Angiomatoid fibrous histiocytoma: clinicopathological and molecular characterisation with emphasis on variant histomorphology

"Putting the cart before the horse": an update on promiscuous gene fusions in soft tissue tumors

The ever-increasing availability and affordability of molecular genetic testing has revolutionized our understanding of the pathogenesis and proper classification of soft tissue tumors but has also brought new challenges. As is known, many soft tissue tumors harbor gene fusion events, and while it was initially thought that individual entities would be defined by single, specific fusions, it quickly became clear that some entities could be caused by several different fusion events (e.g., EWSR1::FLI1, EWSR1::ERG, EWSR1:FEV and others in Ewing sarcoma). More recently, it has become apparent that these fusion events themselves are "promiscuous", appearing in more than one discrete entity (e.g., EWSR1::CREB1 in clear cell sarcoma, angiomatoid fibrous histiocytoma and others). This review article will briefly discuss the best known examples of genetic promiscuity, the EWSR1/FUS::ATF1/CREB1 and ETV6::NTRK3 fusions, and more comprehensively cover recently discovered and less well-known examples of genetic promiscuity, including EWSR1::WT1, MALAT1::GLI1, YAP1::TFE3 and fusions involving members of the FET and ETS gene families.

Case Series of Angiomatoid Fibrous Histiocytoma (AFH)-A Clinico-Radiological and Pathological Conundrum

Angiomatoid fibrous histiocytoma (AFH) is a rare soft tissue tumor, common in children and young adults, often misdiagnosed as either reactive or malignant. This study aims to highlight the clinico-radiological and pathological features of this uncommon entity. Eighteen cases of AFH diagnosed over a period of 20 years were analyzed and correlated with clinical data. The tumor had a wide age distribution with an M:F ratio of 3.5:1. Though swelling was the common clinical presentation, a subset of patients had constitutional symptoms like fever, weight loss, loss of appetite, and anemia. One patient was referred with deranged aPTT and hypergammaglobulinemia. The radiological features were also myriad ranging from infection in a discharging soft tissue swelling to lymphoma (in cases with nodal involvement) to sarcoma (angiosarcoma and telangiectatic osteosarcoma). Sites of occurrence were soft tissue of the upper limb, lower limb, head and neck, bone, and lung. Intra-operatively, these tumors run the risk of bleeding and may require pre-op embolization and support by blood and blood products. Wide local excision was the primary treatment offered. Macroscopically, the average size was 3.5 cm; the cut surface was nodular, cystic with hemorrhage, and gray-white to brownish-yellow in color. Microscopically, the tumors were circumscribed with a fibrous pseudo-capsule and showed mildly pleomorphic spindle cells insheets and fascicles, in a sclerotic to myxoid stroma. A peripheral cuff of lymphoplasmacytic cells was present in all cases. Atypical histological features observed were moderate nuclear pleomorphism, frequent mitosis, solid variant, and myxoid stroma. Immunohistochemically, they were most often positive for desmin, CD68, and EMA. Interestingly, about 55.5% cases had lymphadenopathy of which three showed metastatic tumor. Three of our cases harbored EWSR1 re-arrangement, proven by FISH. Follow up details were available for six patients and none showed recurrence. In conclusion, we emphasize the importance of improved recognition of this rare yet morphologically distinct neoplasm, with varied clinico-radiological presentation.

Clinical and pathological analyses of 14 cases of angiomatoid fibrous histiocytoma

Angiomatoid fibrous histiocytoma (AFH) is a soft tissue tumor of uncertain differentiation. Although its prognosis is good, its diagnosis and differential diagnosis remain a challenge, particularly for tumors with an atypical morphology. We evaluated the clinicopathological characteristics of 14 AFH cases and examined the key factors in its diagnosis or differential diagnosis. The cohort comprised 6 men and 8 women aged 9-65 years (average age: 31.2 years). Most of the tumors (11/14, 79%) were located in soft tissues, whereas 3/14 (21%) were located in the lung (1 case) and brain (2 cases). Tumor cells were spindle-shaped to epithelioid, with a visible fibrous capsule (9/14, 64%), hemorrhagic gap (9/14, 64%), lymphocyte sleeve (7/14, 50%), necrosis (3/14, 21%), and infiltrative boundary (4/14, 29%). The tumors expressed desmin (10/14, 71%) and exhibited low levels of Ki-67. 13 cases (93%) displayed ESWSR1 gene rearrangement. At follow-up, 1 case (7%) experienced local tumor recurrence. AFH is a rare intermediate tumor. Its pathological diagnosis requires a comprehensive analysis of histological, immunophenotypic, and molecular genetic features to avoid misdiagnosis. Our study has further enriched the histological features of AFH, emphasizing the importance of differential diagnosis and providing a reference for clinical practice.

Angiomatoid Fibrous Histiocytoma of the Chest Wall Protruding into the Thoracic Cavity Mimicking Metastasis in a Patient with Breast Cancer

Angiomatoid fibrous histiocytoma (AFH) is a rare soft tissue tumor of intermediate malignancy and uncertain differentiation. To date, only four patients diagnosed with AFH located in the chest wall have been described. Herein, we describe a 44-year-old woman diagnosed with breast infiltrating lobular carcinoma. During the imaging study with positron emission tomography-computerized tomography scan, a 4 cm solid lesion located in the chest wall was identified. Fine-needle aspiration followed by surgical excision with intraoperative frozen section study was performed. The combined histomorphologic, immunohistochemical, and molecular findings confirmed the diagnosis of AFH. In this report, we describe, to the best of our knowledge, the first patient with synchronous AFH and breast cancer.

An extracranial CNS presentation of the emerging "intracranial" mesenchymal tumor, FET: CREB-fusion positive

A novel histomolecular tumor, the "intracranial mesenchymal tumor (IMT), FET::CREB fusion-positive", has recently been identified and added to the 2021 World Health Organization Classification of Tumors of the Central Nervous System. One of the essential diagnostic criteria defined in this classification is the intracranial location of the tumor. Herein, we report a spinal case of IMT with a classical EWSR1::CREM fusion. We compare its clinical, histopathological, immunophenotypical, genetic and epigenetic features with those previously described in IMT, FET::CREB fusion-positive. The current case presented histopathological (epithelioid morphology with mucin-rich stroma, and expression of EMA and desmin), radiological (an extraparenchymal lobulated mass without dural tail), genetic (fusion implicating the EWSR1 and CREM genes), and epigenetic (DNA-methylation profiling) similarities to previously reported cases. This case constitutes the third "extracranial" observation of an IMT. Our results added data suggesting that the terminology "IMT, FET::CREB fusion-positive" is provisional and that further series of cases are needed to better characterize them.

Concurrent intraventricular intracranial myxoid mesenchymal tumor and ependymoma in a long-term Ewing sarcoma survivor

Intracranial myxoid mesenchymal tumor, FET::CREB fusion positive is a rare, recently described central nervous system neoplasm. It is characterized by EWSR1::CREB family transcription factor fusion, typically arises in children and adolescents, and is locally aggressive even after gross total resection. Currently, there are little data available to guide management and gauge long-term prognosis. Furthermore, there have been no reports of these lesions occurring simultaneously with other intracranial neoplasms or in patients with a history of malignancy. Here we describe the first case of a very unusual patient with intracranial myxoid mesenchymal tumor of the right lateral ventricle with a concurrent fourth ventricular ependymoma who had a remote history of Ewing sarcoma of the right fibula.

Brain parenchymal angiomatoid fibrous histiocytoma and spinal myxoid mesenchymal tumor with FET: CREB fusion, a spectrum of the same tumor type

Angiomatoid fibrous histiocytomas (AFH) is a rare soft tissue tumor of intermediate malignant potential, and its histology is diverse. It can occur in several organs including intracranial and soft tissues. Here, we report two cases of brain parenchymal classic AFH and spinal extramedullary myxoid mesenchymal tumor with clinicopathological and molecular investigations by next-generation sequencing and a comprehensive review. The current brain parenchymal AFH occurred in a 79-year-old woman, and the spinal myxoid mesenchymal tumor arose in the thoracic spine of a 28-year-old woman; both harbored FET:CREB fusion. The current brain parenchymal AFH has not recurred for 15-months follow-up period, but the spinal myxoid mesenchymal tumor recurred three times and metastasized to T8 spine level for 30-months follow-up period. We reviewed 40 reported cases of central nervous system (CNS) AFHs/myxoid mesenchymal tumors including our two cases to identify clinicopathological features and biological behaviors. They occur with a slight female predominance (M:F = 1:1.7) in children and young adults (median age: 17 years; range: 4-79 years old). Approximately 80% of CNS AFHs were younger than 30 year. Most of them were dura-based and were not just intracranial tumors as they occurred anywhere in the CNS including spinal dura. EWSR1 rearrangement was the most common driver (98%), including FET:CREB (33%), EWSR1:ATF1 (30%), and EWSR1:CREM (27%) fusions, but FUS:CREM fusion (2%) was also present. During the follow-up period (median: 27 months), 43% (17/40) of CNS AFHs recurred between two months and 11 years, and multiple recurrences were also observed. One case showed metastases to the lymph nodes and vertebrae, and among 11 cases that resulted in death, four cases provided available clinical data. Because these tumors are identical to soft tissue AFH or primary pulmonary myxoid sarcoma with an FET:CREB fusion in morphological and immunohistochemical spectra, the authors propose incorporating the two tumor terms into one.

Myoepithelial and oral intracranial myxoid mesenchymal tumor-like neoplasms as diagnostic considerations of the ever-expanding extracranial myxocollagenous tumors harboring FET-CREB fusions

AIMS

Intracranial myxoid mesenchymal tumors (IMMTs) with fusions between EWSR1/FUS and CREB transcription factors have morphologic overlap with myxoid angiomatoid fibrous histiocytoma (mAFH) and myoepithelial tumor/carcinoma (MET/MEC). We aimed to study the clinicopathologic and genetic spectrum of extracranial IMMT-like tumors and their relationships with mAFH and MET/MEC.

METHODS

Twelve extracranial tumors harboring EWSR1/FUS-CREB fusions across different histologic groups were characterized using RNA sequencing, FISH and/or RT-PCR.

RESULTS

There were 4 IMMT-like neoplasms, 3 MET/MECs, and 5 mAFHs from the tibia (n=1), oral cavity (n=2), and soft tissues (n=9; 5 in the extremities), harboring EWSR1-ATF1 in 4 cases, FUS-CREM and EWSR1-CREM in 3 each, and EWSR1-CREB1 in 2. Multinodular growth, reticular/cording/trabecular arrangements, myxocollagenous matrix, and lymphocytic infiltrates variably prevailed among the 3 groups. mAFHs were characterized by cells with syncytial cytoplasm. IMMT-like neoplasms and MET/MECs shared cells with distinct boundaries, but only MET/MECs expressed GFAP and/or S100. MUC4 and ALK were expressed in some IMMT-like neoplasms (2/4; 2/4) and mAFH (2/5; 1/5). Pan-TRK reactivity was observed in two IMMT-like neoplasms with upregulated NTRK3 mRNA and one MEC. Local recurrences, typically ≥ 12 months postoperatively, developed in 2/3 IMMT-like neoplasms, 1/2 MET/MECs, and 0/4 mAFHs with follow-up. No definite associations were found between fusion types and histology, immunoprofile or outcome.

CONCLUSIONS

We demonstrated the similarities and differences among 3 extracranial myxocollagenous tumor groups sharing EWSR1/FUS-CREB fusions. Oral IMMT-like neoplasms harboring FUS-CREM or EWSR1-ATF1 and FUS-CREM-positive.

A novel SMARCA2-CREM fusion: expanding the molecular spectrum of intracranial mesenchymal tumors beyond the FET genes

A novel histomolecular tumor of the central nervous system, the “intracranial mesenchymal tumor (IMT), FET-CREB fusion-positive” has recently been identified in the literature and will be added to the 2021 World Health Organization Classification of Tumors of the Central Nervous System. However, our latest study using DNA-methylation analyses has revealed that intracranial FET-CREB fused tumors do not represent a single molecular tumor entity. Among them, the main subgroup presented classical features of angiomatoid fibrous histiocytoma, having ultrastructural features of arachnoidal cells, for. Another tumor type with clear cell component and histopathological signs of aggressivity clustered in close vicinity with clear cell sarcoma of soft tissue. Herein, we report one case of IMT with a novel SMARCA2-CREM fusion which has until now never been described in soft tissue or the central nervous system. We compare its clinical, histopathological, immunophenotypic, genetic and epigenetic features with those previously described in IMT, FET-CREB fusion-positive. Interestingly, the current case did not cluster with IMT, FET-CREB fusion-positive but rather presented histopathological (clear cell morphology with signs of malignancy), clinical (with a dismal course with several recurrences, metastases and finally the patient’s death), genetic (fusion implicating the CREM gene), and epigenetic (DNA-methylation profiling) similarities with our previously reported clear cell sarcoma-like tumor of the central nervous system. Our results added data suggesting that different clinical and histomolecular tumor subtypes or grades seem to be included within the terminology “IMT, FET-CREB fusion-positive”, and that further series of cases are needed to better characterize them.

Expression patterns for Bcl-2, EMA, β-catenin, E-cadherin, PAX8, and MIB1 in thymomas

The expression of immunohistochemical markers has been extensively investigated in thymomas to assist in the differential diagnosis. We have studied six select markers to determine their utility in the evaluation of these tumors. A series of 126 thymomas including 33 type A, 27 type AB, 20 type B1, 22 type B2, and 24 type B3, were examined utilizing a tissue microarray (TMA) technique with antibodies to e-cadherin, β-catenin, PAX8, bcl-2, EMA, and MIB-1. Keratin AE1/AE3 and p63 were used for quality control. A significant finding was strong and consistent positivity for bcl-2 in type A (90%) and type AB (88.8%) thymoma, while 100% of B1, B2, and B3 were negative. The distribution of e-cadherin and β-catenin was not useful for differential diagnosis. E-cadherin and β-catenin were expressed in a high proportion of all the tumors (92-100%), except for B2 thymoma which showed only 45% expression. A significant increase in the expression of the MIB-1 proliferation marker (mean: 12.8% nuclear positivity) was also observed in B3 thymoma compared with the other histologic types. Statistical significance was confirmed using Kruskal's non-parameterized test for distribution. EMA was generally negative except for spindle cells in the fibrous septa in types A and AB thymoma. PAX8 showed less consistent nuclear staining than p63 and was only widely expressed in 55.7% of cases. Bcl-2 may serve as a useful marker to separate spindle cell thymomas (Type A and AB) from the other types, and the MIB1 proliferation index may be of use to differentiate type B2 from type B3 thymoma.

SOX9 Immunohistochemistry in the Distinction of Angiomatoid Fibrous Histiocytoma From Histologic Mimics: Diagnostic Utility and Pitfalls

Angiomatoid fibrous histiocytoma (AFH) can be diagnostically difficult because of its varied histologic appearance and potential to occur at unusual sites. The identification of recurrent rearrangements (EWSR1-CREB1, EWSR1-ATF1, and FUS-ATF1) is a helpful diagnostic tool. Additional immunohistochemical markers in AFH could aid in restricting the differential diagnosis and selecting appropriate cases for targeted molecular studies. SOX9 is a transcription factor that is crucial for chondrogenesis and is expressed in neoplasms with chondroid differentiation, and other malignant bone and soft tissue tumors. Recently a role of EWS in regulation of SOX9 expression has been reported, the rearrangements typical of AFH may play a role in SOX9 expression. In this study, we analyzed SOX9 expression in 13 pediatric AFH with varying histology, and an additional 80 cases of other myofibroblastic or fibrohistiocytic lesions. SOX9 expression was present in 11 of 13 AFH, 2 of 53 dermatofibroma (1 aneurysmal and 1 cellular) and 1 calcifying aponeurotic fibroma. The remaining tumors were negative. SOX9 is selectively expressed in AFH and may be a useful maker in combination with desmin, CD99, CD68, and EMA in small biopsies, especially in cases with unusual morphologic features. SOX9 appears to be highly specific for AFH, being weakly expressed in a subset of aneurysmal dermatofibroma and absent in other myofibroblastic lesions, except calcifying aponeurotic fibroma. It should be used with caution when differentiating AFH from malignant neoplasms such as Ewing sarcoma.

An integrative histopathological and epigenetic characterization of primary intracranial mesenchymal tumors, FET:CREB-fused broadening the spectrum of tumor entities in comparison with their soft tissue counterparts

FET:CREB fusions have been described in a variety of tumors from various phenotypes. Recently, these fusion transcripts were reported in intracranial tumors, variably named intracranial mesenchymal myxoid tumors or angiomatoid fibrous histiocytomas. Controversy remains concerning the terminology for these tumors. Here, we report 11 cases of central nervous system mesenchymal tumors with proven FET:CREB fusion. Most DNA methylation profiles were not classifiable using the Heidelberg Brain Tumor or Sarcoma Classifier (v11b4/v12.2). However, by using unsupervised t‐SNE and hierarchical clustering analyses, six of the cases constituted a distinct cluster. The remaining four tumors showed no obvious relation to any of the other referenced classes but were close to the clusters of extra‐CNS angiomatoid fibrous histiocytomas (n = 1), clear cell sarcomas (n = 1), or solitary fibrous tumors (n = 2). Our findings confirm that intracranial FET:CREB‐fused tumors do not represent a single molecular tumor entity, although most samples clustered close to each other, indicating the existence of a distinct epigenetic group that could potentially be partially masked by the low number of cases included. Further analyses are needed to characterize intracranial FET:CREB fused‐defined tumors in more detail.

A case of intracranial myxoid mesenchymal tumor with EWSR1:CREM fusion in an adult female: Extensive immunohistochemical evaluation

Intracranial myxoid mesenchymal tumor (IMMT) is a recently described, extremely rare group of neoplasms characterized by fusions between the female-expressed transcript (FET) family genes and the cAMP response element-binding protein (CREB) family genes. Controversy persists regarding whether the tumor is a myxoid variant of angiomatoid fibrous histiocytoma or a completely distinct clinicopathological entity. Here, we report a case of IMMT arising in the posterior fossa in a 65-year-old woman with a history of breast cancer. We performed total removal of the tumor, which histologically demonstrated features characteristic of IMMT but also bore a partial resemblance to conventional angiomatoid fibrous histiocytoma. Immunohistochemically, tumor cells were diffusely positive for desmin, vimentin, cluster of differentiation (CD) 99 (CD99), glucose transporter-1, and cytokeratin (CK) 8/18 (CK8/18), and focally positive for CK7, epithelial membrane antigen, mucin 4, anaplastic lymphoma kinase, calponin, and CD68. Molecular genetic analysis revealed a fusion between the Ewing sarcoma breakpoint region 1 (EWSR1) gene (EWSR1) and the cAMP-responsive element modulator (CREM) gene (CREM) called EWSR1:CREM fusion, which confirmed the diagnosis. The overlap of the pathological features of IMMTs and angiomatoid fibrous histiocytomas may support the recent theory that these tumors are two manifestations of a single entity. Moreover, our study indicated the broad spectrum of immunohistochemical phenotypes of these tumors, which should be noted during diagnosis. Further studies are needed to elucidate the histopathological concept, long-term prognosis, optimal treatment strategy, and factors associated with the prognosis and therapeutic options of this condition.

Angiomatoid Fibrous Histiocytoma With ALK Expression in an Unusual Location and Age Group

Angiomatoid fibrous histiocytoma (AFH) is a relatively rare soft tissue tumor of intermediate malignant potential, occurring most commonly in young adults, with a recognized propensity for local recurrence and occasional metastasis. A case of AFH occurring on the finger of a 60-year-old man is described in which the unusual location and age group for this entity raised the original wrong diagnosis of an aneurysmal and cellular fibrous histiocytoma. Further workup demonstrated an EWSR1-CREB1 translocation, confirming the correct diagnosis of AFH. Strong anaplastic lymphoma kinase (ALK) expression using the antibody clone D5F3 was demonstrated in our case on immunohistochemistry, which is in concordance with recent findings of anaplastic lymphoma kinase positivity with this antibody in the majority of AFHs.

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.

Distinct clinicopathological features of pulmonary primary angiomatoid fibrous histiocytoma: A report of four new cases and review of the literature

BACKGROUND

The aim of this study was to highlight the clinicopathological features of pulmonary primary angiomatoid fibrous histiocytoma (PPAFH) to assist with a differential diagnosis.

METHODS

There were 10 previous reports in the literature and four new PPAFH cases reviewed in this study. Immunohistochemistry (IHC), fluorescence in situ hybridization (FISH) and DNA and RNA-based next-generation sequencing (NGS) was performed in the four new cases reported here.

RESULTS

In the four new PPAFH cases, the ages of occurrence were in patients age from 33 to 55 years and tumor sizes were from 1.5 to 8 cm. Three of four (75.0%) tumors were located in the endobronchus. The most common morphological changes included delineated fibrous capsule (100%, 4/4), lymphoplasmacytic cuff (100%, 4/4), and dense or richly lymphoplasmatic infiltration (100%, 4/4). IHC analysis revealed that the tumor cells of four cases expressed vimentin and TLE1, ALK and CD163 or CD68 was positive in three cases, epithelial membrane antigen (EMA), desmin was positive in two cases, and SMA focal positive expression was observed in two cases. EWSR1 gene rearrangement was positive in all PPAFH cases (100%, 4/4) by FISH detections and four cases were confirmed as EWSR1-CREB1 fusion variant by DNA and RNA based NGS. No regional lymph nodes and distal metastasis, recurrences and death of disease after surgical excision were recorded in all four cases.

CONCLUSIONS

PPAFH is a very unusual pulmonary primary mesenchymal tumor and the clinicopathological features are like other unusual sites counterparts, but with a smaller tumor size, related with large airway, with a tendency to exhibit benign biological behavior, with EWSR1 gene rearrangement and higher frequency of EWSR1-CREB1 gene fusion.

KEY POINTS

Significant findings in the study: In comparison with "classic somatic" and nonpulmonary visceral angiomatoid fibrous histiocytoma, pulmonary primary angiomatoid fibrous histiocytoma display distinct clinicopathological features and prognosis. What this study adds The study provided the pathological differential diagnostic criteria and clinico-pathological features for pulmonary primary angiomatoid fibrous histiocytoma.

Intracranial mesenchymal tumor with FET-CREB fusion-A unifying diagnosis for the spectrum of intracranial myxoid mesenchymal tumors and angiomatoid fibrous histiocytoma-like neoplasms

Intracranial mesenchymal tumors with FET‐CREB fusions are a recently described group of neoplasms in children and young adults characterized by fusion of a FET family gene (usually EWSR1, but rarely FUS) to a CREB family transcription factor (ATF1, CREB1, or CREM), and have been variously termed intracranial angiomatoid fibrous histiocytoma or intracranial myxoid mesenchymal tumor. The clinical outcomes, histologic features, and genomic landscape are not well defined. Here, we studied 20 patients with intracranial mesenchymal tumors proven to harbor FET‐CREB fusion by next‐generation sequencing (NGS). The 16 female and four male patients had a median age of 14 years (range 4–70). Tumors were uniformly extra‐axial or intraventricular and located at the cerebral convexities (n = 7), falx (2), lateral ventricles (4), tentorium (2), cerebellopontine angle (4), and spinal cord (1). NGS demonstrated that eight tumors harbored EWSR1‐ATF1 fusion, seven had EWSR1‐CREB1, four had EWSR1‐CREM, and one had FUS‐CREM. Tumors were uniformly well circumscribed and typically contrast enhancing with solid and cystic growth. Tumors with EWSR1‐CREB1 fusions more often featured stellate/spindle cell morphology, mucin‐rich stroma, and hemangioma‐like vasculature compared to tumors with EWSR1‐ATF1 fusions that most often featured sheets of epithelioid cells with mucin‐poor collagenous stroma. These tumors demonstrated polyphenotypic immunoprofiles with frequent positivity for desmin, EMA, CD99, MUC4, and synaptophysin, but absence of SSTR2A, myogenin, and HMB45 expression. There was a propensity for local recurrence with a median progression‐free survival of 12 months and a median overall survival of greater than 60 months, with three patients succumbing to disease (all with EWSR1‐ATF1 fusions). In combination with prior case series, this study provides further insight into intracranial mesenchymal tumors with FET‐CREB fusion, which represent a distinct group of CNS tumors encompassing both intracranial myxoid mesenchymal tumor and angiomatoid fibrous histiocytoma‐like neoplasms.

[Angiomatoid fibrous histiocytoma: a literature review and a report of two cases]

Angiomatoid fibrous histiocytoma (AFH) is a rare soft tissue tumor of intermediate malignancy potential, which predominantly affects children and young adults. This paper describes two cases of AFH, as well as a review of literature during 1979 to 2021. It gives data on the epidemiology, clinical features, diagnosis, and genetic characteristics of AFH.

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.

Expanding the Phenotypic Spectrum of Mesenchymal Tumors Harboring the EWSR1-CREM Fusion

ATF1, CREB1, and CREM constitute the CREB family of transcription factors. The genes encoding these factors are involved in gene fusion events in human tumors. EWSR1-ATF1 and EWSR1-CREB1 are the 2 most characterized fusions, whereas EWSR1-CREM has been less studied. To better understand the phenotypic spectrum of mesenchymal tumors associated with the EWSR1-CREM fusion, we investigated archival cases using fluorescence in situ hybridization and/or RNA sequencing. Among 33 clear cell sarcomas of soft tissue tested, we found 1 specimen, a hand tumor bearing the rearrangements of EWSR1 and CREM, with classic histology and immunophenotype. None of 6 clear cell sarcoma-like tumors of the gastrointestinal tract tested harbored the EWSR1-CREM fusion. Among 11 angiomatoid fibrous histiocytomas, we found that 3 tumors of myxoid variant harbored the rearrangements of EWSR1 and CREM. All 3 tumors occurred in middle-aged men and involved the distal extremities (N=2) and the lung (N=1). Prominent lymphoid cuff, fibrous pseudocapsule, and amianthoid fiber were present in 3, 2, and 2 tumors, respectively, whereas none showed pseudoangiomatoid spaces. All 3 tumors were immunohistochemically positive for epithelial membrane antigen and desmin. These cases suggested a closer relationship between angiomatoid fibrous histiocytoma and a recently proposed novel group of myxoid tumors with CREB family fusions. Our cohort also included 2 unclassifiable sarcomas positive for EWSR1-CREM. One of these was an aggressive pediatric tumor of the abdominal cavity characterized by proliferation of swirling spindle cells immunopositive for cytokeratin and CD34. The other tumor derived from the chest wall of an adult and exhibited a MUC4-positive sclerosing epithelioid fibrosarcoma-like histology. Our study demonstrates that a wider phenotypic spectrum is associated with the EWSR1-CREM fusion than previously reported.

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.

Intracranial Myxoid Variant of Angiomatoid Fibrous Histiocytoma: A Case Report and Literature Review

Angiomatoid fibrous histiocytoma (AFH) is a rare and slow-growing soft tissue lesion that typically arises in the extremities of young patients.

Microscopically, AFH is characterized by pseudovascular, blood-filled spaces that are surrounded by a multinodular proliferation of spindle and/or round cells and lymphoid cuffs. However, there is a wide morphological spectrum, including a myxoid variant. Examples with a prominent myxoid matrix are rare and may pose great diagnostic difficulty.

Specific gene fusions have been found to play a significant role in AFH tumorigenesis. Gene fusions of Ewing sarcoma breakpoint region 1 (EWSR1) with members of the cAMP response element-binding protein family (CREB) of transcription factors (CREB1, activating transcription factor 1 (ATF1), and cAMP response element modulator (CREM)) have been described in histopathologically diverse mesenchymal neoplasms such as AFH, hyalinising clear cell carcinomas of salivary glands, primary pulmonary myxoid sarcoma, and clear cell sarcoma. Classically, EWSR1-CREB is known to be the prominent gene fusion in AFH. Recently, a small series of intracranial mesenchymal tumors with EWSR1-CREB family gene fusions has been reported. These tumors seem to show histologic, immunophenotypic, and cytogenic features similar to those observed in the myxoid variant of AFH; therefore, there is a debate on whether these tumors merely represent a variant of AFH or a novel entity.

This case report is of a 58-year-old woman presenting with the first episode of generalized seizure due to an extra-axial lesion with homogenous contrast enhancement in the right parietal lobe, which was initially diagnosed as a World Health Organization (WHO) grade I meningioma. Following a series of pathological investigations, the diagnosis of an intracranial myxoid variant of AFH was made. This case report illustrates the need to consider the myxoid variant of intracranial AFH in the differential diagnosis of meningioma-like tumors. A high index of suspicion is required if the meningioma behaves abnormally with a much higher recurrence rate.

Aneurysmal Fibrous Histiocytoma: Clinicopathology Analysis of 30 Cases of a Rare Variant of Cutaneous Fibrohistiocytoma

Aneurysmal fibrous histiocytoma is often clinically misdiagnosed. In this study, we put forward an insight on how to help diagnose this disease clinically. A retrospective chart review was performed on all patients diagnosed with aneurysmal fibrous histiocytoma from 2007 to 2017 in the Department of Dermatology, Union Hospital, China, and all clinical data were collected from the hospital archives. From a total of 418 patients diagnosed with cutaneous fibrous histiocytoma, only 30 patients were confirmed to have aneurysmal fibrous histiocytoma out of which only 2 patients were clinically diagnosed with aneurysmal fibrous histiocytoma. The remaining 28 patients were diagnosed with various types of vascular tumors although pathology classified them as having aneurysmal fibrous histiocytoma. Among the 30 patients, 9 were male and 21 were female. There were following age groups: 13-19 (mean 16, n=4), 20-29 (mean 26.25, n=8), 30-39 (mean 33, n=7), 40-49 (mean 44, n=4), 50-59 (mean 56.75, n=4), 60 and above (mean 61, n=3). Tumors were present on the head, neck, back, waist, hips and upper and lower extremities. After complete excision, there was no recurrence and no complications. Histologically, lesions showed the typical pseudoangiomatoid spaces without endothelial lining and infiltration of fibrohistiocytes in hemosiderotic pigmentation. It was suggested that although the prognosis of aneurysmal fibrous histiocytoma is good, accurate diagnosis is paramount to avoid clinical misdiagnosis and subsequent complications.

Retroperitoneal Angiomatoid Fibrous Histiocytoma Presenting as a Recurrent Spontaneous Retroperitoneal Hemorrhage in a 9-Year-Old Boy

Angiomatoid fibrous histiocytoma (AFH) is a rare soft tissue tumor that typically presents in children and young adults. Occurrence outside of the extremities and the head and neck region is exceedingly rare. We report the case of a 9-year-old boy who presented with recurrent retroperitoneal hemorrhage initially thought to be a manifestation of an underlying bleeding disorder. After comprehensive diagnostic work-up, including multiple negative biopsies, the patient underwent surgical resection of an extensively hemorrhagic intramuscular mass and to date remains well. Pathologic examination confirmed AFH with EWSR1 gene rearrangement. This first documented report of an AFH in a retroperitoneal location in a child highlights the diagnostic difficulties and clinical challenges of AFH arising in an atypical location.

Pathologically Benign Lymph Nodes Can Mimic Malignancy on Imaging in Patients With Angiomatoid Fibrous Histiocytoma

BACKGROUND

Angiomatoid fibrous histiocytoma (AFH) is a rare soft tissue neoplasm, and its rarity makes studying it difficult. We found that several of our patients with AFH presented with radiologically suspicious local lymph nodes that were sampled because of their imaging characteristics, but the nodes proved to be benign on pathologic evaluation. Although the frequency of this finding is unknown, it seems important for orthopaedic oncologists who care for patients with AFH to know whether suspicious-appearing associated nodes in these patients warrant aggressive management.

QUESTIONS/PURPOSES

(1) How often do patients with newly diagnosed AFH present with radiologically suspicious lymph nodes? (2) How often are the radiologically suspicious nodes malignant on pathologic evaluation?

METHODS

In this retrospective, Health Insurance Portability and Accountability Act-compliant study, we used a hospital database to identify all 54 patients treated at our hospital for AFH between 1993 and 2016. This study was performed with institutional review board waiver. All of the patients were considered potentially eligible for analysis. Of the patients, 19 (35%) had pretherapy imaging; during the period in question, pretherapy imaging generally was obtained when there was uncertainty regarding extent of disease. All patients who had imaging underwent MRI, and four also had fluorodeoxyglucose positron emission tomography (FDG PET/CT). Imaging reports were reviewed to identify which patients had nodes that were called suspicious in the reports. All patients with nodes described as suspicious on imaging underwent subsequent pathologic analysis for the presence or absence of metastatic AFH cells in the node.

RESULTS

Seven of 19 patients with pretherapy imaging had local lymph nodes called suspicious for nodal metastases. Pathologic analysis of these nodes showed they were malignant in only one patient, whereas six patients had nodes that were histologically benign despite suspicious imaging findings. Benign nodes measured as much as 3.2 × 1.8 cm on MRI and showed maximum standardized uptake values up to 10.9 on FDG PET/CT.

CONCLUSIONS

Patients with newly diagnosed AFH present with benign lymph nodes that are mistaken for malignancy on imaging. Orthopaedic surgeons and radiologists should be aware of this finding in patients with AFH. Less-invasive management of suspicious nodes, such as image-guided biopsy, may be preferable to nodal resections, as this will help decrease the aggressiveness of surgery for patients with newly diagnosed AFH.

LEVEL OF EVIDENCE

Level IV, diagnostic study.

EWSR1 Fusions With CREB Family Transcription Factors Define a Novel Myxoid Mesenchymal Tumor With Predilection for Intracranial Location

Recurrent gene fusions involving EWSR1 with members of the cAMP response element binding protein (CREB) family (ATF1 and CREB1) have been reported in a diverse group of tumors including angiomatoid fibrous histiocytoma (AFH), soft tissue and gastrointestinal clear cell sarcoma, primary pulmonary myxoid sarcoma, and hyalinizing clear cell carcinoma of salivary gland. We have recently encountered a group of 5 myxoid mesenchymal tumors positive for EWSR1 fusions with one of the CREB family member (ATF1, CREB1, and CREM), with histologic features distinct from any of the previously described pathologic entities. Tumors occurred in children or young adults (12 to 23 y; mean, 18 y), with equal sex distribution. All except 1 were intracranial (intra-axial, 2; meningeal, 2), whereas 1 was perirectal. Histologically, the tumors were well circumscribed, often lobulated, composed of uniform ovoid to round cells, and arranged in cord-like or reticular structures in a myxoid background. All except 1 displayed unique sunburst amianthoid fibers. Immunohistochemically, tumors were positive for epithelial membrane antigen (5/5; 4 focal, 1 diffuse) and desmin (3/5). A novel EWSR1-CREM fusion was identified by RNA sequencing in the perirectal tumor, which was further confirmed by fluorescence in situ hybridization (FISH) and reverse transcription-polymerase chain reaction (RT-PCR). A second case with similar EWSR1-CREM fusion was identified by RT-PCR and FISH in a meningeal tumor. The remaining cases studied by FISH showed the presence of EWSR1-CREB1 fusion in 2 cases and EWSR1-ATF1 in 1. In conclusion, we report a distinct group of myxoid mesenchymal neoplasms occurring in children or young adults with a predilection for intracranial locations. Although the immunoprofile [epithelial membrane antigen (EMA), desmin] and the fusion type raise the possibility of a myxoid AFH, none of the typical histologic findings of AFH were present, suggesting a novel entity.

Intracranial myxoid mesenchymal tumors with EWSR1-CREB family gene fusions: myxoid variant of angiomatoid fibrous histiocytoma or novel entity?

Intracranial myxoid mesenchymal tumor harboring EWSR1 fusions with CREB family of genes was recently described, and it resembles the myxoid variant of angiomatoid fibrous histiocytoma. We present three pediatric patients with intracranial EWSR1-rearranged myxoid mesenchymal neoplasm and provide a molecular genetic characterization of these tumors. Clinical histories and imaging results were reviewed. Histology, immunohistochemistry, EWSR1, FUS, NR4A3 fluorescence in situ hybridization (FISH), and next-generation sequencing (NGS) were performed. A 12-year-old male (case 1), 14-year-old female (case 2), and 18-year-old male (case 3), presented with headaches, emesis, and seizures, respectively. The magnetic resonance images demonstrated tumors abutting the dura (cases 1 and 3) and in the third ventricle (case 2). All tumors were vascular, with solid sheets of monomorphic oval cells in a prominent myxoid/microcystic matrix. A thin fibrous pseudocapsule was present in all lesions, but definitive lymphocytic cuffing was absent. Morphologically, they closely resembled myxoid variant of angiomatoid fibrous histiocytoma. Mitoses were rare, and necrosis was absent. All tumors expressed desmin and GLUT1, and focal EMA and CD99. The proliferation index was low. FISH and NGS showed EWSR1-CREB1 fusion (cases 1 and 2), and EWSR1-CREM fusion (case 3). There were no FUS (16p11.2) or NR4A3 (9q22.33) rearrangements in case 3. Gains of 5q (including KCNIP1) and 11q (including CCND1) were present in cases 1 and 2. There were no common pathogenic genomic changes other than EWSR1 rearrangements across cases. CNS myxoid mesenchymal neoplasms with histological and immunophenotypic similarities to myxoid variant of AFH are rare, diagnostically challenging, and harbor EWSR1-CREB1 and also a novel EWSR1-CREM fusion not yet described in AFH. Therefore, it is uncertain if these tumors represent variants of AFH or a new entity. The copy number and mutational changes presented here provide support for future studies to further clarify this issue.

Fluorescence in situ hybridization in surgical pathology: principles and applications

Identification of recurrent tumour‐specific chromosomal translocations and novel fusion oncogenes has important diagnostic, therapeutic and prognostic implications. Over the past decade, fluorescence in situ hybridization (FISH) analysis of tumour samples has been one of the most rapidly growing areas in genomic medicine and surgical pathology practice. Unlike traditional cytogenetics, FISH affords a rapid analysis of formalin‐fixed, paraffin‐embedded cells within a routine pathology practice workflow. As more diagnostic and treatment decisions are based on results of FISH, demand for the technology will become more widespread. Common FISH‐detected alterations are chromosome deletions, gains, translocations, amplifications and polysomy. These chromosome alterations may have diagnostic and therapeutic implications for many tumour types. Integrating genomic testing into cancer treatment decisions poses many technical challenges, but rapid progress is being made to overcome these challenges in precision medicine. FISH assessment of chromosomal changes relevant to differential diagnosis and cancer treatment decisions has become an important tool for the surgical pathologist. The aim of this review is to provide a theoretical and practical survey of FISH detected translocations with a focus on strategies for clinical application in surgical pathology practice.

Angiomatoid Fibrous Histiocytoma With Prominent Myxoid Stroma: A Case Report and Review of the Literature

Angiomatoid fibrous histiocytoma is a rare neoplasm of intermediate malignant potential that usually occurs in the dermis or subcutaneous tissues of the extremities in children or young adults. It is characterized by a nodular growth of spindled, histiocytic, or epithelioid cells and blood-filled spaces, surrounded by a fibrous pseudocapsule that contains a lymphocytic cuff. The histological spectrum of this condition has expanded to include cases that contain prominent myxoid stroma. We herein present another instance of myxoid angiomatoid fibrous histiocytoma and review the clinical and histological features, immunohistochemical profile, and molecular genetics of this uncommon variant. We also discuss the diagnostic mimics of this condition, including benign myxoid soft tissue tumors and sarcomas, to illustrate the potential pitfalls in arriving at the diagnosis.

Angiomatoid fibrous histiocytoma: the current status of pathology and genetics

CONTEXT

Angiomatoid fibrous histiocytoma (AFH) is a rare soft tissue neoplasm of intermediate biologic potential and uncertain differentiation, most often arising in the superficial extremities of children and young adults. While it has characteristic histologic features of nodular distributions of ovoid and spindle cells with blood-filled cystic cavities and a surrounding dense lymphoplasmacytic infiltrate, there is a significant morphologic spectrum, which coupled with its rarity and lack of specific immunoprofile can make diagnosis challenging. Angiomatoid fibrous histiocytoma is associated with 3 characteristic gene fusions, EWSR1-CREB1 and EWSR1-ATF1, which are also described in other neoplasms, and rarely FUS-ATF1. Angiomatoid fibrous histiocytoma is now recognized at an increasing number of sites and is known to display a variety of unusual histologic features.

OBJECTIVE

To review the current status of AFH, discussing putative etiology, histopathology with variant morphology and differential diagnosis, and current genetics, including overlap with other tumors harboring EWSR1-CREB1 and EWSR1-ATF1 fusions.

DATA SOURCES

Review of published literature, including case series, case reports, and review articles, in online medical databases.

CONCLUSIONS

The occurrence of AFH at several unusual anatomic sites and its spectrum of morphologic patterns can result in significant diagnostic difficulty, and correct diagnosis is particularly important because of its small risk of metastasis and death. This highlights the importance of diagnostic recognition, ancillary molecular genetic confirmation, and close clinical follow-up of patients with AFH. Further insight into the genetic and epigenetic changes arising secondary to the characteristic gene fusions of AFH will be integral to understanding its tumorigenic mechanisms.

Characterization of metastatic angiomatoid fibrous histiocytoma

Angiomatoid fibrous histiocytoma (AFH) is a soft-tissue tumor of low-grade malignancy and uncommon metastatic behavior. In this study, we describe the clinical findings of a metastatic case of AFH in the pelvis. In addition, we characterize 16 patients in the literature with AFH who metastasized over the last 4 decades. The time of appearance of metastases varied substantially and was reported 5 months to 16 years after primary tumor resection. Nine patients metastasized to lymph nodes. Excision of metastatic lymph nodes was usually curative. Pulmonary metastases were associated with fatal outcome. Long-term monitoring should be considered in patients with AFH.

Angiomatoid fibrous histiocytoma - case series with emphasis on a late fibrotic variant

BACKGROUND

Angiomatoid fibrous histiocytoma (AFH) is a rare, low-grade malignant, subcutaneous neoplasm in children or young adults.

METHODS

AFHs in different disease stages were studied histologically, in part, also immunohistologically, and by fluorescence in situ hybridization.

RESULTS

Depending on the degree of fibrosclerosis, nine AFH were divided into the following categories: classic type (n = 3): well-defined subcutaneous lesions composed of multinodular spindle to epithelioid (histiocytoid) cells surrounding a pseudoangiomatous space filled with blood. Peripherally, there is a fibrous pseudocapsule and an inflammatory infiltrate. Early sclerotic type (n = 4): the fibrous capsule extends more to the inner circle of the lesion, focally replacing the cellular neoplastic component and pseudoangiomatous spaces. Late sclerotic type (n = 2): the architecture of AFH with its zonal arrangement of an outer fibrous and inner cellular component is largely replaced by fibrosis occluding the pseudovascular space in the center of the lesion. Immunohistochemistry was available in 5/9 cases with positivity for EMA (5/5), desmin (3/5), caldesmon (1/2), and CD99 (2/5). One of two cases tested displayed EWSR1 rearrangement.

CONCLUSION

Late-stage AFH may present with marked fibrosis obscuring the real nature of the lesion and may easily be misinterpreted by the unwary as a harmless fibrotic condition.

Recurrent painful perianal subcutaneous angiomatoid fibrous histiocytoma: a case report and review of the literature

Angiomatoid fibrous histiocytoma (AFH) is a rare, low-grade malignant soft-tissue tumor most commonly occurring in the extremities of children and young adults and has a low potential of local recurrence and metastasis. Here, we present a case of recurrent subcutaneous perianal AFH. After an initial diagnosis as a sebaceous cyst, we were able to use immunohistochemical findings to correctly identify the mass as an AFH. The patient was effectively treated after 3 surgical resections. This case emphasizes the need to correctly diagnose soft-tissue tumors using a variety of diagnostic modalities to ensure that the patient receives proper treatment.