Clinical and molecular stratification of disease risk in medulloblastoma

Clinical, Histological, and Molecular Prognostic Factors in Childhood Medulloblastoma: Where Do We Stand?

Medulloblastomas, highly aggressive neoplasms of the central nervous system (CNS) that present significant heterogeneity in clinical presentation, disease course, and treatment outcomes, are common in childhood. Moreover, patients who survive may be diagnosed with subsequent malignancies during their life or could develop treatment-related medical conditions. Genetic and transcriptomic studies have classified MBs into four subgroups: wingless type (WNT), Sonic Hedgehog (SHH), Group 3, and Group 4, with distinct histological and molecular profiles. However, recent molecular findings resulted in the WHO updating their guidelines and stratifying medulloblastomas into further molecular subgroups, changing the clinical stratification and treatment management. In this review, we discuss most of the histological, clinical, and molecular prognostic factors, as well the feasibility of their application, for better characterization, prognostication, and treatment of medulloblastomas.

Liquid biopsy-from bench to bedside

Over the last decade, molecular markers have become an integral part in the management of Central Nervous System (CNS) tumors. Somatic mutations that identify and prognosticate tumors are also detected in the bio-fluids especially the serum and CSF; the sampling of which is known as liquid biopsy (LB). These tumor-derived biomarkers include plasma circulating tumor cells (CTCs), cell-free DNA (cf/ctDNAs), circulating cell-free microRNAs (cfmiRNAs), circulating extracellular vesicles, or exosomes (EVs), proteins, and tumor educated platelets. Established in the management of other malignancies, liquid biopsy is becoming an important tool in the management of CNS tumors as well. This review presents a snapshot of the current state of LB research its potential and the possible pitfalls.

CAR-T Therapy for Pediatric High-Grade Gliomas: Peculiarities, Current Investigations and Future Strategies

High-Grade Gliomas (HGG) are among the deadliest malignant tumors of central nervous system (CNS) in pediatrics. Despite aggressive multimodal treatment - including surgical resection, radiotherapy and chemotherapy - long-term prognosis of patients remains dismal with a 5-year survival rate less than 20%. Increased understanding of genetic and epigenetic features of pediatric HGGs (pHGGs) revealed important differences with adult gliomas, which need to be considered in order to identify innovative and more effective therapeutic approaches. Immunotherapy is based on different techniques aimed to redirect the patient own immune system to fight specifically cancer cells. In particular, T-lymphocytes can be genetically modified to express chimeric proteins, known as chimeric antigen receptors (CARs), targeting selected tumor-associated antigens (TAA). Disialoganglioside GD2 (GD-2) and B7-H3 are highly expressed on pHGGs and have been evaluated as possible targets in pediatric clinical trials, in addition to the antigens common to adult glioblastoma – such as interleukin-13 receptor alpha 2 (IL-13α2), human epidermal growth factor receptor 2 (HER-2) and erythropoietin-producing human hepatocellular carcinoma A2 receptor (EphA2). CAR-T therapy has shown promise in preclinical model of pHGGs but failed to achieve the same success obtained for hematological malignancies. Several limitations, including the immunosuppressive tumor microenvironment (TME), the heterogeneity in target antigen expression and the difficulty of accessing the tumor site, impair the efficacy of T-cells. pHGGs display an immunologically cold TME with poor T-cell infiltration and scarce immune surveillance. The secretion of immunosuppressive cytokines (TGF-β, IL-10) and the presence of immune-suppressive cells – like tumor-associated macrophages/microglia (TAMs) and myeloid-derived suppressor cells (MDSCs) - limit the effectiveness of immune system to eradicate tumor cells. Innovative immunotherapeutic strategies are necessary to overcome these hurdles and improve ability of T-cells to eradicate tumor. In this review we describe the distinguishing features of HGGs of the pediatric population and of their TME, with a focus on the most promising CAR-T therapies overcoming these hurdles.

Bombesin Receptor Family Activation and CNS/Neural Tumors: Review of Evidence Supporting Possible Role for Novel Targeted Therapy

G-protein-coupled receptors (GPCRs) are increasingly being considered as possible therapeutic targets in cancers. Activation of GPCR on tumors can have prominent growth effects, and GPCRs are frequently over-/ectopically expressed on tumors and thus can be used for targeted therapy. CNS/neural tumors are receiving increasing attention using this approach. Gliomas are the most frequent primary malignant brain/CNS tumor with glioblastoma having a 10-year survival <1%; neuroblastomas are the most common extracranial solid tumor in children with long-term survival<40%, and medulloblastomas are less common, but one subgroup has a 5-year survival <60%. Thus, there is an increased need for more effective treatments of these tumors. The Bombesin-receptor family (BnRs) is one of the GPCRs that are most frequently over/ectopically expressed by common tumors and is receiving particular attention as a possible therapeutic target in several tumors, particularly in prostate, breast, and lung cancer. We review in this paper evidence suggesting why a similar approach in some CNS/neural tumors (gliomas, neuroblastomas, medulloblastomas) should also be considered.

Determining a cut-off residual tumor volume threshold for patients with newly diagnosed glioblastoma treated with temozolomide chemoradiotherapy: A multicenter cohort study

Standard-of-care treatment of glioblastomas involves maximal safe resection and adjuvant temozolomide chemo-radiotherapy. Although extent of resection (EOR) is a well-known surgical predictor for overall survival most lesions cannot be completely resected. We hypothesize that in the event of incomplete resection, residual tumor volume (RTV) may be a more significant predictor than EOR. This was a multicenter retrospective review of 147 adult glioblastoma patients (mean age 53 years) that underwent standard treatment. Semiautomatic magnetic resonance imaging segmentation was performed for pre- and postoperative scans for volumetric analysis. Cox proportional hazards regression and Kaplan-Meier survival analyses were performed for prognostic factors including: age, Karnofsky performance score (KPS), O(6)-methylguanine methyltransferase (MGMT) promoter methylation status, EOR and RTV. EOR and RTV cut-off values for improved OS were determined and internally validated by receiver operator characteristic (ROC) analysis for 12-month overall survival. Half of the tumors had MGMT promoter methylation (77, 52%). The median tumor volume, EOR and RTV were 43.20 cc, 93.5%, and 3.80 cc respectively. Gross total resection was achieved in 52 patients (35%). Cox proportional hazards regression, ROC and maximum Youden index analyses for RTV and EOR showed that a cut-off value of <3.50 cc (HR 0.69; 95% CI 0.48-0.98) and ≥84% (HR 0.64; 95% CI 0.43-0.96) respectively conferred an overall survival advantage. Independent overall survival predictors were MGMT promoter methylation (adjusted HR 0.35; 95% CI 0.23-0.55) and a RTV of <3.50 cc (adjusted HR 0.53; 95% CI 0.29-0.95), but not EOR for incompletely resected glioblastomas.

Reproducibility of the NanoString 22-gene molecular subgroup assay for improved prognostic prediction of medulloblastoma

Medulloblastoma is the most frequent malignant brain tumor in children. Four medulloblastoma molecular subgroups, MB_SHH , MB_WNT , MB_GRP3 and MB_GRP4 , have been identified by integrated high-throughput platforms. Recently, a 22-gene panel NanoString-based assay was developed for medulloblastoma molecular subgrouping, but the robustness of this assay has not been widely evaluated. Mutations in the gene for human telomerase reverse transcriptase (hTERT) have been found in medulloblastomas and are associated with distinct molecular subtypes. This study aimed to implement the 22-gene panel in a Brazilian context, and to associate the molecular profile with patients' clinical-pathological features. Formalin-fixed, paraffin-embedded (FFPE) medulloblastoma samples (n = 104) from three Brazilian centers were evaluated. Expression profiling of the 22-gene panel was performed by NanoString and a Canadian series (n = 240) was applied for training phase. hTERT mutations were analyzed by PCR followed by direct Sanger sequencing and the molecular profile was associated with patients' clinicopathological features. Overall, 65% of the patients were male, average age at diagnosis was 18 years and 7% of the patients presented metastasis at diagnosis. The molecular classification was attained in 100% of the cases, with the following frequencies: MB_SHH (n = 51), MB_WNT (n = 19), MB_GRP4 (n = 19) and MB_GRP3 (n = 15). The MB_SHH and MB_GRP3 subgroups were associated with older and younger patients, respectively. The MB_GRP4 subgroup exhibited the lowest 5-year cancer-specific overall survival (OS), yet in the multivariate analysis, only metastasis at diagnosis and surgical resection were associated with OS. hTERT mutations were detected in 29% of the cases and were associated with older patients, increased hTERT expression and MB_SHH subgroup. The 22-gene panel provides a reproducible assay for molecular subgrouping of medulloblastoma FFPE samples in a routine setting and is well-suited for future clinical trials.

A Pre-Clinical Assessment of the Pan-ERBB Inhibitor Dacomitinib in Pediatric and Adult Brain Tumors

Glioblastoma in adults, and medulloblastoma and pineoblastoma that mainly affect children, are aggressive brain tumors. The survival for patients with glioblastoma remains dismal. While the cure rate for medulloblastoma exceeds 70%, this figure has stagnated over the past few decades and survivors still contend with significant long-term debilitating side effects. The prognosis for pineoblastoma is age-dependent, with little chance of a cure for children younger than three years. More effective molecularly targeted strategies are urgently required to treat these cancers. Hyper-activation of epidermal growth factor receptor (EGFR) signaling is characteristic of several different classes of human cancers, including a subset of glioblastoma and medulloblastoma. This has provided the impetus for the development of a suite of EGFR pathway blockers, including second generation irreversible inhibitors, such as dacomitinib. We have developed a comprehensive drug evaluation pipeline, including in vitro interaction analyses and orthotopic xenograft mouse models, to address the efficacy of drugs for brain tumor treatment, enabling the exclusion of potentially ineffective treatments and prioritization of truly beneficial novel treatments for clinical trial. We used this system to examine the effects of dacomitinib as a single agent, or in combination with conventional chemotherapeutics, on the growth of human adult and pediatric brain tumor cell lines. Dacomitinib inhibited EGFR or EGFRvIII activity in vitro in all three tumor types tested, and as a single agent induced a modest increase in survival time for mice bearing glioblastoma, which accurately predicted human clinical trial data. For pediatric medulloblastoma, dacomitinib blocked EGFR/HER signalling in orthotopic xenografts and extended median survival as a single agent, however was antagonistic when used in combination with standard frontline medulloblastoma chemotherapies. The findings caution against the use of dacomitinib for pediatric brain tumor clinical trials.

Inactivation of Ezh2 Upregulates Gfi1 and Drives Aggressive Myc-Driven Group 3 Medulloblastoma

The most aggressive of four medulloblastoma (MB) subgroups are cMyc-driven group 3 (G3) tumors, some of which overexpress EZH2, the histone H3K27 mono-, di-, and trimethylase of polycomb-repressive complex 2. Ezh2 has a context-dependent role in different cancers as an oncogene or tumor suppressor and retards tumor progression in a mouse model of G3 MB. Engineered deletions of Ezh2 in G3 MBs by gene editing nucleases accelerated tumorigenesis, whereas Ezh2 re-expression reversed attendant histone modifications and slowed tumor progression. Candidate oncogenic drivers suppressed by Ezh2 included Gfi1, a proto-oncogene frequently activated in human G3 MBs. Gfi1 disruption antagonized the tumor-promoting effects of Ezh2 loss; conversely, Gfi1 overexpression collaborated with Myc to bypass effects of Trp53 inactivation in driving MB progression in primary cerebellar neuronal progenitors. Although negative regulation of Gfi1 by Ezh2 may restrain MB development, Gfi1 activation can bypass these effects.

Mir-34a mimics are potential therapeutic agents for p53-mutated and chemo-resistant brain tumour cells

Chemotherapeutic drug resistance and relapse remains a major challenge for paediatric (medulloblastoma) and adult (glioblastoma) brain tumour treatment. Medulloblastoma tumours and cell lines with mutations in the p53 signalling pathway have been shown to be specifically insensitive to DNA damaging agents. The aim of this study was to investigate the potential of triggering cell death in p53 mutated medulloblastoma cells by a direct activation of pro-death signalling downstream of p53 activation. Since non-coding microRNAs (miRNAs) have the ability to fine tune the expression of a variety of target genes, orchestrating multiple downstream effects, we hypothesised that triggering the expression of a p53 target miRNA could induce cell death in chemo-resistant cells. Treatment with etoposide, increased miR-34a levels in a p53-dependent fashion and the level of miR-34a transcription was correlated with the cell sensitivity to etoposide. miR-34a activity was validated by measuring the expression levels of one of its well described target: the NADH dependent sirtuin1 (SIRT1). Whilst drugs directly targeting SIRT1, were potent to trigger cell death at high concentrations only, introduction of synthetic miR-34a mimics was able to induce cell death in p53 mutated medulloblastoma and glioblastoma cell lines. Our results show that the need of a functional p53 signaling pathway can be bypassed by direct activation of miR-34a in brain tumour cells.

Inhibition of epidermal growth factor signaling by the cardiac glycoside ouabain in medulloblastoma

Epidermal growth factor (EGF) signaling regulates cell growth, proliferation, and differentiation. Upon receptor binding, EGF triggers cascades of downstream signaling, including the MAPK and phosphoinositide-3-kinase (PI3K)/Akt signaling pathways. Aberrant expression/activation of EGFR is found in multiple human cancers, including medulloblastoma, the most prevalent pediatric brain cancer, and often has been associated with metastasis, poor prognosis, and resistance to chemotherapy. Na,K-ATPase is an ion pump well known for its role in intracellular ion homeostasis. Recent studies showed that Na,K-ATPase also functions as a signaling platform and revealed a role in EGFR, MAPK, and PI3K signaling. While both EGFR and Na,K-ATPase seem to modulate similar signaling pathways, cardiac glycosides that are steroid-like inhibitors of Na,K-ATPase, exhibit antiproliferative and proapoptotic properties in cancer cells. Thus, we sought to better understand the relationship between EGF and cardiac glycoside signaling. Here, we show that in medulloblastoma cells, both EGF and ouabain activate Erk1/2 and PI3K/Akt signaling. Nevertheless, in medulloblastoma cells ouabain did not transactivate EGFR as has been reported in various other cell lines. Indeed, ouabain inhibited EGF-induced Erk1/2 and Akt activation and, moreover, prevented EGF-induced formation of actin stress fibers and cell motility, probably by activating a stress signaling response. Na,K-ATPase has been proposed to act as a signaling scaffold and our studies suggest that in medulloblastoma cells Na,K-ATPase might act as a check point to integrate EGF-associated signaling pathways. Thus, Na,K-ATPase might serve as a valid target to develop novel therapeutic approaches in tumors with aberrant activation of the EGFR signaling cascades.

Mutation and expression analysis in medulloblastoma yields prognostic variants and a putative mechanism of disease for i17q tumors

Current consensus identifies four molecular subtypes of medulloblastoma (MB): WNT, sonic hedgehog (SHH), and groups "3/C" and "4/D". Group 4 is not well characterized, but harbors the most frequently observed chromosomal abnormality in MB, i17q, whose presence may confer a worse outcome. Recent publications have identified mutations in chromatin remodeling genes that may be overrepresented in this group, suggesting a biological role for these genes in i17q. This work seeks to explore the pathology that underlies i17q in MB. Specifically, we examine the prognostic significance of the previously-identified gene mutations in an independent set of MBs as well as to examine biological relevance of these genes and related pathways by gene expression profiling. The previously-implicated p53 signaling pathway is also examined as a putative driver of i17q tumor oncogenesis. The data show gene mutations associated with i17q tumors in previous studies (KMD6A, ZMYM3, MLL3 and GPS2) were correlated with significantly worse outcomes despite not being specific to i17q in this set. Expression of these genes did not appear to underlie the biology of the molecular variants. TP53 expression was significantly reduced in i17q/group 4 tumors; this could not be accounted for by dosage effects alone. Expression of regulators and mediators of p53 signaling were significantly altered in i17q tumors. Our findings support that chromatin remodeling gene mutations are associated with significantly worse outcomes in MB but cannot explain outcomes or pathogenesis of i17q tumors. However, expression analyses of the p53 signaling pathway shows alterations in i17q tumors that cannot be explained by dosage effects and is strongly suggestive of an oncogenic role.

FoxG1 interacts with Bmi1 to regulate self-renewal and tumorigenicity of medulloblastoma stem cells

Brain tumors represent the leading cause of childhood cancer mortality, of which medulloblastoma (MB) is the most frequent malignant tumor. Recent studies have demonstrated the presence of several MB molecular subgroups, each distinct in terms of prognosis and predicted therapeutic response. Groups 1 and 2 are characterized by relatively good clinical outcomes and activation of the Wnt and Shh pathways, respectively. In contrast, groups 3 and 4 ("non-Shh/Wnt MBs") are distinguished by metastatic disease, poor patient outcome, and lack a molecular pathway phenotype. Current gene expression platforms have not detected brain tumor-initiating cell (BTIC) self-renewal genes in groups 3 and 4 MBs as BTICs typically comprise a minority of tumor cells and may therefore go undetected on bulk tumor analyses. Since increasing BTIC frequency has been associated with increasing tumor aggressiveness and poor patient outcome, we investigated the subgroup-specific gene expression profile of candidate stem cell genes within 251 primary human MBs from four nonoverlapping MB transcriptional databases (Amsterdam, Memphis, Toronto, Boston) and 74 NanoString-subgrouped MBs (Vancouver). We assessed the functional relevance of two genes, FoxG1 and Bmi1, which were significantly enriched in non-Shh/Wnt MBs and showed these genes to mediate MB stem cell self-renewal and tumor initiation in mice. We also identified their transcriptional regulation through reciprocal promoter occupancy in CD15+ MB stem cells. Our work demonstrates the application of stem cell data gathered from genomic platforms to guide functional BTIC assays, which may then be used to develop novel BTIC self-renewal mechanisms amenable to therapeutic targeting.

Cytogenetic prognostication within medulloblastoma subgroups

PURPOSE

Medulloblastoma comprises four distinct molecular subgroups: WNT, SHH, Group 3, and Group 4. Current medulloblastoma protocols stratify patients based on clinical features: patient age, metastatic stage, extent of resection, and histologic variant. Stark prognostic and genetic differences among the four subgroups suggest that subgroup-specific molecular biomarkers could improve patient prognostication.

PATIENTS AND METHODS

Molecular biomarkers were identified from a discovery set of 673 medulloblastomas from 43 cities around the world. Combined risk stratification models were designed based on clinical and cytogenetic biomarkers identified by multivariable Cox proportional hazards analyses. Identified biomarkers were tested using fluorescent in situ hybridization (FISH) on a nonoverlapping medulloblastoma tissue microarray (n = 453), with subsequent validation of the risk stratification models.

RESULTS

Subgroup information improves the predictive accuracy of a multivariable survival model compared with clinical biomarkers alone. Most previously published cytogenetic biomarkers are only prognostic within a single medulloblastoma subgroup. Profiling six FISH biomarkers (GLI2, MYC, chromosome 11 [chr11], chr14, 17p, and 17q) on formalin-fixed paraffin-embedded tissues, we can reliably and reproducibly identify very low-risk and very high-risk patients within SHH, Group 3, and Group 4 medulloblastomas.

CONCLUSION

Combining subgroup and cytogenetic biomarkers with established clinical biomarkers substantially improves patient prognostication, even in the context of heterogeneous clinical therapies. The prognostic significance of most molecular biomarkers is restricted to a specific subgroup. We have identified a small panel of cytogenetic biomarkers that reliably identifies very high-risk and very low-risk groups of patients, making it an excellent tool for selecting patients for therapy intensification and therapy de-escalation in future clinical trials.

Somatostatin receptor subtype 2 (sst₂) is a potential prognostic marker and a therapeutic target in medulloblastoma

INTRODUCTION

Neuroectodermal tumors in general demonstrate high and dense expression of the somatostatin receptor subtype 2 (sst₂). It controls proliferation of both normal and neoplastic cells. sst₂ has thus been suggested as a therapeutic target and prognostic marker for certain malignancies.

METHODS

To assess global expression patterns of sst 2 mRNA, we evaluated normal (n = 353) and tumor tissues (n = 340) derived from previously published gene expression profiling studies. These analyses demonstrated specific upregulation of sst 2 mRNA in medulloblastoma (p < 0.001). sst₂ protein was investigated by immunohistochemistry in two independent cohorts.

RESULTS

Correlation of sst₂ protein expression with clinicopathological variables revealed significantly higher levels in medulloblastoma (p < 0.05) compared with CNS-PNET, ependymoma, or pilocytic astrocytoma. The non-SHH medulloblastoma subgroup tumors showed particularly high expression of sst₂, when compared to other tumors and normal tissues. Furthermore, we detected a significant survival benefit in children with tumors exhibiting high sst₂ expression (p = 0.02) in this screening set. A similar trend was observed in a validation cohort including 240 independent medulloblastoma samples.

CONCLUSION

sst₂ is highly expressed in medulloblastoma and deserves further evaluation in the setting of prospective trials, given its potential utility as a prognostic marker and a therapeutic target.

Genetic grouping of medulloblastomas by representative markers in pathologic diagnosis

A recent analysis of the genetic features of medulloblastoma (MB) suggested classification into distinct subgroups according to gene expression profiles, including the Wingless signaling pathway-activated group (WNT group), the Sonic Hedgehog signaling pathway-activated group (SHH group), group 3, and group 4. To classify MB according to genetic features in practice, we analyzed 74 MBs using representative markers of each group. Based on immunohistochemistries (IHC), cytogenetic alterations, and a CTNNB1 mutation study, the patients were divided into the following three groups: cases showing nuclear β-catenin and/or CTNNB1 mutation and/or monosomy 6 were included in the WNT group (14/74, 18.9%); cases expressing GAB1 were included in the SHH group (15/74, 20.2%); cases that did not show positivity for markers of the WNT or SHH group were included in the non-WNT/SHH group (45/74, 60.6%). Immunoexpression of NPR3 seemed to lack sensitivity for classifying group 3, showing diffuse positivity in only two cases. KCNA1 was not specific to group 4 because it was expressed in all groups. Cases in the WNT group showed a slightly better survival than those in the SHH or non-WNT/SHH group, although additional cases are required for statistical significance. Isochromosome 17q (P = .002) and the large cell/anaplastic variant (P = .002) were demonstrated to be poor prognostic indicators in multivariate analysis. The representative IHC and cytogenetic data facilitated the division of MBs into the WNT and SHH groups; however, more specific markers should be added for the identification of group 3 and group 4 in practice.

Multiple CDK/CYCLIND genes are amplified in medulloblastoma and supratentorial primitive neuroectodermal brain tumor

Embryonal brain tumors, which include medulloblastoma and the more aggressive supratentorial primitive neuroectodermal tumor (sPNET), comprise one of the largest group of malignant pediatric brain tumors. We observed in high resolution array comparative genomic hybridization and polymerase chain reaction analyses that several different components of the CDK/CYCLIND/pRB regulatory complex, including the CDK4/6 and CCND1/2 loci, are targets of gene amplification in medulloblastoma and sPNET. CDK6 and CCND1 gene amplification were respectively most common and robust, and overall CDK/CYCLIND gene amplification was more commonly observed in sPNET (25%) than medulloblastoma (1-5%). CDK6 overexpression enhanced in vitro and in vivo oncogenicity and endogenous CDK6 or CCND1 knockdown decreased pRB phosphorylation and impaired cell cycle progression in both medulloblastoma and sPNET cell lines. Although animal models implicate the pRB tumor suppressor pathway in medulloblastoma and sPNET, mutations of RB1 or the related INK4 tumor suppressor loci are rare in primary human tumors. Our data suggest that CDK/CYCLIND gene amplification may represent important mechanisms for functional inactivation of pRB in medulloblastoma and sPNET.

Early recurrence in standard-risk medulloblastoma patients with the common idic(17)(p11.2) rearrangement

Medulloblastoma is diagnosed histologically; treatment depends on staging and age of onset. Whereas clinical factors identify a standard- and a high-risk population, these findings cannot differentiate which standard-risk patients will relapse and die. Outcome is thought to be influenced by tumor subtype and molecular alterations. Poor prognosis has been associated with isochromosome (i)17q in some but not all studies. In most instances, molecular investigations document that i17q is not a true isochromosome but rather an isodicentric chromosome, idic(17)(p11.2), with rearrangement breakpoints mapping within the REPA/REPB region on 17p11.2. This study explores the clinical utility of testing for idic(17)(p11.2) rearrangements using an assay based on fluorescent in situ hybridization (FISH). This test was applied to 58 consecutive standard- and high-risk medulloblastomas with a 5-year minimum of clinical follow-up. The presence of i17q (ie, including cases not involving the common breakpoint), idic(17)(p11.2), and histologic subtype was correlated with clinical outcome. Overall survival (OS) and disease-free survival (DFS) were consistent with literature reports. Fourteen patients (25%) had i17q, with 10 (18%) involving the common isodicentric rearrangement. The presence of i17q was associated with a poor prognosis. OS and DFS were poor in all cases with anaplasia (4), unresectable disease (7), and metastases at presentation (10); however, patients with standard-risk tumors fared better. Of these 44 cases, tumors with idic(17)(p11.2) were associated with significantly worse patient outcomes and shorter mean DFS. FISH detection of idic(17)(p11.2) may be useful for risk stratification in standard-risk patients. The presence of this abnormal chromosome is associated with early recurrence of medulloblastoma.

Molecular genetic analysis of the hepatocyte growth factor/MET signaling pathway in pediatric medulloblastoma

The hepatocyte growth factor (HGF)/MET pathway plays a critical role in the development of the nervous system and has been implicated in medulloblastoma pathogenesis. Recent studies have shown a role for gene amplification of activators of this pathway, as well as silencing of its inhibitors in medulloblastoma pathogenesis. We analyzed exon array data from a cohort of 103 primary medulloblastomas to show that HGF/MET pathway elements are dysregulated in tumors compared to normal cerebellum. To determine if mutation of HGF/MET pathway genes is a mechanism for pathway dysregulation, we conducted a mutational analysis by exon resequencing of three key components of this pathway, including serine protease inhibitor Kunitz-type 1 (SPINT1), serine protease inhibitor Kunitz-type 2 (SPINT2), and MET, in 32 primary human medulloblastoma specimens. From this analysis, we identified multiple coding synonymous and nonsynonymous single nucleotide polymorphisms in these genes among the 32 tumor samples. Interestingly, we also discovered two unreported sequence variants in SPINT1 and SPINT2 in two tumors that resulted in Arginine to Histidine amino acid substitutions at codons 418 and 233, respectively. However, conservation assessment and functional assays of these two variants indicate that they involve nonconserved residues and that they do not affect the function of SPINT1 and SPINT2 as tumor suppressor genes. In conclusion, our data suggest that mutation alone plays a minor role in causing aberrancies of the HGF/MET pathway in medulloblastoma in comparison with other malignancies such as breast, hepatocellular, renal, and lung carcinomas.

The micro-RNA 199b-5p regulatory circuit involves Hes1, CD15, and epigenetic modifications in medulloblastoma

Micro-RNA (miR) 199b-5p targets Hes1 in medulloblastoma, one of the downstream effectors of both the canonical Notch and noncanonical Sonic Hedgehog pathways. In medulloblastoma patients, expression of miR-199b-5p is significantly decreased in metastatic cases, thus suggesting a downregulation mechanism. We studied this mechanism, which is mediated mostly by Hes1 and epigenetic promoter modifications. The miR-199b-5p promoter region was characterized, which identified a Hes1 binding site, thus demonstrating a negative feedback loop of regulation. MiR-199b-5p was shown to be downregulated in several medulloblastoma cell lines and in tumors by epigenetic methylation of a cytosine-phosphate-guanine island upstream of the miR-199b-5p promoter. Furthermore, the cluster of differention (CD) carbohydrate antigen CD15, a marker of medulloblastoma tumor-propagating cells, is an additional direct target of miR-199b-5p. Most importantly, regulation of miR-199b-5p expression in these CD15+/CD133+ tumor-propagating cells was influenced by only Hes1 expression and not by any epigenetic mechanism of regulation. Moreover, reverse-phase protein array analysis showed both the Akt and extracellular-signal-regulated kinase pathways as being mainly negatively regulated by miR-199b-5p expression in several medulloblastoma cell lines and in primary cell cultures. We present here the finely tuned regulation of miR-199b-5p in medulloblastoma, underlining its crucial role by its additional targeting of CD15.

FISH and chips: the recipe for improved prognostication and outcomes for children with medulloblastoma

Rapidly evolving genomic technologies have permitted progressively detailed studies of medulloblastoma biology in recent years. These data have increased our understanding of the molecular pathogenesis of medulloblastoma, identified prognostic markers, and suggested future avenues for targeted therapy. Although current randomized trials are still stratified based largely on clinical variables, the use of molecular markers is approaching routine use in the clinic. In particular, integrated genomics has uncovered that medulloblastoma comprises four distinct molecular and clinical variants: WNT, sonic hedgehog (SHH), group 3, and group 4. Children with WNT medulloblastoma have improved survival, whereas those with group 3 medulloblastoma have a dismal prognosis. Additionally, integrated genomics has shown that adult medulloblastoma is molecularly and clinically distinct from the childhood variants. Prognostic and predictive markers identified by genomics should drive changes in stratification of treatment protocols for medulloblastoma patients on clinical trials once they can be demonstrated to be reliable, reproducible, and practical. Cases with excellent prognoses (WNT cases) should be considered for therapy de-escalation, whereas those with bleak prognoses (group 3 cases) should be prioritized for experimental therapy. In this review, we will summarize the genomic data published over the past decade and attempt to interpret its prognostic significance, relevance to the clinic, and use in upcoming clinical trials.

Medulloblastoma and primitive neuroectodermal tumors

Medulloblastomas and sPNETs remain highly problematic tumors to treat. Prognosis has improved over the past two decades, but many children who survive treatment have significant long-term sequelae. The improvements in outcome have been due to advances in surgical techniques, the wider use of chemotherapy, and the more judicious use of radiotherapy. For further improvements,the recent impressive discoveries concerning molecular mechanisms of embryonal tumor origin, development,and growth will need to be translated into molecularly based, risk-adapted therapy.

Shared molecular targets in pediatric gliomas and ependymomas

BACKGROUND

Recent advances in multidisciplinary treatment approaches have improved the overall prognosis of pediatric brain tumors, but some patients remain refractory to treatment and do poorly. Several molecularly targeted therapies are under development for the treatment of brain tumors, and high-grade gliomas in adults are a particular area of study.

PROCEDURE

To better understand if these new therapies can be used in pediatric populations, we examined the expression of the following seven marker genes involved in signaling pathways targeted by new therapies: β-catenin, suppressor of fused (SUFU), erythroblastic leukemia viral oncogene homolog (ERBB) 2, platelet-derived growth factor receptorα (PDGFRα), proliferating cell nuclear antigen (PCNA), secreted protein acid and rich in cysteine (SPARC), and granulocyte colony-stimulating factor receptor (G-CSFR). Samples from 27 patients with the primitive neuroectodermal tumor (PNET)/medulloblastomas (MBs) (n = 8), ependymomas (n = 5), or gliomas (n = 14) were assessed by quantitative real-time PCR. [Correction made here after initial online publication]. We assigned an EXP score to compare across samples and determined the levels of gene expression among tumor cell types.

RESULTS

Gene expression varied among the different tumors, but, within a tumor type, clear expression patterns were seen. The expression of SUFU, ERBB2, and PCNA in metastatic MBs were greater than that seen in non-metastatic MBs. Most glioma cases highly expressed PDGFRα and G-CSFR. Additionally, the expression patterns of gliomas and ependymomas were similar (r = 0.77, P = 0.04), but PNET/MBs substantially differed from gliomas (r = -0.37, P = 0.41) or ependymomas (r = 0.23, P = 0.62).

CONCLUSIONS

The development of new drugs targeting up-regulated pathways may be useful for the treatment of pediatric brain tumors. As new drugs are developed, gliomas and ependymomas may be treated with similar compounds.

Appraisal of the current staging system for residual medulloblastoma by volumetric analysis

AIM

This study aims to investigate the accuracy of the current staging system of childhood medulloblastoma by using volumetric image analysis on immediate post-operative MRI scans.

MATERIAL AND METHODS

Tumour volume and maximum cross area of residual medulloblastoma were measured on immediate post-operative MR scans of 37 children operated between 1999 and 2005.

RESULTS

Mean preoperative volume was 32 cm(3) (range 4.5-71.9 cm(3)). Mean post-operative volume was 3.3 cm(3) (range 0-23.3 cm(3)). At mean follow-up of 50.08 months (range 6-129), 15 (40%) patients had died. Cut-off limit for residual post-operative tumour volume employed was maximum cross section of 1.5 cm(2), which corresponds to volume of 1.376 cm(3); 14 patients (38%) had no residual tumour, 7 patients (19%) had less than 1.5 cm(2) and 16 patients (43%) had more than 1.5 cm(2) residual tumour in its maximum cross section area. In three patients (8.2%) there was mismatch between the measured maximum cross section area and volume. In particular, in two patients, the cross section areas were more than 1.5 cm(2) but the residual tumour volumes were less than 1.376 cm(3) (the cross section area overestimated the residual volume) and in one case, the cross section area was less than 1.5 cm(2) but the residual tumour volume was more than 1.376 cm(3) (the cross section area underestimated the residual volume; difference statistically significant, Fisher's exact test, p < 0.01).

CONCLUSIONS

It appears that volumetric measurement of residual medulloblastoma on immediate post-operative MRI scans may further improve the accuracy of staging process.

Prognostic classification of pediatric medulloblastoma based on chromosome 17p loss, expression of MYCC and MYCN, and Wnt pathway activation

Pediatric medulloblastoma is considered a highly heterogeneous disease and a new strategy of risk stratification to optimize therapeutic outcomes is required. We aimed to investigate a new risk-stratification approach based on expression profiles of medulloblastoma cohorts. We analyzed gene expression profiles of 30 primary medulloblastomas and detected strong evidence that poor survival outcome was significantly associated with mRNA expression profiles of 17p loss. However, it was not supported in independent cohorts from previously published data (n = 100). We speculated that this discrepancy might come from complex conditions of two important prognostic determinants: loss of tumor suppressors (chromosome 17p) and high expression of oncogenes c-myc (MYCC) or N-myc (MYCN). When patients were stratified into 5 or 7 subgroups based on simultaneous consideration of these 2 factors while defining the Wnt group as independent, obviously different survival expectancies were detected between the subgroups. For instance, predicted 5-year survival probabilities ranged from 19% to 81% in the 5 subgroups. We also found that age became a significant prognostic marker after adjusting for 17p, MYCC, and MYCN status. Diminished survival in age <3 years was more substantial in subgroups with high expression of MYCC, MYCN, or 17p loss but not in other subgroups, indicating that poor survival outcome might be synergistically affected by these 3 factors. Here we suggest a more tailored subgrouping system based on expression profiles of chromosome 17p, MYCC, and MYCN, which could provide the basis for a novel risk-stratification strategy in pediatric medulloblastoma.

The tumor biology and molecular characteristics of medulloblastoma identifying prognostic factors associated with survival outcomes and prognosis

Medulloblastomas (MB) are highly aggressive primitive neuroectodermal tumors (PNET) usually located in the posterior fossa. Current treatment for MBs, which includes a combination of surgery, chemotherapy and radiation, remain challenging especially in younger patients. However, advances in the understanding of regulatory pathways in cerebellar development have elucidated possible areas of dysfunction involved in tumorigenesis. Multiple studies have demonstrated the importance of the sonic hedgehog, Wnt, and Notch pathways in MB pathogenesis at the molecular level. While staging and prognosis are often based on the Chang classification system, future algorithms will involve identifying molecular markers in order to allow for more specific risk stratifications of various MB subtypes and provide improved correlation with staging and prognosis. Future development of novel therapies that target the heterogeneity of MB and are tailored to the tumor's unique molecular profile may yield improved outcomes for these patients.

Novel amplifications in pediatric medulloblastoma identified by genome-wide copy number profiling

Medulloblastoma (MB) is a WHO grade IV, invasive embryonal CNS tumor that mainly affects children. The aggressiveness and response to therapy can vary considerably between cases, and despite treatment, ~30% of patients die within 2 years from diagnosis. Furthermore, the majority of survivors suffer long-term side-effects due to severe management modalities. Several distinct morphological features have been associated with differences in biological behavior, but improved molecular-based criteria that better reflect the underlying tumor biology are in great demand. In this study, we profiled a series of 25 MB with a 32K BAC array covering 99% of the current assembly of the human genome for the identification of genetic copy number alterations possibly important in MB. Previously known aberrations as well as several novel focally amplified loci could be identified. As expected, the most frequently observed alteration was the combination of 17p loss and 17q gain, which was detected in both high- and standard-risk patients. We also defined minimal overlapping regions of aberrations, including 16 regions of gain and 18 regions of loss in various chromosomes. A few noteworthy narrow amplified loci were identified on autosomes 1 (38.89-41.97 and 84.89-90.76 Mb), 3 (27.64-28.20 and 35.80-43.50 Mb), and 8 (119.66-139.79 Mb), aberrations that were verified with an alternative platform (Illumina 610Q chips). Gene expression levels were also established for these samples using Affymetrix U133Plus2.0 arrays. Several interesting genes encompassed within the amplified regions and presenting with transcript upregulation were identified. These data contribute to the characterization of this malignant childhood brain tumor and confirm its genetic heterogeneity.

FSTL5 is a marker of poor prognosis in non-WNT/non-SHH medulloblastoma

PURPOSE

Integrated genomics approaches have revealed at least four distinct biologic variants of medulloblastoma: WNT (wingless), SHH (sonic hedgehog), group C, and group D. Because of the remarkable clinical heterogeneity of group D tumors and the dismal prognosis of group C patients, it is vital to identify molecular biomarkers that will allow early and effective treatment stratification in these non-WNT/non-SHH tumors.

PATIENTS AND METHODS

We combined transcriptome and DNA copy-number analyses for 64 primary medulloblastomas. Bioinformatic tools were used to discover marker genes of molecular variants. Differentially expressed transcripts were evaluated for prognostic value in the screening cohort. The prognostic power of follistatin-like 5 (FSTL5) immunopositivity was tested for 235 nonoverlapping medulloblastoma samples on two independent tissue microarrays.

RESULTS

Comprehensive analyses of transcriptomic and genetic alterations delineate four distinct variants of medulloblastoma. Stable subgroup separation was achieved by using the 300 transcripts that varied the most. Distinct expression patterns of FSTL5 in each molecular subgroup were confirmed by quantitative real-time polymerase chain reaction. Immunopositivity of FSTL5 identified a large cohort of patients (84 of 235 patients; 36%) at high risk for relapse and death. Importantly, more than 50% of non-WNT/non-SHH tumors displayed FSTL5 negativity, delineating a large patient cohort with a good prognosis who would otherwise be considered intermediate or high-risk on the basis of current molecular subgrouping.

CONCLUSION

FSTL5 expression denoted a dismal prognosis both within and across medulloblastoma subgroups. The addition of FSTL5 immunohistochemistry to existing molecular stratification schemes constitutes a reliable and cost-effective tool for prognostication in future clinical trials of medulloblastoma.

Molecular diagnostics in embryonal brain tumors

Embryonal brain tumors are a heterogeneous group of neoplasms united by the presence of poorly differentiated stem-like cells. Molecular details are increasingly being used to separate them into biologically and clinically meaningful groups. For medulloblastoma, integrated mRNA expression profiling and DNA analysis by a number of research groups defines 4-6 distinctive molecular variants. A subset with prominent Wnt activity is associated with good clinical outcomes and classic histology. Medulloblastomas showing a Hedgehog gene expression signature are frequently of the desmoplastic/nodular subtype. Interestingly, Hedgehog activity is found in tumors arising either in infants or older teenagers and adults. The association of clinically aggressive medulloblastoma with MYC expression, large cell/anaplastic change and high levels of photoreceptor differentiation transcripts has also been noted in several studies. Immunohistochemical analysis of just one or two genes per molecular medulloblastoma variant may be sufficient for accurate classification, and this would be of great practical utility if validated. Advances have also been made in the classification of central nervous system (CNS) Primitive Neuroectodermal Tumors (PNET), as several groups have identified an amplicon at chromosome 19q13.41-42, which appears to define a unique PNET subtype associated with prominent true rosettes, young age and very poor outcomes.

Gene expression of growth signaling pathways is up-regulated in CD133-positive medulloblastoma cells

Medulloblastoma (MB) is the most common malignant brain tumor in children. Cancer initiating cells (CICs) have been proposed to be involved in the development of brain tumors including MB. Prominin-1 antigen (CD133) is a candidate surface molecular marker for CICs. In the present study, CD133-positive cells were isolated from human Daoy MB cells and their gene expression was compared with that of control Daoy cells. DNA microarray analysis revealed that there were 398 up-regulated genes (>2-fold increase) and 318 down-regulated genes (<50% decrease) in the CD133-positive cell-enriched fractions. Up-regulated genes included neuregulin-1, cyclin D1, cyclin-dependent kinase 6, vascular endothelial growth factor, inhibin β A, promyelocytic leukemia gene, MYC, and hairy enhancer of split-1, which are components of growth signaling pathways. Molecular studies suggest that developmentally regulated signals important for stem cell maintenance are also involved in MB tumorigenesis. Moreover, these molecules can serve as novel targets for MB treatment.

Predicting relapse in patients with medulloblastoma by integrating evidence from clinical and genomic features

PURPOSE

Despite significant progress in the molecular understanding of medulloblastoma, stratification of risk in patients remains a challenge. Focus has shifted from clinical parameters to molecular markers, such as expression of specific genes and selected genomic abnormalities, to improve accuracy of treatment outcome prediction. Here, we show how integration of high-level clinical and genomic features or risk factors, including disease subtype, can yield more comprehensive, accurate, and biologically interpretable prediction models for relapse versus no-relapse classification. We also introduce a novel Bayesian nomogram indicating the amount of evidence that each feature contributes on a patient-by-patient basis.

PATIENTS AND METHODS

A Bayesian cumulative log-odds model of outcome was developed from a training cohort of 96 children treated for medulloblastoma, starting with the evidence provided by clinical features of metastasis and histology (model A) and incrementally adding the evidence from gene-expression-derived features representing disease subtype-independent (model B) and disease subtype-dependent (model C) pathways, and finally high-level copy-number genomic abnormalities (model D). The models were validated on an independent test cohort (n = 78).

RESULTS

On an independent multi-institutional test data set, models A to D attain an area under receiver operating characteristic (au-ROC) curve of 0.73 (95% CI, 0.60 to 0.84), 0.75 (95% CI, 0.64 to 0.86), 0.80 (95% CI, 0.70 to 0.90), and 0.78 (95% CI, 0.68 to 0.88), respectively, for predicting relapse versus no relapse.

CONCLUSION

The proposed models C and D outperform the current clinical classification schema (au-ROC, 0.68), our previously published eight-gene outcome signature (au-ROC, 0.71), and several new schemas recently proposed in the literature for medulloblastoma risk stratification.

Chromosome 9q and 16q loss identified by genome-wide pooled-analysis are associated with tumor aggressiveness in patients with classic medulloblastoma

Medulloblastoma (MB) is one of the most aggressive pediatric brain tumor. We report genome-wide pooled-analysis of classic MB variant of patients over 3 years of age at diagnosis. We combined array comparative genomic hybridization (aCGH) results from experimental analysis (31 cases) with two public databases (55 cases) in a final evaluation of 86 MBs. The most common chromosome structural aberrations were gains of 17q (45.3%), 1q (22.1%), and losses of 8p (15.1%), 10q (19.8%), 17p (37.2%), and 16q (16.3%). Isochromome (17q) was observed in 29.1% MBs. A significant association between poor patients survival and losses of 9q (p < 0.0023), 10q (p < 0.012), and 16q (p < 0.036) was observed. Univariate analysis showed association of 9q loss (p < 0.008) and 16q loss (p = 0.05) with adverse overall survival (OS). Chromosome 6 monosomy was a protective event although statistically borderline (p = 0.066). After adjusting for confounding factors, a poor OS was found for patients whose tumor has 9q loss [hazard ratio (HR) = 3.97; p < 0.006) or 16q loss (HR = 2.41; p = 0.038). Our results highlight the importance of genomic studies in different MB histological variants and indicate a genotype-phenotype correlation.

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

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

TP53 Mutation Is Frequently Associated With CTNNB1 Mutation or MYCN Amplification and Is Compatible With Long-Term Survival in Medulloblastoma

Purpose

The role of TP53 mutations in the tumorigenesis of sporadic medulloblastoma (MB) and the value of TP53 mutation status as a prognostic marker are not yet definitely elucidated. A recent report identified TP53 mutations in MB as an adverse prognostic marker. Hence, the current study was conducted to validate the prognostic role of TP53 mutation in MB and to understand its contribution to tumorigenesis.

Methods

A comprehensive genetic analysis of 310 MB samples was performed by screening for TP53 mutations and further relating the TP53 mutation status to p53 immunostaining, cytogenetic aberrations, and clinical variables.

Results

Mutation analysis of TP53 revealed mutations in 21 (6.8%) of 310 samples. Germline TP53 mutations were found in two patients with a history suggestive of a hereditary cancer syndrome. TP53 mutation status was not associated with unfavorable prognosis (P = .63) and was not linked to 17p allelic loss but was over-represented in the prognostically favorable WNT subgroup of MB as defined by CTNNB1 mutation (seven of 35 TP53-mutated tumors v 14 of 271 TP53 wild-type tumors; P = .005) and in tumors carrying high-level MYCN amplification (seven of 21 TP53-mutated tumors v 14 of 282 TP53 wild-type tumors; P = .001).

Conclusion

The contradictory results in the recent literature concerning the prognostic value of TP53 mutation might be explained by different frequencies of WNT MBs, different frequencies of patients with Li-Fraumeni syndrome, and different cumulative doses of alkylating drugs applied in these studies.

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

PURPOSE

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

METHODS

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

RESULTS

Metastatic disease and large-cell/anaplastic (LC/A) phenotype were the clinicopathologic variables associated with poor progression-free survival (PFS). Nuclear immunoreactivity for β-catenin, CTNNB1 mutation, and monosomy 6 all identified a group of good-prognosis patients. MYC amplification was associated with poor outcome, but other CNAs were not. Low-risk medulloblastomas were defined as β-catenin nucleopositive tumors without metastasis at presentation, LC/A phenotype, or MYC amplification. High-risk medulloblastomas were defined as tumors with metastatic disease, LC/A phenotype, or MYC amplification. Low-risk, standard-risk, and high-risk categories of medulloblastoma had significantly (P < .0001) different outcomes.

CONCLUSION

Integrating assays of molecular biomarkers undertaken on routinely collected diagnostic FFPE tissue into stratification schemes for medulloblastoma alongside clinical and pathologic outcome indicators can refine current definition of disease risk and guide adjuvant therapy.

Medulloblastoma comprises four distinct molecular variants

PURPOSE

Recent genomic approaches have suggested the existence of multiple distinct subtypes of medulloblastoma. We studied a large cohort of medulloblastomas to determine how many subgroups of the disease exist, how they differ, and the extent of overlap between subgroups.

METHODS

We determined gene expression profiles and DNA copy number aberrations for 103 primary medulloblastomas. Bioinformatic tools were used for class discovery of medulloblastoma subgroups based on the most informative genes in the data set. Immunohistochemistry for subgroup-specific signature genes was used to determine subgroup affiliation for 294 nonoverlapping medulloblastomas on two independent tissue microarrays.

RESULTS

Multiple unsupervised analyses of transcriptional profiles identified the following four distinct, nonoverlapping molecular variants: WNT, SHH, group C, and group D. Supervised analysis of these four subgroups revealed significant subgroup-specific demographics, histology, metastatic status, and DNA copy number aberrations. Immunohistochemistry for DKK1 (WNT), SFRP1 (SHH), NPR3 (group C), and KCNA1 (group D) could reliably and uniquely classify formalin-fixed medulloblastomas in approximately 98% of patients. Group C patients (NPR3-positive tumors) exhibited a significantly diminished progression-free and overall survival irrespective of their metastatic status.

CONCLUSION

Our integrative genomics approach to a large cohort of medulloblastomas has identified four disparate subgroups with distinct demographics, clinical presentation, transcriptional profiles, genetic abnormalities, and clinical outcome. Medulloblastomas can be reliably assigned to subgroups through immunohistochemistry, thereby making medulloblastoma subclassification widely available. Future research on medulloblastoma and the development of clinical trials should take into consideration these four distinct types of medulloblastoma.

Childhood medulloblastoma: novel approaches to the classification of a heterogeneous disease

Increasing recognition of pediatric medulloblastoma as a heterogeneous disease, with histopathological and molecular variants that have distinct biological behaviors, will impact how the disease is classified and treated. A combination of clinicopathological evaluation and assays based on molecular subgroups of disease will allow stratification of patients into risk groups and a more tailored approach to therapy. Patients with low-risk disease could be treated with de-escalated adjuvant therapy to maximize cure while reducing long-term adverse effects, and novel therapies could be sought for patients with high-risk disease. My review encompasses a brief overview of the clinical landscape, the current World Health Organization (WHO) classification of medulloblastoma, the status of molecular subgroups, and how potential stratification schemes might impact pathologists and their practice.

Genetics of medulloblastoma: clues for novel therapies

Medulloblastoma is the most common malignant brain tumor in children. Current medulloblastoma therapy entails surgery, radiation and chemotherapy. The 5-year survival rate for patients ranges from 40 to 70%, with most survivors suffering from serious long-term treatment-related sequelae. Additional research on the molecular biology and genetics of medulloblastoma is needed to identify robust prognostic markers for disease-risk stratification, to improve current treatment regimes and to discover novel and more effective molecular-targeted therapies. Recent advances in molecular biology have led to the development of powerful tools for the study of medulloblastoma tumorigenesis, which have revealed new insights into the molecular underpinnings of this disease. Here we discuss the signaling pathway alterations implicated in medulloblastoma pathogenesis, the techniques used in molecular profiling of these tumors and recent molecular subclassification schemes. Particular emphasis is given to the identification of novel molecular targets for less toxic, patient-tailored therapeutic approaches.

Targeting brain cancer: advances in the molecular pathology of malignant glioma and medulloblastoma

Malignant brain tumours continue to be the cause of a disproportionate level of morbidity and mortality across a wide range of individuals. The most common variants in the adult and paediatric populations - malignant glioma and medulloblastoma, respectively - have been the subject of increasingly intensive research over the past two decades that has led to considerable advances in the understanding of their basic biology and pathogenesis. This Review summarizes these developments in the context of the evolving notion of molecular pathology and discusses the implications that this work has on the design of new treatment regimens.

Childhood medulloblastoma: current status of biology and treatment

Medulloblastoma, a primitive neuro-ectodermal tumour that arises in the posterior fossa, is the most common malignant brain tumour occurring in childhood. Over the past half century, the long-term survival for children with medulloblastoma has improved remarkably from a certain fatal diagnosis to a cancer that is often curable. Although overall survival for children with non-disseminated and non-anaplastic medulloblastoma can approach 80%, the current multidisciplinary therapeutic approach is not without long-term sequelae. Chemotherapy has improved the long-term survival and allowed for reductions in the amount of radiation given, thereby reducing some of the long-term toxicities. In this review, we describe the current understanding of the basic biology of medulloblastoma and report on the current active chemotherapeutic agents utilized in medulloblastoma therapy. Ultimately, our understanding of the basic biology of medulloblastoma may lead to further advances in therapy by providing targets that are more specific and potentially less toxic.

Double high-dose chemotherapy followed by autologous peripheral blood stem cell transplantation for primary disseminated medulloblastoma: a report of 3 cases

We performed double high-dose chemotherapy followed by peripheral blood stem cell transplantation (PBSCT) in 3 children with medulloblastoma and primary leptomeningial dissemination, including spinal metastasis. After resection of the main tumor mass, 30.6 Gy whole craniospinal radiation therapy and 4 or 5 courses of conventional chemotherapy with vincristine (1.5 mg/m), carboplatin (560 mg/m), ifosfamide (9000 mg/m), and etoposide (500 mg/m), and 2 courses of high-dose thiotepa (680 mg/m) and melphalan (240 mg/m) therapy with PBSCT were administered. Two patients with low erythroblastic leukemia viral oncogene homolog 2 (ERBB2) gene expression achieved long-term survival (41 mo and 40 mo) but the patient with high ERBB2 expression relapsed 9 months after the second PBSCT.

Universal poor survival in children with medulloblastoma harboring somatic TP53 mutations

PURPOSE

Medulloblastoma is the prototype of treatment success in modern pediatric neuro-oncology. Unfortunately, 20% to 30% of tumors recur despite maximal resection and multimodal therapy. Multiple biologic prognostic markers have been investigated to predict recurrences, but controversy remains regarding their clinical utility. Because p53 immunopositivity is an adverse prognostic marker in pediatric medulloblastoma and TP53 mutations are associated with chemotherapy and radiation therapy resistance, we aimed to determine the extent and role of TP53 mutations in pediatric medulloblastoma treatment failure.

PATIENTS AND METHODS

One hundred eight of 111 consecutive patients diagnosed with medulloblastoma in our institution from 1995 to 2007 were included. Median follow-up time was 5.3 years in survivors. All samples were immunostained for p53 and erbB-2. Histologic grade and immunostaining were scored by two blinded reviewers. For 49 patients, frozen material was available for TP53 sequencing. The main outcome measures were overall and progression-free survival.

RESULTS

Sixteen percent of sequenced medulloblastomas harbored a TP53 mutation. As a screening test, p53 immunohistochemistry was 100% sensitive and 83% specific for a TP53 mutation. Strikingly, all mutated tumors recurred early, and 5-year survival for average-risk patients was 0% for TP53-mutated medulloblastoma compared with 74% +/- 8% for wild-type medulloblastoma (P < .0001). Furthermore, 75% of recurrences in average-risk patients were associated with TP53 mutations. On multivariate analysis, TP53 mutation status was the strongest adverse prognostic factor (hazard ratio = 10.4, P = .003).

CONCLUSION

Lack of long-term survival in TP53-mutated medulloblastomas highlights the role of TP53 mutations in medulloblastoma resistance to conventional therapies and the need for alternative treatments, and prospective validation of these findings is needed.

The potential impact of tumour biology on improved clinical practice for medulloblastoma: progress towards biologically driven clinical trials

Medulloblastoma is the most common malignant brain tumour of childhood and accounts for around 10% of all childhood cancer deaths. Despite recent improvements in survival rates, the delivery of individualised therapies based on disease-risk remains a major goal; intensified treatment for poor-risk disease, whilst reducing therapy for favourable-risk cases, with the overall aim of maximising survival whilst minimising late effects. Current clinical indices for the prediction of disease course are imprecise, however a series of molecular and histopathological biomarkers have been identified recently, which may allow a more accurate prediction of disease outcome (e.g., beta-catenin status as a favourable-risk marker, MYC gene amplification and large-cell histology as high-risk markers). Pan-European clinical trials being planned for medulloblastoma by the SIOP Brain tumour group will assess the stratification of patients using molecular and histological biomarkers, alongside clinical indices, to select favourable, standard and high-risk treatment groups. This selection will underpin two concurrent trials; PNET 5, which will test whether treatment can be reduced for a favourable-risk disease sub-group, with the aim of maintaining survival rates while reducing late-effects, and PNET 6, which will aim to improve survival rates in the standard-risk group. The implementation of these trials presents important new logistical challenges within routine practice, involving (i) the development of quality-controlled sample collection and handling systems across multiple treatment centres, including the mandatory ascertainment of fresh-frozen tumour material, and (ii) the delivery of standardised central biomarker analysis and histopathological review, within the approximately 30-day post-surgical window, prior to the selection and commencement of adjuvant therapy. Feasibility studies to establish these systems are underway across SIOP Europe national groups. Their success will require a coordinated approach by the entire multidisciplinary team, including neurosurgeons, oncologists and neuropathologists, with the common aim of facilitating targeted delivery of individualised risk-adapted therapies for children with medulloblastoma.

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.