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BRAF V600E, TERT promoter mutations and CDKN2A/B homozygous deletions are frequent in epithelioid glioblastomas: a histological and molecular analysis focusing on intratumoral heterogeneity.

ABSTRACT: Epithelioid glioblastoma (E-GBM) is a rare aggressive variant of IDH-wildtype glioblastoma newly recognized in the 2016 World Health Organization classification, composed predominantly of monotonous, patternless sheets of round cells with laterally positioned nuclei and plump eosinophilic cytoplasm. Approximately 50% of E-GBM harbor BRAF V600E, which is much less frequently found in other types of glioblastomas. Most E-GBM are recognized as primary/de novo lesions; however, several E-GBM with co- or pre-existing lower-grade lesions have been reported. To better understand associations between E-GBM and the lower-grade lesions, we undertook a histological and molecular analysis of 14 E-GBM, 10 of which exhibited lower-grade glioma-like components (8 E-GBM with co-existing diffuse glioma-like components, 1 E-GBM with a co-existing PXA-like component and 1 E-GBM with a pre-existing PXA). Molecular results demonstrated that the prevalence of BRAF V600E, TERT promoter mutations and CDKN2A/B homozygous deletions in E-GBM were 13/14 (93%), 10/14 (71%) and 11/14 (79%), respectively, and concurrent BRAF V600E, TERT promoter mutations and CDKN2A/B homozygous deletions were observed in 7/14 (50%) of E-GBM. These alterations were also frequently seen in the lower-grade lesions irrespective of the histology. Genetic analysis including array comparative genomic hybridization performed for 5 E-GBM with co- and pre-existing lower-grade components revealed that all molecular changes found in the lower-grade components were also observed in the E-GBM components, and additional changes were detected in the E-GBM components. In conclusion, E-GBM frequently exhibit BRAF V600E, TERT promoter mutations and CDKN2A/B homozygous deletions and these alterations tend to coexist in E-GBM. Taken together with the facts that only one PXA preceded E-GBM among these lower-grade lesions, and that co-occurrence of BRAF V600E, TERT promoter mutations and CDKN2A/B homozygous deletions have been reported to be rare in conventional lower-grade diffuse gliomas, the diffuse glioma-like components may be distinct infiltrative components of E-GBM, reflecting intratumoral heterogeneity.

SUBMITTER: Nakajima N

PROVIDER: S-EPMC8028676 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundGenetic alterations in pediatric primary brain tumors can be used as diagnostic and prognostic markers and are the basis for the development of new target therapies that, ideally, would be associated with lower mortality and morbidity. This study evaluates the incidence and interplay of the presence of BRAF V600E mutation and chromosomal 9p21 deletions in a series of 100 pediatric gliomas, aiming to determine the role of these alterations in recurrence and malignant transformation, and to verify if they could be used in the clinical set for stratifying patients for tailored therapies and surveillance.MethodsSanger sequencing was used for the assessment of BRAF mutations at exon 15 and Fluorescent In Situ Hybridization (FISH) with BAC: RP11–14192 for the detection of 9p21 alterations. Expression levels of the CDKN2A and MTAP by real-time PCR were evaluated in cases with 9p21 deletions. Statistical analysis of genetic and clinical data was performed using Graph Pad Prism 5 and SPSS Statistics 24 software.ResultsIn our cohort it was observed that 7 /78 (8,9%) of the low-grade tumors recurred and 2 (2,6%) showed malignant transformation. BRAF V600E mutations were detected in 15 cases. No statistically significant correlations were found between the presence of BRAF V600E mutation and patient’s morphologic or clinical features. Deletions at 9p21 abrogating the CDKN2A/B and MTAP loci were rare in grade I gliomas (12.2%, p?=?0.0178) but frequent in grade IV gliomas (62.5%, p?=?0.0087). Moreover it was found that deletions at these loci were correlated with a shorter overall survival (p?=?0.011) and a shorter progression-free survival (p?=?0.016).ConclusionsIt was demonstrated that in these tumors BRAF V600E mutated and that CDKN2A/B MTAP co-deletions may be used for stratifying patients for a stricter surveillance. The Investigating and defining if glial tumors with CDKN2A/B and MTAP homozygous loss may be vulnerable to new forms of therapy, namely those affecting the methionine salvage pathway, was proven to be of importance.Electronic supplementary materialThe online version of this article (10.1186/s12885-018-5120-0) contains supplementary material, which is available to authorized users.

Project description:Epithelioid sarcomas (ES) are mesenchymal neoplasms subclassified into distal and proximal subtypes based on their distinct clinical presentations and histologic features. Consistent loss of SMARCB1 nuclear expression has been considered as the hallmark abnormality for both subtypes, a feature shared with atypical teratoid/rhabdoid tumor of infancy (ATRT). While virtually all ATRTs harbor underlying SMARCB1 somatic or germline alterations, mechanisms of SMARCB1 inactivation in ES are less well defined. To further define mechanisms of SMARCB1 inactivation a detailed molecular analysis was performed on 40 ES (25 proximal and 15 distal ES, with classic morphology and negative SMARCB1 expression) for their genomic status of SMARCB1 and related genes encoding the SWI/SNF subunits (PBRM1, BRG1, BRM, SMARCC1/2 and ARID1A) by FISH using custom BAC probes. An additional control group was included spanning a variety of 41 soft tissue neoplasms with either rhabdoid/epithelioid features or selected histotypes previously shown to lack SMARCB1 by IHC. Furthermore, 12 ES were studied by array CGH (aCGH) and an independent TMA containing 50 additional ES cases was screened for Aurora Kinase A (AURKA) and cyclin D1 immunoexpression. Homozygous SMARCB1 deletions were found by FISH in 36/40 ES (21/25 proximal-type). One of the distal-type ES displayed homozygous SMARCB1 deletion in the tumor cells, along with a heterozygous deletion within normal tissue, finding confirmed by array CGH. None of the proximal ES lacking homozygous SMARCB1 deletions displayed alterations in other SWI/SNF subunits gene members. Among controls, only the SMARCB1-immunonegative myoepithelial carcinomas displayed SMARCB1 homozygous deletions in 3/5 cases, while no gene specific abnormalities were seen among all other histologic subtypes of sarcomas tested regardless of the SMARCB1 protein status. There was no consistent pattern of AURKA and Cyclin D1 expression. The array CGH was successful in 9/12 ES, confirming the SMARCB1 and other SWI/SNF genes copy numbers detected by FISH. Our study confirms the shared pathogenesis of proximal and distal ES, showing consistent SMARCB1 homozygous deletions. Additionally we report the first ES case associated with a SMARCB1 constitutional deletion, establishing a previously undocumented link with ATRT. Alternative mechanisms of SMARCB1 inactivation in SMARCB1-disomic ES remain to be identified, but appear unrelated to large genomic abnormalities in other SWI/SNF subunits.

Dataset Information

BRAF V600E, TERT promoter mutations and CDKN2A/B homozygous deletions are frequent in epithelioid glioblastomas: a histological and molecular analysis focusing on intratumoral heterogeneity.

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