Clinical outcome of pediatric medulloblastoma patients with Li-Fraumeni syndrome

BACKGROUND

The prognosis for Li-Fraumeni syndrome (LFS) patients with medulloblastoma (MB) is poor. Comprehensive clinical data for this patient group is lacking, challenging the development of novel therapeutic strategies. Here, we present clinical and molecular data on a retrospective cohort of pediatric LFS MB patients.

METHODS

In this multinational, multicenter retrospective cohort study, LFS patients under 21 years with MB and class 5 or class 4 constitutional TP53 variants were included. TP53 mutation status, methylation subgroup, treatment, progression free- (PFS) and overall survival (OS), recurrence patterns, and incidence of subsequent neoplasms were evaluated.

RESULTS

The study evaluated 47 LFS individuals diagnosed with MB, mainly classified as DNA methylation subgroup "SHH_3" (86%). The majority (74%) of constitutional TP53 variants represented missense variants. The 2- and 5-year (y-) PFS were 36% and 20%, and 2- and 5y-OS were 53% and 23%, respectively. Patients who received postoperative radiotherapy (RT) (2y-PFS: 44%, 2y-OS: 60%) or chemotherapy before RT (2y-PFS: 32%, 2y-OS: 48%) had significantly better clinical outcome then patients who were not treated with RT (2y-PFS: 0%, 2y-OS: 25%). Patients treated according to protocols including high-intensity chemotherapy and patients who received only maintenance-type chemotherapy showed similar outcomes (2y-PFS: 42% and 35%, 2y-OS: 68% and 53%, respectively).

CONCLUSIONS

LFS MB patients have a dismal prognosis. In the presented cohort use of RT significantly increased survival rates, whereas chemotherapy intensity did not influence their clinical outcome. Prospective collection of clinical data and development of novel treatments are required to improve the outcome of LFS MB patients.

Data-adaptive and pathway-based tests for association studies between somatic mutations and germline variations in human cancers

Cancer is a disease driven by a combination of inherited genetic variants and somatic mutations. Recently available large-scale sequencing data of cancer genomes have provided an unprecedented opportunity to study the interactions between them. However, previous studies on this topic have been limited by simple, low statistical power tests such as Fisher's exact test. In this paper, we design data-adaptive and pathway-based tests based on the score statistic for association studies between somatic mutations and germline variations. Previous research has shown that two single-nucleotide polymorphism (SNP)-set-based association tests, adaptive sum of powered score (aSPU) and data-adaptive pathway-based (aSPUpath) tests, increase the power in genome-wide association studies (GWASs) with a single disease trait in a case-control study. We extend aSPU and aSPUpath to multi-traits, that is, somatic mutations of multiple genes in a cohort study, allowing extensive information aggregation at both SNP and gene levels.p $p$ -values from different parameters assuming varying genetic architecture are combined to yield data-adaptive tests for somatic mutations and germline variations. Extensive simulations show that, in comparison with some commonly used methods, our data-adaptive somatic mutations/germline variations tests can be applied to multiple germline SNPs/genes/pathways, and generally have much higher statistical powers while maintaining the appropriate type I error. The proposed tests are applied to a large-scale real-world International Cancer Genome Consortium whole genome sequencing data set of 2583 subjects, detecting more significant and biologically relevant associations compared with the other existing methods on both gene and pathway levels. Our study has systematically identified the associations between various germline variations and somatic mutations across different cancer types, which potentially provides valuable utility for cancer risk prediction, prognosis, and therapeutics.

OpenPBTA: The Open Pediatric Brain Tumor Atlas

Pediatric brain and spinal cancers are collectively the leading disease-related cause of death in children; thus, we urgently need curative therapeutic strategies for these tumors. To accelerate such discoveries, the Children's Brain Tumor Network (CBTN) and Pacific Pediatric Neuro-Oncology Consortium (PNOC) created a systematic process for tumor biobanking, model generation, and sequencing with immediate access to harmonized data. We leverage these data to establish OpenPBTA, an open collaborative project with over 40 scalable analysis modules that genomically characterize 1,074 pediatric brain tumors. Transcriptomic classification reveals universal TP53 dysregulation in mismatch repair-deficient hypermutant high-grade gliomas and TP53 loss as a significant marker for poor overall survival in ependymomas and H3 K28-mutant diffuse midline gliomas. Already being actively applied to other pediatric cancers and PNOC molecular tumor board decision-making, OpenPBTA is an invaluable resource to the pediatric oncology community.

Supratentorial Sporadic Hemangioblastoma: A Case Report With Mutation Profiling Using Next-Generation DNA Sequencing

The present study aimed to determine genomic changes in sporadic intracranial hemangioblastoma (HBL), and the mutation patterns were analyzed using next-generation DNA sequencing (NGS). In this NGS analysis of the HBL tumor, 67 variants of 41 genes were identified. Of these, 64 were single-nucleotide variants (SNVs), two were exonic insertions and deletions (INDEL), and one was an intronic INDEL. In total, 15 were missense exonic variants, including an insertion variant in the NRAS gene, c.1_2insA, and a deletion variant, c.745delT, in the HNF1A gene, both of these mutations produced a termination codon. Other exonic missense variants found in the tumor were CTNNB1, FGFR3, KDR, SMO, HRAS, RAI1, and a TP53 variant (c.430C>G). Moreover, the results of the present study revealed a novel variant, c.430C>G, in TP53 and two missense variants of SND1 (c.1810G>C and c.1814G>C), which were also novel. ALK (rs760315884) and FGFR2 (rs1042522) missense variants were reported previously. Notably, a total of 10 previously reported single-nucleotide polymorphisms (SNPs) were found in this tumor in genes including MLH1 (rs769364808), FGFR3 (rs769364808), two variants (rs1873778 and rs2228230) in PDGFRA, KIT (rs55986963), APC (rs41115), and RET (rs1800861). The results of this study revealed a synonymous mutation (SNP) in c.1104 G>T; p. (Ser368Ser) in the MLH1 gene. In this amino acid (AA) codon, two other variants are also known to cause missense substitutions, c.1103C>G; p. (Ser368Trp); COSM6986674) and c.1103C>T; p.(Ser368Leu; COSM3915870), were found in hematopoietic and urinary tract tissue, respectively. However, three SNPs found in genes such as ALK, KDR, and ABL1 in the HBL tumor in this study were not reported in UCSC, COSMIC, and ClinVar databases. Additionally, 19 intronic variants were identified in this tumor. One intronic SNV was present in each of the following genes: EGFR, ERBB4, KDR, SMO, CDKN2B, PTEN, PTPN11, RB1, AKT1, and ERBB2. In PIK3CA and FBXL18 genes, two intronic variants were present, and in the SND1 gene, three intronic variants were detected in the HBL tumor presented in this study. Notably, only one of these was reported in the catalog of somatic mutations in cancer. Only one 3'-untranslated region (UTR) insertion variant in the NRAS gene (c.*2010T>AT) was detected in the tumor of the present study, and this was a splice site acceptor. A TP53 intronic mutation (c.782+1G>T) was the only pathogenic splice_donor_variant found in this HBL tumor. The frequency of variants and Phred scores were markedly high, and the p-values were significant for all of the aforementioned mutations. In summary, a total of 15 missense, 10 synonymous, and 19 intronic variants were identified in the HBL tumor. Results of the present study detected one novel insertion in NRAS and one novel deletion in HNF1A genes, a novel missense variant in the TP53 gene, and two novel missense variants of SND1. Hotspot mutations in other cancer driver genes, such as PTEN, ATM, SMAD4, SMARCB1, STK11, NPM1, CDKN2A, and EGFR, which are frequently affected in gliomas, were not found in the tumor of the present study. Future studies should aim to validate oncogenic mutations that may act as novel targets for the treatment of these tumors.

Provocative non-canonical roles of p53 and AKT signaling: A role for Thymosin β4 in medulloblastoma

The PI3K/AKT and p53 pathways are key regulators of cancer cell survival and death, respectively. Contrary to their generally accepted roles, several lines of evidence, including ours in medulloblastoma, the most common childhood brain cancer, highlight non-canonical functions for both proteins and show a complex context-dependent dynamic behavior in determining cell fate. Interestingly, p53-mediated cell survival and AKT-mediated cell death can dominate in certain conditions, and these interchangeable physiological functions may potentially be manipulated for better clinical outcomes. This review article presents studies in which p53 and AKT behave contrary to their well-established functions. We discuss the factors and circumstances that may be involved in mediating these changes and the implications of these unique roles of p53 and AKT in devising therapeutic strategies. Lastly, based on our recent finding of Thymosin beta 4-mediated chemosensitivity via an AKT-p53 interaction in medulloblastoma cells, we also discuss the possible implications of Thymosin beta-4 in enhancing drug sensitivity in this deadly childhood disease.

Advances in the Immunotherapeutic Potential of Isocitrate Dehydrogenase Mutations in Glioma

Isocitrate dehydrogenase (IDH) is an essential metabolic enzyme in the tricarboxylic acid cycle (TAC). The high mutation frequency of the IDH gene plays a complicated role in gliomas. In addition to affecting gliomas directly, mutations in IDH can also alter their immune microenvironment and can change immune-cell function in direct and indirect ways. IDH mutations mediate immune-cell infiltration and function by modulating immune-checkpoint gene expression and chemokine secretion. In addition, IDH mutation-derived D2-hydroxyglutarate can be absorbed by surrounding immune cells, also affecting their functioning. In this review, we summarize current knowledge about the effects of IDH mutations as well as other gene mutations on the immune microenvironment of gliomas. We also describe recent preclinical and clinical data related to IDH-mutant inhibitors for the treatment of gliomas. Finally, we discuss different types of immunotherapy and the immunotherapeutic potential of IDH mutations in gliomas.

Integration of immunohistochemistry, RNA sequencing, and multiplex ligation-dependent probe amplification for molecular classification of pediatric medulloblastoma

BACKGROUND

Medulloblastoma (MB) is commonly classified into four molecular groups, that is, WNT, SHH, group 3, and group 4, for prognostic and therapeutic purposes.

METHODS

Here we applied immunohistochemistry (IHC) and RNA sequencing (RNA-seq) for the molecular classification of MB, and utilized multiplex ligation-dependent probe amplification (MLPA) to determine chromosomal alterations and specific gene amplifications.

RESULTS

We retrospectively enrolled 37 pediatric MB patients. Twenty-three had genomic material available for gene/RNA analysis. For IHC, β-catenin, GAB1, and YAP were the biomarkers to segregate MB into three subgroups, WNT (1/23), SHH (5/23), and non-WNT/non-SHH (17/23). However, four cases (17.3%) were found to be misclassified after analysis by RNA-seq. The result of MLPA revealed two group 3 tumors carrying MYC amplification, and three SHH tumors harboring MYCN amplification. While IHC provided rapid subgroup stratification, it might result in incorrect subgrouping. Thus, validation of the IHC result with genomic data analysis by RNA-seq or other tools would be preferred. In addition, MLPA can detect important genetic alterations and is helpful for the identifications of high-risk patients.

CONCLUSIONS

Our study revealed that integration of these diagnostic tools can provide a precise and timely classification of MB, optimizing an individualized, risk-directed postoperative adjuvant therapy for these patients. This workflow can be applied in a countrywide fashion to guide future clinical trials for patients with MB.

The Current Landscape of Targeted Clinical Trials in Non-WNT/Non-SHH Medulloblastoma

Simple Summary

Medulloblastoma is a form of malignant brain tumor that arises predominantly in infants and young children and can be divided into different groups based on molecular markers. The group of non-WNT/non-SHH medulloblastoma includes a spectrum of heterogeneous subgroups that differ in their biological characteristics, genetic underpinnings, and clinical course of disease. Non-WNT/non-SHH medulloblastoma is currently treated with surgery, chemotherapy, and radiotherapy; however, new drugs are needed to treat patients who are not yet curable and to reduce treatment-related toxicity and side effects. We here review which new treatment options for non-WNT/non-SHH medulloblastoma are currently clinically tested. Furthermore, we illustrate the challenges that have to be overcome to reach a new therapeutic standard for non-WNT/non-SHH medulloblastoma, for instance the current lack of good preclinical models, and the necessity to conduct trials in a comparably small patient collective.

Abstract

Medulloblastoma is an embryonal pediatric brain tumor and can be divided into at least four molecularly defined groups. The category non-WNT/non-SHH medulloblastoma summarizes medulloblastoma groups 3 and 4 and is characterized by considerable genetic and clinical heterogeneity. New therapeutic strategies are needed to increase survival rates and to reduce treatment-related toxicity. We performed a noncomprehensive targeted review of the current clinical trial landscape and literature to summarize innovative treatment options for non-WNT/non-SHH medulloblastoma. A multitude of new drugs is currently evaluated in trials for which non-WNT/non-SHH patients are eligible, for instance immunotherapy, kinase inhibitors, and drugs targeting the epigenome. However, the majority of these trials is not restricted to medulloblastoma and lacks molecular classification. Whereas many new molecular targets have been identified in the last decade, which are currently tested in clinical trials, several challenges remain on the way to reach a new therapeutic strategy for non-WNT/non-SHH medulloblastoma. These include the severe lack of faithful preclinical models and predictive biomarkers, the question on how to stratify patients for clinical trials, and the relative lack of studies that recruit large, homogeneous patient collectives. Innovative trial designs and international collaboration will be a key to eventually overcome these obstacles.

Regulation of Chemosensitivity in Human Medulloblastoma Cells by p53 and the PI3 Kinase Signaling Pathway

In medulloblastoma, p53 expression has been associated with chemoresistance and radiation resistance and with poor long-term outcomes in the p53-mutated sonic hedgehog, MYC-p53, and p53-positive medulloblastoma subgroups. We previously established a direct role for p53 in supporting drug resistance in medulloblastoma cells with high basal protein expression levels (D556 and DAOY). We now show that p53 genetic suppression in medulloblastoma cells with low basal p53 protein expression levels (D283 and UW228) significantly reduced drug responsiveness, suggesting opposing roles for low p53 protein expression levels. Mechanistically, the enhanced cell death by p53 knockdown in high-p53 cells was associated with an induction of mTOR/PI3K signaling. Both mTOR inhibition and p110α/PIK3CA induction confirmed these findings, which abrogated or accentuated the enhanced chemosensitivity response in D556 cells respectively while converse was seen in D283 cells. Co-treatment with G-actin-sequestering peptide, thymosin β4 (Tβ4), induced p-AKT^S473 in both p53-high and p53-low cells, enhancing chemosensitivity in D556 cells while enhancing chemoresistance in D283 and UW228 cells. IMPLICATIONS: Collectively, we identified an unexpected role for the PI3K signaling in enhancing cell death in medulloblastoma cells with high basal p53 expression. These studies indicate that levels of p53 immunopositivity may serve as a diagnostic marker of chemotherapy resistance and for defining therapeutic targeting.

Immunotherapy in Medulloblastoma: Current State of Research, Challenges, and Future Perspectives

Medulloblastoma (MB), a primary tumor of the central nervous system, is among the most prevalent pediatric neoplasms. The median age of diagnosis is six. Conventional therapies include surgical resection of the tumor with subsequent radiation and chemotherapy. However, these therapies often cause severe brain damage, and still, approximately 75% of pediatric patients relapse within a few years. Because the conventional therapies cause such severe damage, especially in the pediatric developing brain, there is an urgent need for better treatment strategies such as immunotherapy, which over the years has gained accumulating interest. Cancer immunotherapy aims to enhance the body's own immune response to tumors and is already widely used in the clinic, e.g., in the treatment of melanoma and lung cancer. However, little is known about the possible application of immunotherapy in brain cancer. In this review, we will provide an overview of the current consensus on MB classification and the state of in vitro, in vivo, and clinical research concerning immunotherapy in MB. Based on existing evidence, we will especially focus on immune checkpoint inhibition and CAR T-cell therapy. Additionally, we will discuss challenges associated with these immunotherapies and relevant strategies to overcome those.

Medulloblastoma Associated with Down Syndrome: From a Rare Event Leading to a Pathogenic Hypothesis

Down syndrome (DS) is the most common chromosome abnormality with a unique cancer predisposition syndrome pattern: a higher risk to develop acute leukemia and a lower incidence of solid tumors. In particular, brain tumors are rarely reported in the DS population, and biological behavior and natural history are not well described and identified. We report a case of a 10-year-old child with DS who presented with a medulloblastoma (MB). Histological examination revealed a classic MB with focal anaplasia and the molecular profile showed the presence of a CTNNB1 variant associated with the wingless (WNT) molecular subgroup with a good prognosis in contrast to our case report that has shown an early metastatic relapse. The nearly seven-fold decreased risk of MB in children with DS suggests the presence of protective biological mechanisms. The cerebellum hypoplasia and the reduced volume of cerebellar granule neuron progenitor cells seem to be a possible favorable condition to prevent MB development via inhibition of neuroectodermal differentiation. Moreover, the NOTCH/WNT dysregulation in DS, which is probably associated with an increased risk of leukemia, suggests a pivotal role of this pathway alteration in the pathogenesis of MB; therefore, this condition should be further investigated in future studies by molecular characterizations.

Brain Tumor-Derived Extracellular Vesicles as Carriers of Disease Markers: Molecular Chaperones and MicroRNAs

Primary and metastatic brain tumors are usually serious conditions with poor prognosis, which reveal the urgent need of developing rapid diagnostic tools and efficacious treatments. To achieve these objectives, progress must be made in the understanding of brain tumor biology, for example, how they resist natural defenses and therapeutic intervention. One resistance mechanism involves extracellular vesicles that are released by tumors to meet target cells nearby or distant via circulation and reprogram them by introducing their cargo. This consists of different molecules among which are microRNAs (miRNAs) and molecular chaperones, the focus of this article. miRNAs modify target cells in the immune system to avoid antitumor reaction and chaperones are key survival molecules for the tumor cell. Extracellular vesicles cargo reflects the composition and metabolism of the original tumor cell; therefore, it is a source of markers, including the miRNAs and chaperones discussed in this article, with potential diagnostic and prognostic value. This and their relatively easy availability by minimally invasive procedures (e.g., drawing venous blood) illustrate the potential of extracellular vesicles as useful materials to manage brain tumor patients. Furthermore, understanding extracellular vesicles circulation and interaction with target cells will provide the basis for using this vesicle for delivering therapeutic compounds to selected tumor cells.

Wnt activation as a therapeutic strategy in medulloblastoma

Medulloblastoma (MB) is defined by four molecular subgroups (Wnt, Shh, Group 3, Group 4) with Wnt MB having the most favorable prognosis. Since prior reports have illustrated the antitumorigenic role of Wnt activation in Shh MB, we aimed to assess the effects of activated canonical Wnt signaling in Group 3 and 4 MBs. By using primary patient-derived MB brain tumor-initiating cell (BTIC) lines, we characterize differences in the tumor-initiating capacity of Wnt, Group 3, and Group 4 MB. With single cell RNA-seq technology, we demonstrate the presence of rare Wnt-active cells in non-Wnt MBs, which functionally retain the impaired tumorigenic potential of Wnt MB. In treating MB xenografts with a Wnt agonist, we provide a rational therapeutic option in which the protective effects of Wnt-driven MBs may be augmented in Group 3 and 4 MB and thereby support emerging data for a context-dependent tumor suppressive role for Wnt/β-catenin signaling.

The Wnt molecular subgroup of medulloblastoma is associated with better prognosis than the other molecular subgroups. Here, the authors show that activating Wnt signaling impairs tumor development and improves survival in Group 3 and Group 4 medulloblastoma preclinical models.

A Patient-Derived Cell Atlas Informs Precision Targeting of Glioblastoma

Glioblastoma (GBM) is a malignant brain tumor with few therapeutic options. The disease presents with a complex spectrum of genomic aberrations, but the pharmacological consequences of these aberrations are partly unknown. Here, we report an integrated pharmacogenomic analysis of 100 patient-derived GBM cell cultures from the human glioma cell culture (HGCC) cohort. Exploring 1,544 drugs, we find that GBM has two main pharmacological subgroups, marked by differential response to proteasome inhibitors and mutually exclusive aberrations in TP53 and CDKN2A/B. We confirm this trend in cell and in xenotransplantation models, and identify both Bcl-2 family inhibitors and p53 activators as potentiators of proteasome inhibitors in GBM cells. We can further predict the responses of individual cell cultures to several existing drug classes, presenting opportunities for drug repurposing and design of stratified trials. Our functionally profiled biobank provides a valuable resource for the discovery of new treatments for GBM.

DNA methylation profiling is a method of choice for molecular verification of pediatric WNT-activated medulloblastomas

BACKGROUND

Wingless-activated medulloblastoma (WNT MB) represents a well-characterized molecular variant accounting for 10-15% of all MB and is associated with a favorable clinical outcome. Patients with localized WNT MBs could benefit from de-intensification of combined treatment, which would require an accurate diagnosis of these tumors. However, despite the presence of molecular features related with a WNT MB signature (nuclear ß-catenin immunoexpression, CTNNB1 mutation, and monosomy 6), a prompt and reliable diagnostic verification of these tumors is not yet feasible.

METHODS

In the current study, we analyzed 78 samples of WNT MB treated in a single institute through genome-wide DNA methylation and targeted next generation sequencing to elaborate an optimal method for WNT MB molecular verification.

RESULTS

We found that DNA methylation profiling discloses significant advantages for molecular diagnostic of WNT MB. All other "routine" methods applied, such as ß-catenin immunohistochemistry, CTNNB1 mutation analysis, and detection of monosomy 6, failed to identify all WNT MB cases. Survival analysis revealed that application of a reduced radiotherapy protocol for WNT MB treatment had no influence on patients' survival. Only one patient died due to local relapse but recurrent tumor was pathologically and molecularly diagnosed as a secondary glioblastoma.

CONCLUSIONS

DNA methylation analysis should be considered as a method of choice for further clinically relevant stratification of WNT MB and for correct diagnosis of the recurrent tumors. WNT MB patients with localized disease could benefit from treatment de-intensification.

An update on the central nervous system manifestations of Li-Fraumeni syndrome

Li-Fraumeni syndrome (LFS), caused by the germline mutations in the TP53 gene, leads to significant lifetime risk to cancer in the central nervous system. Recognition of LFS, and elucidating its underlying cause has had a remarkable effect on our knowledge of the biology of brain tumors and represents a significant opportunity for cancer surveillance and screening. In this review, we discuss the historical context of the LFS with an emphasis on the clinicopathologic implications in clincal diagnosis, germline testing, and clinical management of brain tumor patients.

Medulloblastoma cancer stem cells: molecular signatures and therapeutic targets

Medulloblastoma (MB) is the most common malignant primary intracranial neoplasm diagnosed in childhood. Although numerous efforts have been made during the past few years to exploit novel targeted therapies for this aggressive neoplasm, there still exist substantial hitches hindering successful management of MB. Lately, progress in cancer biology has shown evidence that a subpopulation of cells within the tumour, namely cancer stem cells (CSCs), are thought to be responsible for the resistance to most chemotherapeutic agents and radiation therapy, accounting for cancer recurrence. Hence, it is crucial to identify the molecular signatures and genetic aberrations that characterise those CSCs and develop therapies that specifically target them. In this review, we aim to give an overview of the main genetic and molecular cues that depict MB-CSCs and provide a synopsis of the novel therapeutic approaches that specifically target this population of cells to attain enhanced antitumorous effects and therefore overcome resistance to therapy.

Humanized Stem Cell Models of Pediatric Medulloblastoma Reveal an Oct4/mTOR Axis that Promotes Malignancy

Medulloblastoma (MB), the most frequent malignant childhood brain tumor, can arise from cellular malfunctions during hindbrain development. Here we generate humanized models for Sonic Hedgehog (SHH)-subgroup MB via MYCN overexpression in primary human hindbrain-derived neuroepithelial stem (hbNES) cells or iPSC-derived NES cells, which display a range of aggressive phenotypes upon xenografting. iPSC-derived NES tumors develop quickly with leptomeningeal dissemination, whereas hbNES-derived cells exhibit delayed tumor formation with less dissemination. Methylation and expression profiling show that tumors from both origins recapitulate hallmarks of infant SHH MB and reveal that mTOR activation, as a result of increased Oct4, promotes aggressiveness of human SHH tumors. Targeting mTOR decreases cell viability and prolongs survival, showing the utility of these varied models for dissecting mechanisms mediating tumor aggression and demonstrating the value of humanized models for a better understanding of pediatric cancers.

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Human iPSC-derived or primary neuroepithelial stem cells can be transformed by MYCN

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MYCN drives infant SHH medulloblastoma with clinically relevant features

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Epigenetically regulated Oct4 promotes mTOR hyperactivation in infant SHH tumors

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mTOR inhibition efficiently targets metastatic SHH medulloblastoma models and PDXs

Medulloblastoma

Medulloblastoma (MB) comprises a biologically heterogeneous group of embryonal tumours of the cerebellum. Four subgroups of MB have been described (WNT, sonic hedgehog (SHH), Group 3 and Group 4), each of which is associated with different genetic alterations, age at onset and prognosis. These subgroups have broadly been incorporated into the WHO classification of central nervous system tumours but still need to be accounted for to appropriately tailor disease risk to therapy intensity and to target therapy to disease biology. In this Primer, the epidemiology (including MB predisposition), molecular pathogenesis and integrative diagnosis taking histomorphology, molecular genetics and imaging into account are reviewed. In addition, management strategies, which encompass surgical resection of the tumour, cranio-spinal irradiation and chemotherapy, are discussed, together with the possibility of focusing more on disease biology and robust molecularly driven patient stratification in future clinical trials.

Childhood Medulloblastoma: Current Therapies, Emerging Molecular Landscape and Newer Therapeutic Insights

Background:

Medulloblastoma is the most common malignant brain tumor in children, currently treated uniformly based on histopathology and clinico-radiological risk stratification leading to unpredictable relapses and therapeutic failures. Identification of molecular subgroups have thrown light on the reasons for these and now reveals clues to profile molecularly based personalized therapy against these tumors.

Methods:

Research and online contents were evaluated for pediatric medulloblastoma which included latest information on the molecular subgroups and their clinical relevance and update on efforts to translate them into clinics.

Results:

Scientific endeavors over the last decade have clearly identified four molecular variants (WNT, SHH, Group 3, and Group 4) and their demographic, genomic, and epigenetic profile. Latest revelations include significant heterogeneity within these subgroups and 12 different subtypes of MB are now identified with disparate outcomes and biology. These findings have important implications for stratification and profiling future clinical trials against these formidable tumors.

Conclusion:

With the continued outpouring of genomic/epigenomic data of these molecular subgroups and evolution of further subtypes in each subgroup, the challenge lies in comprehensive evaluation of these informations. Current and future endeavors are now needed to profile personalized therapy for each child based on the molecular risk stratification of medulloblastoma, with a hope to improve survival outcome and reduce relapses.

[Medulloblastoma. Pathology]

Medulloblastomas, embryonal neuroepithelial tumors developed in the cerebellum or brain stem, are mainly observed in childhood. The treatment of WHO-Grade IV tumors depends on stratifications that are usually based on postoperative data, histopathological subtype, tumor extension and presence of MYC or NMYC amplifications. Recently, molecular biology studies, based on new technologies (i.e. sequencing, transcriptomic, methylomic) have introduced genetic subtypes integrated into the latest WHO-2016 neuropathological classification. According to this classification, the three genetic groups WNT, SHH, with or without mutated TP53 gene, and non-WNT/non-SHH, comprising subgroups 3 and 4, are recalled in this review. The contribution of immunohistochemistry to define these groups is specified. The four histopathological groups are detailed in comparison to the WHO-2007 classification and the molecular data: classic medulloblastoma, desmoplastic/nodular medulloblastoma, medulloblastoma with extensive nodularity, and large cell/anaplastic medulloblastoma. The groups defined on genetic and histopathological grounds are not strictly concordant. Depending on the age of the patients, their correlations are different, as well as their role in the management and prognosis of these tumors. Other embryonal tumors, for which new classifications are in progress and gliomas may be confused with a medulloblastoma and the elements of the differential diagnosis of these entities are discussed. This evolution in classification fully justifies ongoing structuring procedures such as histopathological review (RENOCLIP) and the organization of molecular biology platforms.

Medulloblastoma in the Molecular Era

Medulloblastoma is the most common malignant brain tumor of childhood and remains a major cause of cancer related mortality in children. Significant scientific advancements have transformed the understanding of medulloblastoma, leading to the recognition of four distinct clinical and molecular subgroups, namely wingless (WNT), sonic hedgehog, group 3, and group 4. Subgroup classification combined with the recognition of subgroup specific molecular alterations has also led to major changes in risk stratification of medulloblastoma patients and these changes have begun to alter clinical trial design, in which the newly recognized subgroups are being incorporated as individualized treatment arms. Despite these recent advancements, identification of effective targeted therapies remains a challenge for several reasons. First, significant molecular heterogeneity exists within the four subgroups, meaning this classification system alone may not be sufficient to predict response to a particular therapy. Second, the majority of novel agents are currently tested at the time of recurrence, after which significant selective pressures have been exerted by radiation and chemotherapy. Recent studies demonstrate selection of tumor sub-clones that exhibit genetic divergence from the primary tumor, exist within metastatic and recurrent tumor populations. Therefore, tumor resampling at the time of recurrence may become necessary to accurately select patients for personalized therapy.

Low-dose Actinomycin-D treatment re-establishes the tumoursuppressive function of P53 in RELA-positive ependymoma

Ependymomas in children can arise throughout all compartments of the central nervous system (CNS). Highly malignant paediatric ependymoma subtypes are Group A tumours of the posterior fossa (PF-EPN-A) and RELA-fusion positive (ST-EPN-RELA) tumours in the supratentorial compartment. It was repeatedly reported in smaller series that accumulation of p53 is frequently observed in ependymomas and that immunohistochemical staining correlates with poor clinical outcome, while TP53 mutations are rare. Our TP53 mutation analysis of 130 primary ependymomas identified a mutation rate of only 3%. Immunohistochemical analysis of 398 ependymomas confirmed previous results correlating the accumulation of p53 with inferior outcome. Among the p53-positive ependymomas, the vast majority exhibited a RELA fusion leading to the hypothesis that p53 inactivation might be linked to RELA positivity.

In order to assess the potential of p53 reactivation through MDM2 inhibition in ependymoma, we evaluated the effects of Actinomycin-D and Nutlin-3 treatment in two preclinical ependymoma models representing the high-risk subtypes PF-EPN-A and ST-EPN-RELA. The IC-50 of the agent as determined by metabolic activity assays was in the lower nano-molar range (0.2–0.7 nM). Transcriptome analyses of high-dose (100 nM), low-dose (5 nM) and non-treated cells revealed re-expression of p53 dependent genes including p53 upregulated modulator of apoptosis (PUMA) after low-dose treatment. At the protein level, we validated the Actinomycin-D induced upregulation of PUMA, and of p53 interaction partners MDM2 and p21. Proapoptotic effects of low-dose application of the agent were confirmed by flow cytometry. Thus, Actinomycin-D could constitute a promising therapeutic option for ST-EPN-RELA ependymoma patients, whose tumours frequently exhibit p53 inactivation.

The Oncogenic Relevance of miR-17-92 Cluster and Its Paralogous miR-106b-25 and miR-106a-363 Clusters in Brain Tumors

The fundamental function of ribonucleic acids is to transfer genetic information from DNA to protein during translation process, however, this is not the only way connecting active RNA sequences with essential biological processes. Up until now, many RNA subclasses of different size, structure, and biological function were identified. Among them, there are non-coding single-stranded microRNAs (miRNAs). This subclass comprises RNAs of 19–25 nucleotides in length that modulate the activity of well-defined coding RNAs and play a crucial role in many physiological and pathological processes. miRNA genes are located both in exons, introns, and also within non-translated regions. Several miRNAs that are transcribed from the adjacent miRNA genes are called cluster. One of the largest ones is miR-17-92 cluster known as OncomiR-1 due to its strong link to oncogenesis. Six miRNAs from the OncomiR-1 have been shown to play important roles in various physiological cellular processes but also through inhibition of cell death in many cancer-relevant processes. Due to the origin and similarity of the sequence, miR-17-92 cluster and paralogs, miR-106b-25 and miR-106a-363 clusters were defined. Here we discuss the oncogenic function of those miRNA subgroups found in many types of cancers, including brain tumors.

RITA displays anti-tumor activity in medulloblastomas independent of TP53 status

Current therapy of medulloblastoma, the most common malignant brain tumor of childhood, achieves 40-70% survival. Secondary chemotherapy resistance contributes to treatment failure, where TP53 pathway dysfunction plays a key role. MDM2 interaction with TP53 leads to its degradation. Reactivating TP53 functionality using small-molecule inhibitors, such as RITA, to disrupt TP53-MDM2 binding may have therapeutic potential. We show here that RITA decreased viability of all 4 analyzed medulloblastoma cell lines, regardless of TP53 functional status. The decrease in cell viability was accompanied in 3 of the 4 medulloblastoma cell lines by accumulation of TP53 protein in the cells and increased CDKN1A expression. RITA treatment in mouse models inhibited medulloblastoma xenograft tumor growth. These data demonstrate that RITA treatment reduces medulloblastoma cell viability in both in vitro and in vivo models, and acts independently of cellular TP53 status, identifying RITA as a potential therapeutic agent to treat medulloblastoma.

Molecular mechanisms and therapeutic targets in pediatric brain tumors

Brain tumors are among the leading causes of cancer-related deaths in children. Although surgery, aggressive radiation, and chemotherapy have improved outcomes, many patients still die of their disease. Moreover, those who survive often suffer devastating long-term side effects from the therapies. A greater understanding of the molecular underpinnings of these diseases will drive the development of new therapeutic approaches. Advances in genomics and epigenomics have provided unprecedented insight into the molecular diversity of these diseases and, in several cases, have revealed key genes and signaling pathways that drive tumor growth. These not only serve as potential therapeutic targets but also have facilitated the creation of animal models that faithfully recapitulate the human disease for preclinical studies. In this Review, we discuss recent progress in understanding the molecular basis of the three most common malignant pediatric brain tumors-medulloblastoma, ependymoma, and high-grade glioma-and the implications for development of safer and more effective therapies.

Childhood cancer predisposition syndromes-A concise review and recommendations by the Cancer Predisposition Working Group of the Society for Pediatric Oncology and Hematology

Heritable predisposition is an important cause of cancer in children and adolescents. Although a large number of cancer predisposition genes and their associated syndromes and malignancies have already been described, it appears likely that there are more pediatric cancer patients in whom heritable cancer predisposition syndromes have yet to be recognized. In a consensus meeting in the beginning of 2016, we convened experts in Human Genetics and Pediatric Hematology/Oncology to review the available data, to categorize the large amount of information, and to develop recommendations regarding when a cancer predisposition syndrome should be suspected in a young oncology patient. This review summarizes the current knowledge of cancer predisposition syndromes in pediatric oncology and provides essential information on clinical situations in which a childhood cancer predisposition syndrome should be suspected.

Integrated Proteomic and Transcriptomic-Based Approaches to Identifying Signature Biomarkers and Pathways for Elucidation of Daoy and UW228 Subtypes

Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Patient survival has remained largely the same for the past 20 years, with therapies causing significant health, cognitive, behavioral and developmental complications for those who survive the tumor. In this study, we profiled the total transcriptome and proteome of two established MB cell lines, Daoy and UW228, using high-throughput RNA sequencing (RNA-Seq) and label-free nano-LC-MS/MS-based quantitative proteomics, coupled with advanced pathway analysis. While Daoy has been suggested to belong to the sonic hedgehog (SHH) subtype, the exact UW228 subtype is not yet clearly established. Thus, a goal of this study was to identify protein markers and pathways that would help elucidate their subtype classification. A number of differentially expressed genes and proteins, including a number of adhesion, cytoskeletal and signaling molecules, were observed between the two cell lines. While several cancer-associated genes/proteins exhibited similar expression across the two cell lines, upregulation of a number of signature proteins and enrichment of key components of SHH and WNT signaling pathways were uniquely observed in Daoy and UW228, respectively. The novel information on differentially expressed genes/proteins and enriched pathways provide insights into the biology of MB, which could help elucidate their subtype classification.

Medulloblastoma: Tumor Biology and Relevance to Treatment and Prognosis Paradigm

Medulloblastoma is a malignant embryonic brain tumor arising in the posterior fossa and typically occurring in pediatric patients. Current multimodal treatment regimes have significantly improved the survival rates; however, a marked heterogeneity in therapy response is observed, and one third of all patients die within 5 years after diagnosis. Large-scale genetic and transcriptome analysis revealed four medulloblastoma subgroups (WNT, SHH, Group 3, and Group 4) associated with different demographic parameters, tumor manifestation, and clinical behavior. Future treatment protocols will integrate molecular classification schemes to evaluate subgroup-specific intensification or de-escalation of adjuvant therapies aimed to increase tumor control and reduce iatrogenic induced morbidity. Furthermore, the identification of genetic drivers allows assessing target therapies in order to increase the chemotherapeutic armamentarium. This review highlights the biology behind the current classification system and elucidates relevant aspects of the disease influencing forthcoming clinical trials.

The p53 tumor suppressor protein protects against chemotherapeutic stress and apoptosis in human medulloblastoma cells

Medulloblastoma (MB), a primitive neuroectodermal tumor, is the most common malignant childhood brain tumor and remains incurable in about a third of patients. Currently, survivors carry a significant burden of late treatment effects. The p53 tumor suppressor protein plays a crucial role in influencing cell survival in response to cellular stress and while the p53 pathway is considered a key determinant of anti-tumor responses in many tumors, its role in cell survival in MB is much less well defined. Herein, we report that the experimental drug VMY-1-103 acts through induction of a partial DNA damage-like response as well induction of non-survival autophagy. Surprisingly, the genetic or chemical silencing of p53 significantly enhanced the cytotoxic effects of both VMY and the DNA damaging drug, doxorubicin. The inhibition of p53 in the presence of VMY revealed increased late stage apoptosis, increased DNA fragmentation and increased expression of genes involved in apoptosis, including CAPN12 and TRPM8, p63, p73, BIK, EndoG, CIDEB, P27^Kip1 and P21^cip1. These data provide the groundwork for additional studies on VMY as a therapeutic drug and support further investigations into the intriguing possibility that targeting p53 function may be an effective means of enhancing clinical outcomes in MB.

Medulloblastoma: molecular pathways and histopathological classification

Malignant brain tumors are the leading cause of cancer death among pediatric patients, and medulloblastoma constitutes 20% of them. Currently, the treatment is risk-adapted. Maximum surgical resection is recommended, always followed by chemotherapy and neuroaxis radiotherapy. In spite of the improving survival rate, survivors succumb to treatment-induced side effects. To reduce toxic effects, molecular-targeted treatment is proposed. Medulloblastoma research is very robust, and new articles on the subject are published daily. In the current review we have tried to bring together molecular pathophysiology of the neoplasm and current pathological classification, thus making an effort to relate tumor biology and the histological picture.

Radiation Sensitivity in a Preclinical Mouse Model of Medulloblastoma Relies on the Function of the Intrinsic Apoptotic Pathway

While treatments that induce DNA damage are commonly used as anticancer therapies, the mechanisms through which DNA damage produces a therapeutic response are incompletely understood. Here we have tested whether medulloblastomas must be competent for apoptosis to be sensitive to radiotherapy. Whether apoptosis is required for radiation sensitivity has been controversial. Medulloblastoma, the most common malignant brain tumor in children, is a biologically heterogeneous set of tumors typically sensitive to radiation and chemotherapy; 80% of medulloblastoma patients survive long-term after treatment. We used functional genetic studies to determine whether the intrinsic apoptotic pathway is required for radiation to produce a therapeutic response in mice with primary, Shh-driven medulloblastoma. We found that cranial radiation extended the survival of medulloblastoma-bearing mice and induced widespread apoptosis. Expression analysis and conditional deletion studies showed that Trp53 (p53) was the predominant transcriptional regulator activated by radiation and was strictly required for treatment response. Deletion of Bax, which blocked apoptosis downstream of p53, was sufficient to render tumors radiation resistant. In apoptosis-incompetent, Bax-deleted tumors, radiation activated p53-dependent transcription without provoking cell death and caused two discrete populations to emerge. Most radiated tumor cells underwent terminal differentiation. Perivascular cells, however, quickly resumed proliferation despite p53 activation, behaved as stem cells, and rapidly drove recurrence. These data show that radiation must induce apoptosis in tumor stem cells to be effective. Mutations that disable the intrinsic apoptotic pathways are sufficient to impart radiation resistance. We suggest that medulloblastomas are typically sensitive to DNA-damaging therapies, because they retain apoptosis competence. Cancer Res; 76(11); 3211-23. ©2016 AACR.

p53 and Meduloblastoma

Our understanding of medulloblastoma biology has increased dramatically over the past decade, in part a result of the recognition that there exists tremendous intertumoral heterogeneity not apparent by morphology alone. A particular area that significantly changed our approach to medulloblastoma has been an increased understanding of the role of p53. A role for p53 in medulloblastoma has been established over the past 20 years, however, not until recently has its significance been identified. Recent developments in the understanding of intertumor heterogeneity has clarified the role of TP53 mutations, as the importance of TP53 mutations is highly dependent on the molecular subgroup of medulloblastoma, with TP53 mutant Sonic Hedgehog medulloblastomas forming an extremely high-risk group of patients. As such, there is now a tremendous push to understand the role that p53 plays in treatment resistance of medulloblastoma. In this review, we will summarize the current understanding of p53 in medulloblastoma drawn primarily from recent advances in integrated genomics.

Intracranial cystic lesions: a review

Cysts and cystic-appearing intracranial lesions are common findings with routine cerebral imaging examination. These lesions often represent a challenge in diagnosis. Intracranial cystic lesions have wide pathologic and imaging spectra, of which some require an aggressive and tailored treatment, whereas many others remain asymptomatic and do not require follow-up or intervention. Intracranial cysts can be divided in non-neoplastic lesions that are often of developmental origin but comprise as well infectious cysts and neoplastic lesions that include benign cysts associated with low-grade tumors and cysts as a component of higher grade neoplasms. Reviewed are the pathology, origin, radiologic appearance, differential diagnosis, and therapeutic aspects of intracranial cystic lesions.

Combined MYC and P53 defects emerge at medulloblastoma relapse and define rapidly progressive, therapeutically targetable disease

We undertook a comprehensive clinical and biological investigation of serial medulloblastoma biopsies obtained at diagnosis and relapse. Combined MYC family amplifications and P53 pathway defects commonly emerged at relapse, and all patients in this group died of rapidly progressive disease postrelapse. To study this interaction, we investigated a transgenic model of MYCN-driven medulloblastoma and found spontaneous development of Trp53 inactivating mutations. Abrogation of p53 function in this model produced aggressive tumors that mimicked characteristics of relapsed human tumors with combined P53-MYC dysfunction. Restoration of p53 activity and genetic and therapeutic suppression of MYCN all reduced tumor growth and prolonged survival. Our findings identify P53-MYC interactions at medulloblastoma relapse as biomarkers of clinically aggressive disease that may be targeted therapeutically.

WNT activation by lithium abrogates TP53 mutation associated radiation resistance in medulloblastoma

TP53 mutations confer subgroup specific poor survival for children with medulloblastoma. We hypothesized that WNT activation which is associated with improved survival for such children abrogates TP53 related radioresistance and can be used to sensitize TP53 mutant tumors for radiation. We examined the subgroup-specific role of TP53 mutations in a cohort of 314 patients treated with radiation. TP53 wild-type or mutant human medulloblastoma cell-lines and normal neural stem cells were used to test radioresistance of TP53 mutations and the radiosensitizing effect of WNT activation on tumors and the developing brain. Children with WNT/TP53 mutant medulloblastoma had higher 5-year survival than those with SHH/TP53 mutant tumours (100% and 36.6% ± 8.7%, respectively (p < 0.001)). Introduction of TP53 mutation into medulloblastoma cells induced radioresistance (survival fractions at 2Gy (SF2) of 89% ± 2% vs. 57.4% ± 1.8% (p < 0.01)). In contrast, β-catenin mutation sensitized TP53 mutant cells to radiation (p < 0.05). Lithium, an activator of the WNT pathway, sensitized TP53 mutant medulloblastoma to radiation (SF2 of 43.5% ± 1.5% in lithium treated cells vs. 56.6 ± 3% (p < 0.01)) accompanied by increased number of γH2AX foci. Normal neural stem cells were protected from lithium induced radiation damage (SF2 of 33% ± 8% for lithium treated cells vs. 27% ± 3% for untreated controls (p = 0.05). Poor survival of patients with TP53 mutant medulloblastoma may be related to radiation resistance. Since constitutive activation of the WNT pathway by lithium sensitizes TP53 mutant medulloblastoma cells and protect normal neural stem cells from radiation, this oral drug may represent an attractive novel therapy for high-risk medulloblastomas.

RADIA: RNA and DNA integrated analysis for somatic mutation detection

The detection of somatic single nucleotide variants is a crucial component to the characterization of the cancer genome. Mutation calling algorithms thus far have focused on comparing the normal and tumor genomes from the same individual. In recent years, it has become routine for projects like The Cancer Genome Atlas (TCGA) to also sequence the tumor RNA. Here we present RADIA (RNA and DNA Integrated Analysis), a novel computational method combining the patient-matched normal and tumor DNA with the tumor RNA to detect somatic mutations. The inclusion of the RNA increases the power to detect somatic mutations, especially at low DNA allelic frequencies. By integrating an individual's DNA and RNA, we are able to detect mutations that would otherwise be missed by traditional algorithms that examine only the DNA. We demonstrate high sensitivity (84%) and very high precision (98% and 99%) for RADIA in patient data from endometrial carcinoma and lung adenocarcinoma from TCGA. Mutations with both high DNA and RNA read support have the highest validation rate of over 99%. We also introduce a simulation package that spikes in artificial mutations to patient data, rather than simulating sequencing data from a reference genome. We evaluate sensitivity on the simulation data and demonstrate our ability to rescue back mutations at low DNA allelic frequencies by including the RNA. Finally, we highlight mutations in important cancer genes that were rescued due to the incorporation of the RNA.

Prognostic significance of clinical, histopathological, and molecular characteristics of medulloblastomas in the prospective HIT2000 multicenter clinical trial cohort

This study aimed to prospectively evaluate clinical, histopathological and molecular variables for outcome prediction in medulloblastoma patients. Patients from the HIT2000 cooperative clinical trial were prospectively enrolled based on the availability of sufficient tumor material and complete clinical information. This revealed a cohort of 184 patients (median age 7.6 years), which was randomly split at a 2:1 ratio into a training (n = 127), and a test (n = 57) dataset in order to build and test a risk score for this population. Independent validation was performed in a non-overlapping cohort (n = 83). All samples were subjected to thorough histopathological investigation, CTNNB1 mutation analysis, quantitative PCR, MLPA and FISH analyses for cytogenetic variables, and methylome analysis. By univariable analysis, clinical factors (M-stage), histopathological variables (large cell component, endothelial proliferation, synaptophysin pattern), and molecular features (chromosome 6q status, MYC amplification, subgrouping) were found to be prognostic. Molecular consensus subgrouping (WNT, SHH, Group 3, Group 4) was validated as an independent feature to stratify patients into different risk groups. When comparing methods for the identification of WNT-driven medulloblastoma, this study identified CTNNB1 sequencing and methylation profiling to most reliably identify these patients. After removing patients with particularly favorable (CTNNB1 mutation, extensive nodularity) or unfavorable (MYC amplification) markers, a risk score for the remaining “intermediate molecular risk” population dependent on age, M-stage, pattern of synaptophysin expression, and MYCN copy-number status was identified, with speckled synaptophysin expression indicating worse outcome. Test and independent validation of the score confirmed significant discrimination of patients by risk profile. Methylation subgrouping and CTNNB1 mutation status represent robust tools for the risk stratification of medulloblastoma. A simple clinico-pathological risk score was identified, which was confirmed in a test set and by independent clinical validation.

Duration of the pre-diagnostic interval in medulloblastoma is subgroup dependent

BACKGROUND

Children presenting with medulloblastoma have a wide range of initial presenting symptoms. However, the influence of underlying tumor biology on the initial presentation of medulloblastoma is currently unknown. In light of the recent discovery of distinct medulloblastoma subgroups, we sought to define the initial presentation of childhood medulloblastoma in a subgroup specific manner.

PROCEDURE

We assembled a cohort of 126 medulloblastoma cases at the Hospital for Sick Children between 1994 and 2012 and determined subgroup affiliation using nanoString. Clinical details pertaining to the initial presentation were determined through a retrospective chart review.

RESULTS

The median pre-diagnostic interval across all medulloblastoma cases was 4 weeks (IQR: 4-12 weeks). Strikingly, when the pre-diagnostic interval was then determined in a subgroup specific manner, cases with WNT and Group 4 tumors showed significantly longer median pre-diagnostic intervals of 8 weeks compared to 2 weeks for SHH and 4 weeks for Group 3 (P = 0.0001). Younger age was significantly associated with a prolonged pre-diagnostic interval (P = 0.02 for all). When stratifying by subgroup the association with age was only significant in Group 4 (P = 0.04 for Group 4). Improved survival was significantly associated with a longer pre-diagnostic interval (P = 0.02), however is no longer significant when controlling for subgroup (P = 0.07).

CONCLUSIONS

The duration of the pre-diagnostic interval in childhood medulloblastoma is highly subgroup dependent, further highlighting the clinical heterogeneity and biological relevance of the four principle subgroups of medulloblastoma.

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.

Rubinstein-Taybi syndrome predisposing to non-WNT, non-SHH, group 3 medulloblastoma

Medulloblastomas (MB) are classified in four subgroups: the well defined WNT and Sonic Hedgehog (SHH) subgroups, and the less defined groups 3 and 4. They occasionally occur in the context of a cancer predisposition syndrome. While germline APC mutations predispose to WNT MB, germline mutations in SUFU, PTCH1, and TP53 predispose to SHH tumors. We report on a child with a Rubinstein-Taybi syndrome (RTS) due to a germline deletion in CREBBP, who developed a MB. Biological profilings demonstrate that this tumor belongs to the group 3. RTS may therefore be the first predisposition syndrome identified for non-WNT/non-SHH MB.

The rationale for targeted therapies in medulloblastoma

Medulloblastoma (MB) is the most frequent malignant brain tumor in children. Patients with MB who are classified as having high-risk disease or those with recurrent disease respond poorly to current therapies and have an increased risk of MB-related mortality. Preclinical studies and molecular profiling of MB tumors have revealed upregulation or activation of several key signaling pathways such as the sonic hedgehog and WNT pathways. Although the exact mechanisms underlying MB tumorigenesis remain poorly understood, inhibiting these key pathways with molecularly targeted therapies represents an important approach to improving MB outcomes. Several molecularly targeted therapies are already under clinical investigation in MB patients. We discuss current preclinical and clinical data, as well as data from clinical trials of targeted therapies that are either ongoing or in development for MB.

Pharmacologic activation of wild-type p53 by nutlin therapy in childhood cancer

A peculiar feature of several types of childhood cancer is that loss-of-function mutations of the TP53 (p53) tumor suppressor gene are uncommon, in contrast to many adult tumors. As p53 needs to be inactivated in order for tumor cells to survive and thrive, pediatric tumors typically make use of other mechanisms to keep p53 in check. One of the critical negative regulators of p53 is the MDM2 oncoprotein. Many anticancer drug development efforts in the past decade have therefore been devoted to the discovery and optimization of small molecules that selectively disrupt the interaction between MDM2 and p53, which could provide, in principle, a potent means to restore p53 function in tumor cells with wild-type p53. The nutlins are the class of selective inhibitors of the p53-MDM2 interaction that are currently most advanced in their clinical development. We review here the preclinical data that support the potential therapeutic use of nutlin drugs in the treatment of various pediatric tumors, including neuroblastoma, retinoblastoma, osteosarcoma, Ewing's sarcoma, rhabdomyosarcoma, medulloblastoma, and childhood acute lymphoblastic leukemia.

Role of MYC in Medulloblastoma

Since its discovery as an oncogene carried by the avian acute leukemia virus MC29 in myelocytomatosis (Roussel et al. 1979) and its cloning (Vennstrom et al. 1982), c-MYC (MYC), as well as its paralogs MYCN and MYCL1, has been shown to play essential roles in cycling progenitor cells born from proliferating zones during embryonic development, and in all proliferating cells after birth. MYC deletion induces cell-cycle exit or cell death, depending on the cell type and milieu, whereas MYC and MYCN amplification or overexpression promotes cell proliferation and occurs in many cancers. Here, we review the relationship of MYC family proteins to the four molecularly distinct medulloblastoma subgroups, discuss the possible roles MYC plays in each of these subgroups and in the developing cells of the posterior fossa, and speculate on possible therapeutic strategies targeting MYC.

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.

Subgroup-specific prognostic implications of TP53 mutation in medulloblastoma

PURPOSE

Reports detailing the prognostic impact of TP53 mutations in medulloblastoma offer conflicting conclusions. We resolve this issue through the inclusion of molecular subgroup profiles.

PATIENTS AND METHODS

We determined subgroup affiliation, TP53 mutation status, and clinical outcome in a discovery cohort of 397 medulloblastomas. We subsequently validated our results on an independent cohort of 156 medulloblastomas.

RESULTS

TP53 mutations are enriched in wingless (WNT; 16%) and sonic hedgehog (SHH; 21%) medulloblastomas and are virtually absent in subgroups 3 and 4 tumors (P < .001). Patients with SHH/TP53 mutant tumors are almost exclusively between ages 5 and 18 years, dramatically different from the general SHH distribution (P < .001). Children with SHH/TP53 mutant tumors harbor 56% germline TP53 mutations, which are not observed in children with WNT/TP53 mutant tumors. Five-year overall survival (OS; ± SE) was 41% ± 9% and 81% ± 5% for patients with SHH medulloblastomas with and without TP53 mutations, respectively (P < .001). Furthermore, TP53 mutations accounted for 72% of deaths in children older than 5 years with SHH medulloblastomas. In contrast, 5-year OS rates were 90% ± 9% and 97% ± 3% for patients with WNT tumors with and without TP53 mutations (P = .21). Multivariate analysis revealed that TP53 status was the most important risk factor for SHH medulloblastoma. Survival rates in the validation cohort mimicked the discovery results, revealing that poor survival of TP53 mutations is restricted to patients with SHH medulloblastomas (P = .012) and not WNT tumors.

CONCLUSION

Subgroup-specific analysis reconciles prior conflicting publications and confirms that TP53 mutations are enriched among SHH medulloblastomas, in which they portend poor outcome and account for a large proportion of treatment failures in these patients.

Identification of synthetic lethal pairs in biological systems through network information centrality

The immense availability of protein interaction data, provided with an abstract network approach is valuable for the improved interpretation of biological processes and protein functions globally. The connectivity of a protein and its structure are related to its functional properties. Highly connected proteins are often functionally cardinal and the knockout of such proteins leads to lethality. In this paper, we propose a new approach based on graph information centrality measures to identify the synthetic lethal pairs in biological systems. To illustrate the efficacy of our approach, we have applied it to a human cancer protein interaction network. It is found that the lethal pairs obtained were analogous to the experimental and computational inferences, implying that our approach can serve as a surrogate for predicting the synthetic lethality.