reliable cures while reducing long-term sequelae of therapy.

Review of the prognostic factors in medulloblastoma of children and adults

Medulloblastoma (MB) is rare in adults, accounting for 1% of all primary tumours of the central nervous system (CNS). Based on the assumption that the disease pattern in adults is similar to that in children, adults with medulloblastoma are treated using paediatric protocols. Thanks to progress made in recent years, long-term survival is now possible, with overall ranging from 50 to 60% at 5 years and 40 to 50% at 10 years. However, effective therapy may have devastating long-term side effects, including neuro-psychic and neuro-endocrine sequelae and cognitive dysfunction, especially in young adults. Great interest has been expressed in new biological and molecular prognostic factors, which, combined with clinical variables, may allow a more satisfactory stratification of patients.

Combining Gene Expression Profiles and Clinical Parameters for Risk Stratification in Medulloblastomas

Purpose

Stratification of risk in patients with medulloblastoma remains a challenge. As clinical parameters have been proven insufficient for accurately defining disease risk, molecular markers have become the focus of interest. Outcome predictions on the basis of microarray gene expression profiles have been the most accurate to date. We ask in a multivariate model whether clinical parameters enhance survival predictions of gene expression profiles.

Patients and Methods

In a cohort of 55 young patients (whose medulloblastoma samples have been analyzed previously for gene expression profile), associations between clinical and gene expression variables and survival were assessed using Cox proportional hazards models. Available clinical variables included age, stage (ie, the presence of disseminated disease at diagnosis), sex, histologic subtype, treatment, and status.

Results

Univariate analysis demonstrated expression profiles to be the only significant clinical prognostic factor (P = .03). In multivariate analysis, gene expression profiles predicted outcome independent of other criteria. Clinical criteria did not significantly contribute additional information for outcome predictions, although an exploratory analysis noted a trend for decreased survival of patients with metastases at diagnosis but favorable gene expression profile.

Conclusion

Gene expression profiling predicts medulloblastoma outcome independent of clinical variables. These results need to be validated in a larger prospective study.

Clinical, histopathologic, and molecular markers of prognosis: toward a new disease risk stratification system for medulloblastoma

PURPOSE

To assess the feasibility of performing central molecular analyses of fresh medulloblastomas obtained from multiple institutions and using these data to identify prognostic markers for contemporaneously treated patients.

MATERIALS AND METHODS

Ninety-seven samples of medulloblastoma were collected. Tumor content in samples was judged by frozen section review. Tumor ERBB2 protein and MYCC, MYCN, and TRKC mRNA levels were measured blind to clinical details using Western blotting and real-time polymerase chain reaction, respectively. Histopathologic and clinical review of each case was also performed. All data were subjected to independent statistical analysis.

RESULTS

Sample acquisition and analysis times ranged from 3 to 6 days. Eighty-six samples contained sufficient tumor for analysis, including 38 classic, 30 nodular desmoplastic, and 18 large-cell anaplastic (LCA) medulloblastomas. Protein and mRNA were extracted from 81 and 49 tumors, respectively. ERBB2 was detected in 40% (n=32 of 81) of tumors, most frequently in LCA disease (P=.005), and was independently associated with a poor prognosis (P=.031). A combination of clinical characteristics and ERBB2 expression provided a highly accurate means of discriminating disease risk. One hundred percent (n=26) of children with clinical average-risk, ERBB2-negative disease were alive at 5 years, with a median follow-up of 5.6 years, compared with only 54% for children with average-risk, ERBB2-positive tumors (n=13; P=.0001). TRKC, MYCC, and MYCN expression and histopathologic subtype were not associated with prognosis in this study.

CONCLUSION

Central and rapid molecular analysis of frozen medulloblastomas collected from multiple institutions is feasible. ERBB2 expression and clinical risk factors together constitute a highly accurate disease risk stratification tool.

Medulloblastomas and central nervous system primitive neuroectodermal tumors

Significant advances in the treatment of medulloblastoma and primitive neuroectodermal tumors have been made in the past three decades. Maximal surgical resection is a mainstay of therapy. However, unlike many other central nervous system neoplasms, medulloblastoma and primitive neuroectodermal tumors are radiation and chemotherapy responsive. Despite this response, the prognosis for patients with these tumors remains variable and is relatively poor in infants and patients with metastatic disease. These tumors most commonly arise in children, thus most clinical trials emphasize the reduction of long-term sequelae, in addition to improving survival. All newly diagnosed patients who are eligible should be offered participation in a clinical trial. If a patient is ineligible or declines consent/assent for a clinical trial, the best current treatment approach is surgical resection, followed by radiation therapy (except for children younger than 3 years) with weekly vincristine. For high-risk patients, 36 Gy of craniospinal irradiation should be delivered plus a boost of 19.8 Gy to the posterior fossa/primary tumor bed and sites of bulk metastatic disease. For average-risk patients, the craniospinal irradiation dose may be lowered to 23.4 Gy plus 32.4 Gy to the posterior fossa/tumor bed. After radiation therapy, intensive multimodal chemotherapy should be used for all patients.

Medulloblastoma tumorigenesis diverges from cerebellar granule cell differentiation in patched heterozygous mice

Medulloblastoma is a cerebellar tumor that can arise through aberrant activation of Sonic hedgehog (Shh) signaling, which normally regulates cerebellar granule cell proliferation. Mutations of the Shh receptor PATCHED (PTCH) are associated with medulloblastomas, which have not been found to have loss of PTCH heterozygosity. We address whether patched (Ptc) heterozygosity fundamentally alters granule cell differentiation and contributes to tumorigenesis by increasing proliferation and/or decreasing apoptosis in Ptc+/- mice. Our data show that postnatal Ptc+/- mouse granule cell precursor growth is not globally altered. However, many older Ptc+/- mice display abnormal cerebellar regions containing persistently proliferating granule cell precursors. Since fewer Ptc+/- mice form medulloblastomas, these granule cell rests represent a developmentally disrupted, but uncommitted stage of tumorigenesis. Although Ptc+/- mouse medulloblastomas express neurodevelopmental genes, they diverge from granule cell differentiation in their discordant coexpression of postmitotic markers despite their ongoing growth. Like human medulloblastomas, mouse tumors with reduced levels of the neurotrophin-3 receptor, trkC/Ntrk3, display decreased apoptosis in vivo, illustrating the role of TrkC in regulating tumor cell survival. These results indicate that Ptc heterozygosity contributes to tumorigenesis by predisposing a subset of granule cell precursors to the formation of proliferative rests and subsequent dysregulation of developmental gene expression.

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.

Genetic alterations of human brain tumors as molecular prognostic factors

Despite a number of basic and clinical studies, it is still very difficult to improve the prognosis of patients with high-grade astrocytoma. However, the recent success of procarbazine, N-(2-chloroethyl)-N'-cyclohexyl-N-nitrosourea and vincristine (PCV) chemotherapy for oligodendrogliomas that have lost chromosomes 1p and 19q has encouraged the authors to evaluate the biological behavior of brain tumors by means of genetic analysis. Both the disorders of the p53/MDM2/p14(ARF) and the p16(INK4a)/RB signaling pathways have been found to play an essential role in tumorigenesis of various brain tumors. Herein, the authors summarize the genetic alterations of brain tumors by mainly focusing on two pathways that appear to affect significantly the patient prognosis.

Insulin-like growth factor-I receptor - a potential therapeutic target in medulloblastomas

Medulloblastomas represent nearly 25% of all paediatric intracranial neoplasms. These highly malignant tumours arise from the cerebellum and affect predominantly children between the ages of 5 and 15. Although the aetiology of medulloblastomas has not been elucidated, several reports show that the insulin-like growth factor-I (IGF-I) signalling system is highly activated in medulloblastoma cell lines, medulloblastoma animal models and medulloblastoma biopsies, suggesting its contribution to the development and/or progression of these tumours. In addition, reports from multiple laboratories confirm a critical role for the IGF-I receptor (IGF-IR) in the process of cellular transformation. Taken together, these observations prompt the investigation of different strategies to impair the function of IGF-IR as a potential therapeutic tool, which by compromising growth and survival of medulloblastoma cells could supplement conventional therapeutic regiments against these malignant neoplasms of childhood.

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.

Immunohistochemical markers for prognosis of average-risk pediatric medulloblastomas. The effect of apoptotic index, TrkC, and c-myc expression

Medulloblastomas (MB) are the most common central nervous system malignancies in children. Numerous publications describe certain efforts to identify predictive value of various patterns of MB pathology and immunohistochemistry but received data appear to be controversial. In the present study, the apoptotic index (AI) and immunoexpression of TrkC, and c-myc proteins were investigated in biopsy samples from 68 MB with an average clinical risk to determine their prognostic utility in this tumor category. The number of cases with AI > 1.5% was significantly greater in the group of tumors in patients with recurrent MB and the mean AI was significantly higher in this group -4.7% vs. 1.1%. Furthermore, the number of tumors with AI > 1.5% was greater in the group of tumors in deceased patients and the mean Al was also higher in this group -4.6% vs. 1.2%. Immunoreactivity of the c-myc and TrkC did not show any differences between groups of patients with various clinical outcomes. A close association between Al as a continuous variable and the progression-free and overall survival was found. We found no any differences in survival times for c-myc and TrkC immunoreactivity. Multivariate revealed analysis that AI is a single significant prognostic factor for MB survival. Perhaps, investigations of c-myc and TrkC mRNA levels should be useful for clinical purposes, but in order to introduce these biomolecular markers in clinical protocols its distinct prognostic significance needs to be proved by prospective studies.

Familial medulloblastoma: case report of one family and review of the literature

OBJECTIVE AND IMPORTANCE

Medulloblastoma is the most common malignant brain tumor and the most common malignant solid tumor in children. Most medulloblastomas are sporadic, but rare familial forms have been described. To the best of our knowledge, only 10 case reports of familial medulloblastoma have been published. A variety of candidate genes have been suggested to be involved in familial medulloblastomas. However, the exact pathogenesis and genetics involved in familial medulloblastoma remain unknown.

CLINICAL PRESENTATION

We describe the presentation of medulloblastoma in two siblings (one of each sex) and their great-uncle. The three cases differ with regard to age at onset and pathological subtype of medulloblastoma. INTERVENTION OR TECHNIQUE: Immunostaining of tissue blocks for gene products involved in medulloblastoma differed in the two siblings for beta-catenin and was similar with staining for gli.

CONCLUSION

This article is only the second report in the literature to address the genetics of familial medulloblastoma in the absence of characterized conditions such as Li-Fraumeni's cancer syndrome and basal cell nevus, Rubinstein-Taybi's, and Turcot's syndromes. The discrepancy in beta-catenin staining in the two siblings suggests that the two tumors differentiated through divergent pathways. We briefly summarize all published cases of familial medulloblastoma and review the literature on the genes involved in medulloblastoma formation.

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.

Risk assignment in childhood brain tumors: the emerging role of molecular and biologic classification

Brain tumors as a group are the most common solid tumors of childhood and currently have the highest mortality rate. A major emphasis has historically been placed on stratifying therapy for these tumors based on histologic and clinical prognostic factors. However, with the increasing application of molecular approaches to refine the categorization of these tumors, it has become apparent that histologically comparable lesions may exhibit diverse patterns of gene expression and genomic alterations, which may correspond with important prognostic distinctions. This paper summarizes these observations and discusses how they are being applied in a preliminary fashion as a foundation for risk-adapted stratification of childhood brain tumor therapy.

Expression of Apo-3 and Apo-3L in primitive neuroectodermal tumours of the central and peripheral nervous system

Deregulation of apoptosis has been implicated in the pathogenesis, spontaneous regression and treatment resistance of neuroblastoma. A newly recognised member of the tumour necrosis factor (TNF)-family of death receptors known as Apo-3 has been mapped to human chromosome 1p36.3, a region commonly deleted in aggressive neuroblastoma. Based on its localisation and function, Apo-3 is a candidate for the putative neuroblastoma tumour suppressor gene. Therefore we analysed mRNA expression of the Apo-3 receptor/ligand (Apo-3/Apo-3L) system in a representative panel of 18 neuroblastoma cell lines, 41 primary neuroblastoma and 13 ganglioneuromas/ganglioneuroblastomas by semi-quantitative RT-PCR. We compared the level of expression with the well-established prognostic factors age, stage, histology, MYCN-amplification and TrkA expression, as well as outcome. For comparison, we studied Apo-3/Apo-3L expression in 27 central nervous system (CNS) primitive neuroectodermal tumours/medulloblastomas (PNET/medulloblastoma) and in six normal brain samples. Neuroblastoma cell lines with 1p deletion and MYCN-amplification expressed significantly lower levels of Apo-3 (P=0.009 and P=0.03, respectively) compared with neuroblastoma cell lines without 1p deletion or MYCN-amplification. The mean expression level of Apo-3L was significantly higher in ganglioneuromas/ganglioneuroblastomas compared with neuroblastomas (P=0.001) and in normal brain compared with PNET/medulloblastoma (P<0.0001). Expression of Apo-3L was significantly associated with survival in neuroblastomas (P<0.049) and in PNET/medulloblastomas (P=0.01). Expression of Apo-3 was significantly associated with survival in PNET/medulloblastomas (P=0.03). Thus, the Apo-3 receptor/ligand system might be involved in the regulation of apoptosis in neuroblastomas and PNET.

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.

Review of the molecular genetics and chemotherapeutic treatment of adult and paediatric medulloblastoma

Medulloblastoma is the most common primary brain tumour in children and accounts for 25% of newly diagnosed cases. Recent advances in treatment have extended 5-year survival rates from 3 - > 70% during the past 50 years. These improvements in survival have resulted from a multi-modality approach that includes surgical resection, posterior fossa and craniospinal irradiation and chemotherapy for selected, high-risk patients. The literature regarding chemotherapy of adult and paediatric patients is reviewed in-depth. The most active agents include cisplatin, CCNU, cyclophosphamide, vincristine and carboplatin. Although patients are living longer with their disease, neurocognitive function and quality of life are often impaired following radiation therapy (RT) to the developing brain. To safely allow reductions in the dose of RT, the specificity and efficacy of chemotherapy must be improved. Recent advances in the molecular genetics of medulloblastoma transformation (e.g., myc, PTCH ) are reviewed and discussed. A thorough understanding of these pathways will be critical for the development of more specific, novel drugs. Further clinical trials will be needed to evaluate the activity of these new drugs and determine their role in the treatment plan of patients with medulloblastoma.

Angiogenic profile of childhood primitive neuroectodermal brain tumours/medulloblastomas

Primitive neuroectodermal brain tumours (PNET) including medulloblastomas (PNET/MB) are the most common malignant brain tumours of childhood. Similar to many other brain tumours, PNET/MB often show marked neovascularisation. To determine which angiogenic factors contribute to PNET/MB angiogenesis, we examined the expression of eight angiogenic factors (vascular endothelial growth factors (VEGF, VEGF-B, VEGF-C), basic fibroblast growth factor (bFGF), angiopoetins (Ang-1, Ang-2), transforming growth factor (TGF-alpha), and platelet-derived endothelial growth factor (PDGF-A)) by semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) in six PNET cell lines and 28 primary PNET/MB. Expression levels of angiogenic factors were compared with microvessel density, TrkC mRNA expression, clinical variables and survival outcomes. Our results indicate that all PNET/MB tested produce a wide range of angiogenic factors that are, individually or together, likely to play a direct role in PNET/MB tumour growth. This suggests that anti-angiogenesis approaches targeting VEGF alone may be insufficient in PNET/MB.

Expression profiling of medulloblastoma: PDGFRA and the RAS/MAPK pathway as therapeutic targets for metastatic disease

Little is known about the genetic regulation of medulloblastoma dissemination, but metastatic medulloblastoma is highly associated with poor outcome. We obtained expression profiles of 23 primary medulloblastomas clinically designated as either metastatic (M+) or non-metastatic (M0) and identified 85 genes whose expression differed significantly between classes. Using a class prediction algorithm based on these genes and a leave-one-out approach, we assigned sample class to these tumors (M+ or M0) with 72% accuracy and to four additional independent tumors with 100% accuracy. We also assigned the metastatic medulloblastoma cell line Daoy to the metastatic class. Notably, platelet-derived growth factor receptor alpha (PDGFRA) and members of the downstream RAS/mitogen-activated protein kinase (MAPK) signal transduction pathway are upregulated in M+ tumors. Immunohistochemical validation on an independent set of tumors shows significant overexpression of PDGFRA in M+ tumors compared to M0 tumors. Using in vitro assays, we show that platelet-derived growth factor alpha (PDGFA) enhances medulloblastoma migration and increases downstream MAP2K1 (MEK1), MAP2K2 (MEK2), MAPK1 (p42 MAPK) and MAPK3 (p44 MAPK) phosphorylation in a dose-dependent manner. Neutralizing antibodies to PDGFRA blocks MAP2K1, MAP2K2 and MAPK1/3 phosphorylation, whereas U0126, a highly specific inhibitor of MAP2K1 and MAP2K2, also blocks MAPK1/3. Both inhibit migration and prevent PDGFA-stimulated migration. These results provide the first insight into the genetic regulation of medulloblastoma metastasis and are the first to suggest a role for PDGFRA and the RAS/MAPK signaling pathway in medulloblastoma metastasis. Inhibitors of PDGFRA and RAS proteins should therefore be considered for investigation as possible novel therapeutic strategies against medulloblastoma.

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.

Apoptosis, neuronal maturation, and neurotrophin expression within medulloblastoma nodules

Nodular/desmoplastic medulloblastomas are a well-established histopathological subtype containing reticulin-free nodules or "pale islands' that are comprised of cells with round "neurocytic" nuclei and abundant cytoplasm. Significant neuronal maturation occurs within nodules. We used immunohistochemistry to evaluate neuronal differentiation in the nodules of 6 of these tumors. The neuronal markers NeuN, synaptophysin, and MAP-2 were identified in the "pale islands" of all 6 nodular medulloblastomas examined, and high and medium molecular weight nonphosphorylated neurofilaments were detected in 2 of the 6 cases. We also observed collections of apoptotic cells within nodules. Given the known role of neurotrophin signaling in neuronal maturation and apoptosis, we analyzed immunohistochemically the distribution of neurotrophin receptors TrkA and TrkC and their primary ligands NGF and NT3 in 14 nodular medulloblastomas. TrkA and TrkC were detected in 13 and 10 cases, respectively, and were predominantly localized within nodules. NGF and NT3 were distributed diffusely with some nodular accentuation. The localized expression of Trk receptors within nodules of desmoplastic medulloblastomas suggests neurotrophin signaling is involved in the apoptosis and neuronal differentiation in medulloblastomas. We also examined expression of p53 and BCL-2 in these tumors; both were prominent in internodular regions but only weakly expressed within nodules. Trk receptors, p53, and BCL-2 are all expressed during development of the normal cerebellum. Interestingly, the immunohistochemical expression profile of these proteins in the differentiating nodules of medulloblastomas is in many ways similar to their expression in the developing cerebellum. Thus similar signaling pathways may be operational in cerebellar development and medulloblastoma tumor differentiation.

Prognostic significance of Ki-67 (MIB-1) proliferation index in childhood primitive neuroectodermal tumors of the central nervous system

BACKGROUND

Primitive neuroectodermal tumors (PNET) of the central nervous system, including medulloblastomas, are the most common malignant brain tumors of childhood. Whereas some patients experience prolonged disease control after surgery and adjuvant therapy, others with tumors that appear comparable will relapse and eventually die from progressive disease.

PROCEDURE

Because proliferative activity may provide a potential correlate of biologic aggressiveness, PNETs of 78 well-characterized patients were evaluated by Ki-67 (MIB-1) immunohistochemistry. Proliferation indices (PI) were determined by counting Ki-67 (MIB-1) positive tumor cells either in the highest staining region (hot spot PI), or in at least 15 randomly chosen fields (random PI).

RESULTS

Twenty-five of 78 PNETs showed amore than twofold higher value of hot spot PI (median 9.3%; range 0.6-56%), compared to random PI (median 5.6%; range 0.2-41.3%), Univariate Cox regression analysis revealed that PNETs with a high hot spot PI had a significantly greater risk of progression and death than PNETs with a low hot spot PI (hazard ratio 1.58, P = 0.04). The hazard ratio remained significant after adjusting for M-stage in multivariate analysis. In contrast to hot spot PI, random PI proved not to be a significant prognostic predictor.

CONCLUSIONS

Hot spot PI is a significant and independent prognostic factor in PNETs. Its assessment is uncomplicated, reliable, and may supplement routine histologic examination as a means for improving the accuracy of predicting the biologic behavior of childhood PNETs.

Expression of the neurotrophin receptor TrkB is associated with unfavorable outcome in Wilms' tumor

PURPOSE

Neurotrophins and their receptors regulate the proliferation, differentiation, and death of neuronal cells, and they have been implicated in the pathogenesis and prognosis of neuroblastomas and medulloblastomas. Tyrosine kinase (Trk) receptors also are expressed in extraneural tissues.

PATIENTS AND METHODS

To study the role of neurotrophin receptors and ligands in Wilms' tumor (WT), we determined their expression by semiquantitative duplex reverse transcriptase polymerase chain reaction in 39 patients with primary WT. Comparison of mRNA expression levels with clinical variables was performed by use of Cox regression analysis.

RESULTS

Children with WT that expressed high levels of full-length TrkB mRNA (TrkBfull) had a significantly greater risk of death than children whose tumors had little or no TrkBfull expression (hazard ratio, 9.7; P =.02). The 5-year relapse-free survival was 100% versus 65% for patients with low versus high tumor expression of TrkBfull (P <.003). Conversely, children with tumors that expressed high mRNA levels of a functionally inactive truncated TrkB receptor (TrkBtrunc) had a greater chance of survival than children with low levels of TrkBtrunc (hazard ratio, 0.08; P =.005). The 5-year relapse-free survival was 95% versus 68% for patients with high versus low levels of TrkBtrunc (P =.01). The hazard ratios for TrkBfull and TrkBtrunc remained significant after they were adjusted for tumor stage (P =.01 and P =.017, respectively). All WTs with high levels of TrkB expression also expressed the brain-derived nerve growth factor ligand.

CONCLUSION

Expression of TrkBfull in WT is associated with worse outcome, perhaps because it provides an autocrine survival pathway. Conversely, TrkBtrunc expression is associated with excellent outcome, perhaps as a result of a dominant negative effect.

Biological stability of RNA isolated from RNAlater-treated brain tumor and neuroblastoma xenografts

BACKGROUND

Advances in molecular biological research have led to identification of prognostic factors such as Trk mRNA expression in primitive neuroectodermal tumors of the CNS and neuroblastoma. To study prospectively the importance of these prognostic factors in large groups of homogeneously treated patients, tumor specimens of good quality must be acquired, preserved, and stored at multiple institutions. Immediate freezing of tumor biopsy samples in liquid nitrogen and storage at -70 degrees C are the most commonly used method of tissue preservation for future RNA analysis.

PROCEDURE

To evaluate alternative methods of preserving tissue samples for subsequent RNA analysis, we tested a new RNA stabilization solution. Using tumor tissue of two CNS tumor and one neuroblastoma human xenografts, we compared total RNA isolated from tumor tissue stored for 7 days at room temperature in stabilization solution to that of snap-frozen tissue. The quality of the RNA was studied by spectrophotometry, gel electrophoresis, RT-PCR, and gene expression profiling.

RESULTS

No major differences were observed in the quality of RNA isolated from tumor samples stored at room temperature in the RNA stabilization solution compared to snap-frozen tumor samples stored at -70 degrees C.

CONCLUSIONS

High-quality RNA can be prepared from tumor tissue stored at room temperature. Whenever snap freezing is not feasible, pieces of tumor tissue can be treated with RNAlater for subsequent RNA analysis. Short-term storage and shipment of well-preserved tumor tissue are clearly feasible for all institutions, thereby facilitating large multiinstitutional studies of biological prognostic factors.