Fusion of an ETS-family gene, EIAF, to EWS by t(17;22)(q12;q12) chromosome translocation in an undifferentiated sarcoma of infancy

A Practical Approach to Small Round Cell Tumors Involving the Gastrointestinal Tract and Abdomen

Small round cell neoplasms are diagnostically challenging owing to their clinical and pathologic overlap, necessitating use of large immunopanels and molecular analysis. Ewing sarcomas (ES) are the most common, but EWSR1 is translocated in several diverse neoplasms, some with round cell morphology. Molecular advances enable classification of many tumors previously termed 'atypical ES'. The current WHO Classification includes two new undifferentiated round cell sarcomas (with CIC or BCOR alterations), and a group of sarcomas in which EWSR1 partners with non-Ewing family transcription factor genes. This article reviews the spectrum of small round cell sarcomas within the gastrointestinal tract and abdomen.

Ewing sarcoma from molecular biology to the clinic

In Europe, with an incidence of 7.5 cases per million, Ewing sarcoma (ES) is the second most common primary malignant bone tumor in children, adolescents and young adults, after osteosarcoma. Since the 1980s, conventional treatment has been based on the use of neoadjuvant and adjuvant chemotherapeutic agents combined with surgical resection of the tumor when possible. These treatments have increased the patient survival rate to 70% for localized forms, which drops drastically to less than 30% when patients are resistant to chemotherapy or when pulmonary metastases are present at diagnosis. However, the lack of improvement in these survival rates over the last decades points to the urgent need for new therapies. Genetically, ES is characterized by a chromosomal translocation between a member of the FET family and a member of the ETS family. In 85% of cases, the chromosomal translocation found is (11; 22) (q24; q12), between the EWS RNA-binding protein and the FLI1 transcription factor, leading to the EWS-FLI1 fusion protein. This chimeric protein acts as an oncogenic factor playing a crucial role in the development of ES. This review provides a non-exhaustive overview of ES from a clinical and biological point of view, describing its main clinical, cellular and molecular aspects.

Identification of fusions with potential clinical significance in melanoma

Though uncommon in melanoma, gene fusions may have therapeutic implications. Next generation sequencing-based clinical assays, designed to detect relevant gene fusions, mutations, and copy number changes, were performed on 750 melanomas (375 primary and 375 metastases) at our institution from 2014-2021. These included 599 (80%) cutaneous, 38 (5%) acral, 11 (1.5%) anorectal, 23 (3%) sinonasal, 27 (3.6%) eye (uveal/ conjunctiva), 11 (1.5%) genital (vulva/penile), and 41 (5.5%) melanomas of unknown primary. Sixteen fusions (2%) were detected in samples from 16 patients: 12/599 (2%) cutaneous, 2/38 (5%) acral, 1/9 (11%) vulva, 1/23(4.3%) sinonasal; and 12/16 (75%) fusions were potentially targetable. We identified two novel rearrangements: NAGS::MAST2 and NOTCH1::GNB1; and two fusions that have been reported in other malignancies but not in melanoma: CANT1::ETV4 (prostate cancer) and CCDC6::RET (thyroid cancer). Additional fusions, previously reported in melanoma, included: EML4::ALK, MLPH::ALK, AGAP3::BRAF, AGK::BRAF, CDH3::BRAF, CCT8::BRAF, DIP2B::BRAF, EFNB1::RAF1, LRCH3::RAF1, MAP4::RAF1, RUFY1::RAF1, and ADCY2::TERT. Fusion positive melanomas harbored recurrent alterations in TERT and CDKN2A, among others. Gene fusions were exceedingly rare (0.2%) in BRAF/RAS/NF1-mutant tumors and were detected in 5.6% of triple wild-type melanomas. Interestingly, gene rearrangements were significantly enriched within the subset of triple wild-type melanomas that harbor TERT promoter mutations (18% versus 2%, p < 0.0001). Thirteen (81%) patients were treated with immunotherapy for metastatic disease or in the adjuvant setting. Six of 12 (50%) patients with potentially actionable fusions progressed on immunotherapy, and 3/6 (50%) were treated with targeted agents (ALK and MEK inhibitors), 2 off-label and 1 as part of a clinical trial. One patient with an AGAP3::BRAF fusion positive melanoma experienced a 30-month long response to trametinib. We show that, detecting fusions, especially in triple wild-type melanomas with TERT promoter mutations, may have a clinically significant impact in patients with advanced disease who have failed front-line immunotherapy.

An international working group consensus report for the prioritization of molecular biomarkers for Ewing sarcoma

The advent of dose intensified interval compressed therapy has improved event-free survival for patients with localized Ewing sarcoma (EwS) to 78% at 5 years. However, nearly a quarter of patients with localized tumors and 60–80% of patients with metastatic tumors suffer relapse and die of disease. In addition, those who survive are often left with debilitating late effects. Clinical features aside from stage have proven inadequate to meaningfully classify patients for risk-stratified therapy. Therefore, there is a critical need to develop approaches to risk stratify patients with EwS based on molecular features. Over the past decade, new technology has enabled the study of multiple molecular biomarkers in EwS. Preliminary evidence requiring validation supports copy number changes, and loss of function mutations in tumor suppressor genes as biomarkers of outcome in EwS. Initial studies of circulating tumor DNA demonstrated that diagnostic ctDNA burden and ctDNA clearance during induction are also associated with outcome. In addition, fusion partner should be a pre-requisite for enrollment on EwS clinical trials, and the fusion type and structure require further study to determine prognostic impact. These emerging biomarkers represent a new horizon in our understanding of disease risk and will enable future efforts to develop risk-adapted treatment.

One oncogene, several vulnerabilities: EWS/FLI targeted therapies for Ewing sarcoma

EWS/FLI is the defining mutation of Ewing sarcoma. This oncogene drives malignant transformation and progression and occurs in a genetic background characterized by few other recurrent cooperating mutations. In addition, the tumor is absolutely dependent on the continued expression of EWS/FLI to maintain the malignant phenotype. However, EWS/FLI is a transcription factor and therefore a challenging drug target. The difficulty of directly targeting EWS/FLI stems from unique features of this fusion protein as well as the network of interacting proteins required to execute the transcriptional program. This network includes interacting proteins as well as upstream and downstream effectors that together reprogram the epigenome and transcriptome. While the vast number of proteins involved in this process challenge the development of a highly specific inhibitors, they also yield numerous therapeutic opportunities. In this report, we will review how this vast EWS-FLI transcriptional network has been exploited over the last two decades to identify compounds that directly target EWS/FLI and/or associated vulnerabilities.

Ubiquitin-specific proteases as therapeutic targets in paediatric primary bone tumours?

In children and young adults, primary malignant bone tumours are mainly composed of osteosarcoma and Ewing's sarcoma. Despite advances in treatments, nearly 40% of patients succumb to these diseases. In particular, the clinical outcome of metastatic osteosarcoma or Ewing's sarcoma remains poor, with less than 30% of patients who develop metastases surviving five years after initial diagnosis. Over the last decade, the cancer research community has shown considerable interest in the processes of protein ubiquitination and deubiquitination. In particular, a growing number of studies show the relevance to target the ubiquitin-specific protease (USP) family in various cancers. This review provides an update on the current knowledge regarding the implication of these USPs in the progression of bone sarcoma: osteosarcoma and Ewing's sarcoma.

Chromosomal localization of Ewing sarcoma EWSR1/FLI1 protein promotes the induction of aneuploidy

Ewing sarcoma is a pediatric bone cancer that expresses the chimeric protein EWSR1/FLI1. We previously demonstrated that EWSR1/FLI1 impairs the localization of Aurora B kinase to the midzone (the midline structure located between segregating chromosomes) during anaphase. While localization of Aurora B is essential for faithful cell division, it is unknown whether interference with midzone organization by EWSR1/FLI1 induces aneuploidy. To address this, we generated stable Tet-on inducible cell lines with EWSR1/FLI1, using CRISPR/Cas9 technology to integrate the transgene at the safe-harbor AAVS1 locus in DLD-1 cells. Induced cells expressing EWSR1/FLI1 displayed an increased incidence of aberrant localization of Aurora B, and greater levels of aneuploidy, compared with noninduced cells. Furthermore, the expression of EWSR1/FLI1-T79A, containing a threonine (Thr) to alanine (Ala) substitution at amino acid 79, failed to induce these phenotypes, indicating that Thr 79 is critical for EWSR1/FLI1 interference with mitosis. In contrast, the phosphomimetic mutant EWSR1/FLI1-T79D (Thr to aspartic acid (Asp)) retained the high activity as wild-type EWSR1/FLI1. Together, these findings suggest that phosphorylation of EWSR1/FLI1 at Thr 79 promotes the colocalization of EWSR1/FLI1 and Aurora B on the chromosomes during prophase and metaphase and, in addition, impairs the localization of Aurora B during anaphase, leading to induction of aneuploidy. This is the first demonstration of the mechanism for EWSR1/FLI1-dependent induction of aneuploidy associated with mitotic dysfunction and the identification of the phosphorylation of the Thr 79 of EWSR1/FLI1 as a critical residue required for this induction.

The clinical heterogeneity of round cell sarcomas with EWSR1/FUS gene fusions: Impact of gene fusion type on clinical features and outcome

The genetic hallmark of classic Ewing sarcoma is a recurrent fusion between EWSR1 and FUS gene with a member of the ETS transcription factor family. In contrast, tumors with non-ETS gene partners have been designated until recently "Ewing-like sarcoma," as a provisional molecular entity, as their clinical and pathologic features were still evolving. However, this group was reclassified as "round cell sarcoma with EWSR1-non-ETS fusions" in the latest 2020 WHO classification. Moreover, round cell sarcomas with either CIC or BCOR gene abnormalities, initially classified under Ewing family of tumors, are now regarded as stand-alone pathologic entities based on their distinct features. In this study we investigated the clinical characteristics of 226 confirmed Ewing sarcoma patients (EWSR1-FLI1 [n = 176], EWSR1/FUS-ERG [n = 35], EWSR1/FUS-FEV [n = 12], and EWSR1-ETV1/4 [n = 3]) and 14 round cell sarcoma patients with EWSR1-non-ETS fusion (EWSR1/FUS-NFATC2 [n = 10], EWSR1-PATZ1 [n = 3], and EWSR1-VEZF1 [n = 1]). The impact on overall survival (OS) was assessed in 90 patients with available follow-up, treated between 2011 and 2018. Patients with fusions involving FEV and NFATC2 genes showed an older median age at diagnosis, compared to those with EWSR1-FLI1 (P = .005), while extraskeletal location was more common in tumors with noncanonical EWSR1-FLI1 fusions (P = .001). Axial and pelvic primary sites were more common in patients with EWSR1-FLI1 (72%), while tumors with NFATC2 fusions were more frequent in the limb (78%, P = .006). The 3-year OS in patients with EWSR1-FLI1 was 91%, compared to only 60% in patients with alternative fusions (P = .037); the latter group showing a higher rate of metastases at presentation. However, this OS difference was not significant in patients with localized tumor (P = .585). Our study demonstrates significant correlations between fusion subtype and age at presentation, primary tumor sites, and OS, in both conventional Ewing sarcoma and round cell sarcoma with EWSR1-non ETS fusions patients. Larger studies are needed to determine survival differences in localized tumors.

Current Approaches for Personalized Therapy of Soft Tissue Sarcomas

Soft tissue sarcomas (STS) are a highly heterogeneous group of cancers of mesenchymal origin with diverse morphologies and clinical behaviors. While surgical resection is the standard treatment for primary STS, advanced and metastatic STS patients are not eligible for surgery. Systemic treatments, including standard chemotherapy and newer chemical agents, still play the most relevant role in the management of the disease. Discovery of specific genetic alterations in distinct STS subtypes allowed better understanding of mechanisms driving their pathogenesis and treatment optimization. This review focuses on the available targeted drugs or drug combinations based on genetic aberration involved in STS development including chromosomal translocations, oncogenic mutations, gene amplifications, and their perspectives in STS treatment. Furthermore, in this review, we discuss the possible use of chemotherapy sensitivity and resistance assays (CSRA) for the adjustment of treatment for individual patients. In summary, current trends in personalized management of advanced and metastatic STS are based on combination of both genetic testing and CSRA.

DNA Methylation Profiling for Diagnosing Undifferentiated Sarcoma with Capicua Transcriptional Receptor (CIC) Alterations

Undifferentiated soft tissue sarcomas are a group of diagnostically challenging tumors in the pediatric population. Molecular techniques are instrumental for the categorization and differential diagnosis of these tumors. A subgroup of recently identified soft tissue sarcomas with undifferentiated round cell morphology was characterized by Capicua transcriptional receptor (CIC) rearrangements. Recently, an array-based DNA methylation analysis of undifferentiated tumors with small blue round cell histology was shown to provide a highly robust and reproducible approach for precisely classifying this diagnostically challenging group of tumors. We describe the case of an undifferentiated sarcoma of the abdominal wall in a 12-year-old girl. The patient presented with a voluminous mass of the abdominal wall, and multiple micro-nodules in the right lung. The tumor was unclassifiable with current immunohistochemical and molecular approaches. However, DNA methylation profiling allowed us to classify this neoplasia as small blue round cell tumor with CIC alterations. The patient was treated with neoadjuvant chemotherapy followed by complete surgical resection and adjuvant chemotherapy. After 22 months, the patient is disease-free and in good clinical condition. To put our experience in context, we conducted a literature review, analyzing current knowledge and state-of-the-art diagnosis, prognosis, and clinical management of CIC rearranged sarcomas. Our findings further support the use of DNA methylation profiling as an important tool to improve diagnosis of non-Ewing small round cell tumors.

Omic approaches to pediatric bone sarcomas

Over the last decade, next-generation sequencing technologies have improved our ability to assess biological aspects, at genomic and transcriptomic levels, on a large scale- and have been increasingly used for the management of adult cancers. However, their efficacy and feasibility within pediatrics is still under investigation. "Omic" approaches represent an opportunity to understand the oncogenic mechanisms driving the onset and progression of bone sarcoma and improve the clinical management of young patients with bone sarcomas. This review focuses on the current genomic and transcriptomic characteristics of managing pediatric patients, affected by Ewing sarcoma and osteosarcoma.

Loss of Stag2 cooperates with EWS-FLI1 to transform murine Mesenchymal stem cells

BACKGROUND

Ewing sarcoma is a malignancy of primitive cells, possibly of mesenchymal origin. It is probable that genetic perturbations other than EWS-FLI1 cooperate with it to produce the tumor. Sequencing studies identified STAG2 mutations in approximately 15% of cases in humans. In the present study, we hypothesize that loss of Stag2 cooperates with EWS-FLI1 in generating sarcomas derived from murine mesenchymal stem cells (MSCs).

METHODS

Mice bearing an inducible EWS-FLI1 transgene were crossed to p53^-/- mice in pure C57/Bl6 background. MSCs were derived from the bone marrow of the mice. EWS-FLI1 induction and Stag2 knockdown were achieved in vitro by adenovirus-Cre and shRNA-bearing pGIPZ lentiviral infection, respectively. The cells were then treated with ionizing radiation to 10 Gy. Anchorage independent growth in vitro was assessed by soft agar assays. Cellular migration and invasion were evaluated by transwell assays. Cells were injected with Matrigel intramuscularly into C57/Bl6 mice to test for tumor formation.

RESULTS

Primary murine MSCs with the genotype EWS-FLI1 p53^-/- were resistant to transformation and did not form tumors in syngeneic mice without irradiation. Stag2 inhibition increased the efficiency and speed of sarcoma formation significantly in irradiated EWS-FLI1 p53^-/- MSCs. The efficiency of tumor formation was 91% for cells in mice injected with Stag2-repressed cells and 22% for mice receiving cells without Stag2 inhibition (p < .001). Stag2 knockdown reduced survival of mice in Kaplan-Meier analysis (p < .001). It also increased MSC migration and invasion in vitro but did not affect proliferation rate or aneuploidy.

CONCLUSION

Loss of Stag2 has a synergistic effect with EWS-FLI1 in the production of sarcomas from murine MSCs, but the mechanism may not relate to increased proliferation or chromosomal instability. Primary murine MSCs are resistant to transformation, and the combination of p53 null mutation, EWS-FLI1, and Stag2 inhibition does not confer immediate conversion of MSCs to sarcomas. Irradiation is necessary in this model, suggesting that perturbations of other genes beside Stag2 and p53 are likely to be essential in the development of EWS-FLI1-driven sarcomas from MSCs.

Ewing sarcoma with FEV gene rearrangements is a rare subset with predilection for extraskeletal locations and aggressive behavior

The molecular hallmark of Ewing sarcoma (ES) is a fusion involving the EWSR1 gene and a member of the ETS family of transcription factors. EWSR1-FLI1 is the most common variant, occurring in 90% of cases, followed by EWSR1-ERG. In a small subset, the FUS gene can substitute for EWSR1 in these fusions. Only rare case reports have been described to date of ES with FEV gene rearrangements. In this study, we investigate the clinicopathologic and molecular features of 10 ES patients with FEV-rearrangements, either fused to EWSR1 (n = 4) or to FUS (n = 6). The median age at diagnosis was 38 years (range, 5-61 years); occurring in six males and four females. All tumors were located at extraskeletal sites, occurring more often in the axial soft tissues. Tumors had a similar morphologic appearance and immunophenotype as ES with more common EWSR1-ETS fusions. Of six patients with follow-up data, five patients (83%) developed metastasis and two patients (33%) died of their diseases. The diagnosis was confirmed either by fluorescence in situ hybridization and/or targeted RNA sequencing. In the five cases tested by targeted sequencing, the fusion transcripts were composed of EWSR1 or FUS fused to either exon 1 or 2 of FEV, retaining the FEV ETS DNA binding domain. This is the largest study to date investigating the ES subset with EWSR1/FUS-FEV fusions showing a predilection for extraskeletal sites and aggressive behavior.

Mesenchymal Tumors with EWSR1 Gene Rearrangements

Among the various genes that can be rearranged in soft tissue neoplasms associated with nonrandom chromosomal translocations, EWSR1 is the most frequent one to partner with other genes to generate recurrent fusion genes. This leads to a spectrum of clinically and pathologically diverse mesenchymal and nonmesenchymal neoplasms, variably manifesting as small round cell, spindle cell, clear cell or adipocytic tumors, or tumors with distinctive myxoid stroma. This review summarizes the growing list of mesenchymal neoplasms that are associated with EWSR1 gene rearrangements.

DNA methylation profiling distinguishes Ewing-like sarcoma with EWSR1-NFATc2 fusion from Ewing sarcoma

PURPOSE

Recent studies revealed divergent gene expression patterns in Ewing sarcoma (EwS) with canonical EWSR1-ETS gene fusions and undifferentiated round cell sarcomas (URCS) with EWSR1 rearrangements fused to the non-ETS gene NFATc2. Thus, the question arises whether the latter tumors really belong to EwS.

METHODS

We collected five cases matching the group of URCS with EWSR1-NFATc2 fusion and performed DNA methylation and copy number profiling. Results were compared to methylation data of 30 EwS with various EWSR1-ETS fusions and one EwS with FUS-ERG fusion, 16 URCS with CIC rearrangement and 10 URCS with BCOR alteration and a total of 81 EWSR1-associated soft tissue sarcomas including 7 angiomatoid fibrous histiocytomas, 7 clear cell sarcomas of the soft tissue, 28 desmoplastic small round cell tumors, 10 extraskeletal myxoid chondrosarcomas and 29 myxoid liposarcomas.

RESULTS

Unsupervised hierarchical clustering and t-distributed stochastic neighbor embedding analysis of DNA methylation data revealed a homogeneous methylation cluster for URCS with EWSR1-NFATc2 fusion, which clearly segregated from EwS and the other subtypes. Copy number profiles of EWSR1-NFATc2 cases showed recurrent losses on chromosome 9q and segmental gains on 20q13 and 22q12 involving the EWSR1 and NFATc2 loci, respectively.

CONCLUSION

In summary, URCS with EWSR1-NFATc2 fusion share a distinct DNA methylation signature and carry characteristic copy number alterations, which emphasizes that these sarcomas should be considered separately from EwS.

Ewing-like sarcoma: An emerging family of round cell sarcomas

Ewing-like sarcomas are an emerging subgroup of small round blue cell sarcomas that share various degrees of morphological, immunohistochemical, molecular, and clinical similarity with Ewing sarcoma. Despite these similarities, Ewing-like sarcomas lack the pathognomonic molecular hallmark of Ewing sarcoma: A translocation between a gene of the RNA-binding TET family (EWSR1 or FUS) with a gene of the ETS-transcription family ( FLI1, ERG, ETV1, ETV4, or FEV). Recently, increased use of modern molecular methods based on next-generation sequencing have enabled the identification of distinct subgroups within this previously uncharacterized group of Ewing-like sarcomas based on the discovery of novel molecular driving events. The focus of this review is to provide an update on the main subcategories of Ewing-like sarcomas discovered to date: CIC-rearranged sarcomas, BCOR-rearranged sarcomas, sarcomas with a rearrangement between EWSR1 and a non-ETS family gene, and the substantial fraction of tumors which remain uncharacterized by molecular methods. There is increasing evidence that these tumors represent stand-alone entities with unique characteristics rather than simply a subgroup of Ewing sarcoma; thus, the question of the best therapeutic approach for these often aggressive sarcomas remains of primary importance. Ultimately, large collaborative efforts will be necessary to better determine the characteristics of this rare, heterogeneous family of tumors.

Comprehensive analysis of multi Ewing sarcoma microarray datasets identifies several prognosis biomarkers

Ewing sarcoma (ES) is a common primary malignancy in children and adolescents. Progression of treatment methods hasn't contributed a lot to the imrovement of prognosis. To identify potential prognostic biomarkers, a meta-analysis pipeline of multi-gene expression datasets for ES from the Gene Expression Omnibus (GEO) was performed. Three datasets were screened and differential expression genes (DEGs) in ES samples compared with normal tissues were identified through limma package and subjected to network analysis. As a result, 1,470 DEGs were obtained which were mainly involved in biological processes associated with immune response and transcription regulation. Network analysis obtained 22 core genes with high network degree and fold change. Kaplan-Meier analysis based on ES datasets from The Cancer Genome Atlas identified five genes, including glycogen phosphorylase, muscle-associated, myocyte-specific enhancer factor 2C, tripartite motif containing 63, budding uninhibited by benzimidazoses1 and Ras GTPase-activating protein 1, whose altered expression profiles are significantly associated with survival. Changes of their expression values were further confirmed through RT-qPCR in ES cell and normal cell lines. Those genes may be considered as potential prognostic biomarkers of ES and should be helpful for its early diagnosis and treatment.

Applications of Ancillary Testing in the Cytologic Diagnosis of Soft Tissue Neoplasms

Soft tissue neoplasms are diagnostically challenging, although many advances in ancillary testing now enable accurate classification of fine-needle aspiration biopsies by detection of characteristic immunophenotypes (including protein correlates of molecular alterations) and molecular features. Although there are many useful diagnostic immunohistochemical markers and molecular assays, their diagnostic utility relies on correlation with clinical and morphologic features, judicious application, and appropriate interpretation because no single test is perfectly sensitive or specific. This review discusses applications of ancillary testing for commonly encountered soft tissue neoplasms in cytopathologic practice in the context of a pattern-based approach.

Disruption of mammalian SWI/SNF and polycomb complexes in human sarcomas: mechanisms and therapeutic opportunities

Soft-tissue sarcomas are increasingly characterized and subclassified by genetic abnormalities that represent underlying drivers of their pathology. Hallmark tumor suppressor gene mutations and pathognomonic gene fusions collectively account for approximately one-third of all sarcomas. These genetic abnormalities most often result in global transcriptional misregulation via disruption of protein regulatory complexes which govern chromatin architecture. Specifically, alterations to mammalian SWI/SNF (mSWI/SNF or BAF) ATP-dependent chromatin remodeling complexes and polycomb repressive complexes cause disease-specific changes in chromatin architecture and gene expression across a number of sarcoma subtypes. Understanding the functions of chromatin regulatory complexes and the mechanisms underpinning their roles in oncogenesis will be required for the design and development of new therapeutic strategies in sarcomas. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Cytologic diagnosis of round cell sarcomas in the era of ancillary testing: an updated review

Round cell sarcomas constitute a large proportion of "small round blue cell tumors," which encompass a broad differential diagnosis and can be difficult to distinguish on cytomorphologic grounds alone. Numerous pathogenetic insights and advances in ancillary testing in soft tissue pathology over the last several decades have made accurate classification of soft tissue neoplasms increasingly feasible. Immunohistochemistry and genetic/molecular testing can now be performed on all cytologic preparations, including unstained smears, needle rinses, cell blocks, and liquid-based preparations, and this has greatly increased our diagnostic abilities. Nevertheless, there remain numerous diagnostic challenges, including variable sensitivity and specificity of available immunohistochemical markers, overlapping immunophenotypes between entities, and "promiscuity" of genetic alterations such as EWSR1 rearrangements, present in a multitude of tumor types. Herein we provide a review on the cytologic, immunohistochemical, and genetic features of the more frequently encountered round cell sarcomas, as well as recently described entities, with an emphasis on diagnostic pitfalls and judicious use of ancillary studies.

DNA Methylation-Based Classifier for Accurate Molecular Diagnosis of Bone Sarcomas

Purpose

Pediatric sarcomas provide a unique diagnostic challenge. There is considerable morphologic overlap between entities, increasing the importance of molecular studies in the diagnosis, treatment, and identification of therapeutic targets. We developed and validated a genome-wide DNA methylation based classifier to differentiate between osteosarcoma, Ewing's sarcoma, and synovial sarcoma.

Materials and Methods

DNA methylation status of 482,421 CpG sites in 10 Ewing's sarcoma, 11 synovial sarcoma, and 15 osteosarcoma samples were determined using the Illumina Infinium HumanMethylation450 array. We developed a random forest classifier trained from the 400 most differentially methylated CpG sites within the training set of 36 sarcoma samples. This classifier was validated on data drawn from The Cancer Genome Atlas (TCGA) synovial sarcoma, TARGET Osteosarcoma, and a recently published series of Ewing's sarcoma.

Results

Methylation profiling revealed three distinct patterns, each enriched with a single sarcoma subtype. Within the validation cohorts, all samples from TCGA were accurately classified as synovial sarcoma (10/10, sensitivity and specificity 100%), all but one sample from TARGET-OS were classified as osteosarcoma (85/86, sensitivity 98%, specificity 100%) and 14/15 Ewing's sarcoma samples classified correctly (sensitivity 93%, specificity 100%). The single misclassified osteosarcoma sample demonstrated high EWSR1 and ETV1 expression on RNA-seq although no fusion was found on manual curation of the transcript sequence. Two additional clinical samples, that were difficult to classify by morphology and molecular methods, were classified as osteosarcoma when previously suspected to be a synovial sarcoma and Ewing's sarcoma on initial diagnosis, respectively.

Conclusion

Osteosarcoma, synovial sarcoma, and Ewing's sarcoma have distinct epigenetic profiles. Our validated methylation-based classifier can be used to provide diagnostic assistance when histological and standard techniques are inconclusive.

Update on Families of Round Cell Sarcomas Other than Classical Ewing Sarcomas

This article focuses on families of round cell sarcomas other than classical Ewing sarcomas. Until recently, these tumors were referred to as so-called Ewing-like tumors, as they morphologically resemble Ewing sarcomas but are negative for canonical fusion transcripts of Ewing sarcomas involving gene members of the ETS family of transcription factors. Clinicopathologic and molecular evidence has dramatically influenced the diagnostic approach of these tumors in recent years. Molecular data that support these sarcoma subtypes are biologically distinct from those of Ewing sarcomas, thereby advocating discarding the all-embracing and confusing terminology of "Ewing-like tumors."

The ETS family of oncogenic transcription factors in solid tumours

Findings over the past decade have identified aberrant activation of the ETS transcription factor family throughout all stages of tumorigenesis. Specifically in solid tumours, gene rearrangement and amplification, feed-forward growth factor signalling loops, formation of gain-of-function co-regulatory complexes and novel cis-acting mutations in ETS target gene promoters can result in increased ETS activity. In turn, pro-oncogenic ETS signalling enhances tumorigenesis through a broad mechanistic toolbox that includes lineage specification and self-renewal, DNA damage and genome instability, epigenetics and metabolism. This Review discusses these different mechanisms of ETS activation and subsequent oncogenic implications, as well as the clinical utility of ETS factors.

The spectrum of EWSR1-rearranged neoplasms at a tertiary sarcoma centre; assessing 772 tumour specimens and the value of current ancillary molecular diagnostic modalities

Background:

EWSR1 rearrangements were first identified in Ewing sarcoma, but the spectrum of EWSR1-rearranged neoplasms now includes many soft tissue tumour subtypes including desmoplastic small round cell tumour (DSRCT), myxoid liposarcoma (MLPS), extraskeletal myxoid chondrosarcoma (EMC), angiomatoid fibrous histiocytoma (AFH), clear cell sarcoma (CCS) and myoepithelial neoplasms. We analysed the spectrum of EWSR1-rearranged soft tissue neoplasms at our tertiary sarcoma centre, by assessing ancillary molecular diagnostic modalities identifying EWSR1-rearranged tumours and reviewing the results in light of our current knowledge of these and other Ewing sarcoma-like neoplasms.

Methods:

We retrospectively analysed all specimens tested for EWSR1 rearrangements by fluorescence in situ hybridisation (FISH) and/or reverse transcription–PCR (RT–PCR) over a 7-year period.

Results:

There was a total of 772 specimens. FISH was performed more often than RT–PCR (n=753, 97.5% vs n=445, 57.6%). In total, 210 (27.9%) specimens were FISH-positive for EWSR1 rearrangement compared to 111 (14.4%) that showed EWSR1 fusion transcripts with RT–PCR. Failure rates for FISH and RT–PCR were 2.5% and 18.0%. Of 109 round cell tumours with pathology consistent with Ewing sarcoma, 15 (13.8 %) cases were FISH-positive without an identifiable EWSR1 fusion transcript, 4 (3.7%) were FISH-negative but RT–PCR positive and 4 (3.7%) were negative for both. FISH positivity for DSRCT, MLPS, EMC, AFH and CCS was 86.3%, 4.3%, 58.5%, 60.0% and 87.9%, respectively. A positive FISH result led to diagnostic change in 40 (19.0%) EWSR1-rearranged cases. 13 FISH-positive cases remained unclassifiable.

Conclusions:

FISH is more sensitive for identifying EWSR1 rearrangements than RT–PCR. However, there can be significant morphologic and immunohistochemical overlap between groups of EWSR1-rearranged neoplasms, with important prognostic and therapeutic implications. FISH and RT–PCR should be used as complementary modalities in diagnosing EWSR1-rearranged neoplasms, but as tumour groups harbouring EWSR1 rearrangements are increasingly characterised and because given translocations involving EWSR1 and its partner genes are not always specific for tumour types, it is critical that these are evaluated by specialist soft tissue surgical pathologists noting the morphologic and immunohistochemical context. As RT–PCR using commercial primers is limited to only the most prevalent EWSR1 fusion transcripts, the incorporation of high-throughput sequencing technologies into the standard diagnostic repertoire to assess for multiple molecular abnormalities of soft tissue tumours in parallel (including detection of newly characterised Ewing sarcoma-like tumours) might be the most effective and efficient means of ancillary diagnosis in future.

EWSR1/ELF5 induces acute myeloid leukemia by inhibiting p53/p21 pathway

The Ewing sarcoma breakpoint region 1 (EWSR1) gene is known to fuse with various partner genes to promote the development of the Ewing sarcoma family of tumors and other sarcomas. In contrast, the association of EWSR1 chimeric fusion genes with leukemia has rarely been reported. We identified a novel EWSR1‐associated chimeric fusion gene in a patient with acute myeloid leukemia harboring 46, XY, t (11; 22) (p13; q12) karyotype abnormality. The patient was refractory to intensified chemotherapy including hematopoietic stem cell transplantation. Total RNA paired‐end sequencing identified a novel chimeric fusion gene as EWSR1/ELF5, a member of the E26 transformation‐specific transcription factor family. Transduction of EWSR1/ELF5 to NIH3T3 cells induced transformation by attenuating with the p53/p21‐dependent pathway. The injection of EWSR1/ELF5‐transduced NIH3T3 cells into NSG‐SCID mice systematically induced the development of tumors in vivo. These results revealed the oncogenic potency of EWSR1/ELF5.

Gene fusions AHRR-NCOA2, NCOA2-ETV4, ETV4-AHRR, P4HA2-TBCK, and TBCK-P4HA2 resulting from the translocations t(5;8;17)(p15;q13;q21) and t(4;5)(q24;q31) in a soft tissue angiofibroma

We present an angiofibroma of soft tissue with the karyotype 46,XY,t(4;5)(q24;q31),t(5;8;17)(p15;q13;q21) [8]/46,XY,t(1;14)(p31;q32)[2]/46,XY[3]. RNA-sequencing showed that the t(4;5)(q24;q31) resulted in recombination of the genes TBCK on 4q24 and P4HA2 on 5q31.1 with generation of an in-frame TBCK-P4HA2 and the reciprocal but out-of-frame P4HA2-TBCK fusion transcripts. The putative TBCK-P4HA2 protein would contain the kinase, the rhodanese-like domain, and the Tre-2/Bub2/Cdc16 (TBC) domains of TBCK together with the P4HA2 protein which is a component of the prolyl 4-hydroxylase. The t(5;8;17)(p15;q13;q21) three-way chromosomal translocation targeted AHRR (on 5p15), NCOA2 (on 8q13), and ETV4 (on 17q21) generating the in-frame fusions AHRR-NCOA2 and NCOA2-ETV4 as well as an out-of-frame ETV4-AHRR transcript. In the AHRR-NCOA2 protein, the C-terminal part of AHRR is replaced by the C-terminal part of NCOA2 which contains two activation domains. The NCOA2-ETV4 protein would contain the helix-loop-helix, PAS_9 and PAS_11, CITED domains, the SRC-1 domain of NCOA2 and the ETS DNA-binding domain of ETV4. No fusion gene corresponding to t(1;14)(p31;q32) was found. Our findings indicate that, in spite of the recurrence of AHRR-NCOA2 in angiofibroma of soft tissue, additional genetic events (or fusion genes) might be required for the development of this tumor.

Molecular cytogenetic characterization of two established ESFT cell lines

Ewing's sarcoma/primitive neuroectodermal tumor/Askin's tumor (Ewing`s sarcoma family of tumors: ESFT) is the most common type of malignant tumor of bone and soft tissue in children and young adults, and morphologically is a member of a group of small round cell tumors. We report, here, on the establishment of two human ESFT cell lines, FU-PNET-3 and FU-PNET-4, from the iliac and the chest wall, respectively, the cells of both cell lines were tumorigenic in immunodeficient mice. Histologically, both original and xenograft tumors and cultured cells were composed of small round cells with positive immunoreactivity for CD99 and Nkx2.2. Molecular biological examination demonstrated chimeric transcripts of EWSR1 exon 7 to FLI1 exon 6 in FU-PNET-3 cells, and EWSR1 exon 10 to FLI1 exon 6 in FU-PNET-4 cells. Cytogenetic analysis revealed chromosome translocation t(11;22)(q24;q12) and some secondary changes in both cultured cells. These histological, molecular biological, and cytogenetical findings indicate ESFT in both cell lines. ESFT is well studied, but its recurrent fusion genes are heterogeneous and its biological behaviors are unclear. The FU-PNET-3 and FU-PNET-4 cell lines have been well examined and may become useful tools for studying the genetic and biological behavioral properties of ESFT.

Pediatric soft tissue tumor pathology: A happy morpho-molecular union

Since its foundation by remarkably talented and insightful individuals, prominently including Pepper Dehner, pediatric soft tissue tumor pathology has developed at an immense rate. The morphologic classification of tumoral entities has extensively been corroborated, but has also evolved with refinement or realignment of these classifications, through accruing molecular data, with many derivative ancillary diagnostic assays now already well-established. Tumors of unclear histogenesis, classically morphologically undifferentiated, are prominent amongst pediatric sarcomas, however, the classes of undifferentiated round- or spindle-cell-tumors-not-otherwise-specified are being dismantled gradually with the identification of their molecular underpinnings. Within recent years, for example, numerous subcategories of 'Ewing-like' round cell sarcoma have emerged. Such advances have provided the basis for novel diagnostic and prognostic sub-classifications. Efforts at defining cell- or lineage-of-origin for several tumor types have produced interesting insights especially for rhabdomyosarcoma. The remarkably early onset of pediatric sarcomas defies the theory necessitating stochastic accumulation of several somatic mutations for cancer development and indeed, these tumors may be remarkably genomically stable, often belying their aggressive nature. Much is coming to light recently regarding the role of epigenetic modifications in the evolution of these sarcomas. Indeed the morphologic features of embryonal tumors generally (not just sarcomas) may be highly reminiscent of arrested differentiation, and given the tight epigenetic regulation of cell fate determination and cell identity maintenance, a theory of epigenetically-driven oncogenesis sits easily with these tumors. The age-delimited distinct biologies of 'pediatric' and adult GIST are intriguing, particularly, the SDH-deficient 'pediatric' form, driven by a metabolic defect, but resulting in epigenetic dysregulation with genome-wide DNA methylation changes. There is little doubt that many of the gaps in our understanding of pediatric sarcoma biology will be filled by a deeper appreciation of the role of dysregulated epigenetics including chromatin biology, perhaps best exemplified in malignant rhabdoid tumor. The field of pediatric soft tissue tumor pathology grows ever more interesting. Importantly though, it must be emphasized, that none of this progress could have occurred, or indeed continue, without the initial step of accurate diagnosis, founded solidly on morphology - thank you Pepper for your unparalleled contributions to this field! The opportunity to be your apprentice for five years has been a bigger and more positive influence than words can express.

Recent advances in targeted therapy for Ewing sarcoma

Ewing sarcoma is an aggressive, poorly differentiated neoplasm of solid bone that disproportionally afflicts the young. Despite intensive multi-modal therapy and valiant efforts, 70% of patients with relapsed and metastatic Ewing sarcoma will succumb to their disease. The persistent failure to improve overall survival for this subset of patients highlights the urgent need for rapid translation of novel therapeutic strategies. As Ewing sarcoma is associated with a paucity of mutations in readily targetable signal transduction pathways, targeting the key genetic aberration and master regulator of Ewing sarcoma, the EWS/ETS fusion, remains an important goal.

Ewing's Sarcoma and Peripheral Primitive Neuroectodermal Tumor of Bone and Soft Tissue

The histological diagnosis of Ewing's sarcoma (Es) continues to be a difficult task for pathologists. A number of new Es varieties has been described, leading to further complexity. Conventional Es, atypical Es, and peripheral neuroectodermal tumor (pPNET), including peripheral neuroepithelioma, belong genetically to the same family of neoplasms, displaying common chromosomal rearrangements and analogous gene reorganizations. The main translocations are t(11;22) and t(21;22), with genes EWS, FLI-1 and ERG being involved, as well as other members of the ETS family of transcription factors. The prevalence of morphology should be maintained with the use of conventional histological techniques and supported with the analysis of the expression of CD99 Mic2 (HBA 71, 0.13) antigen, which is present in over 90% of cases, as well as with FLI-1 rearranged gene derived protein. Moreover, FISH and RT-PCR in paraffin-embedded tumor tissue may be of use in extremely difficult cases for differential diagnosis. Nevertheless, a number of mixed tumor types, such as primitive sarcoma or biphenotypic sarcoma, may show structural and genetic diversity, thus rendering their diagnosis even more complex.

Twenty Years on: What Do We Really Know about Ewing Sarcoma and What Is the Path Forward?

Ewing sarcoma (ES) is a highly aggressive bone and soft-tissue tumor with peak incidence among adolescents and young adults. Despite advances in local control and systemic chemotherapy, metastatic relapse after an initial clinical remission remains a significant clinical problem. In addition, metastasis at the time of presentation or at relapse continues to be the leading cause of death for patients diagnosed with ES. Since the discovery of the pathognomonic EWS-FLI1 fusion gene more than 20 years ago, much about the molecular and cellular biology of ES pathogenesis has been learned. In addition, more recent exploitation of advances in stem cell and developmental biology has provided key insights into the cellular origins of ES and the role of epigenetic deregulation in tumor initiation and maintenance. Nevertheless, the mechanisms that drive tumor relapse and metastasis remain largely unknown. These gaps in our knowledge continue to hamper the development of novel therapeutic strategies that may improve outcomes for patients with relapsed and metastatic disease. In this article we review the current status of ES biology research, highlighting areas of investigation that we consider to have the greatest potential to yield findings that will translate into clinically significant advances.

Ewing sarcoma: a chronicle of molecular pathogenesis

Sarcomas have traditionally been classified according to their chromosomal alterations regardless of whether they accompany simple or complex genetic changes. Ewing sarcoma, a classic small round cell bone tumor, is a well-known mesenchymal malignancy that results from simple sarcoma-specific genetic alterations. The genetic alterations are translocations between genes of the TET/FET family (TLS/FUS, EWSR1, and TAF15) and genes of the E26 transformation-specific (ETS) family. In this review, we intend to summarize a chronicle of molecular findings of Ewing sarcoma including recent advances and explain resultant molecular pathogenesis.

Ewing sarcoma with ERG gene rearrangements: A molecular study focusing on the prevalence of FUS-ERG and common pitfalls in detecting EWSR1-ERG fusions by FISH

The genetics of Ewing sarcoma (ES) are characterized by a canonical fusion involving EWSR1 gene and a member of the ETS family of transcription factors, such as FLI1 and ERG. In fact, ERG gene rearrangements represent the second most common molecular alteration, with EWSR1-ERG being identified in 5-10% of cases, while only a handful of reports document a FUS-ERG fusion. In this study, we focus on ES with ERG gene abnormalities, specifically to investigate the prevalence and clinicopathologic features of FUS-ERG fusions in a large cohort of small blue round cell tumors (SBRCTs) and compare to the eight reported FUS-positive ES. Among the 85 SBRCTs tested, seven (8.2%) cases harbored FUS gene rearrangements; six fused to ERG and one with FEV. During this investigation we came across a number of ERG-rearranged ES lacking both EWSR1 and FUS abnormalities by FISH. In one case, RNA sequencing identified an EWSR1-ERG transcript despite the negative EWSR1 rearrangements by FISH. Additional 3-color FISH fusion assay demonstrated the fusion of EWSR1 and ERG signals in all four cases negative for break-apart EWSR1 FISH. These results emphasize a potential pitfall of relying on EWSR1 FISH assay alone for diagnosis of ES. In cases with classic morphology and/or strong CD99 and ERG immunoreactivity, additional molecular testing should be applied, such as ERG FISH or RT-PCR/next generation sequencing, for a more definitive diagnosis. Although our study group is small, there were no differences noted between the clinical, morphologic features and immunoprofile of the different subsets of ERG-rearranged SBRCTs.

Gene fusions in soft tissue tumors: Recurrent and overlapping pathogenetic themes

Gene fusions have been described in approximately one-third of soft tissue tumors (STT); of the 142 different fusions that have been reported, more than half are recurrent in the same histologic subtype. These gene fusions constitute pivotal driver mutations, and detailed studies of their cellular effects have provided important knowledge about pathogenetic mechanisms in STT. Furthermore, most fusions are strongly associated with a particular histotype, serving as ideal molecular diagnostic markers. In recent years, it has also become apparent that some chimeric proteins, directly or indirectly, constitute excellent treatment targets, making the detection of gene fusions in STT ever more important. Indeed, pharmacological treatment of STT displaying fusions that activate protein kinases, such as ALK and ROS1, or growth factors, such as PDGFB, is already in clinical use. However, the vast majority (52/78) of recurrent gene fusions create structurally altered and/or deregulated transcription factors, and a small but growing subset develops through rearranged chromatin regulators. The present review provides an overview of the spectrum of currently recognized gene fusions in STT, and, on the basis of the protein class involved, the mechanisms by which they exert their oncogenic effect are discussed.

Clinical Applications of Molecular Markers in Bone Tumors

Pathologic diagnosis of primary bone neoplasms can be challenging primarily due to rarity of the disease entities, overlapping imaging and histologic findings, and lack of tumor-specific immunohistochemical stains. Although slow to evolve, in recent years there has been a rapid advance in the discovery of new and novel molecular markers in primary bone neoplasms, which has enhanced diagnostic accuracy and has shed light into their pathogenesis. Modern technological approaches such as next-generation sequencing including RNA sequencing are serving as "rapid discovery platforms" for new and novel mutations and translocations with diagnostic, prognostic, and possible therapeutic applicability. As next-generation sequencing technologies are finding their place in clinical laboratories, one could envision routine testing for mutations spanning across a gene or translocations with multiple breakpoints and partner genes. This review will focus on the clinical relevance and applicability of molecular markers in primary bone neoplasms with examples.

PI3K/AKT signaling modulates transcriptional expression of EWS/FLI1 through specificity protein 1

Ewing sarcoma (ES) is the second most frequent bone cancer in childhood and is characterized by the presence of the balanced translocation t(11;22)(q24;q12) in more than 85% of cases, generating a dysregulated transcription factor EWS/FLI1. This fusion protein is an essential oncogenic component of ES development which is necessary for tumor cell maintenance and represents an attractive therapeutic target. To search for modulators of EWS/FLI1 activity we screened a library of 153 targeted compounds and identified inhibitors of the PI3K pathway to directly modulate EWS/FLI1 transcription. Surprisingly, treatment of four different ES cell lines with BEZ235 resulted in down regulation of EWS/FLI1 mRNA and protein by ~50% with subsequent modulation of target gene expression. Analysis of the EWS/FLI1 promoter region (-2239/+67) using various deletion constructs identified two 14 bp minimal elements as being important for EWS/FLI1 transcription. We identified SP1 as modulator of EWS/FLI1 gene expression and demonstrated direct binding to one of these regions in the EWS/FLI1 promoter by EMSA and ChIP experiments. These results provide the first insights on the transcriptional regulation of EWS/FLI1, an area that has not been investigated so far, and offer an additional molecular explanation for the known sensitivity of ES cell lines to PI3K inhibition.

Ewing sarcoma EWS protein regulates midzone formation by recruiting Aurora B kinase to the midzone

Ewing sarcoma is a malignant bone cancer that primarily occurs in children and adolescents. Eighty-five percent of Ewing sarcoma is characterized by the presence of the aberrant chimeric EWS/FLI1 fusion gene. Previously, we demonstrated that an interaction between EWS/FLI1 and wild-type EWS led to the inhibition of EWS activity and mitotic dysfunction. Although defective mitosis is considered to be a critical step in cancer initiation, it is unknown how interference with EWS contributes to Ewing sarcoma formation. Here, we demonstrate that EWS/FLI1- and EWS-knockdown cells display a high incidence of defects in the midzone, a midline structure located between segregating chromatids during anaphase. Defects in the midzone can lead to the failure of cytokinesis and can result in the induction of aneuploidy. The similarity among the phenotypes of EWS/FLI1- and EWS siRNA-transfected HeLa cells points to the inhibition of EWS as the key mechanism for the induction of midzone defects. Supporting this observation, the ectopic expression of EWS rescues the high incidence of midzone defects observed in Ewing sarcoma A673 cells. We discovered that EWS interacts with Aurora B kinase, and that EWS is also required for recruiting Aurora B to the midzone. A domain analysis revealed that the R565 in the RGG3 domain of EWS is essential for both Aurora B interaction and the recruitment of Aurora B to the midzone. Here, we propose that the impairment of EWS-dependent midzone formation via the recruitment of Aurora B is a potential mechanism of Ewing sarcoma development.

Diagnosis and treatment of Ewing sarcoma of the bone: a review article

Ewing sarcoma (ES) is rare in Japanese people, and only 30-40 patients develop the disease annually. To diagnose ES, molecular techniques that aim to detect characteristic fusion genes are commonly used in combination with conventional histological and immunohistochemical examinations. The treatment strategy for ES is characterized by multi-disciplinary collaboration between pediatric oncologists, medical oncologists, radiation oncologists, and orthopedic surgeons. In recent years, numerous large-scale national or international multi-institutional studies of ES have been performed. Pre- and postoperative intensive systemic chemotherapy with multiple anticancer drugs is the standard treatment method for ES. Depending on the obtained surgical margin, postoperative radiation might also be performed. If preoperative radiological examinations indicate that surgical excision would be difficult, preoperative radiation can be administered. As the treatment outcomes of ES have improved, late complications and secondary malignancies have become a problem. After treatment, patients with ES require very long-term follow-up in order to detect secondary malignancies and growth-related musculoskeletal complications.

Round cell tumors of bone: an update on recent molecular genetic advances

Round cell tumors of bone are a divergent group of neoplasms that largely constitute Ewing sarcoma/primitive neuroectodermal tumor, small cell osteosarcoma, Langerhans cell histiocytosis, mensenchymal chondrosarcoma, and hematopoietic malignancies including lymphoma and plasmacytoma/myeloma, along with metastatic round cell tumors including neuroblastoma, rhabdomyosarcoma, and small cell carcinoma. These lesions share many histomorphologic similarities and often demonstrate overlapping clinical and radiologic characteristics, but typically have a diverse clinical outcome, thus warranting differing therapeutic modalities/regimens. Recent advances in molecular and cytogenetic techniques have identified a number of additional novel entities, including round cell sarcomas harboring CIC-DUX4 and BCOR-CCNB3 fusions, respectively. These novel findings have not only enhanced our understanding of the pathogenesis of round cell tumors, but also allowed us to reclassify some entities with potential therapeutic and prognostic significance. This article provides an overview focusing on recent molecular genetic advances in primary, nonhematologic round cell tumors of bone.

Malignant round cell tumor of bone with EWSR1-NFATC2 gene fusion

Gene rearrangements involving the Ewing sarcoma breakpoint region 1 (EWSR1) gene are seen in a broad range of sarcomas and some nonmesenchymal neoplasms. Ewing sarcoma is molecularly defined by a fusion of the EWSR1 gene (or rarely the related FUS gene) to a member of the E26 transformation-specific (ETS) family of transcription factors, frequently the EWSR1-FLI1 fusion. More recently, EWSR1 gene fusion to non-ETS family members, including the nuclear factor of activated T cells, cytoplasmic, calcineurin-dependent 2 (NFATC2) gene, has been reported in a histological variant of Ewing sarcoma. Here, we report a malignant round cell tumor of bone with an EWSR1-NFATC2 fusion gene. This report builds upon the unusual morphological and clinical presentation of bone neoplasms containing an EWSR1-NFATC2 fusion gene.

Ewing sarcoma

Classification of small round cell tumors of bone is often challenging due to overlapping clinicopathologic features. The purpose of this article is to review the clinical, radiological, histologic, and molecular features of Ewing sarcoma and to provide a discussion of the differential diagnosis of small round cell tumors of bone.

High-resolution genome-wide copy-number analyses identify localized copy-number alterations in Ewing sarcoma

Ewing sarcoma family tumors are aggressive sarcomas of childhood and adolescence with continuing poor outcomes. Decades of research on the characteristics of the often solitary-known oncogenic-genomic aberration in Ewing sarcoma family tumors, namely a TET-ETS fusion, have provided little advancement in the understanding of the molecular pathogenesis of Ewing sarcoma or treatment thereof. In this study, the high-resolution single-nucleotide polymorphism technology was used to identify additional/secondary copy-number alterations (CNAs) in Ewing sarcoma that might elucidate the aggressive biology of this sarcoma. We compared paired constitutional and tumor DNA samples. Commonly known genomic alterations including gain of 1q and chromosome 8 were the most frequently detected changes in this study. In addition, deletions and loss of heterozygosity were identified in 10q, 11p, and 17p. Furthermore, tumor-specific CNAs were identified not only in genes previously known to be of interest, including CDKN2A, but also in genes not previously associated with Ewing sarcoma, including SOX6 and PTEN. Selected array-based findings were confirmed by fluorescence in situ hybridization, immunohistochemical studies, or sequencing. The results highlight an unexpected level of cytogenetic complexity associated with several of the samples, 2 of which contained TP53 mutations. In summary, our high-resolution genome-wide copy-number data identify several novel CNAs associated with Ewing sarcoma, which are promising targets for novel therapeutic strategies in this aggressive sarcoma.

Round cell sarcomas beyond Ewing: emerging entities

Primitive small blue round cell tumours (SBRCT) of childhood and young adults have been problematic to diagnose and classify. Diagnosis is also complicated in cases with atypical morphology, aberrant immunoprofiles and unusual clinical presentations. Even with the increased use of ancillary techniques in archival material, such as immunohistochemistry and molecular/genetic methods, a proportion of these tumours cannot be subclassified into specific histological types. A subset of tumours resembling microscopically the Ewing sarcoma family of tumours (EFT), being composed of primitive small round cells and occurring in paediatric or young adult age groups, remain unclassified, being negative for EWSR1, SS18(SYT), DDIT3(CHOP) and FOXO1(FKHR) gene rearrangements by FISH/RT-PCR. A small number of cases sharing the undifferentiated EFT appearance have been characterized recently carrying BCOR-CCNB3 or CIC-DUX4 fusions. However, based on the somewhat limited number of cases, it remains unclear if these newly defined genetic entities belong to any of the pre-existing clinicopathological disorders or represent altogether novel conditions. This review presents the latest molecular findings related to these SBRCTs, beyond the common EWSR1-ETS fusions. Specific attention has been paid to morphological features not associated typically with classic EFT, and the value of ancillary tests that can be applied when dealing with EWSR1-negative SBRCTs is discussed.