CNS Primitive Neuroectodermal Tumors Research Articles

Abstract PR-010: Asc1lb progenitor-specific RB conditional inactivation in zebrafish models rare CNS primitive neuroectodermal tumors

Abstract PR-010: Asc1lb progenitor-specific RB conditional inactivation in zebrafish models rare CNS primitive neuroectodermal tumors

Therapeutic implications of improved molecular diagnostics for rare CNS embryonal tumor entities: results of an international, retrospective study.

Only few data are available on treatment-associated behavior of distinct rare CNS embryonal tumor entities previously treated as "CNS-primitive neuroectodermal tumors" (CNS-PNET). Respective data on specific entities, including CNS neuroblastoma, FOXR2 activated (CNS NB-FOXR2), and embryonal tumors with multilayered rosettes (ETMR) are needed for development of differentiated treatment strategies. Within this retrospective, international study, tumor samples of clinically well-annotated patients with the original diagnosis of CNS-PNET were analyzed using DNA methylation arrays (n = 307). Additional cases (n = 66) with DNA methylation pattern of CNS NB-FOXR2 were included irrespective of initial histological diagnosis. Pooled clinical data (n = 292) were descriptively analyzed. DNA methylation profiling of "CNS-PNET" classified 58 (19%) cases as ETMR, 57 (19%) as high-grade glioma (HGG), 36 (12%) as CNS NB-FOXR2, and 89(29%) cases were classified into 18 other entities. Sixty-seven (22%) cases did not show DNA methylation patterns similar to established CNS tumor reference classes. Best treatment results were achieved for CNS NB-FOXR2 patients (5-year PFS: 63% ± 7%, OS: 85% ± 5%, n = 63), with 35/42 progression-free survivors after upfront craniospinal irradiation (CSI) and chemotherapy. The worst outcome was seen for ETMR and HGG patients with 5-year PFS of 18% ± 6% and 22% ± 7%, and 5-year OS of 24% ± 6% and 25% ± 7%, respectively. The historically reported poor outcome of CNS-PNET patients becomes highly variable when tumors are molecularly classified based on DNA methylation profiling. Patients with CNS NB-FOXR2 responded well to current treatments and a standard-risk CSI-based regimen may be prospectively evaluated. The poor outcome of ETMR across applied treatment strategies substantiates the necessity for evaluation of novel treatments.

MRI Features of Histologically Diagnosed Supratentorial Primitive Neuroectodermal Tumors and Pineoblastomas in Correlation with Molecular Diagnoses and Outcomes: A Report from the Children's Oncology Group ACNS0332 Trial.

Supratentorial primitive neuroectodermal tumors and pineoblastomas have traditionally been grouped together for treatment purposes. Molecular profiling of these tumors has revealed a number of distinct entities and has led to the term "CNS-primitive neuroectodermal tumors" being removed from the 2016 World Health Organization classification. The purpose of this study was to describe the MR imaging findings of histologically diagnosed primitive neuroectodermal tumors and pineoblastomas and correlate them with molecular diagnoses and outcomes. Histologically diagnosed primitive neuroectodermal tumors and pineoblastomas were enrolled in this Children's Oncology Group Phase III trial, and molecular classification was retrospectively completed using DNA methylation profiling. MR imaging features were systematically studied and correlated with molecular diagnoses and survival. Of the 85 patients enrolled, 56 met the inclusion criteria, in whom 28 tumors were in pineal and 28 in nonpineal locations. Methylation profiling revealed a variety of diagnoses, including pineoblastomas (n = 27), high-grade gliomas (n = 17), embryonal tumors (n = 7), atypical teratoid/rhabdoid tumors (n = 3), and ependymomas (n = 2). Thus, 39% overall and 71% of nonpineal tumor diagnoses were discrepant with histopathology. Tumor location, size, margins, and edema were predictors of embryonal-versus-nonembryonal tumors. Larger size and ill-defined margins correlated with poor event-free survival, while metastatic disease by MR imaging did not. In nonpineal locations, only a minority of histologically diagnosed primitive neuroectodermal tumors are embryonal tumors; therefore, high-grade glioma or ependymoma should be high on the radiographic differential. An understanding of molecularly defined tumor entities and their relative frequencies and locations will help the radiologist make more accurate predictions of the tumor types.

Tandem high-dose chemotherapy with topotecan-thiotepa-carboplatin and melphalan-etoposide-carboplatin regimens for pediatric high-risk brain tumors.

High-dose chemotherapy (HDC) and autologous stem-cell transplantation (auto-SCT) are used to improve the survival of children with high-risk brain tumors who have a poor outcome with the standard treatment. This study aims to evaluate the outcome of HDC/auto-SCT with topotecan-thiotepa-carboplatin and melphalan-etoposide-carboplatin (TTC/MEC) regimens in pediatric brain tumors. We retrospectively analyzed the data of 33 children (median age 6years) who underwent HDC/auto-SCT (18 tandem and 15 single) with uniform conditioning regimens. Eleven patients aged < 3years at diagnosis were eligible for HDC/auto-SCT to avoid or defer radiotherapy. In addition, nine patients with high-risk medulloblastoma (presence of metastasis and/or postoperative residual tumor ≥ 1.5cm2), eight with other high-risk brain tumor (six CNS primitive neuroectodermal tumor, one CNS atypical teratoid/rhabdoid tumor, and one pineoblastoma), and five with relapsed brain tumors were enrolled. There were three toxic deaths, and two of which were due to pulmonary complications. The main reason for not performing tandem auto-SCT was due to toxicities and patient refusal. The event-free survival (EFS) and overall survival (OS) rates of all patients were 59.4% and 80.0% at a median follow-up with 49.1months from the first HDC/auto-SCT, respectively. The EFS/OS rates of patients aged < 3years at diagnosis, high-risk medulloblastoma, other high-risk brain tumor, and relapsed tumors were 50.0/81.8%, 87.5/85.7%, 66.7/88.9%, and 20.0/60.0%, respectively. Although tandem HDC/auto-SCT with TTC/MEC regimens showed promising survival rates, treatment modifications are warranted to reduce toxicities. The survival rates with relapsed brain tumors were unsatisfactory despite HDC/auto-SCT, and further study is needed.

Characterization of brain tumor initiating cells isolated from an animal model of CNS primitive neuroectodermal tumors.

CNS Primitive Neuroectodermal tumors (CNS-PNETs) are members of the embryonal family of malignant childhood brain tumors, which remain refractory to current therapeutic treatments. Current paradigm of brain tumorigenesis implicates brain tumor-initiating cells (BTIC) in the onset of tumorigenesis and tumor maintenance. However, despite their significance, there is currently no comprehensive characterization of CNS-PNETs BTICs. Recently, we described an animal model of CNS-PNET generated by orthotopic transplantation of human Radial Glial (RG) cells - the progenitor cells for adult neural stem cells (NSC) - into NOD-SCID mice brain and proposed that BTICs may play a role in the maintenance of these tumors. Here we report the characterization of BTIC lines derived from this CNS-PNET animal model. BTIC’s orthotopic transplantation generated highly aggressive tumors also characterized as CNS-PNETs. The BTICs have the hallmarks of NSCs as they demonstrate self-renewing capacity and have the ability to differentiate into astrocytes and early migrating neurons. Moreover, the cells demonstrate aberrant accumulation of wild type tumor-suppressor protein p53, indicating its functional inactivation, highly up-regulated levels of onco-protein cMYC and the BTIC marker OCT3/4, along with metabolic switch to glycolysis - suggesting that these changes occurred in the early stages of tumorigenesis. Furthermore, based on RNA- and DNA-seq data, the BTICs did not acquire any transcriptome-changing genomic alterations indicating that the onset of tumorigenesis may be epigenetically driven. The study of these BTIC self-renewing cells in our model may enable uncovering the molecular alterations that are responsible for the onset and maintenance of the malignant PNET phenotype.

Review of molecular classification and treatment implications of pediatric brain tumors.

Brain tumors are the most common solid tumors and leading cause of cancer-related death in children. The advent of large-scale genomics has resulted in a plethora of profiling studies that have mapped the genetic and epigenetic landscapes of pediatric brain tumors, ringing in a new era of precision diagnostics and targeted therapies. In this review, we highlight the most recent findings, focusing on studies published after 2015, and discuss how new evidence is changing the care of children with brain tumors. Genome-wide and epigenome-wide profiling data have revealed distinct tumor entities within, virtually, all pediatric brain tumor groups including medulloblastoma; ependymoma; high-grade and low-grade gliomas; atypical teratoid/rhabdoid tumors; and other embryonal tumors, previously called CNS primitive neuroectodermal tumors. Whenever integrated with clinical information, many molecular alterations emerge as powerful prognostic markers and should thus be used to stratify patients and tailor therapies. Optimal integration of this newly emerging knowledge in a timely and meaningful way into clinical care is a remarkable task and a matter of active debate. The historical morphology-based classification of tumors is being replaced by a genetic-based classification, and the first generation of molecularly informed clinical trials is underway.

Stabilization of HIF-1α and HIF-2α, up-regulation of MYCC and accumulation of stabilized p53 constitute hallmarks of CNS-PNET animal model.

Recently, we described a new animal model of CNS primitive neuroectodermal tumors (CNS-PNET), which was generated by orthotopic transplantation of human Radial Glial (RG) cells into NOD-SCID mice’s brain sub-ventricular zone. In the current study we conducted comprehensive RNA-Seq analyses to gain insights on the mechanisms underlying tumorigenesis in this mouse model of CNS-PNET. Here we show that the RNA-Seq profiles derived from these tumors cluster with those reported for patients’ PNETs. Moreover, we found that (i) stabilization of HIF-1α and HIF-2α, which are involved in mediation of the hypoxic responses in the majority of cell types, (ii) up-regulation of MYCC, a key onco-protein whose dysregulation occurs in ~70% of human tumors, and (iii) accumulation of stabilized p53, which is commonly altered in human cancers, constitute hallmarks of our tumor model, and might represent the basis for CNS-PNET tumorigenesis in this model. We discuss the possibility that these three events might be interconnected. These results indicate that our model may prove invaluable to uncover the molecular events leading to MYCC and TP53 alterations, which would be of broader interest considering their relevance to many human malignancies. Lastly, this mouse model might prove useful for drug screening targeting MYCC and related members of its protein interaction network.

Abstract 4179: Expression profiling of zebrafish rb1- neuroectodermal-like brain tumors: A new model of CNS PNETs

Abstract We examined the gene expression signature of zebrafish brain tumors induced by somatic inactivation of the retinoblastoma tumor suppressor rb1 to determine the similarity with human CNS primitive neuroectodermal tumors (PNETs). Childhood CNS PNETs are aggressive tumors characterized by undifferentiated cells with features of the embryonic neuroepithelium. Previously our histological analysis showed the majority of zebrafish rb1- lesions were proliferative neuroectodermal-like tumors composed of neoplastic cells with small hyperchromatic nuclei that form rosettes. To obtain the transcription profile of the zebrafish rb1- tumors, RNA-Seq was performed on 10 tumors from fish ranging in age from 3.5 to 10 months of age. Duplicate RNA-Seq libraries were synthesized for each tumor and multiplex sequenced on an Illumina HiSeq NextGen Sequencer at the Genome Sequencing Core, Kansas University. Our initial gene expression profiling of the zebrafish rb1- brain tumors revealed a molecular signature consistent with an undifferentiated tumor phenotype. In each zebrafish tumor sample, standard markers of neuronal differentiation (sypa, sypb, neurod1/2, neurog1/2) and glial differentiation (GFAP, S100β) were not significantly expressed. In contrast, the neural stem/progenitor marker sox2 was highly expressed in all tumors, consistent with the primitive neuroectodermal-like tumor histology. Comparison with human childhood CNS-PNET gene expression analysis revealed a similar profile. Four of the nine genes that define the human oligoneural (group 2) molecular subgroup (olig2, bcan, sox8b, sox10 and ascl1) described by Picard et al, 2012 were highly expressed in the zebrafish tumors. Together, the data indicate the zebrafish brain tumors induced by somatic inactivation of rb1 model human CNS PNETs. Additional gene expression, pathway, and cross-species comparative analyses are in progress. The zebrafish rb1- tumor model will be useful for investigating the molecular pathways driving the aggressive and undifferentiated features of CNS PNETs. Citation Format: Maura A. McGrail, Staci L. Solin, Jeffrey A. Haltom, Laura E. Schultz, Jeffrey J. Essner, Heather R. Shive. Expression profiling of zebrafish rb1- neuroectodermal-like brain tumors: A new model of CNS PNETs. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4179.

MPTH-15MOLECULAR RECLASSIFICATION OF CNS-PRIMITIVE NEUROECTODERMAL TUMORS INTO WELL-KNOWN AND NOVEL TUMOR ENTITIES

CNS-primitive neuroectodermal tumors (CNS-PNETs) are poorly differentiated embryonal tumors with early onset and aggressive clinical behavior. Histological diagnosis is complicated by morphological heterogeneity and divergent differentiation. Recent studies suggest the existence of molecular subgroups of CNS-PNETs sharing biological characteristics with other CNS tumors. To investigate this we have analyzed 301 fresh-frozen or paraffin-embedded CNS-PNET samples using DNA methylation (n = 301) and expression (n = 76) arrays. (Epi-)genetic profiles of CNS-PNETs were compared to >200 reference cases of other pediatric and adult brain tumors representing more than 20 well-known entities. DNA methylation and gene expression patterns segregated brain tumors by histological entities and molecular subgroups. Solely, CNS-PNET profiles showed a significant overlap with various well-defined entities, including AT/RT, ETMR, high-grade glioma, medulloblastoma, ependymoma, and others. When screening CNS-PNETs with profiles highly resembling other entities, hallmark genetic alterations of these, such as amplification of 19q13.42, mutations in IDH1 or H3F3A, or mutations/deletions of the SMARCB1 locus, were frequently detected. Also, established protein markers, such as INI-1, LIN28A, and OLIG2, confirmed the reclassification of these CNS-PNETs. Strikingly, a subset (∼25%) of CNS-PNETs, which could not be reclassified, segregated into at least five distinct molecular subgroups, each with its own characteristic pattern of DNA-methylation, copy number aberrations, gene expression, and recurrent mutations. Extending our clustering cohort to include larger series of non CNS PNET tumours, we identified additional brain tumors from various entities to resemble DNA methylation and mutation patterns of these five new molecular subgroups. The correct classification of CNS-PNETs based solely on histology remains challenging. The majority of cases can reliably be reclassified using molecular markers, indicating that a significant proportion of CNS-PNETs represents a variety of other brain tumor subtypes. The remaining CNS PNETs comprise five novel tumour groups with distinct molecular features that overlap with tumors previously diagnosed as non PNETs.

Pediatric Brain Tumors: Innovative Genomic Information Is Transforming the Diagnostic and Clinical Landscape.

Pediatric neuro-oncology has undergone an exciting and dramatic transformation during the past 5 years. This article summarizes data from collaborative group and institutional trials that have advanced the science of pediatric brain tumors and survival of patients with these tumors. Advanced genomic analysis of the entire spectrum of pediatric brain tumors has heralded an era in which stakeholders in the pediatric neuro-oncology community are being challenged to reconsider their current research and diagnostic and treatment strategies. The incorporation of this new information into the next-generation treatment protocols will unleash new challenges. This review succinctly summarizes the key advances in our understanding of the common pediatric brain tumors (ie, medulloblastoma, low- and high-grade gliomas, diffuse intrinsic pontine glioma, and ependymoma) and some selected rare tumors (ie, atypical teratoid/rhabdoid tumor and CNS primitive neuroectodermal tumor). The potential impact of this new information on future clinical protocols also is discussed. Cutting-edge genomics technologies and the information gained from such studies are facilitating the identification of molecularly defined subgroups within patients with particular pediatric brain tumors. The number of evaluable patients in each subgroup is small, particularly in the subgroups of rare diseases. Therefore, international collaboration will be crucial to draw meaningful conclusions about novel approaches to treating pediatric brain tumors.

A mouse model of human primitive neuroectodermal tumors resulting from microenvironmentally-driven malignant transformation of orthotopically transplanted radial glial cells.

There is growing evidence and a consensus in the field that most pediatric brain tumors originate from stem cells, of which radial glial cells constitute a subtype. Here we show that orthotopic transplantation of human radial glial (RG) cells to the subventricular zone of the 3rd ventricle - but not to other transplantation sites - of the brain in immunocompromised NOD-SCID mice, gives rise to tumors that have the hallmarks of CNS primitive neuroectodermal tumors (PNETs). The resulting mouse model strikingly recapitulates the phenotype of PNETs. Importantly, the observed tumorigenic transformation was accompanied by aspects of an epithelial to mesenchymal transition (EMT)-like process. It is also noteworthy that the tumors are highly invasive, and that they effectively recruit mouse endothelial cells for angiogenesis. These results are significant for several reasons. First, they show that malignant transformation of radial glial cells can occur in the absence of specific mutations or inherited genomic alterations. Second, they demonstrate that the same radial glial cells may either give rise to brain tumors or differentiate normally depending upon the microenvironment of the specific region of the brain to which the cells are transplanted. In addition to providing a prospect for drug screening and development of new therapeutic strategies, the resulting mouse model of PNETs offers an unprecedented opportunity to identify the cancer driving molecular alterations and the microenvironmental factors that are responsible for committing otherwise normal radial glial cells to a malignant phenotype.

Abstract 3089: (Epi)genetic profiling enables molecular re-classification of CNS-primitive neuroectodermal tumors

Abstract According to the current WHO classification of CNS tumors, childhood CNS primitive neuro-ectodermal tumors (CNS-PNETs; WHO °IV) are poorly differentiated embryonal tumors with early onset and aggressive clinical behavior. Histological diagnosis can be complicated by morphological heterogeneity and divergent differentiation. Recent studies suggest the existence of molecular subgroups of CNS-PNETs sharing biological characteristics with other childhood CNS tumors. Here, we aimed at a comprehensive molecular characterization of CNS-PNETs and compared our results to profiles of other brain tumor classes in order to define the biological nature of tumors diagnosed as CNS-PNETs. A collective of 197 fresh-frozen or paraffin-embedded tumor samples with an institutional diagnosis “CNS-PNET” was profiled for genome-wide DNA methylation patterns and copy-number alterations, complemented by transcriptomic profiling of a subset (n=63). (Epi-)genetic profiles of CNS-PNETs were compared to those of &amp;gt;1.000 other childhood brain tumors including embryonal, astrocytic, and ependymal entities, and their respective molecular subgroups. We screened selected groups of tumors for recurrent mutations and expression of established molecular markers. Five experienced neuropathologists independently revisited the histology of 48 CNS-PNETs. Bioinformatic analysis of DNA methylation and gene expression profiles using clustering methods and class prediction algorithms resulted in a clear segregation of pediatric brain tumors by histological entities and molecular subgroups. Exceptionally, profiles of tumors classified as “CNS-PNET” suggested significant overlap with various well-defined entities, including AT/RT, ETMR, high-grade glioma, medulloblastoma, and ependymoma. When screening CNS-PNETs with DNA methylation profiles highly resembling other entities, hallmark genetic alterations of these, such as amplification of 19q13.42, mutations in IDH1 or H3F3A, or mutations/deletions of the SMARCB1 locus, were frequently detected. Molecularly distinct tumor subsets were associated with differential protein expression patterns of previously established subgroup markers INI-1, LIN28A, and OLIG2. Blinded histopathological evaluation resulted in a large proportion of CNS-PNETs being re-classified in line with affiliations suggested by molecular diagnostic tools. The correct classification of CNS-PNET remains challenging. Based on the detection of recurrent genetic aberrations, many cases can be reliably re-classified, indicating that a significant proportion of CNS-PNETs may comprise a variety of other tumor subtypes. These findings suggest that the use of established and novel subgroups markers is needed in order to assist the histopathological evaluation of these tumors. The molecular biology underlying distinct subsets of CNS-PNETs only remains to be elucidated. Citation Format: Dominik Sturm, Paul A. Northcott, David T.W. Jones, Andrey Korshunov, Daniel Picard, Peter Lichter, Annie Huang, Stefan M. Pfister, Marcel Kool. (Epi)genetic profiling enables molecular re-classification of CNS-primitive neuroectodermal tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3089. doi:10.1158/1538-7445.AM2014-3089

MOLECULAR (RE-)CLASSIFICATION OF CNS-PRIMITIVE NEUROECTODERMAL TUMORS

BACKGROUND: According to the current WHO classification of CNS tumors, childhood CNS primitive neuro-ectodermal tumors (CNS-PNETs; WHO °IV) are poorly differentiated embryonal tumors with early onset and aggressive clinical behavior. Histological diagnosis can be complicated by morphological heterogeneity and divergent differentiation. Recent studies suggest the existence of molecular subgroups of CNS-PNETs sharing biological characteristics with other childhood CNS tumors. Here, we aimed at a comprehensive molecular characterization of CNS-PNETs and compared our results to profiles of other brain tumor entities in order to define the biological nature of tumors diagnosed as CNS-PNETs. METHODS: A collection of 211 fresh-frozen or paraffin-embedded tumor samples with an institutional diagnosis “CNS-PNET” was profiled for genome-wide DNA methylation patterns and copy-number alterations, complemented by transcriptomic profiling of a subset (n = 71). (Epi-)genetic profiles of CNS-PNETs were compared to those of >3000 other childhood brain tumors including embryonal, astrocytic, and ependymal entities, and their respective molecular subgroups. We screened selected groups of tumors for recurrent mutations and expression of established molecular markers. RESULTS: DNA methylation and gene expression profiles showed a clear segregation of pediatric brain tumors by histological entities and molecular subgroups. Interestingly, CNS-PNET profiles showed a significant overlap with various well-defined entities, including AT/RT, ETMR, high-grade glioma, medulloblastoma, and ependymoma. When screening CNS-PNETs with profiles highly resembling other entities, hallmark genetic alterations of these, such as amplification of 19q13.42, mutations in IDH1 or H3F3A, or mutations/deletions of the SMARCB1 locus, were frequently detected. Also, established protein markers, such as INI-1, LIN28A, and OLIG2, confirmed the reclassification of these CNS-PNETs. Strikingly, a subset (∼25%) of CNS-PNETs which could not be reclassified segregated into 3-4 distinct molecular subgroups, each with its own characteristic pattern of copy-number aberrations, DNA-methylation and gene expression. Currently, whole genome and RNA-sequencing of these distinct subgroups of CNS-PNETs is ongoing to reveal their underlying genetics. CONCLUSIONS: The correct classification of CNS-PNETs remains challenging. Based on the detection of recurrent genetic aberrations, many cases can be reliably re-classified, indicating that a significant proportion of CNS-PNETs may comprise a variety of other tumor subtypes. These findings suggest that the use of established and novel subgroups markers is needed in order to assist the histopathological evaluation of these tumors. In addition, we have identified a number of true CNS-PNET subtypes and are currently analyzing them in more detail in order to elucidate the genetics of these distinct groups. SECONDARY CATEGORY: Tumor Biology.

MRI characteristics of ependymoblastoma: results from 22 centrally reviewed cases.

Ependymoblastoma is a malignant embryonal tumor that develops in early childhood and has a dismal prognosis. Categorized by the World Health Organization as a subgroup of CNS-primitive neuroectodermal tumor, ependymoblastoma is histologically defined by "ependymoblastic rosettes." Because it is so rare, little is known about specific MR imaging characteristics of ependymoblastoma. We systematically analyzed and discussed MR imaging features of ependymoblastoma in a series of 22 consecutive patients. Ependymoblastoma cases were obtained from the database of the German multicenter HIT trials between 2002 and 2013. All cases within this study were centrally reviewed for histopathology, MR imaging findings, and multimodal therapy. For systematic analysis of initial MR imaging scans at diagnosis, we applied standardized criteria for reference image evaluation of pediatric brain tumors. Ependymoblastomas are large tumors with well-defined tumor margins, iso- to hyperintense signal on T2WI, and diffusion restriction. Contrast enhancement is variable, with a tendency to mild or moderate enhancement. Subarachnoid spread is common in ependymoblastoma but can be absent initially. There was a male preponderance (1.75:1 ratio) for ependymoblastoma in our cohort. Mean age at diagnosis was 2.1 years. With this study, we add the largest case collection to the limited published database of MR imaging findings in ependymoblastoma, together with epidemiologic data. However, future studies are needed to systematically compare MR imaging findings of ependymoblastoma with other CNS-primitive neuroectodermal tumors and ependymoma, to delineate imaging criteria that might help distinguish these pediatric brain tumor entities.

Endoscopic removal of an intraventricular primitive neuroectodermal tumor: retrieval of a free-floating fragment using a urological basket retriever

The endoscopic resection of intraventricular tumors represents a unique challenge to the neurological surgeon. These neoplasms are invested deep within the brain parenchyma and are situated among neurologically vital structures. Additionally, the cerebrospinal fluid system presents a dynamic pathway for resected tumors to be mobilized and entrapped in other regions of the brain. In 2011, the authors treated a 3-year-old girl with a third ventricular mass identified on stereotactic brain biopsy as a WHO Grade IV CNS primitive neuroectodermal tumor. After successful neoadjuvant chemotherapy, endoscopic resection was performed. Despite successful resection of the tumor, the operation was complicated by mobilization of the resected tumor and entrapment in the atrial horn of the lateral ventricle. Using a urological stone basket retriever, the authors were able to retrieve the intact tumor without additional complications. The flexibility afforded by the nitinol urological stone basket was useful in the endoscopic removal of a free-floating intraventricular tumor. This device may prove to be useful for other practitioners performing these complicated intraventricular resections.

Antiangiogenic metronomic therapy for children with recurrent embryonal brain tumors

Median survival time of recurrent embryonal brain tumors is short regardless of salvage chemotherapy used. An evolving alternative approach to conventional chemotherapy is to target neovascularization by interfering with tumor angiogenesis at various levels. From November 2006 to December 2010, 16 patients (median age: 9 years) with recurrent (9 first, 7 multiple) embryonal brain tumors were treated with an antiangiogenic multidrug combination regimen (bevacizumab, thalidomide, celecoxib, fenofibrate, etoposide, and cyclophophamide) and additional intraventricular therapy (etoposide and liposomal cytarabine). At a median of 33 months, 10/16 patients are alive. 4/4 patients with CNS primitive neuroectodermal tumors (CNS PNET) and 1/7 patients with medulloblastoma (MB) died of tumor progression during the first year. Another patient with MB died of an accident after 23 months, the remaining five patients with MB are alive for 12, 33, 33, 37, and 58 months. For the seven patients with MB, both overall survival (OS) and event free survival (EFS) after 6 months was 100%, after 12 months 85.7 ± 13%, and after 24 months 68.6 ± 19%. In contrast, for patients with CNS PNET, both OS and EFS after 6 months was 75.0 ± 22% and 0.0% and all patients had died by 12 months. Low-dose oral etoposide and cyclophosphamide was reduced after a median of 2 months and discontinued after a median of 11 months. Toxicities were manageable and therapy was generally well tolerated. Our results suggest that the chosen antiangiogenic drug combination is particularly beneficial for patients with MB and warrants further investigation.

Intraspinal primitive neuroectodermal tumor in a man with neurofibromatosis type 1: Case report and review of the literature

Background:The occurrence of primitive neuroectodermal tumors (PNET) in patients with neurofibromatosis type 1 (NF1) has only been reported in two other cases in English-Language literature. Owing to the rarity of intraspinal PNET and the extremely high gene mutation variability in NF1, there is currently no conclusive evidence to suggest that PNET is associated with NF1. Here, we report a case of intradural PNET in a patient with NF1.Case Description:A 27-year-old male underwent a C1-C3 laminectomy for resection of an intramedullary mass. Histopathology and immunohistopathology analysis was performed. Microscopic examination and immunohistochemical staining indicated the mass was a primitive neuroectodermal tumor. Within 1 month after tumor resection, the patient developed leptomeningeal carcinomatosis. The patient was not a candidate for radiation therapy but underwent palliative systemic chemotherapy. He subsequently developed neutropenia and died 3 months after tumor resection.Conclusion:To our knowledge, this is the first reported intraspinal PNET associated with NF1. Genetic analysis of CNS PNETs suggests a possible correlation, but larger case series are needed to support this theory.

Pediatric brain tumor cancer stem cells: cell cycle dynamics, DNA repair, and etoposide extrusion

Reliable model systems are needed to elucidate the role cancer stem cells (CSCs) play in pediatric brain tumor drug resistance. The majority of studies to date have focused on clinically distinct adult tumors and restricted tumor types. Here, the CSC component of 7 newly established primary pediatric cell lines (2 ependymomas, 2 medulloblastomas, 2 gliomas, and a CNS primitive neuroectodermal tumor) was thoroughly characterized. Comparison of DNA copy number with the original corresponding tumor demonstrated that genomic changes present in the original tumor, typical of that particular tumor type, were retained in culture. In each case, the CSC component was approximately 3–4-fold enriched in neurosphere culture compared with monolayer culture, and a higher capacity for multilineage differentiation was observed for neurosphere-derived cells. DNA content profiles of neurosphere-derived cells expressing the CSC marker nestin demonstrated the presence of cells in all phases of the cell cycle, indicating that not all CSCs are quiescent. Furthermore, neurosphere-derived cells demonstrated an increased resistance to etoposide compared with monolayer-derived cells, having lower initial DNA damage, potentially due to a combination of increased drug extrusion by ATP-binding cassette multidrug transporters and enhanced rates of DNA repair. Finally, orthotopic xenograft models reflecting the tumor of origin were established from these cell lines. In summary, these cell lines and the approach taken provide a robust model system that can be used to develop our understanding of the biology of CSCs in pediatric brain tumors and other cancer types and to preclinically test therapeutic agents.

Molecular diagnostics of CNS embryonal tumors

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

Role of high‐dose chemotherapy for recurrent medulloblastoma and other CNS primitive neuroectodermal tumors

We summarize data presented on the use of high-dose chemotherapy (HDCT) with stem cell rescue for patients with recurrent medulloblastoma and other primitive neuroectodermal tumors as presented at an international consensus and state of the art workshop held in Milan in 2006. Eight, mainly institutional, studies were presented that included 159 patients who received HDCT of whom 22% were disease-free survivors at the time of reporting. Of those receiving HDCT and who relapsed having received previous radiotherapy, 17.3% were disease-free survivors at the time of reporting. However, from the two national studies that reported results from the time of relapse, only 4.2% were event free survivors. The outlook for previously irradiated patients with recurrent PNETs remains extremely poor and more effective therapeutic approaches are needed.