Expanding the Spectrum of Intraosseous Rhabdomyosarcoma: Correlation Between 2 Distinct Gene Fusions and Phenotype

Rhabdomyosarcoma With FUS::TFCP2 Fusion in the Mandible: A Rare Aggressive Subtype, but Can Be Misdiagnosed as Ossifying Fibroma

Rhabdomyosarcoma (RMS) with TFCP2 rearrangement has been identified recently. This entity has a distinctive clinicopathologic features: a rapidly aggressive clinical course, a preference for the craniofacial bones, a spindle and epithelioid histomorphology, and positive immunohistochemistry for epithelial markers, ALK, and myogenic markers. RMS with TFCP2 rearrangement is rare and may be misdiagnosed as other spindle cell tumors. Here, we report a case of this entity arising in the mandible, which was initially diagnosed as ossifying fibroma in primary tumor in another hospital. A 26-year-old man presented with a recurred mass in the mandible for 1 month after the operation of mandibular tumor. The first excisional specimen was initially diagnosed as ossifying fibroma in another hospital. Histopathologic examination revealed the tumor with a hybrid spindle cell and epithelioid cytomorphology, spindle cells and spindle-to-epithelioid cells with eosinophilic and rich cytoplasm, with high-grade features, prominent nucleoli and some atypical mitosis. Immunohistochemical analysis revealed positivity for desmin, MYOD1, pan-keratin, ALK (5A4), ALK (D5F3). Based on the morphology and immunophenotype, molecular studies were performed, which revealed a FUS::TFCP2 fusion transcript, confirming the diagnosis of Rhabdomyosarcoma with FUS::TFCP2 fusion. Making a correct diagnosis is primarily dependent on awareness by the pathologist of this rare subtype of RMS and careful histopathological evaluation, supported by immunohistochemical and molecular analysis, to avoid potential diagnostic pitfalls.

Mandibular rhabdomyosarcoma with TFCP2 rearrangement and osteogenic differentiation: a case misdiagnosed as fibrous dysplasia or low-grade central osteosarcoma

Rhabdomyosarcoma with TFCP2-related fusions (TFCP2-RMS) is a rare entity that commonly affects young adults with a predilection for skeletal involvement. We herein report a 40-year-old female patient with TFCP2-RMS who was misdiagnosed as fibrous dysplasia or low-grade central osteosarcoma of the mandible by referring institutions. Histologically, the tumor showed dominant spindle cells and focal epithelioid cells with marked immature woven bone formation. Immunophenotypically, in addition to the characteristic expression of myogenic markers, ALK, and cytokeratins, tumor cells also unusually expressed osteogenic markers, such as MDM2 and SATB2. Through fluorescence in situ hybridization, the tumor cells showed EWSR1::TFCP2 gene fusion and no MDM2 gene amplification. This is a rare case of TFCP2-RMS, which was misdiagnosed as low-grade central osteosarcoma due to its presenting immunophenotype of MDM2 and SATB2, as well as extensive osteoid matrix formation.

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.

The "Other" Uterine Mesenchymal Neoplasms: Recent Developments and Emerging Entities

Uterine mesenchymal neoplasms are a challenging group of tumors that often show overlapping morphologic features and immunohistochemical profiles. The increasing use of molecular testing in these tumors has enabled a better appreciation of their pathobiology, resulting in a wave of emerging neoplasms and improved characterization of ones previously considered exceptionally rare. Identification of specific molecular alterations has permitted targeted therapy options in tumors that were typically unresponsive to conventional therapies, as well as recognition that a subset can have a hereditary basis. This review will discuss the more "common" of the uncommon uterine mesenchymal neoplasms, including inflammatory myofibroblastic tumor, perivascular epithelioid cell tumor, uterine tumor resembling ovarian sex cord tumor, and embryonal rhabdomyosarcoma. This will be followed by an overview of emerging entities, including NTRK-rearranged uterine sarcoma, SMARCA4-deficient uterine sarcoma, KAT6B/A::KANSL1 fusion uterine sarcoma, and MEIS1::NCOA2/1 fusion sarcoma.

Spindle cell rhabdomyosarcomas: With TFCP2 rearrangements, and novel EWSR1::ZBTB41 and PLOD2::RBM6 gene fusions. A study of five cases and review of the literature

AIMS

Spindle-cell/sclerosing rhabdomyosarcomas (SS-RMS) are clinically and genetically heterogeneous. They include three well-defined molecular subtypes, of which those with EWSR1/FUS::TFCP2 rearrangements were described only recently. This study aimed to evaluate five new cases of SS-RMS and to perform a clinicopathological and statistical analysis of all TFCP2-rearranged SS-RMS described in the English literature to more comprehensively characterize this rare tumour type.

METHODS AND RESULTS

Cases were retrospectively selected and studied by immunohistochemistry, fluorescence in situ hybridization with EWSR1/FUS and TFCP2 break-apart probes, next-generation sequencing (Archer FusionPlex Sarcoma kit and TruSight RNA Pan-Cancer Panel). The PubMed database was searched for relevant peer-reviewed English reports. Five cases of SS-RMS were found. Three cases were TFCP2 rearranged SS-RMS, having FUSex6::TFCP2ex2 gene fusion in two cases and triple gene fusion EWSR1ex5::TFCP2ex2, VAX2ex2::ALKex2 and VAX2intron2::ALKex2 in one case. Two cases showed rhabdomyoblastic differentiation and spindle-round cell/sclerosing morphology, but were characterized by novel genetic fusions including EWSR1ex8::ZBTB41ex7 and PLOD2ex8::RBM6ex7, respectively. In the statistical analysis of all published cases, CDKN2A or ALK alterations, the use of standard chemotherapy and age at presentation in the range of 18-24 years were negatively correlated to overall survival.

CONCLUSION

EWSR1/FUS::TFCP2-rearranged SS-RMS is a rare rhabdomyosarcoma subtype, affecting predominantly young adults with average age at presentation 34 years (median 29.5 years; age range 7-86 years), with a predilection for craniofacial bones, rapid clinical course with frequent bone and lung metastases, and poor prognosis (3-year overall survival rate 28%).

Sarcomas with EWSR1::Non-ETS Fusion (EWSR1::NFATC2 and EWSR1::PATZ1)

The wide application of increasingly advanced molecular studies in routine clinical practice has allowed a detailed, albeit still incomplete, genetic subclassification of undifferentiated round cell sarcomas. The WHO classification continues to include provisional molecular entities, whose clinicopathologic features are in the early stages of evolution. This review focuses on the clinicopathologic, molecular, and prognostic features of undifferentiated round cell sarcomas with EWSR1/FUS::NFATC2 or EWSR1::PATZ1 fusions. Classic histopathologic findings, uncommon variations, and diagnostic pitfalls are addressed, along with the utility of recently developed immunohistochemical and molecular markers.

Inflammatory Rhabdomyoblastic Tumor: From a Nebulous Smooth Muscle Neoplasm to a Novel Skeletal Muscle Tumor Subtype

Inflammatory rhabdomyoblastic tumor is a recently introduced name for neoplasms currently included in the World Health Organization classification of soft tissue tumors under the rubric inflammatory leiomyosarcoma. Inflammatory rhabdomyoblastic tumor is an excellent example of how surgical pathologists working in conjunction with tumor biologists can greatly improve tumor classification to the benefit of patients. Over the last 28 years, understanding of this entity has undergone a fascinating evolution. This review serves as a summary of the latest findings in inflammatory rhabdomyoblastic tumor research and a diagnostic manual for the practicing surgical pathologist.

Pediatric spindle cell/sclerosing rhabdomyosarcoma with FUS-TFCP2 fusion: a case report and literature review

Background

FUS-TFCP2 gene fusion is a recently identified and highly distinct molecular subtype of spindle cell/sclerosing rhabdomyosarcoma (RMS), with fewer than 40 cases being reported to date. Due to its low incidence, clinical studies on this subtype are limited. Here, we report a new case of this rare entity to describe and summarize its unique clinical characteristics and treatment process, aiming to emphasize the importance of molecular testing for spindle cell/sclerosing RMS and increase the understanding of this subtype. By summarizing and comparing with previous reports on RMS with the EWSR1/FUS-TFCP2 fusion mutation, we hope to make some new hints for its management.

Case Description

In this report, we describe a rare case of spindle cell/sclerosing RMS in a 13-year-old boy, who had a massive destructive lesion involving the mandible. Next-generation sequencing of tumor tissue revealing a FUS-TFCP2 fusion. The tumor was extremely aggressive and showed resistance to polychemotherapy, after 4 cycles of multi drug combined chemotherapy, the primary tumor still continued to grow, and suspicious chest metastasis occurred. Even after aggressive total resection of the primary tumor and postoperative chemotherapy, systemic metastasis to the vertebra and chest could not be prevented yet, ultimately with a fatal outcome within 6 months. We additionally summarize 37 cases of RMS with the EWSR1/FUS-TFCP2 fusion mutation reported in the literature. This subtype was found to be almost exclusively primary in bone and histologically showed a common origin of epithelium and muscle. The high aggressiveness made the conventional standard chemoradiotherapy ineffective. Because most tumors of this subtype express ALK protein, ALK inhibitors seem to be a new target for its therapy.

Conclusions

Spindle cell/sclerosing RMS with FUS-TFCP2 fusion has its unique clinical characteristics and progression. It shows a marked skeletal predilection and an aggressive clinical course, typically resistant to traditional standard treatments for RMS. Therefore, molecular detection is crucial in managing this subtype. Once the diagnosis is clear, a more aggressive treatment plan is needed. In addition, almost all cases were found to have a positive expression of ALK. So ALK inhibitors can be a choice of targeted therapy.

Multi-omic and functional analysis for classification and treatment of sarcomas with FUS-TFCP2 or EWSR1-TFCP2 fusions

Linking clinical multi-omics with mechanistic studies may improve the understanding of rare cancers. We leverage two precision oncology programs to investigate rhabdomyosarcoma with FUS/EWSR1-TFCP2 fusions, an orphan malignancy without effective therapies. All tumors exhibit outlier ALK expression, partly accompanied by intragenic deletions and aberrant splicing resulting in ALK variants that are oncogenic and sensitive to ALK inhibitors. Additionally, recurrent CKDN2A/MTAP co-deletions provide a rationale for PRMT5-targeted therapies. Functional studies show that FUS-TFCP2 blocks myogenic differentiation, induces transcription of ALK and truncated TERT, and inhibits DNA repair. Unlike other fusion-driven sarcomas, TFCP2-rearranged tumors exhibit genomic instability and signs of defective homologous recombination. DNA methylation profiling demonstrates a close relationship with undifferentiated sarcomas. In two patients, sarcoma was preceded by benign lesions carrying FUS-TFCP2, indicating stepwise sarcomagenesis. This study illustrates the potential of linking precision oncology with preclinical research to gain insight into the classification, pathogenesis, and therapeutic vulnerabilities of rare cancers.

Myxoid epithelioid smooth muscle tumor of the vulva: A distinct entity with MEF2D::NCOA2 gene fusion

Smooth muscle tumors are the most common mesenchymal tumors of the female genital tract, including the vulva. Since vulvar smooth muscle tumors are rare, our understanding of them compared to their uterine counterparts continues to evolve. Herein, we present two cases of morphologically distinct myxoid epithelioid smooth muscle tumors of the vulva with novel MEF2D::NCOA2 gene fusion. The tumors involved 24 and 37-year-old women. Both tumors presented as palpable vulvar masses that were circumscribed, measuring 2.8 and 5.1 cm in greatest dimension. Histologically, they were composed of epithelioid to spindle-shaped cells with minimal cytologic atypia and prominent myxoid matrix. Rare mitotic figures were present (1-3 mitotic figures per 10 high-power field (HPF)), and no areas of tumor necrosis were identified. By immunohistochemistry, the neoplastic cells strongly expressed smooth muscle actin, calponin, and desmin, confirming smooth muscle origin. Next-generation sequencing identified identical MEF2D::NCOA2 gene fusions. These two cases demonstrate that at least a subset of myxoid epithelioid smooth muscle tumors of the vulva represent a distinct entity characterized by a novel MEF2D::NCOA2 gene fusion. Importantly, recognition of the distinct morphologic and genetic features of these tumors is key to understanding the biological potential of these rare tumors.

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.

Uterine MEIS1::NCOA2 Fusion Sarcoma With Lung Metastasis: A Case Report and Review of the Literature

MEIS1::NCOA1/2 fusion sarcomas are a recently described novel entity arising in a variety of locations with a predilection for the genitourinary tract and gynecologic organs. Despite multiple locoregional recurrences, these tumors are thought to behave in a low-grade malignant manner. Here we report a uterine MEIS1::NCOA2 fusion sarcoma with lung metastasis. The patient was a 47-yr-old woman with a history of abnormal uterine bleeding who was found to have a myometrial mass confirmed by pathology to be uterine sarcoma. The tumor was predominantly composed of monotonous spindle cells with scant cytoplasm, crowded nuclei, and brisk mitotic activity, growing in a fascicular and streaming pattern. The morphologic and immunophenotypic features were nonspecific and a diagnosis of high-grade uterine sarcoma with a differential of leiomyosarcoma versus high-grade endometrial stromal sarcoma was rendered. At the 27-mo follow-up, the patient was found to have a lung metastasis consisting of a monotonous round cell sarcoma. A retrospective RNA-based and DNA-based next-generation sequencing of the primary uterine sarcoma revealed a MEIS1::NCOA2 gene fusion, a c.94G>C/p.D32H mutation in exon 3 of CTNNB1 gene, HMGA2 , and CDK4 gene amplification, and an intermediate/marginal level of MDM2 gene amplification. Polymerase chain reaction-based molecular analysis further demonstrated that the MEIS1::NCOA2 gene fusion and CTNNB1 somatic mutation were also present in the lung metastasis. This case represents the first case of such gynecologic sarcoma with distant (lung) metastasis, and the second metastatic case among all reported MEIS1::NCOA1/2 fusion sarcomas, highlighting the malignant metastatic potential of this emerging entity. Our case also indicates that HMGA2/CDK4/MDM2 region amplification and CTNNB1 somatic mutation might be recurrent genetic events in this rare sarcoma subtype.

Cutaneous rhabdomyosarcoma with FUS::TFCP2 fusion: A case report emphasizing early detection

Rhabdomyosarcoma with TFCP2 rearrangement is a recently identified malignant neoplasm characterized by immunohistochemical evidence of rhabdomyoblastic differentiation, keratin expression, upregulation of ALK, and an aggressive clinical course. This neoplasm has a tendency to affect craniofacial bones, with only a few reported cases of extra-osseous tumors. Here, we present a case of cutaneous rhabdomyosarcoma with FUS::TFCP2 fusion in a 35-year-old female. Notably, the tumor exhibited a pathologic spectrum, initially resembling sclerosing dermatitis at presentation but progressing into a high-grade malignant tumor within 8 months. The distinctive immunoprofile of this neoplasm highlights the importance of early molecular studies for diagnosis, even in the presence of low-grade cytomorphology. Early detection may offer an opportunity for timely resection before the tumor becomes unresectable.

Emerging mesenchymal tumour types and biases in the era of ubiquitous sequencing

New tumour types are being described at increasing frequency, and most new tumour types are now identified via retrospective review of next-generation sequencing data. This contrasts with the traditional, morphology-based method of identifying new tumour types, and while the sequencing-based approach has accelerated progress in the field, it has also introduced novel and under-recognised biases. Here, we discuss tumour types identified based on morphology, including superficial CD34-positive fibroblastic tumour, pseudoendocrine sarcoma and cutaneous clear cell tumour with melanocytic differentiation and ACTIN::MITF fusion. We also describe tumour types identified primarily by next-generation sequencing, including epithelioid and spindle cell rhabdomyosarcoma, round cell neoplasms with EWSR1::PATZ1 fusion, cutaneous melanocytic tumour with CRTC1::TRIM11 fusion, clear cell tumour with melanocytic differentiation and MITF::CREM fusion and GLI1-altered mesenchymal neoplasms, including nested glomoid neoplasm.

Fusion-driven Spindle Cell Rhabdomyosarcomas of Bone and Soft Tissue: A Clinicopathologic and Molecular Genetic Study of 25 Cases

The evolving classification of rhabdomyosarcoma (RMS) now includes spindle cell RMS (SRMS). Bone/soft tissue SRMS often harbor TFCP2, or less often MEIS1 rearrangements. We studied 25 fusion-driven SRMS involving bone (n = 19) and soft tissue (n = 6). Osseous SRMS occurred in 13 women and 6 men (median age: 41 years) and involved the pelvis (5), sacrum (2), spine (4), maxilla (4), mandible (1), skull (1), and femur (2). Follow-up (median: 5 months) demonstrated local recurrence in 2/16 and distant metastases in 8/17 patients (median time to metastasis: 1 month). Eight patients died of disease; 9 were alive with disease. Soft tissue SRMS occurred in 4 men and 2 women (median: 50 years). Follow-up (median: 10 months) revealed distant metastasis at diagnosis (1), alive with unresected tumor (1), and no evidence of disease (4). Next-generation sequencing demonstrated FUS::TFCP2 (12), EWSR1::TFCP2 (3) and MEIS1::NCOA2 (2); FISH identified EWSR1 (2) rearrangements. Most TFCP2-rearranged SRMS (13/17) showed spindled/epithelioid morphology, rarely with rhabdomyoblasts. The bone tumors were diffusely desmin and MyoD1 positive with limited myogenin; 10/13 were ALK -positive and 6/15 were keratin positive. Soft tissue SRMS harbored EWSR1::TFCP2, MEIS1::NCOA2, ZFP64::NCOA2, MEIS1::FOXO1, TCF12::VGLL3 and DCTN1::ALK, and displayed spindled/epithelioid, leiomyomatous, and myxofibrosarcoma-like morphologies. Immunohistochemistry (IHC) was positive for MyoD1 (6/6), focal desmin (5/6), myogenin (3/6), and keratin (1/6). We conclude that TFCP2-rearranged SRMS of bone and soft tissue show consistent morphologic and IHC features, likely representing a distinct subset of RMS. Non-TFCP2 fusion-positive SRMS could represent a single RMS subset, multiple subtypes of RMS, or "fusion-defined" sarcomas with rhabdomyoblastic differentiation.

Epithelioid and spindle cell rhabdomyosarcoma with EWSR1::TFCP2 fusion mimicking metastatic lung cancer: A case report and literature review

Rhabdomyosarcoma (RMS) with EWSR1/FUS::TFCP2 fusion is an emerging, molecularly defined, rare subtype of RMS. It can affect patients in a wide age range and follows an aggressive clinical course according to the reported cases. Due to its unusual clinical and pathohistological features, with a typical intraosseous presentation and common cytokeratin expression, the diagnosis is challenging, and metastatic undifferentiated/sarcomatoid carcinoma can be an important differential diagnosis. We report here a case of a 55-year-old woman with an RMS with EWSR1::TFCP2 fusion mimicking metastatic lung cancer in view of the clinical and microscopic presentation. However, further molecular workup, including RNA sequencing, led to the proper diagnosis. Although these tumors are rare, knowledge of their unique features is essential for correct diagnosis as a basis for clinical management and optimization of therapeutic approaches.

Intraosseous Spindle Cell Rhabdomyosarcoma with MEIS1::NCOA2 Fusion - Case Report with Substantial Clinical Follow-up and Review of the Literature

Spindle cell/sclerosing rhabdomyosarcoma (SSRMS) is a clinicopathologically and molecularly heterogeneous disease. Gene fusions have been identified in intraosseous SSRMS, consisting predominantly of EWSR1/FUS::TFCP2 and MEIS1::NCOA2. The former often follow an aggressive clinical course; there is limited clinical follow-up available for the latter. We report here a new case of the very rare intraosseous SSRMS with MEIS1::NCOA2 gene fusion and include the detailed treatment course and 52 months of clinical follow-up. SSRMS with MEIS1::NCOA2 gene fusion appears biologically distinct from other intraosseous SSRMS, following a course characterized by local recurrence with rare reports of metastasis to date.

Small biopsies in the head and neck: Bone and soft tissue

Bone and soft tissue lesions in the head and neck encompass not only a broad morphologic spectrum but also significant inherent clinicopathologic overlap. Epidemiology, radiology, and location - similar to the diagnostic assessment in other sites - are especially important considerations in the context of an established mesenchymal proliferation. Herein, the approach towards diagnosis is stratified by morphology (spindle, sarcomatoid, epithelioid, round cell), cellular lineage (fibroblastic, nerve sheath, rhabdomyogenic), and tumor grade (benign, low- to high-grade malignant) as the basis of further immunohistochemical or molecular investigation.

Spindle Cell Rhabdomyosarcoma of the Inguinal Region Mimicking a Complicated Hernia in the Adult-An Unexpected Finding

Rhabdomyosarcoma is a rare tumor that is diagnosed mostly in children and adolescents, rarely in adults, representing 2-5% of all soft tissue sarcomas. It has four subtypes that are recognized: embryonal (50%), alveolar (20%), pleomorphic (20%), and spindle cell/sclerosing (10%). The diagnosis of rhabdomyosarcoma is based on the histological detection of rhabdomyoblasts and the expression of muscle-related biomarkers. Spindle cell/sclerosing rhabdomyosarcoma consists morphologically of fusiform cells with vesicular chromatin arranged in a storiform pattern or long fascicles, with occasional rhabdomyoblasts. Also, dense, collagenous, sclerotic stroma may be seen more commonly in adults. We present a rare case of an adult who presented to the hospital with a tumor in the left inguinal area, was first diagnosed with a left strangulated inguinal hernia and was operated on as an emergency, although the diagnosis was ultimately a spindle cell rhabdomyosarcoma of the inguinal region.

[Special mesenchymal neoplasms of the head and neck: Update from the 2022 WHO]

Similar to the approach adopted in the classification of tumors in other organs, a new feature of the current Word Health Organization (WHO) classification of the head and neck tumors is the exclusion of soft tissue tumors from single organs and their inclusion in a separate chapter devoted to them. This applies to tumors that are principally ubiquitous but show a predilection for the head and neck sites. The only exception to this rule represents those entities that are almost restricted to a specific head and neck site/organ (such as nasopharyngeal angiofibroma, sinonasal glomangiopericytoma, and biphenotypic sinonasal sarcoma), which remain in their respective organ chapters. Included among soft tissue tumors are some old but still underrecognized entities, such as phosphaturic mesenchymal tumors, and newly defined entities, such as GLI1-altered tumors. The aim of including these entities is to enhance recognition of these uncommon but likely under-recognized entities to better characterize them in the future. This review summarizes the main features of these rare entities and discusses their differential diagnoses.

Rhabdomyosarcoma with TFCP2 Rearrangement or Typical Co-expression of AE1/AE3 and ALK: Report of Three New Cases in the Head and Neck Region and Literature Review

BACKGROUND

Rhabdomyosarcoma (RMS) harboring EWSR1/FUS-TFCP2 fusions has been recently described as a distinct form of RMS with an aggressive course and predilection for the craniofacial bones, especially the jaws.

METHODS

We report three new cases of this rare entity, two from Brazil and one from Guatemala, with detailed clinicopathologic, immunohistochemical, and molecular descriptions. Additionally, we explored the English-language literature searching RMS with TFCP2 rearrangement or typical immunophenotype with co-expression of AE1/AE3 and ALK in the head and neck region.

RESULTS

Case 1 is a 58-year-old male with a 3-month history of painful swelling in the anterior maxilla. Case 2 is a 22-year-old male presenting with right facial swelling and proptosis. Case 3 is a 43-year-old female with a rapidly growing tumor located in the zygomatic region. Imaging examinations revealed highly destructive intraosseous masses in the first two cases, and a soft tissue tumor with bone invasion in case 3. Microscopically, all cases showed a hybrid spindle and epithelioid phenotype of tumor cells which expressed desmin, myogenin and/or Myo-D1, AE1/AE3, and ALK. FISH confirmed molecular alterations related to TFCP2 rearrangement in Cases 1-2. In case 3, there was no available material for molecular analysis. The patients were subsequently referred to oncologic treatment. Additionally, we summarized the clinicopathologic, immunohistochemical, and molecular features of 27 cases of this rare RMS variant in the head and neck region reported in the English-language literature.

CONCLUSION

RMS with TFCP2 rearrangement is a rare and aggressive tumor with a particular predilection for craniofacial bones, especially the jaws. Knowing its clinicopathologic and immunohistochemical profile can avoid misdiagnosis.

Rhabdomyosarcoma Arising in Inflammatory Rhabdomyoblastic Tumor: A Genetically Distinctive Subtype of Rhabdomyosarcoma

"Inflammatory rhabdomyoblastic tumor" (IRMT) is a recently coined name for a distinctive soft tissue neoplasm characterized by slow growth, a dense histiocytic infiltrate, scattered, bizarre-appearing tumor cells with morphologic and immunohistochemical evidence of skeletal muscle differentiation, a near-haploid karyotype with retained biparental disomy of chromosomes 5 and 22, and usually indolent behavior. There are 2 reports of rhabdomyosarcoma (RMS) arising in IRMT. We studied the clinicopathologic and cytogenomic features of 6 cases of IRMT with progression to RMS. Tumors occurred in the extremities of 5 men and 1 woman (median patient age, 50 years; median tumor size, 6.5 cm). Clinical follow-up (6 patients: median, 11 months; range 4-163 months) documented local recurrence and distant metastases in 1 and 5 of 6 patients, respectively. Therapy included complete surgical resection (4 patients) and adjuvant/neoadjuvant chemo/radiotherapy (6 patients). One patient died of disease, 4 were alive with metastatic disease, and one was without evidence of disease. All primary tumors contained conventional IRMT. Progression to RMS appeared as follows: (1) overgrowth of monomorphic rhabdomyoblasts with diminished histiocytes, (2) monomorphic spindle cell morphology with variably pleomorphic rhabdomyoblasts and low mitotic activity, or (3) morphologically undifferentiated spindle cell and epithelioid sarcoma. All but one were diffusely desmin-positive, with more limited MyoD1/myogenin expression. All RMS arising in IRMT, either primary or metastatic, demonstrated widespread loss of heterozygosity with retained heterozygosity of chromosomes 5 and 20, and all but one displayed additional gains and losses involving loci containing oncogenes/ tumor suppressor genes, most often CDKN2A and CDKN2B. RMS arising in IRMT have unique clinicopathologic and cytogenomic features, warranting classification as a distinct, potentially aggressive RMS subtype. It should be distinguished from other RMSs, particularly fusion-driven spindle cell RMS and pleomorphic RMS.

Clinicopathological and Molecular Characteristics of Intraosseous Rhabdomyosarcoma Involving Head and Neck Region: A Systematic Review and Meta-Analysis

Rhabdomyosarcoma with TFCP2 rearrangement is a newly introduced spindle cell neoplasm showing predilection for craniofacial bones exhibiting highly aggressive nature and poor prognosis. Therefore, an attempt was made to delineate the entity for improved understanding and treatment outcomes through comprehensive analysis of the clinicopathological and molecular characteristics. An electronic search was carried out using MEDLINE by PubMed, Scopus, Google scholar, Cochrane library, and EMBASE databases. Original articles and case reports involving intraosseous rhabdomyosarcoma arising in head and neck region with TFCP2 fusion were included. Data were compiled and risk of bias was analyzed using JBI tool. Thirteen eligible articles were included for the quantitative analysis, which revealed 33 cases with TFCP2 fusion. Majority of the affected individuals were females (58%) with mandible being the common site. Most of the patients died within few months after diagnosis demonstrating a low mean survival rate (30 months). Odds ratio, overall survival and disease-free survival were calculated and analyzed statistically concluding that intraosseous rhabdomyosarcomas harboring TFCP2 fusion are found to be novel and dreadful neoplasms. The predilection for young age with poor prognosis exhibited by these lesions demand early diagnosis and specific treatment planning to curtail mortality.

Spindle Cell Sarcoma of the Uterus Harboring MEIS1::NCOA1 Fusion Gene and Mimicking Endometrial Stromal Sarcoma

MEIS1::NCOA1/2 sarcomas are a newly recognized group of exceedingly rare low-grade spindle cell sarcomas that often involve the genitourinary and gynecologic tracts. Due to its deceptively low-grade morphology and the non-specific immunoprofile, these neoplasms may pose a diagnostic challenge by histologically mimicking other entities such as endometrial stromal sarcoma, smooth muscle tumor, or uterine perivascular epithelioid cell tumor (PEComa). Histologically, MEIS1::NCOA1/2 sarcomas typically show spindle cell proliferation with hyperchromatic nuclei and a generalized cytologic uniformity, arranged in short fascicles and exhibiting alternating zones of hypo- and hypercellularity. Among the previously reported cases, molecular analysis revealed the MEIS1::NCOA2 fusion as the most commonly detected fusion gene, whereas the MEIS1::NCOA1 fusion gene has been reported in only a single case that involved kidney. Herein we report the first case of uterine sarcoma harboring the MEIS1::NCOA1 fusion gene that was initially misclassified as low-grade endometrial stromal sarcoma, demonstrating its clinicopathologic features, and highlighting the essential role of molecular pathology to arrive at the accurate diagnosis that may alter disease classification and inform therapy.

Epithelioid and spindle rhabdomyosarcoma with TFCP2 rearrangement in abdominal wall: a distinctive entity with poor prognosis

BACKGROUND

Epithelioid and spindle rhabdomyosarcoma (ES-RMS) with TFCP2 rearrangement is a recently discovered rare variant of rhabdomyosarcoma composed of epithelioid and spindle cells, because it shows extraordinarily adverse prognosis and is easily misdiagnosed as other epithelioid or spindle cell tumors.

METHODS

A rare case of ES-RMS with TFCP2 rearrangement was presented and English literatures in Pubmed online up to 01 July 2022 were gathered by two authors for a systematic review according to the inclusion and exclusion criteria.

CASE PRESENTATION/RESULTS

We report a case of ES-RMS in an early 30s-years-old female, the neoplastic cells are remarkably immunoreactive with CK(AE1/AE3), and partially with ALK protein. Unexpectedly, the tumor shows TFCP2 rearrangement with coexistence of increased copy numbers of EWSR1 and ROS1 gene and MET gene mutation. Besides, Next-generation sequencing for genetic mutational profiling revealed frequent MET exon14 mutations in chromosome 7, most of which are C > T nonsynonymous SNV, and exon42 of ROS1 in chromosome 6 showed frequent G > T mutation up to 57.54%. In addition, neither MyoD1 mutation nor gene fusions were detected. Moreover, the patient shows high tumor mutational burden (TMB) up to 14.11 counts/Mb. Finally, as many cases of ES-RMS including our case had local progression or metastasis, we find, similar to epithelioid rhabdomyosarcoma (median survival time is 10 month), ES-RMS shows a more aggressive behavior and adverse prognosis (median survival time is 17 month) than spindle cell/sclerosing rhabdomyosarcoma (median survival time is 65 month) according previous studies.

CONCLUSIONS

ES-RMS with TFCP2 rearrangement is a rare malignant tumor and easily confused with other epithelioid or spindle cell tumors, it may harbor additional gene alteration in addition to TFCP2 rearrangement, such as MET mutation, increased copy numbers of EWSR1 and ROS1 gene, high TMB. Most importantly, it may show very poor outcome with extensive metastasis.

"E-MGNET": Extra-Enteric Malignant Gastrointestinal Neuroectodermal Tumor- A Clinicopathological and Molecular Genetic Study of 11 Cases

Malignant gastrointestinal neuroectodermal tumors (MGNET), also known as "gastrointestinal clear cell sarcoma-like tumor", are very rare, aggressive sarcomas characterized by enteric location, distinctive pathologic features, and EWSR1/FUS::ATF1/CREB1 fusions. Despite identical genetics, the clinicopathologic features of MGNET are otherwise quite different from clear cell sarcoma of soft parts (CCS). Only exceptional extra-enteric MGNET (E-MGNET) have been reported. We report a series of 11 E-MGNET, the largest to date. Cases diagnosed as MGNET and occurring in non-intestinal locations were retrieved. Clinical follow-up was obtained. The tumors occurred in 3 males and 8 females (14-70 years of age, median 33 years) and involved the soft tissues of the neck (3), shoulder (1), buttock (2), orbit (1), and tongue/parapharyngeal space (1), the urinary bladder (1) and the falciform ligament/liver (1). Tumors showed morphologic features of enteric MGNET (small, relatively uniform, round to ovoid cells with round, regular nuclei containing small nucleoli, growing in multinodular and vaguely lobular patterns, with solid, pseudoalveolar and pseudopapillary architecture). Immunohistochemical results were: S100 protein (11/11), SOX10 (11/11), synaptophysin (3/10), CD56 (7/9), CD117 (3/9), DOG1 (0/4), ALK (4/8), chromogranin A (0/10), HMB45 (0/11), Melan-A (0/11), tyrosinase (0/4), MiTF (0/11). NGS results were: EWSR1::ATF1 (7 cases), EWSR1::CREB1 (3 cases) and EWSR1::PBX1 (1 case). The EWSR1::PBX1-positive tumor was similar to other cases, including osteoclast-like giant cells, and negative for myoepithelial markers. Clinical follow-up (range: 10 to 70 months; median 34 months) showed 4 patients dead of disease (10.5, 12, 25 and 64 months after diagnosis), 1 patient alive with extensive metastases (43 months after diagnosis), 1 patient alive with persistent local disease (11 months after diagnosis), and 4 alive without disease (10, 47, 53 and 70 months after diagnosis). One case is too recent for follow-up. The clinicopathologic and molecular genetic features of rare E-MGNET are essentially identical to those occurring in intestinal locations. Otherwise-typical E-MGNET may harbor EWSR1::PBX1, a finding previously unreported in this tumor type. As in enteric locations, the behavior of E-MGNET is aggressive, with metastases and/or death from disease in at least 50% of patients. E-MGNET should be distinguished from CCS and other tumors with similar fusions. ALK expression appears to be a common feature of tumors harboring EWSR1/FUS::ATF1/CREB1 fusion but is unlikely to predict therapeutic response to ALK inhibition. Future advances in our understanding of these unusual tumors will hopefully lead to improved nomenclature.

Bone and soft tissue tumors: clinicoradiologic-pathologic molecular-genetic correlation of novel fusion spindled, targetable-ovoid, giant-cell-rich, and round cell sarcomas

BACKGROUND

New entities in the classification of bone and soft tissue tumors have been identified by use of advanced molecular-genetic techniques, including next-generation sequencing. Clinicoradiologic and pathologic correlation supports diagnostic classification.

METHODS

Tumors from four morphologically grouped areas are selected to enhance diagnosis and awareness among the multidisciplinary team. These include select round cell tumors, spindle cell tumors, targetable tyrosine kinase/RAS::MAPK pathway-ovoid (epithelioid to spindled) tumors, and giant-cell-rich tumors of bone and soft tissue.

RESULTS

Round cell tumors of bone and soft tissue include prototypical Ewing sarcoma, newer sarcomas with BCOR genetic alteration and CIC-rearranged, as well as updates on FUS/EWSR1::NFATc2, an EWSR1 non-ETS tumor that is solid with additional amplified hybridization signal pattern of EWSR1. This FUS/EWSR1::NFATc2 fusion has now been observed in seemingly benign to low-grade intraosseous vascular-rich and simple (unicameral) bone cyst tumors. Select spindle cell tumors of bone and soft tissue include rhabdomyosarcoma with FUS/EWSR1::TFCP2, an intraosseous high-grade spindle cell tumor without matrix. Targetable tyrosine-kinase or RAS::MAPK pathway-tumors of bone and soft tissue include NTRK, ALK, BRAF, RAF1, RET, FGFR1, ABL1, EGFR, PDGFB, and MET with variable ovoid myopericytic to spindled pleomorphic features and reproducible clinicopathologic and radiologic clues to their diagnosis. Giant-cell-rich tumors of bone, joint, and soft tissue are now respectively characterized by H3F3A mutation, CSF1 rearrangement (targetable), and HMGA2::NCOR2 fusion.

CONCLUSION

This article is an update for radiologists, oncologists, surgeons, and pathologists to recognize these novel ovoid, spindled, giant-cell-rich, and round cell tumors, for optimal diagnostic classification and multidisciplinary team patient care.

Clinicopathological features of rhabdomyosarcoma with novel FET::TFCP2 and TIMP3::ALK fusion: report of two cases and literature review

AIMS

The aim of this study was to evaluate the clinicopathological features, immunophenotype, differential diagnosis, molecular genetic features and prognosis of spindle cell rhabdomyosarcoma with TFCP2 rearrangement.

METHODS

Two cases of spindle cell rhabdomyosarcoma with FET::TFCP2 gene fusion were included in this study. Samples were collected and evaluated through histological observation, immunohistochemistry, fluorescence in-situ hybridisation and high-throughput gene sequencing and previous findings.

RESULTS

The tumour tissues mainly comprised spindle cells and epithelioid cells, which expressed striated muscle markers, and exhibited high expression levels of CK and ALK protein markers. Molecular detection showed that the FET::TFCP2 gene was fused. A rare case with TIMP3::ALK and FUS::TFCP2 double-fusion was observed in this study.

CONCLUSIONS

A case with double fusion of ALK and TFCP2 was reported in rhabdomyosarcoma for the first time in this study, which provides information on the molecular characteristic of the tumour. Spindle cell rhabdomyosarcoma with FET::TFCP2 fusion is characterised by histological, immunohistochemical and genetic changes. The tumour is aggressive, with poor prognosis and poor response to radiotherapy and chemotherapy. The efficacy of targeted therapy for ALK should be explored through more clinical studies.

VGLL2-NCOA2 leverages developmental programs for pediatric sarcomagenesis

Clinical sequencing efforts are rapidly identifying sarcoma gene fusions that lack functional validation. An example is the fusion of transcriptional coactivators, VGLL2-NCOA2, found in infantile rhabdomyosarcoma. To delineate VGLL2-NCOA2 tumorigenic mechanisms and identify therapeutic vulnerabilities, we implement a cross-species comparative oncology approach with zebrafish, mouse allograft, and patient samples. We find that VGLL2-NCOA2 is sufficient to generate mesenchymal tumors that display features of immature skeletal muscle and recapitulate the human disease. A subset of VGLL2-NCOA2 zebrafish tumors transcriptionally cluster with embryonic somitogenesis and identify VGLL2-NCOA2 developmental programs, including a RAS family GTPase, ARF6. In VGLL2-NCOA2 zebrafish, mouse, and patient tumors, ARF6 is highly expressed. ARF6 knockout suppresses VGLL2-NCOA2 oncogenic activity in cell culture, and, more broadly, ARF6 is overexpressed in adult and pediatric sarcomas. Our data indicate that VGLL2-NCOA2 is an oncogene that leverages developmental programs for tumorigenesis and that reactivation or persistence of ARF6 could represent a therapeutic opportunity.

Case Report: An NTRK1 fusion-positive embryonal rhabdomyosarcoma: clinical presentations, pathological characteristics and genotypic analyses

Rhabdomyosarcoma (RMS) is a prevalent form of soft tissue sarcoma that primarily affects children. Pediatric RMS is characterized by two distinct histological variants: embryonal (ERMS) and alveolar (ARMS). ERMS is a malignant tumor with primitive characteristics resembling the phenotypic and biological features of embryonic skeletal muscles. With the widespread and growing application of advanced molecular biological technologies, such as next-generation sequencing (NGS), it has been possible to determine the oncogenic activation alterations of many tumors. Specifically for soft tissue sarcomas, the determination of tyrosine kinase gene and protein related changes can be used as diagnostic aids and may be used as predictive markers for targeted tyrosine kinase inhibition therapy. Our study reports a rare and exceptional case of an 11-year-old patient diagnosed with ERMS, who tested positive for MEF2D-NTRK1 fusion. The case report presents a comprehensive overview of the clinical, radiographic, histopathological, immunohistochemical, and genetic characteristics of a palpebral ERMS. Furthermore, this study sheds light on an uncommon occurrence of NTRK1 fusion-positive ERMS, which may provide theoretical basis for therapy and prognosis.

Shedding a Light on the Challenges of Adolescents and Young Adults with Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a typical tumour of childhood but can occur at any age. Several studies have reported that adolescent and young adult (AYA) patients with RMS have poorer survival than do younger patients. This review discusses the specific challenges in AYA patients with pediatric-type RMS, exploring possible underlying factors which may influence different outcomes. Reasons for AYA survival gap are likely multifactorial, and might be related to differences in tumor biology and intrinsic aggressiveness, or differences in clinical management (that could include patient referral patterns, time to diagnosis, enrolment into clinical trials, the adequacy and intensity of treatment), as well as patient factors (including physiology and comorbidity that may influence treatment tolerability, drug pharmacokinetics and efficacy). However, improved survival has been reported in the most recent studies for AYA patients treated on pediatric RMS protocols. Different strategies may help to further improve outcome, such as supporting trans-age academic societies and national/international collaborations; developing specific clinical trials without upper age limit; defining integrated and comprehensive approach to AYA patients, including the genomic aspects; establishing multidisciplinary tumor boards with involvement of both pediatric and adult oncologists to discuss all pediatric-type RMS patients; developing dedicated projects with specific treatment recommendations and registry/database.

Intraosseous Spindle Cell/Epithelioid Rhabdomyosarcoma with TFCP2 Rearrangement: A Recent Recognized Subtype with Partial Response to Alectinib

Rhabdomyosarcoma affects mainly pediatric patients and is currently classified into four categories: embryonal, alveolar, pleomorphic, and spindle cell/sclerosing. Recently, a molecular group of spindle cell/sclerosing rhabdomyosarcoma demonstrated new fusion transcripts involving FET-family genes with TFCP2. In this report, we describe a rare case of spindle cell/sclerosing rhabdomyosarcoma in a 19-year-old woman, presenting as a destructive lesion involving the condyle of mandible. Next generation sequencing was performed, revealing a FUS::TFCP2 fusion and deletion of ALK gene. Alectinib therapy was initiated, which resulted in a favorable response for 4 months. However, the patient died due progression of the tumor. To make an accurate diagnosis and ensure appropriate patient management, it is necessary to be aware of this variant and use proper immunohistochemical stains when facing malignant mesenchymal bone lesions, expanding its differential diagnosis.

Recurrent VGLL3 fusions define a distinctive subset of spindle cell rhabdomyosarcoma with an indolent clinical course and striking predilection for the head and neck

The mammalian Vestigial-like (VGLL) transcriptional cofactor family of proteins VGLL1-4 has recently emerged as an important player in the tumorigenesis of diverse neoplasms. The role of VGLL3 in soft tissue tumors is exemplified by its amplification in myxoinflammatory fibroblastic sarcoma and its rearrangement (fused to CHD7, CHD9, or MAMLD1) in hybrid schwannoma-perineurioma. This study characterizes a distinctive low-grade myogenic neoplasm with a striking predilection for the head and neck, characterized by VGLL3 fusions. The study includes five males and one female patient, aged 30-71 years (median, 56). Three tumors originated in the tongue, with one case each in the nasopharynx, oral cavity, and oropharynx. The VGLL3 fusion partners included TCF12 (n = 3), EP300 (n = 2), and PPARGC1A (n = 1). The tumor size range was 0.8-1.6 cm (all, but one, was <1 cm). Histologically, all tumors displayed bland spindle to ovoid cells arranged into vague fascicular and diffuse patterns. Mitotic activity ranged from 1 to 7 per 10 HPFs. Five tumors were muscle-centered and infiltrative, and one was centered beneath nasopharyngeal mucosa. Immunohistochemistry revealed consistent expression of desmin (diffuse in four and patchy in two cases) associated with patchy smooth muscle actin expression (4/6), and focal reactivity for myogenin (5/6) and myoD1 (1/3). All patients were managed surgically; one patient each received adjuvant radio- or chemotherapy. Three patients with follow-up were without disease at 8, 19, and 60 months and one was alive with unknown disease status at 24 months. All VGLL3 fusions were in-frame and involved exon 2, fused with either TCF12 exon 16, EP300 exon 31, or PPARGC1A exon 5, respectively. This series characterizes a distinctive subset of spindle cell rhabdomyosarcoma (RMS) with a predilection for the head and neck in adults, defined by VGLL3 fusions, likely indolent behavior and limited rhabdomyoblastic differentiation. Further delineation of this entity and differentiation from more aggressive molecular subtypes of spindle cell RMS is mandatory to define the most appropriate therapeutic strategy and avoid overtreatment.

Rhabdomyosarcoma With FUS::TFCP2 Fusion in the Scalp: A Rare Case Report Depicting Round and Spindle cell Morphology

Rhabdomyosarcoma (RMS) is a nonepithelial malignant tumor that differentiates into immature skeletal muscle. It is currently classified into 4 main subtypes according to the WHO classification. However, based on clinicopathological and molecular findings, there has been an increasing number of cases that do not fit into any of these subtypes. TFCP2-rearranged RMS is a rare tumor with characteristic clinicopathological findings including a preference for the craniofacial bones, a spindle and epithelioid histomorphology, and positive immunohistochemistry for epithelial markers, ALK, and myogenic markers. In this report, we describe a rare case of RMS with FUS::TFCP2 fusion in the scalp of a 58-year-old man. Histologically, the tumor showed a biphasic pattern, with solid proliferation of round cells in the superficial areas and of spindle cells in the deep areas. Immunohistochemically, tumor cells were positive for pan keratin, myogenic markers (desmin, MYOD1, and myogenin), and ALK. Additionally, fluorescence in situ hybridization using a break-apart FUS probe revealed FUS rearrangement. RMS with FUS::TFCP2 fusion was suspected, and the fusion gene was finally confirmed by target fusion sequencing. We believe that detailed histological, immunohistochemical, and genetic findings were important for the diagnosis. The unique traits of this tumor were the biphasic histological appearance consisting of round and spindle cells and development in the skin and soft tissue.

ZFP64::NCOA3 gene fusion defines a novel subset of spindle cell rhabdomyosarcoma

Spindle cell rhabdomyosarcoma represents a rare neoplasm characterized by monomorphic spindle cells with a fascicular architecture and variable skeletal muscle differentiation. Following incidental identification of a ZFP64::NCOA3 gene fusion in an unclassified spindle cell sarcoma resembling adult-type fibrosarcoma, we performed a retrospective archival review and identified four additional cases with a similar histology and identical gene fusion. All tumors arose in adult males (28-71 years). The neoplasms were found in the deep soft tissues, two were gluteal, and one each arose in the thigh, abdominal wall, and chest wall. Morphologically, the tumors were characterized by spindle cells with a distinctive herringbone pattern and variable collagenous to myxoid stroma. The nuclei were relatively monomorphic with variable mitotic activity. Three tumors had immunoreactivity for MyoD1, and four contained variable expression of desmin and smooth muscle actin. All cases tested for myogenin, CD34, S100, pankeratin, and epithelial membrane antigen were negative. Targeted RNA sequencing revealed a ZFP64::NCOA3 fusion product in all five tumors. Three patients developed distant metastases, and two ultimately succumbed to their disease within 2 years of initial diagnosis. This study suggests ZFP64::NCOA3 fusions define a novel subtype of rhabdomyosarcoma with a spindle cell morphology and aggressive clinical behavior. The potential for morphologic and immunohistochemical overlap with several other sarcoma types underscores the value of molecular testing as a diagnostic adjunct to ensure accurate classification and management of these neoplasms.

Molecular profile of head and neck rhabdomyosarcomas: A systematic review and meta-analysis

OBJECTIVE

This systematic review aimed to identify the molecular alterations of head and neck rhabdomyosarcomas (HNRMS) and their prognostic values.

STUDY DESIGN

An electronic search was performed using PubMed, Embase, Scopus, and Web of Science with a designed search strategy. Inclusion criteria comprised cases of primary HNRMS with an established histopathological diagnosis and molecular analysis. Forty-nine studies were included and were appraised for methodological quality using the Joanna Briggs Institute Critical Appraisal tools. Five studies were selected for meta-analysis.

RESULTS

HNRMS predominantly affects pediatric patients (44.4%), and the parameningeal region (57.7%) is the most common location. The alveolar variant (43.2%) predominates over the embryonal and spindle cell/sclerosing types, followed by the epithelioid and pleomorphic variants. PAX-FOXO1 fusion was observed in 103 cases of alveolar RMS (79.8%). MYOD1 mutation was found in 39 cases of sclerosing/spindle cell RMS (53.4%). FUS/EWSR1-TFCP2 gene fusions were identified in 21 cases of RMS with epithelioid and spindle cell morphologies (95.5%). The 5-year overall survival rate of patients was 61.3%, and MYOD1 mutation correlated with significantly higher mortality.

CONCLUSION

The genotypic profile of histologic variants of HNRMS is widely variable, and MYOD1 mutation could be a potential prognostic factor, but more studies are required to establish this.

Molecular testing of rhabdomyosarcoma in clinical trials to improve risk stratification and outcome: A consensus view from European paediatric Soft tissue sarcoma Study Group, Children's Oncology Group and Cooperative Weichteilsarkom-Studiengruppe

Rhabdomyosarcomas (RMSs) are the most common soft tissue sarcomas in children/adolescents less than 18 years of age with an annual incidence of 1-2/million. Inter/intra-tumour heterogeneity raise challenges in clinical, pathological and biological research studies. Risk stratification in European and North American clinical trials previously relied on clinico-pathological features, but now, incorporates PAX3/7-FOXO1-fusion gene status in the place of alveolar histology. International working groups propose a coordinated approach through the INternational Soft Tissue SaRcoma ConsorTium to evaluate the specific genetic abnormalities and generate and integrate molecular and clinical data related to patients with RMS across different trial settings. We review relevant data and present a consensus view on what molecular features should be assessed. In particular, we recommend the assessment of the MYOD1-LR122R mutation for risk escalation, as it has been associated with poor outcomes in spindle/sclerosing RMS and rare RMS with classic embryonal histopathology. The prospective analyses of rare fusion genes beyond PAX3/7-FOXO1 will generate new data linked to outcomes and assessment of TP53 mutations and CDK4 amplification may confirm their prognostic value. Pathogenic/likely pathogenic germline variants in TP53 and other cancer predisposition genes should also be assessed. DNA/RNA profiling of tumours at diagnosis/relapse and serial analyses of plasma samples is recommended where possible to validate potential molecular biomarkers, identify new biomarkers and assess how liquid biopsy analyses can have the greatest benefit. Together with the development of new molecularly-derived therapeutic strategies that we review, a synchronised international approach is expected to enhance progress towards improved treatment assignment, management and outcomes for patients with RMS.

EWSR1-TFCP2 in an adolescent represents an extremely rare and aggressive form of intraosseous spindle cell rhabdomyosarcomas

The WHO Classification of Tumors of Soft Tissue and Bone subdivides rhabdomyosarcomas (RMS) into alveolar, embryonal, pleomorphic, and spindle cell RMS. Advances in molecular genetic diagnostics have made it possible to identify new RMS subgroups within traditional morphological entities. One of these subgroups comprises rare tumors characterized by epithelioid and spindle cell morphology, highly aggressive clinical course with pronounced tendency to intraosseous growth, and the presence of pathognomonic recurring genetic aberrations- chimeric genes/transcripts EWSR1::TFCP2, FUS::TFCP2, or MEIS1::NCOA2. Starting from 2018, only 26 reported cases of RMS have been assigned to this subgroup. The rarity of such tumors hampers their correct diagnostics for both anatomic pathologists and molecular oncologists. Here we describe a clinical case of intraosseous spindle cell RMS expressing EWSR1::TFCP2 fusion gene, encountered for the first time in our practice, in a 16-year-old female patient presenting with mandibular lesion. The diagnostic process took considerable time and involved RNA sequencing; a high-throughput method of molecular genetic research. The tumor was extremely aggressive, showing resistance to polychemotherapy, radiation therapy, and crizotinib targeted therapy, with the fatal outcome.

Pigmented PRRX1::NCOA1-rearranged Fibroblastic Tumor: A Rare Morphologic Variant of an Emerging Mesenchymal Tumor

PRRX::NCOAx-rearranged fibroblastic tumor is a recently described, morphologically distinctive subcutaneous fibroblastic tumor with benign behavior. To date, 12 cases have been reported. Here, we report a new case of PRRX::NCOAx-rearranged fibroblastic tumor showing a prominent pigmented component. The lesion occurred on the shoulder of a 23-year-old male. It was an at least 2.5 cm subcutaneous tumor with a multinodular and plexiform appearance. Morphologically, the tumor was characterized by a variably cellular proliferation of uniform oval to spindle cells arranged in fascicles and cords within a myxo-collagenous stroma. Irregular, elongated, dilated vessels were prominent at the periphery of tumor nodules. In addition, nests and clusters of pigment-laden epithelioid and dendritic cells were present. Immunohistochemically, the non-pigmented tumor cells showed patchy positivity for factor XIIIa and focal positivity for S100 protein. The pigmented cells were positive for S100 protein, SOX10, MITF, and a pan-melanocytic cocktail (Melan A, HMB-45, and tyrosinase). Next-generation RNA sequencing identified an in-frame PRRX1::NCOA1 fusion. In summary, this case highlights a rare pigmented variant of PRRX::NCOAx-rearranged fibroblastic tumor, expanding the morphologic spectrum of this newly described mesenchymal tumor. This article is protected by copyright. All rights reserved.

Intraosseous rhabdomyosarcoma of the maxilla with TFCP2 fusion: A rare aggressive subtype with predilection for the gnathic bones

Rhabdomyosarcomas (RMS) are malignant tumors with skeletal muscle differentiation extremely rare in intraosseous sites. We reported a rare case of an aggressive intraosseous RMS found in the maxilla of a 17-year-old female patient with five months of evolution. Computed tomography revealed a large osteolytic lesion extending from tooth 21 to 27, causing buccal and lingual cortical plate perforation. Microscopically, the lesion showed a proliferation of spindle-shaped cells with elongated nuclei and eosinophilic cytoplasm, arranged in an interlaced fascicle pattern. The nuclei ranged from vesicular with distinct nucleoli to hyperchromatic. A focal component of plump to epithelioid cells with a moderate amount of eosinophilic cytoplasm was seen at the periphery of the tumor. The immunohistochemical analysis revealed positivity for desmin, MyoD1, and myogenin (scattered cells). S-100, SOX10, HMB45, β-catenin, and CD34 were negative. Ki-67 was positive in 30% of tumor cells. Fluorescence in situ hybridization (FISH) analysis showed the presence of a FUS-TFCP2 fusion. The diagnosis was intraosseous RMS with TFCP2 fusion. Surgical excision followed by chemo- and radiotherapy was carried out; however, the patient died of disease nine months after the treatment. Because of the rarity and non-specific signs and symptoms, the clinical diagnosis of intraosseous RMS is difficult and often overlooked. Therefore, careful histopathological evaluation, supported by immunohistochemical and molecular analysis, is essential to correct diagnosis. Early surgical excision with tumor-free margins and prolonged follow-up are strongly recommended.

Epithelioid and Spindle Cell Rhabdomyosarcoma of the Oral Mucosa with FUS Rearrangement

The spectrum of rhabdomyosarcomas continues to expand beyond the more widely recognized embryonal and alveolar types as newer and novel subtypes are identified. These variants are typically classified on the basis of recurring mutations or translocations and frequently show distinctive clinical, morphologic and immunophenotypic features. A case of newly characterized FUS gene rearranged epithelioid and spindle cell rhabdomyosarcoma presenting as an intra-oral mucosal lesion without evidence of an osseous component is described. The characteristic features of an FET-TFCP2 fusion rhabdomyosarcoma were present, including strong pancytokeratin expression. This uncommon and aggressive entity displays a predilection for head and neck sites and familiarity may help avoid diagnostic pitfalls.

Genomic profiling identifies genes and pathways dysregulated by HEY1-NCOA2 fusion and shines a light on mesenchymal chondrosarcoma tumorigenesis

Mesenchymal chondrosarcoma is a rare, high‐grade, primitive mesenchymal tumor. It accounts for around 2–10% of all chondrosarcomas and mainly affects adolescents and young adults. We previously described the HEY1–NCOA2 as a recurrent gene fusion in mesenchymal chondrosarcoma, an important breakthrough for characterizing this disease; however, little study had been done to characterize the fusion protein functionally, in large part due to a lack of suitable models for evaluating the impact of HEY1–NCOA2 expression in the appropriate cellular context. We used iPSC‐derived mesenchymal stem cells (iPSC‐MSCs), which can differentiate into chondrocytes, and generated stable transduced iPSC‐MSCs with inducible expression of HEY1–NCOA2 fusion protein, wildtype HEY1 or wildtype NCOA2. We next comprehensively analyzed both the DNA binding properties and transcriptional impact of HEY1–NCOA2 expression by integrating genome‐wide chromatin immunoprecipitation sequencing (ChIP‐seq) and expression profiling (RNA‐seq). We demonstrated that HEY1–NCOA2 fusion protein preferentially binds to promoter regions of canonical HEY1 targets, resulting in transactivation of HEY1 targets, and significantly enhances cell proliferation. Intriguingly, we identified that both PDGFB and PDGFRA were directly targeted and upregulated by HEY1‐NCOA2; and the fusion protein, but not wildtype HEY1 or NCOA2, dramatically increased the level of phospho‐AKT (Ser473). Our findings provide a rationale for exploring PDGF/PI3K/AKT inhibition in treating mesenchymal chondrosarcoma. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Update from the 5th Edition of the World Health Organization Classification of Head and Neck Tumors: Soft Tissue Tumors

The fifth (5th) edition of the World Health Organization (WHO) Classification of Head and Neck Tumors introduces a new chapter dedicated to soft tissue neoplasms commonly affecting the head and neck. While the diversity, rarity, and wide anatomic range of soft tissue tumors precludes a discussion of all entities that may be found in the head and neck, the addition of this new chapter to the head and neck "blue book" aims to provide a more comprehensive and uniform reference text, including updated diagnostic criteria, of mesenchymal tumor types frequently (or exclusively) arising at head and neck sites. Since publication of the previous edition in 2017, there have been numerous advances in our understanding of the pathogenesis of many soft tissue tumors which have facilitated refinements in tumor classification, identification of novel entities, development of diagnostic markers, and improved prognostication. This review will provide a focused discussion of the soft tissue tumors included in the 5th edition WHO Head and Neck classification, with an emphasis on updates.

Proceedings of the North American Society of Head and Neck Pathology, Los Angeles, CA, March 20, 2022. Emerging Bone and Soft Tissue Neoplasms in the Head and Neck Region

In the past decade, several emerging bone and soft tissue neoplasms of the head and neck region have been described in the literature, including GLI1-altered mesenchymal tumors, (intraosseous) rhabdomyosarcoma with TFCP2 fusion, and adamantinoma-like Ewing sarcoma. This review provides a summary of the clinical features, histologic characteristics, immunoprofile, key diagnostic features, and differential diagnoses of these emerging entities. Notably, all three entities show epithelioid morphology and cytokeratin immunopositivity, highlighting the need to consider these mesenchymal neoplasms in the differential diagnoses of cytokeratin-positive epithelioid tumors in the head and neck region. Appropriate workups including detection of the characteristic molecular alterations are essential for the correct diagnosis.

An Integrative Morphologic and Molecular Approach for Diagnosis of Rhabdomyosarcoma and Subclassification of Rhabdomyosarcoma

CONTEXT.—

Rhabdomyosarcoma, the most common soft tissue sarcoma of children, is currently classified into the following 4 subtypes: embryonal rhabdomyosarcoma, alveolar rhabdomyosarcoma, spindle cell/sclerosing rhabdomyosarcoma, and pleomorphic rhabdomyosarcoma, based on recent molecular genetic knowledge and morphologic features.

OBJECTIVE.—

To highlight the most recent advances of molecular genetic alterations, and to familiarize pathologists with most recent genotype and phenotype correlation in rhabdomyosarcoma.

DATA SOURCES.—

Data were derived from the World Health Organization Classification of Soft Tissue and Bone Tumors, fifth edition, recently published literature (PubMed), and clinical practice experience.

CONCLUSIONS.—

Current classification has been significantly impacted by genotype and phenotype correlation, especially with PAX-FOXO1 fusion-positive rhabdomyosarcoma versus fusion-negative rhabdomyosarcoma, and with emergence of 3 distinct new subtypes of spindle cell/sclerosing rhabdomyosarcoma. Although all rhabdomyosarcomas were considered to be a single diagnostic entity in the past, they are now considered to be a group of histologically similar but biologically diverse entities because their clinical behavior and underlying molecular alterations dramatically differ. This review outlines recent molecular genetic developments, corresponding morphologic features, and current challenges faced by pathologists in daily practice.

Primary Fallopian Tube Mullerian Adenosarcoma With Sarcomatous Overgrowth and a Previously Unreported MEIS1-NCOA2 Gene Fusion

Extrauterine Mullerian adenosarcomas (MA) are rare and often associated with endometriosis. We report a 55-yr-old patient seen in consultation for abdominal pain and bloating. Imaging was suggestive of a left adnexal mass and "peritoneal carcinomatosis". Pathological examination of the specimen revealed a MA arising in the left fallopian tube, with sarcomatous overgrowth, diffuse peritoneal involvement and omental "caking". Next-generation sequencing identified a MEIS1-NCOA2 gene fusion, previously unreported in MA.

Evolving classification of rhabdomyosarcoma

Rhabdomyosarcomas comprise the single largest category of soft tissue sarcomas in children and adolescents in the United States, occurring in 4.5 million people aged below 20 years. Based on the clinicopathological features and genetic abnormalities identified, rhabdomyosarcomas are classified into embryonal, alveolar, spindle cell/sclerosing and pleomorphic subtypes. Each subtype shows distinctive morphology and has characteristic genetic abnormalities. This review discusses the evolution of the classification of rhabdomyosarcoma to the present day, together with a discussion of key histomorphological and genetic features of each subtype and the diagnostic approach to these tumours.