Ewing and Ewing-like sarcomas: A morphological guide through genetically-defined entities

Superficial Neurocristic EWSR1::FLI1 Fusion Tumor: A Distinctive, Clinically Indolent, S100 Protein/SOX10-Positive Neoplasm

It is now understood that identical gene fusions may be shared by different entities. We report a distinctive neoplasm of the skin and subcutis, harboring the Ewing sarcoma-associated EWSR1::FLI1 fusion but differing otherwise from Ewing sarcoma. Slides and blocks for 5 cutaneous neoplasms coded as other than Ewing sarcoma and harboring EWSR1::FLI1 were retrieved. Immunohistochemical and molecular genetic results were abstracted from reports. Methylation profiling was performed. Clinical information was obtained. The tumors occurred in 4 men and 1 woman (median: 25 years of age; range: 19-69 years) and involved the skin/subcutis of the back (2), thigh, buttock, and chest wall (median: 2.4 cm; range: 1-11 cm). Two tumors were present "years" before coming to clinical attention. The lesions were multinodular and circumscribed and consisted of nests of bland, round cells admixed with hyalinized collagenous bands containing spindled cells. Hemorrhage and cystic change were often present; necrosis was absent. All were diffusely S100 protein/SOX10-positive; 4 of 5 were CD99-negative. One tested case was strongly positive for NKX2.2. A variety of other tested markers were either focally positive (glial fibrillary acidic protein, p63) or negative. Molecular genetic results were as follows: EWSR1 exon 7::FLI1 exon 8, EWSR1 exon 11::FLI1 exon 5, EWSR1 exon 11::FLI1 exon 6, EWSR1 exon 7::FLI1 exon 6, and EWSR1 exon 10::FLI1 exon 6. Methylation profiling (3 cases) showed these to form a unique cluster, distinct from Ewing sarcoma. All patients underwent excision with negative margins; one received 1 cycle of chemotherapy. Clinical follow-up showed all patients to be alive without disease (median: 17 months; range: 11-62 months). Despite similar gene fusions, the morphologic, immunohistochemical, epigenetic, and clinical features of these unique EWSR1::FLI1-fused neoplasms of the skin and subcutis differ substantially from Ewing sarcoma. Interestingly, EWSR1 rearrangements involved exons 10 or 11, only rarely seen in Ewing sarcoma, in a majority of cases. Superficial neurocristic EWSR1::FLI1 fusion tumors should be rigorously distinguished from true cutaneous Ewing sarcomas.

Extraskeletal Ewing's sarcoma presenting as a mediastinal mass with vena cava superior syndrome: A rare case report

INTRODUCTION

Extraskeletal Ewing's Sarcoma is a rare entity of sarcoma that develops rapidly within soft tissue in any anatomic region, and the symptoms depend on its location.

CASE PRESENTATION

The X-ray examination of a 28-year-old man with shortness of breath, cough, weight loss, and chest pain showed malignant round cell, in which confirmed by immunohistochemical examination. The examination indicated positive Vimentin findings in the cytoplasm and positive FLI-1 in the nuclei of the tumour cells. The diagnosis was consistent with extraskeletal Ewing's sarcoma. The patient submitted to a chest conference and received radiotherapy related to SVCS before debulking surgery.

DISCUSSION

The diagnostic challenges associated with Ewing's sarcoma may arise due to its diverse histological spectrum. Further examination is required in order to distinguish Ewing's sarcoma from other tumours, as its radiological specificity is limited. A multimodal approach for treatment and therapy is necessary to highlight the specific requirements of the patient's condition.

CONCLUSION

Imaging modalities including X-rays and thoracic CT scans, supported by histopathological examination and immunohistochemistry, are essential for accurately diagnosing Extraskeletal Ewing's sarcoma. A multimodal approach may be considered as the best treatment for the patient with mediastinal Ewing's sarcoma.

Sarcoma of the Lung and Mediastinum

Primary sarcoma of the lung and mediastinum is rare. The diagnosis requires careful exclusion of sarcomatoid carcinoma, sarcomatoid mesothelioma, and metastases from extra-thoracic sites. This review summarizes the key morphologic, immunohistochemical, and molecular characteristics of sarcomas that are encountered in the lung and mediastinum. The tumor types discussed are synovial sarcoma, well-differentiated/dedifferentiated liposarcoma, myxoid pleomorphic liposarcoma, intimal sarcoma of the pulmonary artery, inflammatory myofibroblastic tumor, epithelioid hemangioendothelioma, primary pulmonary myxoid sarcoma, malignant peripheral nerve sheath tumor, Ewing sarcoma, and CIC-rearranged sarcoma. Relevant differential diagnoses are also addressed.

Decoding BCOR-ITD Sarcomas: Case Report of a Rare Pediatric Tumor With Challenges in Diagnosis

Sarcomas characterized by BCOR gene alterations, are a distinct clinico-pathological group of high-grade tumors, that represent 5% of small round cell tumors without EWSR or FUS fusion. Diverse genetic alterations characterize this group, including BCOR-CCNB3 gene fusion being the most common alteration and less frequently internal tandem duplications (ITDs). We present a compelling case of a 3-year-old girl diagnosed with a high-grade nasoethmoidal sarcoma exhibiting BCOR-ITD. The diagnostic process illustrates the histological and immunophenotypic spectrum, requiring an extensive immunohistochemical panel and diverse molecular tests for accurate classification. Additionally, this case highlights the challenges in detecting BCOR-ITDs using different NGS panels, advocating for alternative molecular approaches. Our patient after 10 months since diagnosis is alive with progressive disease. This emphasizes the urgency for ongoing research to refine diagnostic methods and develop effective therapeutic strategies for these rare and aggressive tumors.

Updates on WHO classification for small round cell tumors: Ewing sarcoma vs. everything else

The WHO Classification of Soft Tissue and Bone Tumours currently recognizes four categories of undifferentiated small round cell sarcoma: Ewing sarcoma, round cell sarcoma with EWSR1-non-ETS fusions including NFATc2 and PATZ1, CIC-rearranged sarcoma, and sarcoma with BCOR genetic alterations. These neoplasms frequently pose significant diagnostic challenges due to rarity and overlapping morphologic and immunohistochemical findings. Further, molecular testing, with accompanying pitfalls, may be needed to establish a definitive diagnosis. This review summarizes the clinical, histologic, immunohistochemical, and molecular features of these neoplasms. In addition, differential diagnosis and areas of uncertainty and ongoing investigation are discussed.

CIC-Rearranged Sarcoma

CIC-rearranged sarcoma is a rare type of small round cell sarcoma. The tumors often affect the deep soft tissues of patients in a wide age range. They are highly aggressive, respond poorly to chemotherapy, and have a worse outcome than Ewing sarcoma. CIC-rearranged sarcoma has characteristic and recognizable histology, including lobulated growth, focal myxoid changes, round to epithelioid cells, and minimal variation of nuclear size and shape. Nuclear ETV4 and WT1 expression are useful immunohistochemical findings. CIC fusion can be demonstrated using various methods; however, even next-generation sequencing suffers from imperfect sensitivity, especially for CIC::DUX4.

Sarcomas Harboring EWSR1::PATZ1 Fusions: A Clinicopathologic Study of 17 Cases

Soft tissue sarcomas harboring EWSR1::PATZ1 are a recently recognized entity with variable morphology and a heterogeneous immunohistochemical profile. We studied 17 such tumors. The tumors occurred in 12 men and 5 women (median age, 50 years; range, 15-71 years), involved the thoracoabdominal soft tissues (14 cases; 82%), lower extremities (2 cases; 12%), and tongue (1 case; 6%), and ranged from 0.7 to 11.3 cm (median, 4.7 cm). All but 1 patient received complete surgical resection; 7 were also treated with neoadjuvant chemo/radiotherapy. All cases showed typical features of EWSR1::PATZ1 sarcoma, including uniform round to spindled cells, fibromyxoid matrix, fibrous bands, hyalinized vessels, and pseudoalveolar/microcystic spaces. Unusual features, seen in a subset of cases, included degenerative-appearing nuclear atypia, epithelioid cytomorphology, mature fat, abundant rhabdomyoblasts, high mitotic activity, and foci with increased cellularity and nuclear atypia. Positive immunohistochemical results were desmin (16/17, 94%), MyoD1 (13/14, 93%), myogenin (6/14, 43%), GFAP (10/10, 100%), S100 protein (15/17, 88%), SOX10 (7/13, 54%), keratin (10/17, 59%), CD99 (4/11, 36%), H3K27me3 (retained expression 9/9, 100%), p16 (absent expression 1/4, 25%), and p53 (wild type 3/3, 100%). Fusion events included EWSR1 exon 8::PATZ1 exon 1 (14/17, 82%), EWSR1 exon 9::PATZ1 exon 1 (2/17, 12%), and EWSR1 exon 7::PATZ1 exon 1 (1/17, 6%). No evaluated tumor had alterations of CDKN2A/B and/or TP53, or MDM2 amplification. Clinical follow-up (16 patients: median, 13.5 months; range, 1-77 months) showed distant metastases in 3 patients (1/3 at time of presentation) and no local recurrences. At the time of last follow-up, 14 patients were disease free, 1 was alive with disease, 1 was dead of disease (at 13 months), and 1 had an indeterminant pulmonary nodule. We conclude that the morphologic spectrum of EWSR1::PATZ1 is broader than has been previously appreciated. Although more long-term follow-up is needed, the prognosis of these very rare sarcomas may be more favorable than previously reported.

NUT carcinoma and thoracic SMARCA4-deficient undifferentiated tumour: facts and controversies

NUT carcinoma and thoracic SMARCA4-deficient undifferentiated tumour are unique entities in the 5th edition of the World Health Organisation (WHO) Classification of Thoracic Tumours, whose definitions include molecular genetic abnormalities. These aggressive tumours require rapid work-ups on biopsies, but a broad list of differential diagnoses poses challenges for practising pathologists. This review provides an update on their key clinicopathological and molecular characteristics, as well as controversies regarding tumour classification and diagnostic strategy. Phenotypical assessment plays a substantial role in diagnosis because recurrent and predictable clinicopathological findings exist, including robust immunohistochemical phenotypes. Accurate diagnosis is crucial for appropriate management and a clearer understanding of the disease.

Expression of NKX2.2 in Non-Ewing Tumors With Round Cell Morphology

Background Round cell sarcomas pose diagnostic challenges due to overlapping histopathological features, necessitating precise immunohistochemical markers for accurate categorization. NKX2.2 has emerged as a sensitive diagnostic tool, particularly in Ewing sarcoma. This study extends this understanding to various round-cell sarcomas, shedding light on the potential diagnostic utility of NKX2.2 beyond its established role. The nuanced exploration of NKX2.2 expression aims to enhance diagnostic strategies, prognostic assessments, and therapeutic developments in the landscape of sarcoma research. Methodology Cases were retrieved from the surgical pathology and consultation files of Shaukat Khanum Memorial Cancer Hospital and Research Center, Lahore, Pakistan. Representative hematoxylin and eosin-stained slides of six different types of already confirmed tumors, including lymphoblastic lymphoma, neuroblastoma, rhabdomyosarcoma, synovial sarcoma, Wilms tumor, and Ewing sarcoma, were reviewed by a panel of pathologists. Immunohistochemistry, utilizing a rabbit anti-NKX2.2 monoclonal antibody, was performed on formalin-fixed paraffin-embedded tissue sections. The presence of NKX2.2 was defined as moderate or high nuclear immunoreactivity in at least 5% of cells. Results The histopathological examination revealed characteristic features in each sarcoma subtype, aligning with established diagnostic criteria. In Lymphoblastic lymphoma, T-cell lineage was confirmed through TdT expression, while the atypical finding of focal NKX 2.2 expression hinted at genetic diversity. Neuroblastoma exhibited the expected salt and pepper chromatin pattern, with NKX 2.2 expression raising questions about its prognostic significance. Rhabdomyosarcoma presented primitive cells expressing desmin, and NKX 2.2 focal expression echoed previous subtype-associated studies. Synovial sarcoma displayed both monophasic and biphasic growth patterns and TLE1 expression, with NKX 2.2 variation suggesting tumor heterogeneity. In Wilms tumor, the characteristic WT1 expression was observed, while NKX2.2's absence reaffirmed its irrelevance in this context. Ewing sarcoma displayed the anticipated homogenous cell population, strong NKX2.2 expression, and CD99 positivity across various sites. Furthermore, age and gender impact on this range of sarcomas found no significant relation with an expression of NKX2.2. Conclusion In conclusion, the diverse expression profiles of diagnostic markers discovered in this study, particularly the atypical expression of NKX2.2 beyond its established role in Ewing sarcoma, signify a significant advancement. This unique finding accentuates the potential diagnostic importance of NKX2.2 in various sarcomas, presenting a novel dimension to our understanding of these malignancies.

KDM2B-Rearranged Soft Tissue Sarcomas Expand the Concept of BCOR-Associated Sarcoma

Sarcomas with BCOR genetic alterations (BCOR-associated sarcomas) represent a recently recognized family of soft tissue and bone tumors characterized by BCOR fusion, BCOR internal tandem duplication, or YWHAE::NUTM2B fusion. Histologically, the tumors demonstrate oval to spindle cell proliferation in a variably vascular stroma and overexpression of BCOR and SATB2. Herein, we describe 3 soft tissue sarcomas with KDM2B fusions that phenotypically and epigenetically match BCOR-associated sarcomas. The cases included 1 infant, 1 adolescent, and 1 older patient. All tumors showed histologic findings indistinguishable from those of BCOR-associated sarcomas and were originally diagnosed as such based on the phenotype. However, none of the tumors had BCOR or YWHAE genetic alterations. Instead, targeted RNA sequencing identified in-frame KDM2B::NUTM2B, KDM2B::CREBBP, and KDM2B::DUX4 fusions. KDM2B fusions were validated using reverse-transcription PCR, Sanger sequencing, and in situ hybridization assays. Genome-wide DNA methylation analysis matched all 3 tumors with BCOR-associated sarcomas using the Deutsches Krebsforschungszentrum (DKFZ) classifier and t-distributed stochastic neighbor embedding analysis. One localized tumor showed a flat genome-wide copy number profile, and the patient remained disease-free after treatment. The other tumors showed multiple copy number alterations, including MDM2/CDK4 amplification and/or CDKN2A/B loss, and both tumors metastasized, leading to the patient's death in one of the cases. When tested using KDM2B immunohistochemistry, all 3 KDM2B-rearranged sarcomas showed diffuse strong staining, and all 13 sarcomas with BCOR genetic alterations also demonstrated diffuse, strong, or weak staining. By contrast, among 72 mimicking tumors, only a subset of synovial sarcomas showed focal or diffuse weak KDM2B expression. In conclusion, our study suggests that KDM2B-rearranged soft tissue sarcomas belong to the BCOR-associated sarcoma family and expand its molecular spectrum. This may be related to the known molecular relationship between KDM2B and BCOR in the polycomb repressive complex 1.1. Immunohistochemical analysis of KDM2B is a potentially valuable diagnostic tool for BCOR-associated sarcomas, including those with KDM2B rearrangement.

Extra-skeletal Ewing's sarcoma of the leg with multiple skeletal and pulmonary metastases: A rare pediatric case report

Being the second most common malignant bone tumor in children and young adults, Ewing's sarcoma can also occur as a primary soft-tissue tumor called extraosseous or extra-skeletal Ewing's sarcoma. It is a rare entity, especially in the pediatric population. We report the case of an adolescent who presented to our department for lower extremity magnetic resonance imaging to explore leg swelling. It revealed an extra-skeletal Ewing's sarcoma with multiple bone metastases. By reporting this case, we also review the literature on this rare abnormality.

A Rare Case of Sinonasal Ewing Sarcoma With Radiologic-Pathologic Correlation

An 89-year-old male presented with syncope and worsening difficulty in breathing through the left nostril. Computed tomography demonstrated a tumor in the anterior ethmoid air cells and maxillary sinus, which extended into the frontal lobe. Magnetic resonance imaging similarly demonstrated an aggressive lesion. This mass was difficult to differentiate from more commonly seen lesions at this location such as an esthesioneuroblastoma or nasopharyngeal carcinoma. Direct visualization, biopsy, and subsequent pathologic analysis eventually confirmed the diagnosis of malignant Ewing sarcoma (EWS). Our case explores the radiological findings of EWS originating from the ethmoid sinus, compares EWS with other common carcinomas in the same location, confirms the diagnosis through pathological correlation, and investigates the prognosis and treatment of these lesions. This case highlights the importance of a multidisciplinary approach to diagnose EWS when it occurs in an atypical location. The clinical team relied on input from the radiology, surgery, ENT, neurology, and pathology departments to make an accurate diagnosis and plan treatment for this aggressive tumor.

Keratin-positive fibrotic extraskeletal myxoid chondrosarcoma: a close mimic of myoepithelial tumour

AIMS

Extraskeletal myxoid chondrosarcoma (EMC) is a rare form of adult sarcoma with distinct histology and NR4A3 gene fusion. Immunohistochemically, EMCs are variably positive for S100 protein and neuroendocrine markers. Unlike histologically similar soft-tissue myoepithelial tumours, keratin expression is rare. Prompted by two recent EMC cases with diffuse keratin expression, we investigated the expression of epithelial markers in a molecularly confirmed cohort of EMC and identified two additional similar cases.

METHODS AND RESULTS

Four keratin-positive EMCs occurred in one man and three women aged 46-59 years. All tumours displayed nonclassic histology with prominent stromal fibrosis, and keratin AE1/AE3 was expressed either diffusely (N = 2) or focally (N = 2). In one tumour, keratin expression was limited to the sclerotic area. All tumours coexpressed epithelial membrane antigen and two additionally expressed S100 protein or glial fibrillary acidic protein. All tumours harboured NR4A3 fusions, including TAF15::NR4A3 (N = 1) and EWSR1::NR4A3 (N = 3). Two cases were initially considered as most consistent with myoepithelial tumours based on widespread stromal fibrosis and keratin expression. DNA methylation analysis classified two tumours tested as EMCs.

CONCLUSIONS

We identified a small subset of EMCs characterised by keratin expression and prominent stromal fibrosis. This histological pattern must be recognised in the differential diagnosis of myoepithelial tumours because misclassification may lead to the erroneous prediction of tumour behaviour and may alter patient management. NR4A3 genetic analysis should be considered even in the face of keratin expression and prominent stromal fibrosis.

Targeted treatment of solid tumors in pediatric precision oncology

The treatment of childhood solid cancer has markedly evolved in recent years following a refined molecular characterization and the introduction of novel targeted drugs. On one hand, larger sequencing studies have revealed a spectrum of mutations in pediatric tumors different from adults. On the other hand, specific mutations or immune dysregulated pathways have been targeted in preclinical and clinical studies, with heterogeneous results. Of note, the development of national platforms for tumor molecular profiling and, in less measure, for targeted treatment, has been essential in the process. However, many of the available molecules have been tested only in relapsed or refractory patients, and have proven poorly effective, at least in monotherapy. Our future approaches should certainly aim at improving the access to molecular characterization, to obtain a deeper picture of the distinctive phenotype of childhood cancer. In parallel, the implementation of access to novel drugs should not only be limited to basket or umbrella studies but also to larger, multi-drug international studies. In this paper we reviewed the molecular features and the main available therapeutic options in pediatric solid cancer, focusing on available targeted drugs and ongoing investigations, aiming at providing a useful tool to navigate the heterogeneity of this promising but complex field.