FUS rearrangements are rare in 'pure' sclerosing epithelioid fibrosarcoma

Case report: A rare case of malignant solitary fibrous tumor in an adult with an epithelioid pattern in the occipital region

We illustrated a rare case of malignant solitary fibrous tumor (MSFT) with epithelioid morphology in the occipital region of a 59-year-old female, in which a rare NAB2ex7-STAT6 exon15/16 double fusion subtype was detected by the Next-generation sequencing (NGS) and STAT6 immunohistochemistry (IHC) was diffusely and strongly positively expressed, without recurrence after 20 months of postoperative follow-up. The morphological and molecular genetic aspects and the differential diagnosis are described, and the relevant literature was assessed in order to broaden our understanding and diagnostic capability of this malignancy.

Sclerosing Epithelioid Fibrosarcoma

Sclerosing epithelioid fibrosarcoma (SEF) is a distinctive sarcoma that may arise in nearly any soft tissue site or bone. While there has been past controversy as to whether it is related to low-grade fibromyxoid sarcoma (LGFMS), it has been shown to behave far more aggressively than LGFMS. SEF has a propensity to metastasize to the lungs and bone and arise within the abdominal cavity. Histologically, it is characterized by uniform nuclei embedded in a densely collagenous stroma simulating osteoid. By immunohistochemistry, it is often strongly positive for MUC4. The majority (75%) have EWSR1 gene rearrangement, most commonly with CREB3L1 as a fusion partner, although a variety of FUS/EWSR1 and CREB3L1/CREB3L2/CREB3L3 fusions have been described in addition to others. SEF is currently recalcitrant to nearly all chemotherapy and radiation therapy.

Sclerosing epithelioid fibrosarcoma of bone with hybrid features: clinicopathologic, radiologic, and molecular analysis of three cases

Sclerosing epithelioid fibrosarcoma (SEF) occurring as a primary bone tumor is exceptionally uncommon. Even more rare are cases of SEF that show morphologic overlap with low-grade fibromyxoid sarcoma (LGFMS). Such hybrid lesions arising within the bone have only rarely been reported in the literature. Due to their variegated histomorphology and non-specific radiologic features, these tumors may pose diagnostic difficulties. Herein we describe three molecularly confirmed primary bone cases of sclerosing epithelioid fibrosarcoma that demonstrated prominent areas showing the features of LGFMS and with areas resembling so-called hyalinizing spindle cell tumor with giant rosettes (HSCTGR). Two patients were female and one was male aged 26, 47, and 16, respectively. The tumors occurred in the femoral head, clavicle, and temporal bone. Imaging studies demonstrated relatively well-circumscribed radiolucent bone lesions with enhancement on MRI. Cortical breakthrough and soft tissue extension were present in one case. Histologically the tumors all demonstrated hyalinized areas with SEF-like morphology as well as spindled and myxoid areas with LGFMS-like morphology. Two cases demonstrated focal areas with rosette-like architecture as seen in HSCTGR. The tumors were all positive for MUC4 by immunohistochemistry and cytogenetics, fluorescence in-situ hybridization, and next-generation sequencing studies identified EWSR1 gene rearrangements confirming the diagnosis in all three cases.Hybrid SEF is exceedingly rare as a primary bone tumor and can be difficult to distinguish from other low-grade spindled and epithelioid lesions of bone. MUC4 positivity and identification of underlying EWSR1 gene rearrangements help support this diagnosis and exclude other tumor types.

Sclerosing Epithelioid Fibrosarcoma (SEF) versus Low Grade Fibromyxoid Sarcoma (LGFMS): Presentation and outcome in the nationwide NETSARC+ series of 330 patients over 13 years

Sclerosing Epithelioid Fibrosarcoma (SEF) and Low Grade Fibromyxoid Sarcoma (LGFMS) are ultrarare sarcomas sharing common translocations whose natural history are not well known. We report on the nationwide exhaustive series of 330 patients with SEF or LGFMS in NETSARC+ since 2010.

PATIENTS AND METHODS

NETSARC (netsarc.org) is a network of 26 reference sarcoma centers with specialized multidisciplinary tumor boards (MDTB). Since 2010, (i) pathological review has been mandatory for sarcoma,and (ii) tumour/patients' characteristics have been collected in the NETSARC+ nationwide database. The characteristics of patients with SEF and LGFMS and their outcome are compared.

RESULTS

35/73 (48%) and 125/257(49%) of patients with SEF and LGFMS were female. More visceral, bone and trunk primary sites were observed in SEF (p < 0.001). 30% of SEF vs 4% of LGFMS patients had metastasis at diagnosis (p < 0.0001). Median size of the primary tumor was 51 mm (range 10-90) for LGFMS vs 80 (20-320) for SEF (p < 0.001). Median age for LGFMS patients was 12 years younger than that of SEF patients (43 [range 4-98] vs 55 [range 10-91], p < 0.001). Neoadjuvant treatment was more often given to SEF (16% vs 9%, p = 0.05). More patients with LGFMS were operated first in reference centers (51% vs 26%, p < 0.001). The R0 rate on the operative specimen was 41% in LGFMS vs 16% in SEF (p < 0.001). Median event-free survival (EFS) of patients with SEF and LGFMS were 32 vs 136 months (p < 0.0001). The median overall survival (OS) was not reached. Fifty-months OS was 93% vs 81% for LGFMS vs SEF (p = 0.05). Median OS was 77 months after first relapse, similar for SEF and LGFMS. In multivariate analysis, age, tumor size, metastasis at diagnosis were independent prognostic factors for OS in LGFMS.

CONCLUSIONS

Although sharing close molecular alterations, SEF and LGFMS have a different natural history, clinical presentation and outcome, with a higher risk of metastatic relapse in SEF. Survival after relapse is longer than with other sarcomas, and similar for SEF and LGFMS.

Response to Immunotherapy in Sclerosing Epithelioid Fibrosarcoma: Case Report and Literature Review

Sclerosing epithelioid fibrosarcoma (SEF) is an extremely rare subtype of sarcoma that appears histologically low-grade yet usually has a clinically aggressive course with a high rate of local recurrence and distant metastasis. However, these recurrences and metastases often occur years after initial treatment. Metastases can be to the lung as well as extra-pulmonary sites. In this case report, we discuss a patient who developed SEF in the deep soft tissue with metastases. This patient underwent checkpoint inhibitor therapy, with disease response. Thus, SEF is a sarcoma subtype with a unique tumor biology, and immunotherapy may be a promising avenue for treatment.

Progressive insights into fibrosarcoma diagnosis and treatment: leveraging fusion genes for advancements

Fibrosarcoma, originating from fibroblast cells, represents a malignant neoplasm that can manifest across all genders and age groups. Fusion genes are notably prevalent within the landscape of human cancers, particularly within the subtypes of fibrosarcoma, where they exert substantial driving forces in tumorigenesis. Many fusion genes underlie the pathogenic mechanisms triggering the onset of this disease. Moreover, a close association emerges between the spectrum of fusion gene types and the phenotypic expression of fibrosarcoma, endowing fusion genes not only as promising diagnostic indicators for fibrosarcoma but also as pivotal foundations for its subcategorization. Concurrently, an increasing number of chimeric proteins encoded by fusion genes have been substantiated as specific targets for treating fibrosarcoma, consequently significantly enhancing patient prognoses. This review comprehensively delineates the mechanisms behind fusion gene formation in fibrosarcoma, the lineage of fusion genes, methodologies employed in detecting fusion genes within fibrosarcoma, and the prospects of targeted therapeutic interventions driven by fusion genes within the fibrosarcoma domain.

Low-grade fibromyxoid sarcoma of the breast: genetic characterization and immunohistochemical comparison to morphologic mimics

Spindle cell lesions of the breast elicit a specific, relatively limited differential diagnosis, and accurate classification often requires careful morphologic evaluation and immunohistochemical workup. Low-grade fibromyxoid sarcoma (LGFMS) is a rare malignant fibroblastic tumor with deceptively bland spindle cell morphology. Involvement of the breast is exceedingly rare. We examined the clinicopathologic and molecular characteristics of three cases of breast/axillary LGFMS. In addition, we interrogated the immunohistochemical expression of MUC4, a commonly used marker of LGFMS, in other breast spindle cell lesions. LGFMS presented in women at 23, 33, and 59 years of age. Tumor size ranged from 0.9 to 4.7 cm. Microscopically, they were circumscribed nodular masses composed of bland spindle cells with fibromyxoid stroma. Immunohistochemically, tumors were diffusely positive for MUC4 and negative for keratin, CD34, S100 protein, and nuclear beta-catenin. Fluorescence in-situ hybridization demonstrated FUS (n = 2) or EWSR1 (n = 1) rearrangements. Next-generation sequencing identified FUS::CREB3L2 and EWSR1::CREB3L1 fusions. MUC4 immunohistochemistry performed on 162 additional breast lesions demonstrated only weak and limited expression in a subset of cases of fibromatosis (10/20, ≤30% staining), scar (5/9, ≤10%), metaplastic carcinoma (4/23, ≤5%), and phyllodes tumor (3/74, ≤10%). MUC4 was entirely negative in cases of pseudoangiomatous stromal hyperplasia (n = 9), myofibroblastoma (n = 6), periductal stromal tumor (n = 3), and cellular/juvenile fibroadenoma (n = 21). LGFMS can rarely occur in the breast and should be considered in the differential diagnosis of breast spindle cell lesions. Strong and diffuse MUC4 expression is highly specific in this histologic context. Detection of an FUS or EWSR1 rearrangement can confirm the diagnosis.

Superficial low-grade fibromyxoid sarcoma

BACKGROUND

Low-grade fibromyxoid sarcoma (LGFMS) typically involves deep soft tissue (beneath the fascia) of the proximal extremities and trunk. Long-term follow-up has shown a high rate of local recurrence, metastasis, and death. To the best of our knowledge, there is only one previous large series focusing on superficial LGFMS suggesting superficial tumors are disproportionately more common in children and may have a better prognosis. Our study's primary goals are to confirm these findings and increase general awareness that LGFMS may arise in superficial soft tissue.

METHODS

We retrieved our cases of superficial LGFMS diagnosed between 2008 and 2020. Available slides were reviewed, and clinical data and follow-up information were obtained.

RESULTS

The patients included nine males and 14 females with a median age of 29 years; eight (35%) were children (<18 years) and five (22%) were young adults (18-30 years). The majority involved the lower extremities (65%). The tumors were primarily centered in the subcutis (91%) and dermis (9%). Microscopically, they had typical features of LGFMS with alternating fibrous and myxoid zones composed of bland, slightly hyperchromatic spindled cells. All were positive for MUC4 by immunohistochemistry and/or FUS rearrangement by FISH. Follow-up on 14 cases ranged from 11 to 148 months (median 61 months) with no evidence of recurrences or distant metastases.

CONCLUSIONS

Compared to conventional deep-seated counterparts, superficial LGFMS is more likely to occur in the extremities of children and young adults and may have a better clinical outcome. Further studies with longer follow-up will likely help support these findings.

Sclerosing Epithelioid Fibrosarcoma of the Thoracic Vertebrae: An Fairly Unusual Case Report With a Short Review of Literature

Sclerosing epithelioid fibrosarcoma (SEF) is a rare subtype of soft tissue tumors, and SEF originating from the side of the spine is even rarer. We report that a 28-year-old young woman suffered from chest pain and back pain for 3 years, and thereafter she went to see a doctor because her condition deteriorated. Enhanced CT showed that the right posterior upper chest wall mass invaded the adjacent bone, and the boundary between the lesion and the surrounding tissues was relatively clear. She then underwent posterior tumor removal surgery. The pathological examination confirmed the diagnosis of SEF. In histomorphology, the tumor displayed a typical epithelioid clear cell morphology, accompanied by extensive vitrification and fibrosis, which better helped to differentiate the tumor from low grade fibromyxoid sarcoma, solitary fibrous tumor and other entities. The immunohistochemical analysis showed a diffuse positive reaction to MUC4, a highly specific marker of SEF, which was detected by Immunohistochemistry (IHC), and fluorescence in-situ hybridization (FISH) confirmed that the EWSR1 gene was rearranged, while the FUS gene was not rearranged. This is the first time that we have encountered such this rare case and thus report this case with updated literature related to this tumor.

Metastatic Pediatric Sclerosing Epithelioid Fibrosarcoma

Sclerosing epithelioid fibrosarcoma (SEF) is a rare and aggressive soft-tissue sarcoma thought to originate in fibroblasts of the tissues comprising tendons, ligaments, and muscles. Minimally responsive to conventional cytotoxic chemotherapies, >50% of SEF patients experience local recurrence and/or metastatic disease. SEF is most commonly discovered in middle-aged and elderly adults, but also rarely in children. A common gene fusion occurring between the EWSR1 and CREB3L1 genes has been observed in 80%–90% of SEF cases. We describe here the youngest SEF patient reported to date (a 3-yr-old Caucasian male) who presented with numerous bony and lung metastases. Additionally, we perform a comprehensive literature review of all SEF-related articles published since the disease was first characterized. Finally, we describe the generation of an SEF primary cell line, the first such culture to be reported. The patient described here experienced persistent disease progression despite aggressive treatment including multiple resections, radiotherapy, and numerous chemotherapies and targeted therapeutics. Untreated and locally recurrent tumor and metastatic tissue were sequenced by whole-genome, whole-exome, and deep-transcriptome next-generation sequencing with comparison to a patient-matched normal blood sample. Consistent across all sequencing analyses was the disease-defining EWSR1–CREB3L1 fusion as a single feature consensus. We provide an analysis of our genomic findings and discuss potential therapeutic strategies for SEF.

Sclerosing epithelioid fibrosarcoma: in-depth review of a genetically heterogeneous tumor

First described in 1995 by Meis-Kindbloom et al. as a variant of fibrosarcoma simulating carcinoma, sclerosing epithelioid fibrosarcoma (SEF) is a malignant soft tissue sarcoma characterized by epithelioid cells in dense sclerotic stroma, frequent immunoreactivity for MUC4 and heterogeneous genetic profile with recurrent EWSR1 gene rearrangement. It typically affects middle-age adults with a predilection for the lower extremity. It is believed that SEF is closely related to low-grade fibromyxoid sarcoma (LGFMS), both tumors show overlapping features in morphology, immunophenotype, and molecular profile. In this review, we discuss the clinical, morphologic, and immunohistochemical features of SEF with particular emphasis on its molecular diversity and relation to LGFMS.

Giant Sclerosing Epithelioid Fibrosarcoma of the Thigh: A Case Report

CASE

We present a case of a 35-year-old-man with a giant sclerosing epithelioid fibrosarcoma (SEF) of the thigh. The patient presented with a history of a painful thigh mass. Plain radiographs revealed a soft-tissue mass with extensive calcifications, whereas on magnetic resonance imaging, a lobulated mass between the adductors and the posterior muscles of the thigh was noted. A wide en block resection was undertaken, and the histopathology confirmed the diagnosis of SEF. Postoperative radiation therapy was followed. The patient had no signs of recurrence at the 4-year follow-up.

CONCLUSION

The clinicopathological, imaging characteristics, and treatment options of this rare soft-tissue tumor are discussed.

Sclerosing Epithelioid Fibrosarcoma: A Distinct Sarcoma With Aggressive Features

Since its original description in 1995, the concept of sclerosing epithelioid fibrosarcoma (SEF) as a distinctive tumor has evolved in the literature. Subsequent studies suggested that the presence of low grade fibromyxoid sarcoma (LGFMS)-like zones, occasional FUS gene rearrangements, and immunoreactivity for MUC4 all pointed to a close inter-relationship with LGFMS; however, more recent studies showed that SEF is genetically distinct from LGFMS with predominantly EWSR1-CREB3L1 fusion and complex secondary genomic alterations. To better understand the relationship between these tumors, we studied 51 cases of SEF, the largest reported series to date, and directly compared them to a previously published series of LGFMS from the same institution. The male-to-female ratio was 1.4:1 with a median age of 45 years. Tumors occurred primarily in the lower extremity (12), intra-abdominal area/visceral organs (9) and chest wall/paraspinal region (9) with a median size of 8.2 cm. The median follow-up was 49 months in 45 patients: 12 developed local recurrences and 36 developed metastases, mainly to lung and bone. Molecular studies showed EWSR1 gene rearrangement in 13 cases, 3' deletion of EWSR1 in 6, monosomy for EWSR1 in 2; FUS gene rearrangements in 3; EWSR1-CREB3L1 fusion in 7; EWSR1-CREB3L2 fusion in 1; and YAP1-KMT2A fusion in 2. Overall survival of SEF was significantly less compared with LGFMS (P≤0.0001). These results indicate that SEF is a distinct sarcoma that behaves more aggressively than LGFMS with a shorter survival, higher metastatic rate, and greater propensity to involve deep soft tissue and bone.

Sclerosing epithelioid fibrosarcoma of bone: morphological, immunophenotypical, and molecular findings of 9 cases

Primary sclerosing epithelioid fibrosarcoma (SEF) of bone is a rare and scarcely reported neoplasm. We document clinicopathological and molecular features of 9 additional cases. Five males and 4 females had a mean age of 39 years (14-71 years). Most tumors affected flat/irregular bones; only 3 cases involved a long bone. By radiology, it has characteristic radiographic features of a predominantly lytic expansile lesion with a sclerotic rim. Referring diagnoses were SEF (n = 2), low-grade osteosarcoma (n = 2), chondrosarcoma (n = 1), and chondromyxoid fibroma (n = 1). Histologically, five cases revealed classical morphology of SEF of soft tissue. Remaining cases were classified as hybrid SEF/low-grade fibromyxoid sarcoma, characterized by spindle or stellate cells, prominent stroma, and giant hyalinized areas. Various morphological deviations such as prominent vasculature (n = 3), osteoid-like material (n = 4), or parallel bone trabeculae (n = 2) were observed. Immunohistochemically, all cases showed diffuse and strong MUC4 expression. SATB2 was observed in 5/8 cases. Using FISH, EWSR1, and FUS rearrangements were detected in 4 cases and 1 case, respectively. EWSR1-CREB3L1 fusion was identified in 1 additional case by next-generation sequencing. Recurrence and metastasis were observed in 1 case and 2 cases, respectively. All but one patient were alive with disease for a mean interval of 31 months. SEF of bone is a relatively indolent sarcoma of adults, most commonly located in the flat/irregular bones. Due to overlapping histological features, it is often misdiagnosed as osteosarcoma or a chondroid tumor. Most SEF of bone exhibit EWSR1 rearrangements, but rare cases may harbor a FUS gene fusion.

Perspectives on Low-grade Sarcomas: The Extraordinary Contributions of Sharon W. Weiss, MD

Soft-tissue pathology encompasses a wide spectrum of neoplasms that represent some of the most challenging and problematic tumors in surgical pathology. Owing to the intensive work of dedicated pathologists, this once esoteric field has become increasingly well defined. In this review, Dr Sharon Weiss' monumental contributions to low-grade sarcomas, including low-grade fibromyxoid sarcoma/so-called hyalinizing spindle cell tumor, atypical lipomatous tumor/well-differentiated liposarcoma and dedifferentiated liposarcoma, epithelioid hemangioendothelioma, and dermatofibrosarcoma protuberans with fibrosarcomatous transformation will be discussed.

Primary pulmonary clear cell sarcoma-the first two reported cases

We report two cases (male patients 50 and 55 years old) of clear cell sarcoma ("melanoma of soft parts") arising in the lung, of which one case showed regional lymph node metastases. Histologically, both tumors displayed varying clear epithelioid and spindle neoplastic cells arranged in storiform and nested growth patterns, separated by thin fibrovascular septa. Immunohistochemical studies demonstrated positive expression of S-100 protein, HMB-45 and Melan-A in one case and S-100 protein only in the other. Fluorescence in situ hybridization showed positive EWSR1 gene rearrangement, and a presence of EWS-ATF1 fusion transcript was confirmed by RT-PCR and sequencing in one case.

The Evolution of Pediatric Soft Tissue Sarcoma Classification in the Last 50 Years

This review discusses the history of the classification of soft tissue sarcomas in children and adolescents, the current transition toward integration of morphology and molecular genetics as new entities emerge, and future perspectives.

Morphologic Mimics of Invasive Lobular Carcinoma

Invasive lobular carcinoma of the breast is a relatively common diagnosis. However, other carcinomatous as well as noncarcinomatous neoplasms, either primary or metastatic to the breast, may mimic invasive lobular carcinoma. As treatment may differ, establishing the correct diagnosis is paramount to providing the appropriate care for these patients. This review outlines important mimics of invasive lobular carcinoma and the key clinicopathologic and immunohistochemical features as well as additional studies helpful in establishing their diagnoses.

The New Kids on the Block: Recently Characterized Soft Tissue Tumors

Soft tissue pathology is a rapidly changing subspecialty. New entities are described relatively often, and new molecular findings for soft tissue tumors are reported in the literature almost every month. This article summarizes the major features and diagnostic approach to several recently characterized entities: superficial CD34-positive fibroblastic tumor, fibrosarcoma-like lipomatous neoplasm, angiofibroma of soft tissue, low-grade sinonasal sarcoma with neural and myogenic features, malignant gastrointestinal neuroectodermal tumor, hemosiderotic fibrolipomatous tumor, and epithelioid inflammatory myofibroblastic sarcoma. Additionally, the article also provides a summary table of recent molecular findings in soft tissue tumors.

Ossifying fibromyxoid tumor: a clinicopathologic analysis of 26 subcutaneous tumors with emphasis on differential diagnosis and prognostic factors

INTRODUCTION

Ossifying fibromyxoid tumor (OFMT) is rare and may present diagnostic difficulty. We describe 26 subcutaneous examples of OFMT emphasizing differential diagnosis and prognostic features.

METHODS

Histopathology and follow-up data from archival/consultation cases were reviewed. Prognostic features were assessed according to proposed criteria.

RESULTS

Patients (16 female, 10 male) ranged from 26 to 88 years (median 54). The tumors (median 2.3 cm, range 0.8-8.5) involved lower limb (11), trunk (7), head/neck (4), or arm (4). All showed combinations of corded, nested and trabecular patterns in a fibromyxoid stroma. Out of 26 cases 13 had peripheral ossification. Sixteen of 22 cases showed S100 protein expression. Nuclear grade was low (14); intermediate (8) and high (4) while cellularity was low (14); moderate (7) and high (5), with overall good interobserver agreement. Median mitotic rate was 3/50HPF (0-61). Five met criteria for malignant OFMT showing high nuclear grade or high cellularity and mitotic rate >2/50HPF or both. Thirteen OFMTs were atypical. Follow-up (16/26, median 45.5 months, range 8-108) showed that patients with typical OFMT (3) and atypical OFMT (9) remained disease-free. Three malignant examples of OFMT recurred and one metastasized to the lung. No deaths were recorded.

CONCLUSIONS

Our results validate proposed prognostic classification of OFMT. Dermatopathologists should be aware of this unusual superficial tumor given its potentially aggressive behavior.

An update on the application of newly described immunohistochemical markers in soft tissue pathology

CONTEXT

During the last 5 to 10 years, significant progress has been made in the molecular characterization of soft tissue tumors, predominantly with the identification of recurrent translocations or amplification of certain genes in different tumor types. Alongside this, translational efforts have identified many novel and diagnostically useful immunohistochemical markers for many of these tumor types.

OBJECTIVE

This article reviews a select group of recently described immunohistochemical markers of particular use in the evaluation of mesenchymal neoplasms; the underlying biology of the protein product, practical utility, and limitations of each marker are discussed in detail.

DATA SOURCES

Literature review, authors' research data, and personal practice experience serve as sources.

CONCLUSIONS

There are many diagnostically useful immunohistochemical markers to help confirm the diagnosis of many different soft tissue tumor types, some of which have reduced the need for additional, and more costly, studies, such as fluorescence in situ hybridization. However, no one marker is 100% specific for a given tumor, and knowledge of potential pitfalls and overlap in patterns of staining among other tumor types is crucial to ensure the appropriate application of these markers in clinical practice.

Contemporary diagnostics: sarcoma pathology update

Sarcoma diagnosis continues to evolve as new information is discovered. Certain tumors have been downgraded (dermal leiomyosarcoma) and an atypical category designed for others. Recently entities include myxoinflammatory fibroblastic sarcoma, myoepithelioma, and pseudomyogenic hemangioendothelioma. The terms malignant fibrous histiocytoma and hemangiopericytoma are outdated. New immunostains (STAT6, SOX10, ERG) add diagnostic specificity, and new risk assessment models are described for sarcomas where grading and staging has failed to provide adequate prognosis.

A genetic dichotomy between pure sclerosing epithelioid fibrosarcoma (SEF) and hybrid SEF/low-grade fibromyxoid sarcoma: a pathologic and molecular study of 18 cases

Sclerosing epithelioid fibrosarcoma (SEF) is a rare soft tissue tumor exhibiting considerable morphologic overlap with low-grade fibromyxoid sarcoma (LGFMS). Moreover, both SEF and LGFMS show MUC4 expression by immunohistochemistry. While the majority of LGFMS cases are characterized by a FUS-CREB3L1 fusion, both FUS-CREB3L2 and EWSR1-CREB3L1 fusions were recently demonstrated in a small number of LGFMS and SEF/LGFMS hybrid tumors. In contrast, recent studies pointed out that SEF harbor frequent EWSR1 rearrangements, with only a minority of cases showing FUS-CREB3L2 fusions. In an effort to further characterize the molecular characteristics of pure SEF and hybrid SEF/LGFMS lesions, we undertook a clinicopathologic, immunohistochemical and genetic analysis of a series of 10 SEF and 8 hybrid SEF/LGFMS tumors. The mortality rate was similar between the two groups, 44% within the pure SEF group and 37% in the hybrid SEF/LGFMS with a mean overall follow-up of 66 months. All but one pure SEF and all hybrid SEF/LGFMS-tested cases showed MUC4 immunoreactivity. The majority (90%) of pure SEF cases showed EWSR1 gene rearrangements by fluorescence in situ hybridization with only one case exhibiting FUS rearrangement. Of the nine EWSR1 positive cases, six cases harbored CREB3L1 break-apart, two had CREB3L2 rearrangement (a previously unreported finding) and one lacked evidence of CREB3L1/2 abnormalities. In contrast, all hybrid SEF/LGFMS tumors exhibited FUS and CREB3L2 rearrangements. These results further demarcate a relative cytogenetic dichotomy between pure SEF, often characterized by EWSR1 rearrangements, and hybrid SEF/LGFMS, harboring FUS-CREB3L2 fusion; the latter group recapitulating the genotype of LGFMS.

Sclerosing epithelioid fibrosarcoma presenting as intraabdominal sarcomatosis with a novel EWSR1-CREB3L1 gene fusion

We report a case of intraabdominal sclerosing epithelioid fibrosarcoma (SEF) with a t (11;22)(p11.2;q12.2) Ewing sarcoma breakpoint region 1-cAMP-responsive element-binding protein 3-like 1 translocation. A 43-year old man presented with massive ascites and shortness of breath. Imaging studies revealed a large mesenteric-based mass with extensive omental/peritoneal disease. After resection and cytoreductive surgery, the tumor recurred with metastasis to the lungs; the patient is still alive with disease. Histologically, there was a uniform population of epithelioid cells arranged in cords and nests, embedded in a dense collagenous matrix; no areas of low-grade fibromyxoid sarcoma were identified. All immunohistochemical markers were nonreactive. Fluorescence in situ hybridization studies showed rearrangement of Ewing sarcoma breakpoint region 1. Genomic profiling by clinical grade next-generation sequencing revealed a fusion gene between intron 11 of Ewing sarcoma breakpoint region 1 (22q12.2) and intron 5 of cAMP-responsive element-binding protein 3-like 1 (11p11.2). This is the first report of "pure" or true SEF presenting as intraabdominal sarcomatosis with confirmation of the recently described unique Ewing sarcoma breakpoint region 1-cAMP-responsive element-binding protein 3-like 1 gene fusion in SEF without areas of low-grade fibromyxoid sarcoma.

Selected topics in the pathology of epithelioid soft tissue tumors

Epithelioid morphology, mimicking carcinoma, is a key or defining feature of several soft tissue tumors and may be seen in a wide variety of other tumors. This review will focus on those tumors defined at least in part by their epithelioid morphology, in particular epithelioid sarcoma, epithelioid malignant peripheral nerve sheath tumor, and sclerosing epithelioid fibrosarcoma. The role of loss of the SMARCB1 tumor-suppressor gene in the pathogenesis of these epithelioid soft tissue tumors will be discussed, as will their differential diagnosis with non-mesenchymal tumors, in particular carcinoma and melanoma.

Fibrosarcoma: a review and update

Adult fibrosarcoma, defined by the World Health Organization as a 'malignant neoplasm composed of fibroblasts with variable collagen production and, in classical cases, a "herringbone" architecture', is a very rare soft tissue sarcoma. Once considered the most common adult sarcoma, the incidence of adult fibrosarcoma has declined dramatically over the past several decades. This is due to (i) evolution in the classification of soft tissue tumours (ii) recognition of clinically, morphologically and genetically distinctive subtypes of fibrosarcoma and (iii) increased understanding of the many other mesenchymal and non-mesenchymal tumours that may mimic fibrosarcoma. This review article will summarize the current state of our knowledge about strictly defined adult fibrosarcoma and discuss important entities in its differential diagnosis, including various fibrosarcoma variants, monophasic synovial sarcoma and other potential mesenchymal and non-mesenchymal mimics.

The evolving classification of soft tissue tumours - an update based on the new 2013 WHO classification

The new World Health Organization (WHO) classification of soft tissue tumours was published in early 2013, almost 11 years after the previous edition. While the number of newly recognized entities included for the first time is fewer than that in 2002, there have instead been substantial steps forward in molecular genetic and cytogenetic characterization of this family of tumours, leading to more reproducible diagnosis, a more meaningful classification scheme and providing new insights regarding pathogenesis, which previously has been obscure in most of these lesions. This brief overview summarizes changes in the classification in each of the broad categories of soft tissue tumour (adipocytic, fibroblastic, etc.) and also provides a short summary of newer genetic data which have been incorporated in the WHO classification.

Unusual histologic variant of a low-grade fibromyxoid sarcoma in a 3-year-old boy with complex chromosomal translocations involving 7q34, 10q11.2, and 16p11.2 and rearrangement of the FUS gene

Low-grade fibromyxoid sarcomas are rare, histologically deceptive, cytologically bland tumors that are infrequently encountered in pediatric patients. Our knowledge of histologic spectrum of these tumors is limited. A histologically unusual variant of a low-grade fibromyxoid sarcoma arising in a 3-year-old boy and containing islands of cohesive epithelioid cells is described. The diagnosis was, given the patient's age and the presence of epithelioid islands, very difficult and was verified by the presence of 3-way chromosomal translocations involving 7q34, 10q11.2, and 16p11.2 by rearrangement of the FUS gene and by immunoreactivity for mucin 4.