Low-grade small round cell tumor of the cauda equina with EWSR1-WT1 fusion and indolent clinical course

EWSR1::WT1 Fusions in Neoplasms Other Than Conventional Desmoplastic Small Round Cell Tumor: Three Tumors Occurring Outside the Female Genital Tract

Desmoplastic small round cell tumor (DSRCT) is a high-grade, primitive round cell sarcoma classically associated with prominent desmoplastic stroma, coexpression of keratin and desmin, and a characteristic EWSR1::WT1 gene fusion. DSRCT typically arises in the abdominopelvic cavity of young males with diffuse peritoneal spread and poor overall survival. Although originally considered to be pathognomonic for DSRCT, EWSR1::WT1 gene fusions have recently been detected in rare tumors lacking the characteristic morphologic and immunohistochemical features of DSRCT. Here, we report 3 additional cases of neoplasms other than conventional DSCRCT with EWSR1::WT1 gene fusions that occurred outside the female genital tract. Two occurred in the abdominopelvic cavities of a 27-year-old man and a 12-year-old girl, whereas the third arose in the axillary soft tissue of an 85-year-old man. All cases lacked prominent desmoplastic stroma and were instead solid and cystic with peripheral fibrous pseudocapsules and occasional intervening fibrous septa. Necrosis was either absent (1/3) or rare (2/3), and mitotic activity was low (<1 to 3 per 10 hpf). In immunohistochemical studies, there was expression of smooth muscle actin (3/3) and desmin (3/3), rare to focal reactivity for EMA (2/3), and variable expression of CK AE1/AE3 (1/3). Myogenin and MyoD1 were negative, and C-terminus-specific WT1 was positive in both cases tested (2/2). All 3 tumors followed a more indolent clinical course with 2 cases demonstrating no evidence of disease at 20 and 44 months after resection. The patient from case 3 died of other causes at 14 months with no evidence of recurrence. DNA methylation profiling showed that the 3 cases clustered with DSRCT; however, they demonstrated fewer copy number variations with 2 cases having a flat profile (0% copy number variation). Differential methylation analysis with hierarchical clustering further showed variation between the 3 cases and conventional DSRCT. Although further study is needed, our results, in addition to previous reports, suggest that EWSR1::WT1 gene fusions occur in rare and seemingly distinctive tumors other than conventional DSRCT with indolent behavior. Proper classification of these unusual soft tissue tumors with EWSR1::WT1 gene fusions requires direct correlation with tumor morphology and clinical behavior, which is essential to avoid overtreatment with aggressive chemotherapy.

Mesenchymal tumours of the pleura: review and update

Primary mesenchymal tumours of the pleura are uncommon and can be diagnostically challenging due to their overlapping histopathologic and immunophenotypic features. Herein we discuss selected mesenchymal tumours of the pleura, including solitary fibrous tumour, calcifying fibrous tumour, desmoid fibromatosis, synovial sarcoma, schwannoma, malignant peripheral nerve sheath tumour, inflammatory myofibroblastic tumour, follicular dendritic cell sarcoma, epithelioid hemangioendothelioma, and desmoplastic small round cell tumour. We review their clinicopathologic characteristics, along with an update on the relevant immunohistochemical and molecular features.

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.

Highlighting the Diversity of Desmoplastic Small Round Cell Tumor: A Case Series

Desmoplastic small round cell tumor (DSRCT) is a rare malignant tumor that occurs mainly in the retroperitoneum of children and young adults. In its prototypical form, DSCRT displays characteristic morphology with nested primitive small round cells in a desmoplastic stroma and a distinctive immunophenotype with polyphenotypic differentiation. However, DSCRT can also exhibit a broader clinical, histologic and immunohistochemical spectrum and, therefore, cause diagnostic difficulties. Given that DSCRT is an aggressive and nearly universally fatal disease, making the correct diagnosis is critically important. Herein, we report three patients with DSRCT and unusual clinical, morphologic or immunohistochemical characteristics, in order to highlight its remarkable diversity and increase awareness of this unusual, distinctive neoplasm.

Selective Immunoreactivity for WT1 Carboxy-Terminus Distinguishes Desmoplastic Small Round Cell Tumor From its Histologic Mimics

Desmoplastic small round cell tumor (DSRCT) is an aggressive pediatric round cell sarcoma containing a characteristic EWSR1-WT1 gene fusion. In the absence of genetic data, distinguishing DSRCT from other small round cell tumors of childhood can be problematic due to overlapping histologic and immunohistochemical features. We studied the utility of immunohistochemistry with antibodies targeting both the amino-terminal and carboxy-terminal regions of the Wilms tumor-1 (WT1) protein in differentiating these groups of tumors. The study cohort included 33 cases of genetically confirmed pediatric round cell tumors (10 DSRCTs, 12 Wilms tumors, 10 Ewing sarcomas, and 1 CIC-rearranged sarcoma). Immunoreactivities and immunolocalization of both the WT1 amino-terminus and carboxy-terminus were scored and documented. All DSRCTs displayed selective reactivity for only the WT1 carboxy-terminus (10/10), while dual immunoreactivity for both the WT1 carboxy-terminus (12/12) and amino-terminus antibodies (12/12) were characteristic of Wilms tumors. CIC-rearranged sarcoma showed variable WT1 nuclear immunopositivity (1/1, 1/1) and Ewing sarcomas were consistently WT1-negative for both the WT1 amino-terminus (0/10) and carboxy-terminus (0/10). Dual WT1 amino-terminus and carboxy-terminus immunohistochemistry remains a helpful diagnostic tool in discriminating intraabdominal small round cell tumors, which serves as an adjunct to the genetic information in preventing misdiagnosis.

Desmoplastic Small Round Cell Tumor of the Uterus: A Report of Molecularly Confirmed Case with EWSR1-WT1 Fusion

We report a case of a 49-year-old female with desmoplastic small round cell tumor of the uterus (DSRCT). Histologically, in some areas the tumor showed typical features with ample desmoplastic stroma, while in other areas the tumor cells diffusely infiltrated myometrium with only focal desmoplastic reaction. Immunohistochemically, the tumor cells showed diffuse positivity for desmin, CD56, CD57, EMA and cyclin D1. Focal positivity was present for antibodies against cytokeratin AE1/3, BerEP4, NSE, IFITM1 and CD10. The WT-1 antibody (against the N-terminus) showed cytoplasmic positivity in some tumor cells, while the nuclei were negative. P53 expression was wild-type. The Ki-67 index (MIB1 antibody) was about 55%. Other markers examined including transgelin, myogenin, synaptophysin, chromogranin, h-caldesmon, PAX8, and CD117 were all negative. NGS analysis revealed a fusion transcript of the EWSR1 and WT1 genes. DSRCT of the uterus is a rare neoplasm, as only two cases have been reported so far. However, only one of these cases was examined molecularly with a confirmation of the characteristic EWSR1-WT1 fusion. We report a second case of molecularly confirmed DSRCT of the uterus and discuss its clinical features, differential diagnosis and the significance of molecular testing.

EWSR1-The Most Common Rearranged Gene in Soft Tissue Lesions, Which Also Occurs in Different Bone Lesions: An Updated Review

EWSR1 belongs to the FET family of RNA-binding proteins including also Fused in Sarcoma (FUS), and TATA-box binding protein Associated Factor 15 (TAF15). As consequence of the multifunctional role of EWSR1 leading to a high frequency of transcription of the chromosomal region where the gene is located, EWSR1 is exposed to aberrations such as rearrangements. Consecutive binding to other genes leads to chimeric proteins inducing oncogenesis. The other TET family members are homologous. With the advent of widely used modern molecular techniques during the last decades, it has become obvious that EWSR1 is involved in the development of diverse benign and malignant tumors with mesenchymal, neuroectodermal, and epithelial/myoepithelial features. As oncogenic transformation mediated by EWSR1-fusion proteins leads to such diverse tumor types, there must be a selection on the multipotent stem cell level. In this review, we will focus on the wide variety of soft tissue and bone entities, including benign and malignant lesions, harboring EWSR1 rearrangement. Fusion gene analysis is the diagnostic gold standard in most of these tumors. We present clinicopathologic, immunohistochemical, and molecular features and discuss differential diagnoses.

Identification of EWSR1-NFATC2 fusion in simple bone cysts

AIMS

Simple bone cysts are benign intramedullary tumours primarily involving the long bones in skeletally immature individuals. Several mechanisms have been proposed for their pathogenesis. Although the diagnosis is typically straightforward, the interpretation can be problematic, because of superimposed fracture causing them to resemble aneurysmal bone cysts and other tumours. EWSR1-NFATC2 or FUS-NFATC2 fusions, which are characteristic of a subset of aggressive round cell sarcomas, have been recently detected in simple bone cysts. The aim of this study was to examine the clinicopathological and molecular features in a series of simple bone cysts.

METHODS AND RESULTS

Using RNA-based next-generation sequencing and/or fluorescence in-situ hybridisation, we investigated the presence of EWSR1 or FUS rearrangements in nine simple bone cysts. The patients were five females and four males, aged 3-23 years (median, 14 years); the tumours ranged from 19 mm to 160 mm (median, 46 mm) in size, and involved the femur (n = 3), humerus (n = 2), fibula (n = 2), tibia (n = 1), and iliac wing (n =1). We identified three cases with EWSR1-NFATC2 fusion (showing identical breakpoints to those in EWSR1-NFATC2 sarcomas) and one additional case with FUS rearrangement. Unlike in EWSR1-NFATC2 sarcomas, immunohistochemical expression of NKX3.1 and NKX2.2 was absent in two simple bone cysts tested.

CONCLUSIONS

More than 40% of simple bone cysts harbour genetic alterations confirming that they are neoplastic, investigation of EWSR1 and/or FUS rearrangement may help to distinguish simple bone cysts from mimics, and NFATC2 rearrangement is not pathognomonic of malignancy.

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.

Desmoplastic Small Round Cell Tumor of the Kidney: Report of a Case, Literature Review, and Comprehensive Discussion of the Distinctive Morphologic, Immunohistochemical, and Molecular Features in the Differential Diagnosis of Small Round Cell Tumors Affecting the Kidney

Desmoplastic small round cell tumor (DSRCT) is a rare, highly aggressive neoplasm typically presenting with widespread involvement of the abdominopelvic peritoneum of adolescent males, usually without organ-based primary. Although it is believed to originate from the serous (mainly peritoneal) membranes, intracranial, sinonasal, intraosseous, and other soft tissue sites are also documented. A chromosomal translocation t(11:22)(p13;q12) signature that fuses EWSR1 and WT1 genes results in the production of a chimeric protein with transcriptional regulatory activity that drives oncogenesis. Integration of clinical, morphologic, immunohistochemical, and genetic data is necessary to arrive at the correct diagnosis, especially when the tumor arises in an atypical site. A 15-year-old male presented with hematuria and was found to have a large renal tumor associated with adrenal, liver, lung, and bone metastases. Histopathologic and immunophenotypic features were distinctive for DSRCT. This diagnosis was confirmed by means of fluorescence in situ hybridization and cytogenetic analysis, which documented the pathognomonic t(11;22) translocation, and by reverse transcription polymerase chain reaction on snap-frozen tissue, which revealed the EWSR1/WT1-specific chimeric transcript. Despite high-dose chemotherapy and radiation therapy targeted to a single T11 vertebral metastasis, the disease progressed, and the patient died 4 years after the diagnosis. A search of electronic databases for DSRCT yielded 16 cases of well-documented renal primaries out of around 1570 cases from all sites gathered from the global literature. Desmoplastic small round blue cell tumor and other primary renal tumors considered in the differential diagnosis with DSRCT are discussed.

Subcutaneous desmoplastic small round-cell tumor: An unusual primary location expanding the differential of superficial round-cell tumors

Desmoplastic small round-cell tumor (DSRCT) is a rare, aggressive malignant tumor, which in the great majority of cases arises at abdominal-pelvic sites. Nevertheless, rare cases of primary extra-abdominal tumors have been reported. In challenging cases, its molecular hallmark, the EWSR1-WT1 reciprocal translocation, can be exploited diagnostically by various molecular techniques. Herein, we report an extremely rare case of primary subcutaneous DSRCT in an effort to raise awareness among our dermatopathology colleagues by expanding the differential of superficial round-cell tumors.

Update on selected advances in the immunohistochemical and molecular genetic analysis of soft tissue tumors

Although traditional morphological evaluation remains the cornerstone for the diagnosis of soft tissue tumors, ancillary diagnostic modalities such as immunohistochemistry and molecular genetic analysis are of ever-increasing importance in this field. New insights into the molecular pathogenesis of soft tissue tumors, often obtained from high-throughput sequencing technologies, has enabled significant progress in the characterization and biologic stratification of mesenchymal neoplasms, expanding the spectrum of immunohistochemical tests (often aimed towards recently discovered genetic events) and molecular genetic assays (most often fluorescence in situ hybridization and reverse transcription-polymerase chain reaction). This review discusses selected novel molecular and immunohistochemical assays with diagnostic applicability in mesenchymal neoplasms, with emphasis on diagnosis, refinement of tumor classification, and treatment stratification.

Multimodal treatment of an extremely rare desmoplastic small round cell tumor primary to the brachial plexus - A case report and review of literature

Background:

Desmoplastic small round cell tumor (DSRCT) is a rare and aggressive malignant neoplasm typically located in the abdomen or pelvis. Other possible locations are the chest, pleura, scrotum, and central nervous system. DSRCT originally arising from the brachial plexus (BP) is extremely rare, to the best of our knowledge, only two cases have been previously described in the English scientific literature.

Case Description:

The authors present one new case of DSRCT arising from the left BP, the first in this location with rapid progression and in a female patient. We also highlight the importance of multimodal therapy, which included resection and both adjuvant radiation and chemotherapy. Macroscopic and microscopic characteristics of the lesion are detailed, as well as the patient’s status at 56-month follow-up.

Conclusion:

For primary BP DSRCT, aggressive subtotal resection followed by radiation and chemotherapy can be satisfactory for disease control and for maintaining or improving the neurological status.

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.

Primary desmoplastic small round cell tumor in the left orbit: a case report and literature review

PURPOSE

Desmoplastic small round cell tumor is a rare malignant neoplasm that most often occurs in the abdomen or pelvis of young men. We herein describe a rare case of desmoplastic small round cell tumor arising from the left orbit in a 16-year-old male.

METHODS AND RESULTS

A biopsy was performed and the histology showed the nests of tumor cells with small round cell morphology. The tumor cells showed immunopositivity for desmin, CD99, CD56, SMA, NSE, CgA, SYN, Ki67 and vimentin. Fluorescence in situ hybridization study using EWSR1 break-apart probe was positive for EWSR1 gene rearrangement. After complete surgical resection of the tumor, we did not find tumor recurrence or metastasis with one-year follow-up. Furthermore, a review of the relevant English literature has been discussed.

CONCLUSIONS

In the present study, for the first time, we report a case of desmoplastic small round cell tumor which is located in the orbital region.

Desmoplastic small round cell tumor: evaluation of reverse transcription-polymerase chain reaction and fluorescence in situ hybridization as ancillary molecular diagnostic techniques

Desmoplastic small round cell tumor (DSRCT) is a rare, biologically aggressive soft tissue neoplasm of uncertain differentiation, most often arising in the abdominal and pelvic cavities of adolescents and young adults with a striking male predominance. Histologically, it is characterized by islands of uniform small round cells in prominent desmoplastic stroma, and it has a polyimmunophenotypic profile, typically expressing WT1 and cytokeratin, desmin, and neural/neuroendocrine differentiation markers to varying degrees. Tumors at other sites and with variant morphology are more rarely described. DSRCT is associated with a recurrent t(11;22)(p13;q12) translocation, leading to the characteristic EWSR1-WT1 gene fusion. Fluorescence in situ hybridization (FISH), to detect EWSR1 rearrangement, and reverse transcription-polymerase chain reaction (RT-PCR) to assess for EWSR1-WT1 fusion transcripts are routine diagnostic ancillary tools. We present a large institutional comparative series of FISH and RT-PCR for DSRCT diagnosis. Twenty-six specimens (from 25 patients) histologically diagnosed as DSRCT were assessed for EWSR1 rearrangement and EWSR1-WT1 fusion transcripts. Of these 26 specimens, 24 yielded positive results with either FISH or RT-PCR or both. FISH was performed in 23 samples, with EWSR1 rearrangement seen in 21 (91.3%). RT-PCR was performed in 18 samples, of which 13 (72.2%) harbored EWSR1-WT1 fusion transcripts. The sensitivity of FISH in detecting DSRCT was 91.3%, and that of RT-PCR was 92.8% following omission of four technical failures. Therefore, both methods are comparable in terms of sensitivity. FISH is more sensitive if technical failures for RT-PCR are taken into account, and RT-PCR is more specific in confirming DSRCT. Both methods complement each other by confirming cases that the other method may not. In isolation, FISH is a relatively non-specific diagnostic adjunct due to the number of different neoplasms that can harbor EWSR1 rearrangement, such as Ewing sarcoma. However, in cases with appropriate morphology and a typical pattern of immunostaining, FISH is confirmatory of the diagnosis.

Desmoplastic Small Round Cell Tumor

Desmoplastic small round cell tumor (DSRCT) is an aggressive small round cell neoplasm which predominantly occurs intra-abdominally in adolescents and young adults with a male predominance, and which is characterized by a recurrent t(11;22)(p13;q12) translocation leading to formation of the EWSR1-WT1 fusion gene, which generates a chimeric protein with transcriptional regulatory activity. Histologically, DSRCT has a characteristic morphology, of islands of monotonous small cells within prominent sparsely cellular fibroblastic stroma, and immunohistochemically it shows polyphenotypic multidirectional differentiation, with expression of epithelial, muscle, and neural markers. However, DSRCT can arise more rarely in other sites and exhibit a spectrum of both histologic features and immunoprofile, which may confuse diagnosis with other small round cell neoplasms. Correct diagnosis is important to ensure correct treatment and prognostication; DSRCT are almost universally fatal neoplasms with patients usually succumbing to disease within the first 2 years of diagnosis. While combination treatment strategies can confer a survival benefit, the overall prognosis remains poor. Further insight into the tumorigenic molecular changes generated by the fusion oncogene may lead to the generation of specific targeted therapies. We review DSRCT, discussing morphology and immunohistochemistry, molecular genetic findings, potential targeted treatments, and the differential diagnosis.

Solid-Pattern Desmoplastic Small Round Cell Tumor

Desmoplastic small round cell tumor (DSRCT) is an aggressive small round cell sarcoma that typically occurs intra-abdominally in adolescents and young adults, and is characterized by a recurrent t(11;22)(p13;q12) translocation leading to generation of the EWSR1-WT1 fusion gene, which codes for a chimeric protein with transcriptional regulatory activity. DSRCT has a characteristic histologic appearance of nests of uniform small cells within prominent fibroblastic stroma and immunohistochemically it shows multidirectional differentiation, with expression of epithelial, neural, and muscle markers. We illustrate a case of DSRCT that presented as a large intra-abdominal mass, which harbored EWSR1 rearrangement by fluorescence in situ hybridization and EWSR1-WT1 fusion transcripts by reverse transcription-polymerase chain reaction (RT-PCR), and which histologically had an entirely solid morphology, lacking evidence of desmoplastic stroma. This purely solid variant emphasizes that even when occurring at a typical location, DSRCT may be difficult to recognize when lacking nonclassical morphology. This is of clinical relevance, as DSRCT with this pattern could be misdiagnosed as Ewing sarcoma if RT-PCR is not performed, with resulting prognostic and therapeutic implications.