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Delineation of Two Clinically and Molecularly Distinct Subgroups of Posterior Fossa Ependymoma

ABSTRACT: Gene expression (mRNA) profiling of human ependymomas Despite the histological similarity of ependymomas from throughout the neuraxis, the disease likely comprises multiple independent entities, each with a distinct molecular pathogenesis. Transcriptional profiling of two large independent cohorts of ependymoma reveals the existence of two demographically, transcriptionally, genetically, and clinically distinct groups of posterior fossa (PF) ependymoma. Group-A patients are younger, have laterally located tumors with a balanced genome, and are much more likely to exhibit recurrence, secondary metastasis, and death as compared to Group-B patients. Identification and optimization of immunohistochemical markers for PF ependymoma subgroups allowed validation of our findings on a third independent group of tumors using a human ependymoma tissue microarray, and provides a tool for prospective prognostication and stratification of PF ependymoma patients.

ORGANISM(S): Homo sapiens

PROVIDER: GSE27279 | GEO | 2011/08/15

SECONDARY ACCESSION(S): PRJNA137319

REPOSITORIES: GEO

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Project description:Ependymomas are neuroepithelial tumors of the central nervous system (CNS), presenting in both adults and children but accounting for almost 10% of all pediatric CNS tumors and up to 30% of CNS tumors in children under 3 years (Bouffet et al., 2009; McGuire et al., 2009; Rodriguez et al., 2009). In children, most ependymomas arise in the posterior fossa, while most adult ependymomas present around the lower spinal cord and spinal nerve roots. Ependymomas display a wide range of morphological features, and several variants are listed in the World Health Organization (WHO) classification (Ellison et al., 2016). These variants are assigned to three WHO grades (I-III), but the clinical utility of this classification is acknowledged to be limited (Ellison et al., 2011). An increasing understanding of the genomic landscape of ependymoma and the discovery of distinct molecular groups by DNA methylation or gene expression profiling have begun to refine approaches to disease classification and prognostication, but have yet to be translated into clinical routine (Hoffman et al., 2014; Mack et al., 2014; Pajtler et al., 2017; Pajtler et al., 2015; Parker et al., 2014; Wani et al., 2012; Witt et al., 2011). Our comprehensive study of DNA methylation profiling across the entire disease demonstrated three molecular groups for each major anatomic compartment: supratentorial (ST), posterior fossa (PF), and spinal (SP) (Pajtler et al., 2015). In the ST compartment, two molecular groups (ST-EPN-RELA and ST-EPN-YAP1) align with tumors harboring specific genetic alterations, RELA and YAP1 fusion genes, which were initially discovered in a whole genome sequencing study (Parker et al., 2014). Among PF ependymomas, two of three molecular groups, PFA (PF-EPN-A) and PFB (PF-EPN-B), account for nearly all tumors; PF-SE tumors are rare, generally showing the morphology of a subependymoma (Pajtler et al., 2015). PFA tumors are found mainly in infants and young children (median age ≈ 3yrs) and have a relatively poor outcome, while PFB tumors are generally found in young adults (median age ≈ 30yrs) and are associated with a better prognosis (Pajtler et al., 2015; Witt et al., 2011). PFA tumors show few copy number alterations (CNAs), while PFB tumors harbor multiple CNAs that tend to affect entire chromosomes. While recurrent structural variants (SVs) are found in ST ependymomas, recurrent SVs or other mutations, such as single nucleotide variants (SNVs) and insertions or deletions (indels), have not been identified in PF ependymomas to date (Mack et al., 2014; Parker et al., 2014).

Project description:Background: The high incidence of recurrence and unpredictable clinical outcome for paediatric ependymoma reflect the imprecision of current therapeutic staging and need for novel risk stratification markers. Gain of chromosome 1q has been reported as a frequent aberration and correlate of adverse outcome in ependymoma. We therefore evaluated a prognostic role for 1q25 gain across three age-defined European clinical trial cohorts of paediatric intracranial ependymoma. Methods: The frequency of 1q gain in paediatric ependymoma was assessed across 51 tumours (42 primary, 9 recurrent) using Affymetrix® 500K SNP arrays. Gain of 1q25 was evaluated by interphase FISH (iFISH) across 189 primary intracranial ependymomas from children treated on the CCLG/SIOP CNS9204 (n = 60) and BBSFOP (n = 65) adjuvant chemotherapy trials, or with primary post-operative radiotherapy (SIOP CNS9904/RT group, n = 64). Results were correlated with clinical, histological and survival data. Findings: Gain of 1q was the most frequent imbalance in primary (7/42, 17 %) and recurrent ependymomas (3/9, 33 %). Gain of 1q25 was the strongest independent predictor of tumour progression in both CNS9204 (HR 3·36, p = 0·0009) and BBSFOP (HR 4·10, p = 0·0009) trial cohorts. In contrast, 1q25 gain was not prognostic for the older CNS9904/RT only group (PFS: p = 0·37, OS: p = 0·95). Clinical variables implicated in adverse outcome amongst cohorts included incomplete tumour resection and posterior fossa location. Interpretation: This is the first study to prospectively identify then validate a prognostic genomic marker for childhood ependymoma across independent prospective trial groups. 1q25 gain predicts progression in primary chemotherapy cohorts but not those treated by post-operative radiotherapy. We propose 1q25 gain is incorporated as an adverse marker into future European chemotherapeutic clinical trial design. Affymetrix SNP arrays were performed according to the manufacturer's directions on DNA extracted from flash frozen tumour specimens and patient-matched peripheral blood Copy number analysis of Affymetrix 500K SNP arrays was performed for DNA from 51 ependymomas and 40 constitutional DNA samples. Analysing broad genomic aberrations in 51 paediatric ependymomas, looking particularly at 1q gain.

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Delineation of Two Clinically and Molecularly Distinct Subgroups of Posterior Fossa Ependymoma

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