EWSR1/FUS-CREB fusions define a distinctive malignant epithelioid neoplasm with predilection for mesothelial-lined cavities

Malignant Epithelioid Mesenchymal Neoplasm with FUS::CREM Gene Fusion Arising in the Tongue: A Case Report Detailing Clinicopathological, Imaging, and Molecular Features

FUS::CREM fusion is a distinct primary driver in rare neoplasms of the head and neck and other anatomic sites. Herein, we describe the clinicopathological, imaging, and molecular features of a malignant epithelioid mesenchymal neoplasm harboring FUS::CREM fusion, arising in the tongue of a 46-year-old male. Clinically, the patient presented with a left upper neck mass. Imaging revealed a 4.0 cm mass at the left base of tongue. Histologically, the tumor consisted of sheets of loosely cohesive, small round to ovoid cells with moderate cytoplasm, small nuclei with coarse chromatin, frequent nuclear pseudoinclusions, and dense peripheral lymphoplasmacytic and histiocytic infiltrates. Malignant features, including tumor necrosis, perineural invasion, and increased mitotic activity were observed; however, lymphovascular invasion was absent with no evidence metastatic disease in the examined lymph nodes. A comprehensive panel of immunohistochemical stains showed positivity for synaptophysin and ALK, with negative results for all other markers. RNA-based next-generation sequencing using anchored multiplex polymerase chain reaction (PCR) was performed and detected FUS::CREM fusion gene. The patient was treated by excision and postsurgical chemoradiation with no evidence of recurrence after four months. Additional cases supported by comprehensive clinical data collected over an extended period are necessary to precisely characterize epithelioid mesenchymal neoplasms harboring FUS::CREM fusion in the head and neck.

Update on gene fusions and the emerging clinicopathological landscape of peritoneal and pleural mesotheliomas and other neoplasms

BACKGROUND

Mesothelioma is a rare and aggressive malignant neoplasm arising from mesothelial cells, which occasionally manifests recurrent fusions. EWSR1/FUS-CREB, YY1, MAP3K8, NR4A3, and ALK-rearranged proliferations have been reported in limited series with no clear histological or clinical correlations, limiting clinicians' ability to assess prognosis and integrate these new entities into therapeutic decisions. The aim of this study was to better characterize these rearranged proliferations histologically, molecularly, and clinically.

METHODS

Clinical, pathological, and comprehensive transcriptome and mutation data were collected for each case.

RESULTS

A total of 41 tumors were included, encompassing 7 ALK, 10 MAP3K8, 4 NR4A3, 8 ESWR1/FUS::ATF1, 8 EWSR1::YY1, and 4 SUFU-fused cases. We found a female predominance, except for cases harboring NR4A3 and SUFU; and most patients were around 60 years of age, but those harboring ALK or EWSR1/FUS::ATF1 gene fusions were younger. Each group exhibited distinct histological, immunohistochemical, molecular features, and oncological courses. Specifically, MAP3K8 and ALK presented PAX8+ papillary proliferations, ESWR1/FUS::ATF1 and EWSR1::YY1 displayed angiomatoid fibrous histiocytoma-like patterns, while SUFU showcased 'tissue culture'-like spindle cell proliferation. Poor prognosis factors were the pleural site, male sex, Ki67 ≥10%, and ESWR1/FUS::ATF1 or SUFU gene fusions.

CONCLUSIONS

This study significantly broadens the spectrum of mesothelial tumors associated with fusions, offering insight into novel epithelioid (mesothelial) proliferations with distinctive histological appearances, molecular profiles, and prognoses to guide adapted treatments for patients.

EWSR1::ATF1 fusions characterize a group of extra-abdominal epithelioid and round cell mesenchymal neoplasms, phenotypically overlapping with sclerosing epithelioid fibrosarcomas, and intra-abdominal FET::CREB fusion neoplasms

With the increasing use of next generation sequencing in soft tissue pathology, particularly in neoplasms not fitting any World Health Organization (WHO) category, the spectrum of EWSR1 fusion-associated soft tissue neoplasms has been expanding significantly. Although recurrent EWSR1::ATF1 fusions were initially limited to a triad of mesenchymal neoplasms including clear cell sarcoma of soft tissue, angiomatoid fibrous histiocytoma and malignant gastrointestinal neuroectodermal tumor (MGNET), this family has been expanding. We herein describe 4 unclassified extra-abdominal soft tissue (n = 3) and bone (n = 1) neoplasms displaying epithelioid and round cell morphology and carrying an EWSR1::ATF1 fusion. Affected were 3 males and 1 female aged 20-56 years. All primary tumors were extra-abdominal and deep-seated (chest wall, mediastinum, deltoid, and parapharyngeal soft tissue). Their size ranged 4.4-7.5 cm (median, 6.2). One patient presented with constitutional symptoms. Surgery with (2) or without (1) neo/adjuvant therapy was the treatment. At last follow-up (8-21 months), 2 patients developed progressive disease (1 recurrence; 1 distant metastasis). The immunophenotype of these tumors is potentially misleading with variable expression of EMA (2 of 3), pankeratin (2 of 4), synaptophysin (2 of 3), MUC4 (1 of 3), and ALK (1 of 3). All tumors were negative for S100 and SOX10. These observations point to the existence of heretofore under-recognized group of epithelioid and round cell neoplasms of soft tissue and bone, driven by EWSR1::ATF1 fusions, but distinct from established EWSR1::ATF1-associated soft tissue entities. Their overall morphology and immunophenotype recapitulate that of the emerging EWSR1/FUS::CREB fusion associated intra-abdominal epithelioid/round cell neoplasms. Our cases point to a potentially aggressive clinical behavior. Recognizing this tumor type is mandatory to delineate any inherent biological and/or therapeutic distinctness from other, better-known sarcomas in the differential diagnosis including sclerosing epithelioid fibrosarcoma.

Epigenetic determinants of fusion-driven sarcomas: paradigms and challenges

We describe exciting recent advances in fusion-driven sarcoma etiology, from an epigenetics perspective. By exploring the current state of the field, we identify and describe the central mechanisms that determine sarcomagenesis. Further, we discuss seminal studies in translational genomics, which enabled epigenetic characterization of fusion-driven sarcomas. Important context for epigenetic mechanisms include, but are not limited to, cell cycle and metabolism, core regulatory circuitry, 3-dimensional chromatin architectural dysregulation, integration with ATP-dependent chromatin remodeling, and translational animal modeling. Paradoxically, while the genetic requirements for oncogenic transformation are highly specific for the fusion partners, the epigenetic mechanisms we as a community have uncovered are categorically very broad. This dichotomy prompts the question of whether the investigation of rare disease epigenomics should prioritize studying individual cell populations, thereby examining whether the mechanisms of chromatin dysregulation are specific to a particular tumor. We review recent advances focusing on rhabdomyosarcoma, synovial sarcoma, alveolar soft part sarcoma, clear cell sarcoma, undifferentiated round cell sarcoma, Ewing sarcoma, myxoid/round liposarcoma, epithelioid hemangioendothelioma and desmoplastic round cell tumor. The growing number of groundbreaking discoveries in the field, motivated us to anticipate further exciting advances in the area of mechanistic epigenomics and direct targeting of fusion transcription factors in the years ahead.

Metastatic Testicular Sex Cord Tumor Harboring a EWSR1::ATF1 Gene Fusion-A Case Report of a Novel Neoplasm: "Inflammatory and Nested Testicular Sex Cord Tumor"

We present a case report of a 54-year-old male with a metastatic testicular sex cord tumor harboring a EWSR1::ATF1 gene fusion. The tumor displayed a solid and nested architecture with sclerotic stroma and variable inflammatory infiltrate, and was positive for SF-1, inhibin, EMA, CD30, and WT1 expression. Further genetic analysis identified a EWSR1::ATF1 gene fusion. Overall findings were consistent with an "inflammatory and nested testicular sex cord tumor," a recently described testicular neoplasm characterized by EWSR1::ATF1 gene fusion and aggressive clinical behavior. Due to the aggressive nature of this entity and the limited response to current treatment options available, identification of potential biomarkers for early diagnosis and targeted therapies are critical. This case report provides important insights into the genomic landscape of testicular sex cord-stromal tumors, especially within the CTNNB1-negative subset of patients with an aggressive clinical course, and further supports the distinction of "inflammatory and nested testicular sex cord tumor" as a separate entity from Sertoli cell tumors due to its characteristic morphological, immunohistochemical and molecular, features and clinical behavior.

Intra-Abdominal Epithelioid Neoplasm With EWSR1::CREB Fusions Involving the Kidney: A Clinicopathologic and Molecular Characterization With an Emphasis on Differential Diagnosis

Soft tissue neoplasms, harboring fusions between EWSR1 and FUS with genes encoding CREB transcription factors family (ATF1, CREB1, and CREM), are an emerging heterogeneous group of mesenchymal tumors that differ significantly in morphology, immunophenotypes, and behavior. Recently, EWSR1/FUS::CREB fusions have been recognized to define a group of aggressive neoplasms of epithelioid morphology with multiple growth patterns and a striking predilection for mesothelial-lined cavities. These neoplasms presenting as a primary neoplasm of intra-abdominal visceral organs are rare, which could elicit a wide range of differential diagnoses because of their diverse morphologies and immunohistochemical profiles. We report 3 cases of intra-abdominal epithelioid neoplasms with EWSR1::CREB fusions involving the kidney. This study included 2 female patients and 1 male patient, with age at presentation ranging from 17 to 61 years (mean: 32 years). All the patients underwent radical nephrectomy without adjunctive therapies. Grossly, the tumors were large, and all were solitary masses with sizes ranging from 5.6 to 30.0 cm (mean: 14.5 cm). Histologically, the neoplasms showed infiltrating and indistinct borders and were composed predominantly of monomorphic round-to-epithelioid cells with variable amounts of pale-to-clear cytoplasm, arranged in cords, nests, and sheets and embedded in a sclerotic hyalinized stroma with variable lymphoid cuffing either intermixed or at the periphery. Notably, a hemangiopericytomatous growth pattern was commonly seen. Nuclear atypia was mild, and mitotic activity was scarce. Immunohistochemically, all 3 cases were at least focally positive for epithelial membrane antigen and keratin AE1/AE3, with 2 tumors showing focal MUC4 expression and 1 case displaying diffuse CD34 and focal CAIX positivity. Targeted RNA sequencing identified EWSR1::CREM fusion in 2 cases and EWSR1::ATF1 fusion in 1 case. Subsequent fluorescence in situ hybridization analysis confirmed the RNA sequencing results. On follow-up, 1 patient developed multiple spinal bone metastases 5 months after the surgery while the other 2 patients were free of disease 9 and 120 months after diagnosis, respectively. Our findings demonstrate that intra-abdominal epithelioid neoplasms with EWSR1::CREB fusions may rarely occur primarily in the kidney and should be included in the differential diagnosis of primary renal epithelioid mesenchymal neoplasms.

Back to the future! Selected bone and soft tissue neoplasms with shared genetic alterations but differing morphological and immunohistochemical phenotypes

Bone and soft tissue tumors (BST) are a highly heterogeneous group largely classified by their line of differentiation, based on their resemblance to their normal counterpart in adult tissue. Yet, rendering a specific diagnosis can be challenging, primarily due to their rarity and overlapping histopathologic features or clinical presentations. Over the past few decades, seemingly histogenetic-specific gene fusions/translocations and amplifications have been discovered, aiding in a more nuanced classification, leading to well-established objective diagnostic criteria and the development of specific surrogate ancillary tests targeting these genetic aberrations (e.g., immunohistochemistry). Ironically, the same research also has revealed that some specific tumor subtypes may be the result of differing and often multiple gene fusions/translocations, but, more interestingly, identical gene fusions may be present in more than one phenotypically and biologically distinct neoplasm, sometimes with entirely different clinical behavior. Prime examples include, EWSR1::ATF1 and, less commonly, EWSR1::CREB1 gene fusions present in both clear cell sarcoma, a malignant high-grade tumor with melanocytic differentiation, and angiomatoid fibrous histiocytoma, a mesenchymal neoplasm of intermediate malignancy with a generally indolent course. Similarly, MDM2 amplification, once deemed to be pathognomonic for atypical lipomatous tumor/well differentiated and dedifferentiated liposarcoma, has been documented in a range of additional distinct tumors, including low grade osteosarcomas (e.g. low grade central and surface parosteal) and high-grade intimal sarcomas, amongst others. Such findings reinforce the importance of careful attention to morphological and clinicoradiological features and correlation with molecular testing before rendering a specific diagnosis. Future classification systems in BST neoplasms cannot be solely based on molecular events and ideally will balance morphologic features with molecular analysis. Herein, we provide a narrative literature review of the more common BST neoplasms with shared genetic events but differing demographics, morphology, immunophenotype, and clinical behavior, re-emphasizing the importance of the hematoxylin and eosin slide and the "eye" of the practicing pathologist.

Molecular and Immunohistochemical Testing in Mesothelioma and Other Mesothelial Lesions

CONTEXT.—

Molecular testing has increasingly been utilized in the evaluation of mesothelioma. Diffuse mesothelioma comprises multiple distinct genetic subgroups. While most diffuse mesotheliomas lack oncogenic kinase mutations and instead harbor alterations involving tumor suppressors and chromatin regulators, a minor subset of tumors is characterized by uncommon alterations such as germline mutations, genomic near-haploidization, ALK rearrangement, ATF1 rearrangement, or EWSR1::YY1 fusion.

OBJECTIVE.—

To provide updates on the salient molecular features of diffuse mesothelioma, mesothelioma in situ, and other mesothelial lesions: well-differentiated papillary mesothelial tumor, adenomatoid tumor, peritoneal inclusion cyst, and others. We consider the diagnostic, prognostic, and predictive utility of molecular testing in mesothelial lesions.

DATA SOURCES.—

We performed a literature review of recently described genetic features, molecular approaches, and immunohistochemical tools, including BAP1, MTAP, and merlin in mesothelioma and other mesothelial lesions.

CONCLUSIONS.—

Our evolving understanding of the molecular diversity of diffuse mesothelioma and other mesothelial lesions has led to considerable changes in pathology diagnostic practice, including the application of immunohistochemical markers such as BAP1, MTAP, and merlin (NF2), which are surrogates of mutation status. In young patients and/or those without significant asbestos exposure, unusual mesothelioma genetics such as germline mutations, ALK rearrangement, and ATF1 rearrangement should be considered.

Elucidating the Diagnostic Complexity of Round Cell Sarcoma with EWSR1-CREM Fusion: A Comprehensive Case Study

Sarcomas, particularly undifferentiated small round cell sarcomas of bone and soft tissue, pose significant diagnostic challenges due to their nonspecific morphology and the necessity for comprehensive molecular analyses. This paper discusses a rare case of round cell sarcoma exhibiting the EWSR1-CREM fusion, offering insights into the complexities of its diagnosis and management. The patient, a 15-year-old female with a history of Type 1 diabetes, presented with persistent right thigh tenderness and swelling. MRI revealed a large necrotic mass in the retroperitoneal region. Histological analysis showed a well-demarcated tumor with diverse cellular morphologies and distinct necrotic areas. Immunohistochemical (IHC) tests identified dot-like staining for Desmin and Vimentin but negative results for several markers, including Cytokeratin and CD45. Strong ALK positivity was noted. Next-generation sequencing with the Illumina TruSight™ Oncology 500 assay revealed the fusion gene EWSR1-CREM, along with benign and uncertain mutations in other genes. The tumor's morphology and immunoprofile, along with molecular findings, led to a diagnosis of round cell sarcoma with EWSR1-CREM fusion. This case adds to the spectrum of tumors associated with this fusion, often presenting diverse morphologies. The rarity of EWSR1-CREM fusion sarcomas poses a challenge in treatment, highlighted by the development of pulmonary metastases and disease progression after surgical excision in this patient despite the lack of an effective targeted therapy. In conclusion, this case emphasizes the need for a multidisciplinary diagnostic approach in complex sarcomas and highlights the importance of continued research on rare sarcomas, their genetic underpinnings, and potential therapeutic targets.

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.

NR1D1-rearranged soft tissue tumour: A clinicopathological and molecular analysis of four additional cases

AIMS

Nuclear receptor subfamily 1 group D member 1 (NR1D1)-rearranged soft tissue tumour is a newly described entity with an epithelioid morphology and a potential for aggressive behaviour. Largely due to under-recognition, this tumour type has not yet been widely acknowledged. Herein, we report four additional cases to further expand its clinicopathological and molecular spectrum.

METHODS AND RESULTS

Four mesenchymal tumours with NR1D1 rearrangement were identified from our consultation files. There were one male and three females with ages ranging from 19 to 47 years (median = 28.5 years). Tumour occurred in the tongue, neck, hip and index finger, respectively. Histologically, two tumours were composed predominantly of epithelioid cells; one tumour had admixed epithelioid-spindle cells and one tumour consisted of monomorphic small round to ovoid cells. By immunohistochemistry, none of the tumours expressed lineage-specific markers. Targeted RNA-sequencing identified NR1D1 fusions in all four tumours, the partner genes being MAML2, MAML3, KMT2A and NCOA2, respectively. The novel MAML3 and NCOA2 rearrangements were confirmed by fluorescence in-situ hybridisation analysis. On follow-up (2-23 months), one patient experienced local recurrence due to incomplete resection and one patient developed lung metastasis. The other two patients were alive without disease.

CONCLUSIONS

This study adds more support for NR1D1-rearranged soft tissue tumour as an emerging entity. The occurrence of two additional tumours in the head and neck region, description of a small round cell variant and identification of novel MAML3, KMT2A and NCOA2 partners further expand its clinicopathological and molecular spectrum. More studies on larger series are necessary to validate the fully malignant potential of NR1D1-rearranged soft tissue tumour.

Complementary value of molecular analysis to expert review in refining classification of uncommon soft tissue tumors

The classification of many soft tissue tumors remains subjective due their rarity, significant overlap in microscopic features and often a non-specific immunohistochemical (IHC) profile. The application of molecular genetic tools, which leverage the underlying molecular pathogenesis of these neoplasms, have considerably improved the diagnostic abilities of pathologists and refined classification based on objective molecular markers. In this study, we describe the results of an international collaboration conducted over a 3-year period, assessing the added diagnostic value of applying molecular genetics to sarcoma expert pathologic review in a selected series of 84 uncommon, mostly unclassifiable mesenchymal tumors, 74 of which originated in soft tissues and 10 in bone. The case mix (71% historical, 29% contemporary) included mostly unusual and challenging soft tissue tumors, which remained unclassified even with the benefit of expert review and routine ancillary methods, including broad IHC panels and a limited number of commercially available fluorescence in situ hybridization (FISH) probes. All cases were further tested by FISH using a wide range of custom bacterial artificial chromosome probes covering most of known fusions in sarcomas, whereas targeted RNA sequencing was performed in 13 cases negative by FISH, for potential discovery of novel fusion genes. Tumor-defining molecular alterations were found in 48/84 tumors (57%). In 27 (32%) cases the tumor diagnosis was refined or revised by the additional molecular work-up, including five cases (6%), in which the updated diagnosis had clinical implications. Sarcoma classification is rapidly evolving due to an increased molecular characterization of these neoplasms, so unsurprisingly 17% of the tumors in this series harbored abnormalities only very recently described as defining novel molecularly defined soft tissue tumor subsets.

New developments in mesothelial pathology

This review article examines some new and some problem areas in mesothelial pathology, four of which are discussed, as follows. (1) The concept of mesothelioma in situ: this lesion is defined as a single layer of bland mesothelial cells without evidence of invasion, but that have lost BAP1 and/or MTAP by immunohistochemistry. Benign reactions can exactly mimic mesothelioma in situ, but a hint to the correct diagnosis is a story of recurrent pleural effusions/ascites of unknown aetiology without radiological or direct visual evidence of tumour. (2) The nature of well-differentiated papillary mesothelial tumour (WDPMT): WDPMT has a long history of arguments regarding its behaviour, and this uncertainty can now be seen to arise, in part, from the observation that some forms of mesothelioma in situ microscopically look exactly like WDPMT. Hence, it is recommended to always run at least a BAP1 stain on any lesion that looks like WDPMT. Both flat and WDPMT-like mesothelioma in situ are strongly associated with eventual development of invasive mesothelioma, but this process is relatively slow. (3) New immunostains for separating mesothelioma from other tumours: here, it is proposed that in most cases, and particularly when the differential is epithelioid mesothelioma versus non-small cell lung cancer, one can make this separation with extremely high sensitivity and specificity using just two stains: HEG1 and claudin-4. (4) Markers for separating benign from malignant mesothelial proliferations: this topic is briefly reviewed, with an indication of which markers are generally accepted and the best utilisation and possible limitations of each marker.

Expanding the Spectrum of EWSR1::CREM Fusion Tumors: An Unusual Pediatric Intranasal Myxoid Tumor

EWSR1::CREM gene fusions are increasingly being recognized in a diverse number of soft tissue tumors, including well-defined entities such as angiomatoid fibrous histiocytoma or clear cell sarcoma, and other unclassifiable tumors. As a group, EWSR1::CREM fused tumors often demonstrate primitive spindle or epithelioid cells, myxoid stroma, and a broad immunophenotype. Herein we present an unusual case of a child diagnosed with an intranasal malignant myxoid tumor harboring an EWSR1::CREM gene fusion. To the best of our knowledge, this is the first case of intranasal myxoid tumor with this particular fusion. Diagnosis and management of the case is discussed.

Ovarian epithelioid malignant peripheral nerve sheath tumor with EWSR1-CREM fusion: A case report and literature review

Epithelioid malignant peripheral nerve sheath tumor (EMPNST) is a rare soft tissue sarcoma. The authors report the first case of EMPNST arising in the ovary (OEMPNST). A 7-year-old child underwent left salpingo-oophorectomy due to tumor rupture and the pathology suggested a juvenile granulosa cell tumor (JGCT). Six cycles of bleomycin, etoposide, and carboplatin were administrated. A second surgery was applied due to relapse 4 months after the last cycle of chemotherapy, and the pathology revealed JGCT with extensive abdominopelvic seedings even after interinstitutional consultation in two hospitals. Next-generation sequencing demonstrated EWSR1 exon12-CREM exon6 fusion with neurofibromatosis-2 gene deletion, and no mutation was detected in either FOXL2 or DICER1. However, pathology consultation in two other hospitals suggested the diagnosis of OEMPNST, and additional immunohistochemical (IHC) staining revealed positive H3K27me3. Nonetheless, she was treated with nine courses of chemotherapy but experienced a second recurrence of extensive abdominal metastases approximately 3 months after ceasing chemotherapy. Neither elevated tumor makers nor abnormal sex hormones level was noted since the initial presentation. Repeated cytoreductive surgery was conducted and IHC staining showed expression of SOX10, S-100, INI-1, and α-inhibin in tumor tissue. A final diagnosis of OEMPNST with EWSR1-CREM fusion was established, indicating that the probability of OEMPNST could not be excluded when treatment for JGCT showed poor response. A comprehensive evaluation including biological characteristics, morphology, IHC staining, and molecular features is vital in the differential diagnosis between JGCT and OEMPNST.

Hyalinising clear cell carcinoma with a novel fusion gene: Insights into the diagnosis

Hyalinising clear cell carcinoma (HCCC) is a rare salivary gland neoplasm characterised by an EWSR1::ATF1 fusion. Rare cases showing EWSR1::CREB1 rearrangements have been reported. This article presents a case of HCCC with a novel EWSR1-CREB1 fusion, diffuse eosinophilic appearance, novel cytomorphological findings, PAS-negativity, and late regional and distant lymph node metastases.

Case report: The activity of multi-kinase VEGF inhibitor, Pazopanib, in metastatic undifferentiated round cell sarcomas harboring EWSR1::CREM fusion: clinicopathological series of two cases and literature review

Soft tissue sarcomas harboring EWSR1::CREM fusion are rare and challenging to treat. Pazopanib, a multi-tyrosine kinase inhibitor, is FDA-approved for advanced soft tissue sarcomas, but predictive biomarkers for its efficacy remain unidentified. We conducted a study on > 240,000 neoplasms submitted to Caris Life Sciences (Phoenix, AZ) to detect rearrangements using whole transcriptome sequencing. Two sarcoma-experienced, board-certified pathologists performed histological reviews, and treatment/outcome information was collected. Among the identified cases (n = 18), we observed a diverse range of sarcoma and other cancers, including an intracranial myxoid mesenchymal tumor, mesothelioma, hyalinizing clear cell carcinomas of the head and neck, clear cell sarcomas, and undifferentiated round cell sarcomas, as well as histologically malignant tumors with epithelioid morphology. Notably, two undifferentiated, metastatic, abdominal round cell sarcoma cases treated with pazopanib demonstrated significant sustained partial response and clinical benefit. To explore the genetic factors associated with the efficacy of pazopanib in these cases, next-generation sequencing and fluorescence in situ hybridization were analyzed for alterations in the tumors. The genomic analysis provided compelling evidence confirming the presence of EWSR1::CREM fusion in both cases, with no other pathogenic gene variants or copy number alterations detected. These cases demonstrate the potential of Pazopanib as a promising therapeutic option for patients with EWSR1::CREM fusion-positive soft tissue sarcomas, including metastatic undifferentiated round cell sarcomas. The sustained clinical benefit and partial responses observed in these cases warrant further research to validate these findings and explore the wider utility of Pazopanib in this rare and challenging subset of soft tissue sarcomas. Case studies: Case 1: A 49-year-old man presented with abdominal pain, weight loss, and chronic cough. A computed tomography (CT) of the chest, abdomen, and pelvis showed multiple lung nodules and masses and a right rectus mass that was biopsied and revealed an undifferentiated round cell sarcoma with a rare fusion EWSR1-CREM. No additional pathogenic gene variants or copy number alterations were detected. He received neoadjuvant chemotherapy with three cycles of Vincristine, Adriamycin, and Ifosfamide (VAI) and seven cycles of Vincristine/Irinotecan and Temodar (VIT). After cycle 7 of VIT, he had surgical resection of the abdominal mass and received radiation for lung metastasis. He completed 13 cycles of VIT after which he presented with progression of disease and switched to monotherapy with Pazopanib. At the time of this analysis he had stable disease for 28 months. Case 2: A 75-year-old woman presented with pelvic pain and new onset constipation. CT abdomen showed a large pelvic mass and intraperitoneal tumor spread. Exploratory laparotomy revealed a ruptured pelvic mass and a small bowel tumor. Both tumors were proved to be high-grade, poorly differentiated sarcoma. Genomic analysis demonstrated an EWSR1::CREM fusion but no other pathogenic gene variants or copy number alterations. She was treated initially for a primitive neuroectodermal tumor (PNET) with four cycles of Vincristine/Adriamycin/Cytoxan/Olaratumab but declined additional chemotherapy after progression. Two years later, she presented with recurrent abdominal mass and received one cycle of Temodar/Irinotecan, then she began Pozapanib and underwent palliative radiation to the entire pelvis. She has been on Pazopanib for 23 months with stable disease.

Mesotheliomas in Children

Mesotheliomas are rare and aggressive tumors that originate from mesothelial cells. Although exceedingly rare, these tumors may occur in children. Different from adult mesotheliomas, however, environmental exposures particularly to asbestos do not appear to play a major role in mesotheliomas in children, in whom specific genetic rearrangements driving these tumors have been identified in recent years. These molecular alterations may increasingly offer opportunities for targeted therapies in the future, which may provide better outcomes for these highly aggressive malignant neoplasms.

NR4A3 fusions characterize a distinctive peritoneal mesothelial neoplasm of uncertain biological potential with pure adenomatoid/microcystic morphology

A focal adenomatoid-microcystic pattern is not uncommon in peritoneal mesothelioma, but tumors composed almost exclusively of this pattern are distinctly rare and have not been well characterized. A small subset of mesotheliomas (mostly in children and young adults) are characterized by gene fusions including EWSR1/FUS::ATF1, EWSR1::YY1, and NTRK and ALK rearrangements, and often have epithelioid morphology. Herein, we describe five peritoneal mesothelial neoplasms (identified via molecular screening of seven histologically similar tumors) that are pure adenomatoid/microcystic in morphology and unified by the presence of an NR4A3 fusion. Patients were three males and two females aged 31-70 years (median, 40 years). Three presented with multifocal/diffuse and two with a localized disease. The size of the individual lesions ranged from 1.5 to 8 cm (median, 4.7). The unifocal lesions originated in the small bowel mesentery and the mesosigmoid. Treatment included surgery, either alone (three) or combined with hyperthermic intraperitoneal chemotherapy (two), and neoadjuvant or adjuvant chemotherapy (one case each). At the last follow-up (6-13 months), all five patients were alive and disease-free. All tumors were morphologically similar, characterized by extensive sieve-like microcystic growth with bland-looking flattened cells lining variably sized microcystic spaces and lacked a conventional epithelioid or sarcomatoid component. Immunohistochemistry confirmed mesothelial differentiation, but most cases showed limited expression of D2-40 and calretinin. Targeted RNA sequencing revealed an NR4A3 fusion (fusion partners were EWSR1 in three cases and CITED2 and NIPBL in one case each). The nosology and behavior of this morphomolecularly defined novel peritoneal mesothelial neoplasm of uncertain biological potential and its distinction from adenomatoid variants of conventional mesothelioma merit further delineation as more cases become recognized.

CREB fusion-associated epithelioid mesenchymal neoplasms of the female adnexa: three cases documenting a novel location of an emerging entity and further highlighting an ambiguous misleading immunophenotype

EWSR1/FUS-CREB-rearranged mesenchymal neoplasms are an emerging heterogeneous group of soft tissue tumors that encompasses low-grade lesions (angiomatoid fibrous histiocytoma/AFH) and a group of predominantly intra-abdominal aggressive sarcomas with epithelioid morphology and frequent keratin expression. Both entities occasionally harbor EWSR1::ATF1 fusions as alternate to the more frequent EWSR1/FUS::CREB1/CREM fusions. Although EWSR1/FUS-CREB-rearranged epithelioid malignant neoplasms have been described in diverse intra-abdominal sites, none involved the female adnexa. Herein, we describe three cases involving uterine adnexa in young females (41, 39, and 42-year-old); two associated with constitutional inflammatory symptoms. The tumors presented as a serosal surface mass of the ovary without parenchymal involvement (Case 1), as circumscribed nodule within ovarian parenchyma (Case 2), and as a periadnexal mass extending into the lateral uterine wall with lymph node metastasis (Case 3). They were composed of sheets and nests of large epithelioid cells with numerous stromal lymphocytes and plasma cells. The neoplastic cells expressed desmin and EMA, and variably WT1. One tumor expressed in addition AE1/AE3, MUC4, synaptophysin, chromogranin, and ALK. None expressed sex cord-associated markers. RNA sequencing identified EWSR1::ATF1 fusions in two cases and an EWSR1::CREM fusion in one. Exome-based RNA capture sequencing and clustering methods showed high transcriptomic proximity of tumor 1 with soft tissue AFH. This novel subset of female adnexal neoplasms should be included in the differential diagnosis of any epithelioid neoplasm involving female adnexa. Their aberrant immunophenotype can be misleading, underlining a wide spectrum of differential diagnosis.

Gene fusions in superficial mesenchymal neoplasms: Emerging entities and useful diagnostic adjuncts

Cutaneous mesenchymal neoplasms are diagnostically challenging because of their overlapping morphology, and, often, the limited tissue in skin biopsy specimens. Molecular and cytogenetic techniques have identified characteristic gene fusions in many of these tumor types, findings that have expanded our understanding of disease pathogenesis and motivated development of useful ancillary diagnostic tools. Here, we provide an update of new findings in tumor types that can occur in the skin and superficial subcutis, including dermatofibrosarcoma protuberans, benign fibrous histiocytoma, epithelioid fibrous histiocytoma, angiomatoid fibrous histiocytoma, glomus tumor, myopericytoma/myofibroma, non-neural granular cell tumor, CIC-rearranged sarcoma, hybrid schwannoma/perineurioma, and clear cell sarcoma. We also discuss recently described and emerging tumor types that can occur in superficial locations and that harbor gene fusions, including nested glomoid neoplasm with GLI1 alterations, clear cell tumor with melanocytic differentiation and ACTIN::MITF translocation, melanocytic tumor with CRTC1::TRIM11 fusion, EWSR1::SMAD3-rearranged fibroblastic tumor, PLAG1-rearranged fibroblastic tumor, and superficial ALK-rearranged myxoid spindle cell neoplasm. When possible, we discuss how fusion events mediate the pathogenesis of these tumor types, and we also discuss the related diagnostic and therapeutic implications of these events.

A novel SMARCA2-CREM fusion expending the molecular spectrum of salivary gland hyalinazing clear cell carcinoma beyond the FET genes

Hyalinizing clear cell carcinoma (HCCC) is a rare salivary gland carcinoma with a generally indolent behavior, characterized by recurrent chromosomal translocation involving EWSR1 (22q12.2) leading to two fusion genes EWSR1::ATF1 or EWSR1::CREM. We report one case of HCCC with a novel SMARCA2::CREM fusion, identified by targeted RNA next generation sequencing by LD-RT-PCR, which has until now never been described in salivary glands. The exon 4 of SMARCA2 is fused to exon 5 of CREM. This fusion has been described previously in only one tumor, a central nervous system tumor (intracranial mesenchymal tumor) but not in other FET::CREB fused tumors. This fusion was confirmed by CREM break-apart FISH and reverse transcriptase polymerase chain reaction (RT-PCR). The tumor cells showed retained expression of INI1, SMARCA2, and SMARCA4 by immunohistochemistry. We compare its clinical, histopathological, immunophenotypic, genetic features with those previously described in HCCC, FET::CREB fusion-positive. Our results added data suggesting that different histomolecular tumor subtypes seem to be included within the terminology "HCCC, FET::CREB fusion-positive," and that further series of cases are needed to better characterize them.

Malignant undifferentiated epithelioid neoplasms with MAML2 rearrangements: A clinicopathologic study of seven cases demonstrating a heterogenous entity

Among mesenchymal tumors, MAML2 gene rearrangements have been described in a subset of composite hemangioendothelioma and myxoinflammatory fibroblastic sarcoma (MIFS). However, we have recently encountered MAML2-related fusions in a group of seven undifferentiated malignant epithelioid neoplasms that do not fit well to any established pathologic entities. The patients included five males and two female, aged 41-71 years old (median 65 years). The tumors involved the deep soft tissue of extremities (hip, knee, arm, hand), abdominal wall, and the retroperitoneum. Microscopically, the tumors consisted of solid sheets of atypical epithelioid to histiocytoid cells with abundant cytoplasm. Prominent mitotic activity and necrosis were present in 4 cases. In 3 cases, the cells displayed hyperchromatic nuclei or conspicuous macronucleoli, and were admixed with background histiocytoid cells and a lymphoplasmacytic infiltrate. By immunohistochemistry (IHC), the neoplastic cells had a nonspecific phenotype. On targeted RNA sequencing, MAML2 was the 3' partner and fused to YAP1 (4 cases), ARHGAP42 (2 cases), and ENDOD1 (1 case). Two cases with YAP1::MAML2 harbored concurrent RAF kinase fusions (RBMS3::RAF1 and AGK::BRAF, respectively). In 2 cases with targeted DNA sequencing, mutations in TP53, RB1 and PTEN were detected in 1 case, and PDGFRB mutations, CCNE1 amplifications and CDKN2A/2B deletion were detected in another case, which showed strong and diffuse PDGFRB expression by IHC. Of the 4 cases with detailed clinical history (median follow-up period 8 months), three developed distant metastatic disease (one of which died of disease); one case remained free of disease 3 years following surgical excision. In conclusion, we describe a heterogeneous series of MAML2-rearranged undifferentiated malignant epithelioid neoplasms, a subset of which may overlap with a recently described MIFS variant with YAP1::MAML2 fusions, further expanding the clinicopathologic spectrum of mesenchymal neoplasms with recurrent MAML2 gene rearrangements.

Imaging and treatment with 68Gallium and 177Lutetium-DOTATATE in a rare SSTR2 and ESWR1-CREM fusion positive undifferentiated round cell tumour of the lung

The authors present a 45-year-old lady with a rare undifferentiated round cell tumour of the lung with a ESWR1-CREM fusion gene that progressed despite multiple lines of therapy. The tumour was Somatostatin Receptors Type 2 (SSTR2) positive and avid on ⁶⁸Gallium-DOTATATE imaging. This allowed for novel treatment with Peptide Receptor Radionuclide Therapy (PRRT) using ¹⁷⁷Lutetium-DOTATATE after all other standard of care options were exhausted.

Epithelioid mesenchymal neoplasm with FUS::CREM gene fusion in the tongue: Report of a rare and challenging diagnosis

FET (encompassing both EWSR1 and FUS) fusions with genes from the CREB family (CREB1, ATF1, and CREM) are involved in a variety of neoplasms. Recently, FET::CREB fusions were recognized in a group of malignant epithelioid neoplasm with a striking predilection to mesothelial-lined cavities and frequent cytokeratin immunoexpression. Herein, we report a rare mesenchymal neoplasm with epithelioid morphology and nonspecific immunoprofile harboring a FUS::CREM fusion arising in the oral tongue of a 53-year-old man. Histology showed a well-circumscribed tumor composed of epithelioid cells with eosinopohilic or clear cytoplasm with sparse stroma, accompanied by peripheral lymphoplasmacytic infiltrates. Immunohistochemically, an extensive panel revealed only patchy expression of synaptophysin and weak-to-moderate nuclear expression of TFE3, and negativity for other markers including cytokeratins, epithelial membrane antigen, p63/p40, vimentin, S100, smooth muscle actin, CD34, desmin, SOX10, glial fibrillary acidic protein, melan-A, HMB45, and CD68. A FUS::CREM gene fusion was detected by next generation sequencing at an outside institution, and subsequent fluorescence in situ hybridization analysis confirmed the presence of FUS gene rearrangement. The identification and analysis of additional cases should help to clarify the nosologic status and the biologic potential of this tumor.

Advances in the management of peritoneal malignancies

Peritoneal surface malignancies (PSMs) are usually associated with a poor prognosis. Nonetheless, in line with advances in the management of most abdominopelvic metastatic diseases, considerable progress has been made over the past decade. An improved understanding of disease biology has led to the more accurate prediction of neoplasia aggressiveness and the treatment response and has been reflected in the proposal of new classification systems. Achieving complete cytoreductive surgery remains the cornerstone of curative-intent treatment of PSMs. Alongside centralization in expert centres, enabling the delivery of multimodal and multidisciplinary strategies, preoperative management is a crucial step in order to select patients who are most likely to benefit from surgery. Depending on the specific PSM, the role of intraperitoneal chemotherapy and of perioperative systemic chemotherapy, in particular, in the neoadjuvant setting, is established in certain scenarios but questioned in several others, although more prospective data are required. In this Review, we describe advances in all aspects of the management of PSMs including disease biology, assessment and improvement of disease resectability, perioperative management, systemic therapy and pre-emptive management, and we speculate on future research directions.

Comprehensive genomic profiling of EWSR1/FUS::CREB translocation-associated tumors uncovers prognostically significant recurrent genetic alterations and methylation-transcriptional correlates

To elucidate the mechanisms underlying the divergent clinicopathologic spectrum of EWSR1/FUS::CREB translocation-associated tumors, we performed a comprehensive genomic analysis of fusion transcript variants, recurrent genetic alterations (mutations, copy number alterations), gene expression, and methylation profiles across a large cohort of tumor types. The distribution of the EWSR1/FUS fusion partners-ATF1, CREB1, and CREM-and exon involvement was significantly different across different tumor types. Our targeted sequencing showed that secondary genetic events are associated with tumor type rather than fusion type. Of the 39 cases that underwent targeted NGS testing, 18 (46%) had secondary OncoKB mutations or copy number alterations (29 secondary genetic events in total), of which 15 (52%) were recurrent. Secondary recurrent, but mutually exclusive, TERT promoter and CDKN2A mutations were identified only in clear cell sarcoma (CCS) and associated with worse overall survival. CDKN2A/B homozygous deletions were recurrent in angiomatoid fibrous histiocytoma (AFH) and restricted to metastatic cases. mRNA upregulation of MITF, CDH19, PARVB, and PFKP was found in CCS, compared to AFH, and correlated with a hypomethylated profile. In contrast, S100A4 and XAF1 were differentially upregulated and hypomethylated in AFH but not CCS. Unsupervised clustering of methylation profiles revealed that CREB family translocation-associated tumors form neighboring but tight, distinct clusters. A sarcoma methylation classifier was able to accurately match 100% of CCS cases to the correct methylation class; however, it was suboptimal when applied to other histologies. In conclusion, our comprehensive genomic profiling of EWSR1/FUS::CREB translocation-associated tumors uncovered mostly histotype, rather than fusion-type associated correlations in transcript variants, prognostically significant secondary genetic alterations, and gene expression and methylation patterns.

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.

Endobronchial Primary Pulmonary Angiomatoid Fibrous Histiocytoma in a Patient with Testicular Germ Cell Tumor: An Evidence Against Somatic Transformation

Primary Pulmonary Angiomatoid Fibrous Histiocytoma is a recently described soft tissue tumor with challenging differential diagnosis both clinically and pathologically due to its rarity in this location. It may also occur as a secondary malignancy and its occurrence either as a somatic malignancy arising in the germ cell tumor or as a secondary malignancy after chemotherapy is questionable. In this report, we present a 29-year-old male patient with a mass in the lower lobe of the left lung, who underwent orchiectomy and received adjuvant chemotherapy due to a mixed germ cell tumor 8 years ago. Morphology, immunophenotype, and molecular findings were consistent with the diagnosis of primary pulmonary angiomatoid fibrous histiocytoma. Fluorescent in situ hybridization was unable to demonstrate the presence of 12p amplification or isochromosome 12p, which is known as the key event in the development of testicular germ cell neoplasia even present in somatic malignancies arising in germ cell tumors. Our results support that angiomatoid fibrous histiocytoma arising as a secondary malignancy does not represent the somatic transformation of germ cell tumors.

Emerging glioneuronal and neuronal tumors: case-based review

Glioneuronal and neuronal tumors (GNTs) are rare heterogeneous central nervous system tumors characterized by slow growth and favorable outcomes, but are often associated with diagnostic difficulties. A thorough analysis of three rare and recently recognized GNTs was performed in the context of clinicopathological features and molecular genetic characterization. The current spinal diffuse leptomeningeal glioneuronal tumor (DLGNT) was characterized with oligodendroglioma-like tumor with chromosome 1p/19q codeletion without IDH mutations and KIAA1549:BRAF fusion. The current occipital multinodular and vacuolating neuronal tumor (MVNT) was characteristic of the variable-sized vague nodules consisted of gangliocytic tumor cells with intracytoplasmic and pericellular vacuolation and the next-generation sequencing (NGS) revealed MAP2K1 p.Q56_V60del. A diffuse glioneuronal tumor with oligodendroglioma-like features and nuclear clusters (DGONC) of the amygdala was characterized by oligodendroglia-like cells and nuclear clusters, and monosomy 14. From the current cases and literature review, we found that DLGNT commonly occurs in the spinal cord and can make mass and more commonly have KIAA1549:BRAF fusion; MVNT is a neoplasm rather than malformation and MAP2K1 deletion is one of the hallmarks of this tumor; although DGONC may require a methylation profile, we can reach a diagnosis through its unique histology, monosomy 14, and exclusion diagnosis without a methylation profile.

The cAMP-signaling cancers: Clinically-divergent disorders with a common central pathway

The cAMP-signaling cancers, which are defined by functionally-significant somatic mutations in one or more elements of the cAMP signaling pathway, have an unexpectedly wide range of cell origins, clinical manifestations, and potential therapeutic options. Mutations in at least 9 cAMP signaling pathway genes (TSHR, GPR101, GNAS, PDE8B, PDE11A, PRKARA1, PRKACA, PRKACB, and CREB) have been identified as driver mutations in human cancer. Although all cAMP-signaling pathway cancers are driven by mutation(s) that impinge on a single signaling pathway, the ultimate tumor phenotype reflects interactions between five critical variables: (1) the precise gene(s) that undergo mutation in each specific tumor type; (2) the effects of specific allele(s) in any given gene; (3) mutations in modifier genes (mutational "context"); (4) the tissue-specific expression of various cAMP signaling pathway elements in the tumor stem cell; and (5) and the precise biochemical regulation of the pathway components in tumor cells. These varying oncogenic mechanisms reveal novel and important targets for drug discovery. There is considerable diversity in the "druggability" of cAMP-signaling components, with some elements (GPCRs, cAMP-specific phosphodiesterases and kinases) appearing to be prime drug candidates, while other elements (transcription factors, protein-protein interactions) are currently refractory to robust drug-development efforts. Further refinement of the precise driver mutations in individual tumors will be essential for directing priorities in drug discovery efforts that target these mutations.

Intracranial mesenchymal tumors with FET-CREB fusion are composed of at least two epigenetic subgroups distinct from meningioma and extracranial sarcomas

‘Intracranial mesenchymal tumor, FET‐CREB fusion‐positive’ occurs primarily in children and young adults and has previously been termed intracranial angiomatoid fibrous histiocytoma (AFH) or intracranial myxoid mesenchymal tumor (IMMT). Here we performed genome‐wide DNA methylation array profiling of 20 primary intracranial mesenchymal tumors with FET‐CREB fusion to further study their ontology. These tumors resolved into two distinct epigenetic subgroups that were both divergent from all other analyzed intracranial neoplasms and soft tissue sarcomas, including meningioma, clear cell sarcoma of soft tissue (CCS), and AFH of extracranial soft tissue. The first subgroup (Group A, 16 tumors) clustered nearest to but independent of solitary fibrous tumor and AFH of extracranial soft tissue, whereas the second epigenetic subgroup (Group B, 4 tumors) clustered nearest to but independent of CCS and also lacked expression of melanocytic markers (HMB45, Melan A, or MITF) characteristic of CCS. Group A tumors most often occurred in adolescence or early adulthood, arose throughout the neuroaxis, and contained mostly EWSR1‐ATF1 and EWSR1‐CREB1 fusions. Group B tumors arose most often in early childhood, were located along the cerebral convexities or spinal cord, and demonstrated an enrichment for tumors with CREM as the fusion partner (either EWSR1‐CREM or FUS‐CREM). Group A tumors more often demonstrated stellate/spindle cell morphology and hemangioma‐like vasculature, whereas Group B tumors more often demonstrated round cell or epithelioid/rhabdoid morphology without hemangioma‐like vasculature, although robust comparison of these clinical and histologic features requires future study. Patients with Group B tumors had inferior progression‐free survival relative to Group A tumors (median 4.5 vs. 49 months, p = 0.001). Together, these findings confirm that intracranial AFH‐like neoplasms and IMMT represent histologic variants of a single tumor type (‘intracranial mesenchymal tumor, FET‐CREB fusion‐positive’) that is distinct from meningioma and extracranial sarcomas. Additionally, epigenomic evaluation may provide important prognostic subtyping for this unique tumor entity.

Malignant Peritoneal Mesothelioma With EWSR1-ATF1 Fusion: A Case Report

Malignant mesothelioma with EWSR1-ATF1 fusion is a rare malignancy described in young adults without asbestos exposure. To the best of our knowledge, outcomes to local and systemic therapies for this subtype of malignant mesothelioma have not been described. This case report describes the clinical course of a 19-year-old man diagnosed with malignant peritoneal mesothelioma with EWSR1-ATF1 fusion localized to the abdomen. His disease followed an aggressive course and resulted in limited survival (18 mo). There was treatment resistance to several lines of conventional local and systemic treatments for peritoneal mesothelioma and biologically targeted MET inhibition with crizotinib. More research is required in this rare subtype of peritoneal mesothelioma.

Malignant Mesothelioma With EWSR1-ATF1 Fusion in Two Adolescent Male Patients

Malignant mesothelioma is a neoplasm of serosal surfaces, most commonly affecting the pleura. The peritoneum, pericardium, and tunica vaginalis are less frequently involved. Malignant mesothelioma with EWSR1-ATF1 fusion in young adults was recently reported in the literature. Here, we present two pediatric cases of EWSR1-ATF1 translocation-associated malignant mesothelioma in the peritoneum and pericardium respectively. Both cases lacked a known exposure history. Microscopy in both cases showed predominantly epithelioid morphology with ample eosinophilic cytoplasm, and immunohistochemistry was positive for pan-keratin, calretinin, and WT1. Both cases showed EWSR1-ATF1 gene rearrangement by RNA sequencing, which was instrumental in confirming the diagnosis of malignant mesothelioma and to exclude more common pediatric sarcomas, especially in the context of limited sampling.

FUS-CREM-rearranged malignant epithelioid neoplasm mimicking neuroendocrine neoplasm of unknown primary

A 76-year-old women presented with abdominal pain. Diagnostic investigations suggested peritoneal carcinomatosis. Histological examination of laparoscopic biopsies showed large epithelioid cells forming sheets intermingled with some lymphocytes. There was no clearly distinguishable stroma. Immunohistochemistry showed diffuse and strong expression of cytokeratin AE1/AE3, synaptophysin and chromogranin-A.

Mesenchymal/non-epithelial mimickers of neuroendocrine neoplasms with a focus on fusion gene-associated and SWI/SNF-deficient tumors

Mimickers of neuroendocrine neoplasms (NEN) include a number of important pitfall tumors. Here, we describe our experience with mesenchymal mimics of NENs to illustrate their spectrum and draw the attention particularly to a group of mesenchymal/non-epithelial neoplasms (MN) that combine epithelioid histology with neuroendocrine (NE-) features and peculiar genetic abnormalities. In a consultation series of 4498 cases collected between 2009 and 2021, 2099 neoplasms expressing synaptophysin and/or chromograninA were reviewed and analyzed. A total of 364 (18%) were diagnosed as non-NENs, while the remaining tumors were NEN. The group of mesenchymal/non-epithelial neoplasms with NE-features (MN-NE) included 31/364 (8%) cases. These mostly malignant neoplasms showed an epithelioid morphology. While all but one tumor expressed synaptophysin, mostly patchy, only 10/29 (34%) co-expressed chromograninA. A total of 13/31 (42%) of the MN-NE showed EWSR1-related gene fusions (6 Ewing sarcomas, 5 clear cell sarcomas, and 1 desmoplastic small round cell tumor, 1 neoplasm with FUS-CREM gene fusion) and 7 (23%) were SWI/SNF (SMARCB1 or SMARCA4)-deficient neoplasms. The remaining MN-NE included synovial sarcoma, sclerosing epithelioid mesenchymal neoplasm, melanoma, alveolar soft part sarcoma, solitary fibrous tumor, and chordoma. A total of 27/31 MN-NE were from the last 8 years, and 6 of them were located in the pancreas. Eleven MN-NE were initially diagnosed as neuroendocrine carcinomas (NECs). MN-NE with epithelioid features play an increasing role as mimickers of NECs. They mostly belong to tumors with gene fusions involving the EWSR1 gene, or with SWI/SNF complex deficiency. Synaptophysin expression is mostly patchy and chromograninA expression is infrequent in MN-NE of this series and data extracted from literature.

Unclassified low grade spindle cell sarcoma with storiform pattern characterized by recurrent novel EWSR1/FUS-NACC1 fusions

Despite extraordinary advances in the molecular characterization of soft tissue tumors as a result of the widespread application of next generation sequencing in clinical practice, a subset of lesions remain difficult to diagnose. In this study we describe 3 unclassified spindle cell sarcomas with a monomorphic cytomorphology and distinctive storiform growth, characterized by novel fusions between EWSR1 or FUS1, and NACC1 genes. The tumors occurred in 3 young adult females (age range: 29-31) involving deep soft tissues, two located in the lower extremity and one in the abdominal wall. All three tumors showed patchy positivity for S100 protein, while being negative for SOX10 and retained H3K27me3 expression. All cases were negative for epithelial or muscle markers. As the findings were non-specific, molecular studies using targeted panels of RNA sequencing were performed, including one case tested by TruSight RNA Fusion Panel and 2 cases by Archer FusionPlex. The results showed 2 cases were positive for FUS-NACC1 and one for EWSR1-NACC1 fusions. These findings were further confirmed by FISH using custom BAC probes for a dual-color fusion assay. These results suggest the possibility of a previously undescribed soft tissue neoplasm characterized by a uniform spindle cell phenotype arranged in a storiform and fascicular pattern, expressing S100 protein and harboring NACC1-related fusions. The biologic behavior of this tumor remains to be determined.

Expression of Transcription Factor CREM in Human Tissues

Cyclic AMP element modulator (CREM) is a transcription factor best known for its intricate involvement in spermatogenesis. The CREM gene encodes for multiple protein isoforms, which can enhance or repress transcription of target genes. Recent studies have identified fusion genes, with CREM as a partner gene in many neoplastic diseases. EWSR1-CREM fusion genes have been found in several mesenchymal tumors and in salivary gland carcinoma. These genes encode fusion proteins that include the C-terminal DNA-binding domain of CREM. We used a transcriptomic approach and immunohistochemistry to study the expression of CREM isoforms that include DNA-binding domains across human tissues. We found that CREM protein is widely expressed in almost all normal human tissues. A transcriptomic analysis of normal tissues and cancer showed that transcription of CREM can be altered in tumors, suggesting that also wild-type CREM may be involved in cancer biology. The wide expression of CREM protein in normal human tissues and cancer may limit the utility of immunohistochemistry for identification of tumors with CREM fusions:

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.

Intra-abdominal EWSR1/FUS-CREM-rearranged malignant epithelioid neoplasms: two cases of an emerging aggressive entity with emphasis on misleading immunophenotype

CREB family (CREB1, ATF1, and CREM) gene fusions are defining markers in diverse mesenchymal neoplasms (clear cell sarcoma, angiomatoid fibrous histiocytoma, and others). However, neoplasms harboring EWSR1-CREM/FUS-CREM fusions are rare and poorly characterized. We describe two cases (55-year-old male with 7.5 cm renal mass and 32-year-old female with 5.5 cm mesenteric mass) illustrating their misleading immunophenotypes. Histologically, both showed eosinophilic and focally clear epithelioid cells arranged into sheets, nests, and trabeculae. Immunohistochemistry showed ALK, EMA, and AE1/AE3 immunoreactivity suggesting ALK-rearranged renal cell carcinoma (Case 1) and coexpression of keratin, EMA, synaptophysin, and chromogranin-A, suggesting neuroendocrine neoplasm (Case 2). Targeted RNA sequencing revealed EWSR1-CREM (Case 1) and FUS-CREM (Case 2) fusions. These cases add to the spectrum of CREM fusion-positive intra-abdominal epithelioid neoplasms. Their unusual immunophenotype and unexpected sites represent major pitfalls, underline a wide differential diagnosis, and emphasize the value of molecular testing in correctly diagnosing them.

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.

A novel BRD4-LEUTX fusion in a pediatric sarcoma with epithelioid morphology and diffuse S100 expression

Malignant epithelioid soft tissue tumors encompass a wide spectrum of lesions. Among them, Epithelioid Malignant Peripheral Nerve Sheath Tumors (MPNST) constitute a distinct subgroup, accounting for <5% of all MPNST. Epithelioid MPNST are infrequently associated with neurofibromatosis type 1, occasionally arise in a schwannoma and show diffuse S100 and CD34 expression, often combined with INI-1 loss. However, the molecular mechanisms underlying the tumorigenesis of epithelioid MPNST remain largely unknown. We describe a case of a 10-year-old girl with an epithelioid malignancy of the orbit. The tumor proved positive for S100, CD34 and SOX10, and, although INI-1 expression was maintained, the overall features suggested the possibility of an epithelioid MPNST, arising in an unusual location. NGS analysis revealed a novel in-frame BRD4-LEUTX fusion gene. LEUTX plays an important role in embryonal genome activation and its expression is mostly suppressed postnatally. We were able to detect increased levels of LEUTX transcript in the tumor, indicating that BRD4-LEUTX fusion leads to LEUTX re-activation. To our knowledge, this fusion has never been reported previously. Whether the current case represents an example of epithelioid MPNST or a distinct tumor entity remains to be determined.

Cytokeratin-positive Malignant Tumor in the Abdomen With EWSR1/FUS-CREB Fusion: A Clinicopathologic Study of 8 Cases

ATF1, CREB1, and CREM, which encode the CREB family of transcription factors, are fused with EWSR1 or FUS in human neoplasms, such as angiomatoid fibrous histiocytoma. EWSR1/FUS-CREB fusions have recently been reported in a group of malignant epithelioid tumors with a predilection to the peritoneal cavity and frequent cytokeratin expression. Here, we studied 8 cytokeratin-positive abdominal malignancies with these fusions for further characterization. The tumors affected males (15 to 76 y old) and presented as intra-abdominal masses with concurrent or subsequent peritoneal dissemination, ascites, and/or metastases to the liver or lymph nodes. Four patients died of the disease within 18 to 140 months. Cases 1 to 5 showed multinodular growth of monomorphic epithelioid cells with focal serous cysts. Lymphoplasmacytic infiltration was prominent and was associated with systemic inflammatory symptoms. Two patients suffered from membranous nephropathy with nephrosis. The tumors displayed partly overlapping phenotypes with malignant mesothelioma, including diffuse strong expression of AE1/AE3 and WT1 and membranous positivity of sialylated HEG1, although calretinin was negative. Case 6 showed similar histology to cases 1 to 5, but expressed smooth muscle actin diffusely, lacked WT1 and HEG1, and harbored prominent pseudoangiomatous spaces. Cases 7 and 8 displayed dense growth of small oval to short spindle cells, with occasional molding and minor swirling, superficially resembling small cell carcinoma. Lymphoplasmacytic infiltration was not observed. The tumors were positive for AE1/AE3 and CD34 (focal), whereas calretinin, WT1, and HEG1 were negative. The detected fusions were FUS-CREM (n=4), EWSR1-ATF1 (n=2), EWSR1-CREB1 (n=1), and EWSR1-CREM (n=1). We confirmed the prior observation that these tumors do not fit perfectly with known entities and provided additional novel clinicopathologic information. The tumors require wider recognition because of more aggressive behavior than angiomatoid fibrous histiocytoma despite similar genetics, and potential misdiagnosis as unrelated diseases, such as neuroendocrine neoplasms.