FET(EWSR1)-TFCP2 Rhabdomyosarcoma: An Additional Example of this Aggressive Variant with Predilection for the Gnathic Bones

TFCP2 Fusion-Positive Rhabdomyosarcomas: A Report of 10 Cases and a Review of the Literature

Background/Objectives: The fusion of the TFCP2 gene with either EWSR1 or FUS typically results in a spindle cell and/or epithelioid variant of rhabdomyosarcoma. This is an ultra-rare type of sarcoma, with most of our knowledge about these coming from case reports and small case series. Herein, we describe the clinical characteristics and treatment course of 10 patients with TFCP2 fusion sarcomas. Methods: We identified 10 patients in our hospital system with TFCP2 fusion sarcomas and 43 previously reported cases in the literature. We assessed primary tumor characteristics, treatment regimens, and survival rates among all cases. Results: We find that TFCP2 fusion sarcomas most commonly occur in young adults (median age: 33 years) and arise in craniofacial bones (7/10, 70%). Concomitant ALK alterations and ALK overexpression is nearly universal, and two of our patients were treated with ALK inhibitors; one patient had a near complete response before eventual progression, while the other patient had progressive disease after 2 months. For most, the prognosis was poor. The median overall survival in this cohort was 24.7 months (range: 5.9-29.7 months). Four patients were treated with upfront surgery, and all four developed recurrent disease. The median time to recurrence following upfront surgery was 2.1 months (range: 0.73-6.9 months). Five patients received systemic therapy, and the median progression-free survival from the start of treatment to progression was 1.6 months (range: 0.97-2.7). We also review the 53 total cases of TFCP2 fusion sarcomas in the literature, again highlighting the dismal outcomes in this disease. Conclusions:TFCP2 fusion sarcomas are proven to be aggressive and have poor prognosis. Additional work is needed to define the optimal treatment course for TFCP2 fusion sarcomas.

A Rare Case Report of Intraosseous Spindle and Epithelioid Rhabdomyosarcoma With TFCP2 Rearrangement: A Pathological Diagnostic Conundrum and Literature Review

Rhabdomyosarcoma is a highly malignant tumor with striated muscle differentiation, which is histologically classified as alveolar, embryonal, pleomorphic, and spindle cell/sclerosing histological subtype. Rhabdomyosarcoma with TFCP2 rearrangement, which usually occurs in the bone, is a newly identified rare spindle and epithelioid rhabdomyosarcoma with characteristic clinicopathological features and molecular alterations. We report a 39-year-old female patient who underwent local excision of the mandibular lesion. Microscopically, the intraosseous tumor was composed of spindle-shaped, epithelioid, and rhabdomyoblastic cells with atypical nuclei and atypical mitotic figures. In addition, TFCP2 rearrangement was revealed by the fluorescence in situ hybridization. The tumor was thus correctly diagnosed as rhabdomyosarcoma with TFCP2 rearrangement. The patient was scheduled to undergo radiotherapy, and triple-agent chemotherapy after surgery, and no tumor recurrence or metastasis was detected during the 3-month postoperative follow up. Since this tumor is relatively rare and newly recognized, it can be easily misdiagnosed or missed and might be a conundrum of pathological diagnosis. Familiarity with its clinicopathological features and molecular alterations is essential for its correct diagnosis. Therefore, we summarized the clinicopathological, immunohistochemical, and molecular alterations of 43 cases of this rare rhabdomyosarcoma variant in the English-language literature. In addition, the differential diagnosis of this lesion is crucial either.

[Of muscle and bone: Diagnostic challenge of an uncommonly located rhabdomyosarcoma]

Rhabdomyosarcomas form a heterogeneous group of malignant soft tissue tumors characterized by immature striated muscle differentiation. Epithelioid and spindle cell rhabdomyosarcoma is a recently described entity, mainly localized intraosseously and predominantly found in young patients. Its late diagnosis and high aggressiveness confer a grim prognosis to this tumor, highlighting the importance of early recognition and appropriate management. We present herein the clinical, histopathological, immunohistochemical, and molecular aspects of this entity through a case of misleading presentation.

Primary Intraosseous Spindle Cell Rhabdomyosarcoma: A Case Report in an Unusual Location

Spindle cell/sclerosing rhabdomyosarcoma is an infrequent subtype of rhabdomyosarcoma according to the World Health Organization Classification of Soft Tissue and Bone Tumours, which includes a novel category of intraosseous spindle-cell rhabdomyosarcomas (ISCRMS) with EWSR1:: or FUS::TFCP2 fusions. We report a case of ISCRMS with EWSR1::TFCP2 fusion presenting in the femur mimicking osteosarcoma in this unusual primary location. We present an 18-year-old male with relapsed widely metastatic sarcoma, morphologically identical to osteosarcoma responding poorly to chemotherapy, initially presenting in the distal femur. Sections showed a high-grade malignant neoplasm with sheets of epithelioid and spindled cells without obvious rhabdomyoblastic differentiation morphologically containing focal areas resembling new bone/osteoid formation. Molecular sequencing identified t(12;22) EWSR1::TFCP2. The tumor cells were diffusely positive for pancytokeratin, MyoD1, and ALK by retrospective immunohistochemistry. Desmin and SATB2 were focally positive. Myogenin was negative, and INI-1 expression was retained. ISCRMS commonly involves craniofacial and pelvic bones, but rarely originates in long bones, as in this case. Initially, osteosarcoma was the primary diagnostic consideration based on distal long bone location, patient age, and evidence of osteoid formation. Distinction between the two entities may be nearly impossible on morphologic grounds alone, which presents a diagnostic pitfall without molecular or extensive immunoprofiling data.

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.

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%).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Novel EWSR1-UBP1 fusion expands the spectrum of spindle cell rhabdomyosarcomas

Over the last decade, the development of next-generation sequencing techniques has led to the molecular dismantlement of adult and pediatric sarcoma, with the identification of multiple gene fusions associated with specific subtypes and currently integrated into diagnostic classifications. In this report, we describe and discuss the identification of a novel EWSR1-UBP1 gene fusion in an adult patient presenting with multi-metastatic sarcoma. Extensive pathological, transcriptomic, and genomic characterization of this tumor in comparison with a cohort of different subtypes of pediatric and adult sarcoma revealed that this fusion represents a novel variant of spindle cell rhabdomyosarcoma with features of TFCP2-rearranged subfamily.

Novel fusion genes in spindle cell rhabdomyosarcoma: The spectrum broadens

Rhabdomyosarcoma (RMS) encompasses a heterogeneous group of tumors with striated muscle differentiation. RMSs are classified as alveolar, embryonal, spindle cell/sclerosing, and pleomorphic types and molecular analysis of these tumors has identified aberrations that are useful in their further subclassification. Spindle cell rhabdomyosarcoma (SpRMS) is uncommon and has been described with VGLL2 fusions, EWSR1/FUS-TFCP2 rearrangements, and myoD1 mutations-the mutations are associated with significantly different prognoses. In addition, the NCOA2-MEIS1 fusion gene was recently described in two primary intraosseous RMS that contained spindle cell components. Herein, we report three cases of SpRMS harboring different novel fusion genes, one possessing EP300-VGLL3, a second with NCOA2-MEIS1 and CAV1-MET, and the third case had HMGA2-NEGR1 and multiple amplified genes.

Head and neck rhabdomyosarcoma with TFCP2 fusions and ALK overexpression: a clinicopathological and molecular analysis of 11 cases

AIMS

Primary intraosseous rhabdomyosarcoma (RMS) is a rare entity defined by EWSR1/FUS-TFCP2 or, less commonly, MEIS1-NCOA2 fusions. The lesions often show a hybrid spindle and epithelioid phenotype, frequently coexpress myogenic markers, ALK, and cytokeratin, and show a striking propensity for the pelvic and craniofacial bones. The aim of this study was to investigate the clinicopathological and molecular features of 11 head and neck RMSs (HNRMSs) characterised by the genetic alterations described in intraosseous RMS.

METHODS AND RESULTS

The molecular abnormalities were analysed with fluorescence in-situ hybridisation and/or targeted RNA/DNA sequencing. Seven cases had FUS-TFCP2 fusions, four had EWSR1-TFCP2 fusions, and none had MEIS1-NCOA2 fusions. All except one case were intraosseous, affecting the mandible (n = 4), maxilla (n = 3), and skull (n = 3). One case occurred in the superficial soft tissue of the neck. The median age was 29 years (range, 16-74 years), with an equal sex distribution. All tumours showed mixed epithelioid and spindle morphology. Immunohistochemical coexpression of desmin, myogenin, MyoD1, ALK, and cytokeratin was seen in most cases. An intragenic ALK deletion was seen in 43% of cases. Regional and distant spread were seen in three and four patients, respectively. Two patients died of their disease.

CONCLUSIONS

We herein present the largest series of HNRMSs with TFCP2 fusions to date. The findings show a strong predilection for the skeleton in young adults, although we also report an extraosseous case. The tumours are characterised by a distinctive spindle and epithelioid phenotype and a peculiar immunoprofile, with coexpression of myogenic markers, epithelial markers, and ALK. They are associated with a poor prognosis, including regional or distant spread and disease-related death.