The diversity of soft tissue tumours with EWSR1 gene rearrangements: a review

Many soft tissue sarcomas have chromosomal translocations with resultant formation of new fusion genes. Among the genes that can be rearranged, the EWSR1 gene has been identified as a partner in a wide variety of clinically and pathologically diverse sarcomas as well as some non‐mesenchymal tumours. The former include Ewing sarcoma and similar (Ewing‐like) small round cell sarcomas, desmoplastic small round cell tumour, myxoid liposarcoma, extraskeletal myxoid chondrosarcoma, angiomatoid fibrous histiocytoma, clear cell sarcoma of soft tissue and clear cell sarcoma‐like tumours of the gastrointestinal tract, primary pulmonary myxoid sarcoma, extrasalivary myoepithelial tumours and sporadic examples of low‐grade fibromyxoid sarcoma, sclerosing epithelioid fibrosarcoma and mesothelioma. EWSR1 is a ‘promiscuous’ gene that can fuse with many different partner genes, but sometimes this results in phenotypically identical tumours. EWSR1 can, conversely, partner with the same genes in morphologically and behaviourally different neoplasms. This paper reviews the diversity of the several soft tissue tumour types that are associated with rearrangement of the EWSR1 gene.     

Ewing family tumours: a paediatric perspective

Sarcomas are malignant tumours of the connective tissues and are proportionately much more common in children than in adults. The Ewing family of tumours (EFT) is a group of sarcomas sharing rearrangement of the EWSR1 gene on 22q12, and include Ewing sarcoma/primitive neuroectodermal tumour, desmoplastic small round cell tumour, angiomatoid fibrous histiocytoma and clear cell sarcoma. Other tumours harbouring EWSR1 rearrangements include myoepithelial tumours, myxoid liposarcoma and extraskeletal chondrosarcoma. In addition, a group of Ewing-like primitive round cell sarcomas have been recently described in a paediatric population, further expanding the list of EFT. This review will focus on the histopathological, immunohistochemical and molecular genetic features of EFT, with an emphasis on those predominantly occurring in the paediatric population.     

The spectrum of rare central nervous system (CNS) tumors with EWSR1‐non‐ETS fusions: experience from three pediatric institutions with review of the literature

The group of CNS mesenchymal (non‐meningothelial) and primary glial/neuronal tumors in association with EWSR1‐non‐ETS rearrangements comprises a growing spectrum of entities, mostly reported in isolation with incomplete molecular profiling. Archival files from three pediatric institutions were queried for unusual cases of pediatric (≤21 years) CNS EWSR1‐rearranged tumors confirmed by at least one molecular technique. Extra‐axial tumors and cases with a diagnosis of Ewing sarcoma (EWSR1‐ETS family fusions) were excluded. Additional studies, including anchored multiplex‐PCR with next‐generation sequencing and DNA methylation profiling, were performed as needed to determine fusion partner status and brain tumor methylation class, respectively. Five cases (median 17 years) were identified (M:F of 3:2). Location was parenchymal (n = 3) and undetermined (n = 2) with topographic distributions including posterior fossa (n = 1), frontal (n = 1), temporal (n = 1), parietal (n = 1) and occipital (n = 1) lobes. Final designation with fusion findings included desmoplastic small round cell tumor (EWSR1‐WT1; n = 1) and tumors of uncertain histogenesis (EWSR1‐CREM, n = 1; EWSR1‐CREB1, n = 1; EWSR1‐PLAGL1, n = 1; and EWSR1‐PATZ1, n = 1). Tumors showed a wide spectrum of morphology and biologic behavior. For EWSR1‐CREM, EWSR1‐PLAGL1 and EWSR1‐PATZ1 tumors, no significant methylation scores were reached in the known brain tumor classes. Available outcome (4/5) was reported as favorable (n = 2) and unfavorable (n = 2) with a median follow‐up of 30 months. In conclusion, we describe five primary EWSR1‐non‐ETS fused CNS tumors exhibiting morphologic and biologic heterogeneity and we highlight the clinical importance of determining specific fusion partners to improve diagnostic accuracy, treatment and monitoring. Larger prospective clinicopathological and molecular studies are needed to determine the prognostic implications of histotypes, anatomical location, fusion partners, breakpoints and methylation profiles in patients with these rare tumors.     

Recently characterized molecular events in uncommon gynaecological neoplasms and their clinical importance

The introduction of new sequencing technologies has resulted in the discovery of commonly mutated genes in uncommon cancers, including non‐epithelial ovarian neoplasms and other rare gynaecological tumours, such as cervical embryonal rhabdomyosarcoma. In some of these neoplasms, mutations in certain genes are both frequent and specific enough for the genomic mutations and sometimes their associated protein loss or overexpression to be used as an aid to diagnosis. In this review, we contrast previous gene identification methods with newer ones, and discuss how the new sequencing technologies (collectively referred to as ‘next‐generation sequencing’) have permitted the identification of specific molecular events that characterize several rare gynaecological neoplasms. We highlight the value of using sequencing to complement traditional pathological methods when diagnosing certain tumours, and provide practical advice to pathologists dealing with these neoplasms. We focus on adult granulosa cell tumours (somatic monoallelic mutations in FOXL2), Sertoli–Leydig cell tumours, gynaecological embryonal rhabdomyosarcomas (germline and somatic mutations in DICER1), and small‐cell carcinoma of the ovary, hypercalcaemic type (biallelic mutations in SMARCA4). The new genetic findings provided by next‐generation sequencing in these uncommon neoplasms have brought these disorders back into focus, and point the way towards new diagnostic, preventive and therapeutic avenues.     

‘I Can’t Keep Up!’: an update on advances in soft tissue pathology occurring after the publication of the 2020 World Health Organization classification of soft tissue and bone tumours

Progress in our understanding of the pathogenesis and diagnosis of soft tissue neoplasia is exceptionally rapid. Although the most recent World Health Organization classification of soft tissue tumours contains many new entities and refinements of older ones, even this comprehensive document is by now incomplete or in need of modification. This review will attempt to summarise the developments in soft tissue pathology that have occurred since 2020, emphasising lesions for which morphology and genetics intersect in a complementary fashion. Novel entities discussed include KMT2A-rearranged sarcoma, PRRX::NCOAx fibroblastic tumours, EWSR1::PATZ1 sarcomas, BRAF-altered infantile fibrosarcoma-like lesions, NUTM1-rearranged colorectal sarcomas, and a variety of interesting giant cell-rich and matrix-producing lesions. In addition, recently described mimics of atypical lipomatous tumour/well-differentiated liposarcoma are covered, as is a wholly new, morphologically defined and genetically confirmed entity, pseudoendocrine sarcoma. Finally, exciting new developments in the use of immunohistochemistry as a surrogate for molecular genetic techniques are discussed.     

Endometrial stromal sarcoma – the new genetic paradigm

Endometrial stromal sarcoma (ESS) is a gynaecological sarcoma that is composed of cells that resemble those of proliferative‐phase endometrial stroma. The 2014 World Health Organization tumour classification system separates ESS into low‐grade and high‐grade types, which are histologically, genetically and clinically distinct from undifferentiated uterine sarcoma (UUS). Low‐grade ESSs frequently contain chromosomal rearrangements that result in JAZF1–SUZ12 fusion or equivalent genetic fusions. Although most low‐grade ESSs show classic histological features that closely resemble those of proliferative‐phase endometrial stroma, there are several histological variants that are associated with the same genetic fusions as seen in the classic type. High‐grade ESS is defined by the presence of YWHAE–NUTM2A/B (YWHAE–FAM22A/B) fusions. High‐grade ESSs are clinically more aggressive than low‐grade ESSs, but are associated with a lower mortality rate than UUSs. The histological and immunophenotypic features of these different types of ESS, and their diagnostic considerations, are the subjects of this review.