Low-grade myofibroblastic sarcoma: analysis of 18 cases in the spectrum of myofibroblastic tumors

Recurrent USP6 rearrangement in a subset of atypical myofibroblastic tumours of the soft tissues: low-grade myofibroblastic sarcoma or atypical/malignant nodular fasciitis?

AIMS

Low-grade myofibroblastic sarcoma (LGMS) is a rarely metastasizing myofibroblastic tumour mostly affecting extremities and the head and neck of adults. Histologically, it shows long infiltrative fascicles of spindle cells with moderate nuclear atypia. By immunohistochemistry, it stains positive for smooth muscle actin (SMA) and sometimes for desmin. To date, no recurrent genetic abnormalities have been described. Ubiquitin-specific peptidase 6 (USP6) gene rearrangement is typically found in some benign bone and soft-tissue tumours including nodular fasciitis (NF), among others. Nevertheless, rare cases of USP6-rearranged tumours resembling NF with atypical features have been reported.

METHODS AND RESULTS

One index case of LGMS of the deltoid in a 56-year-old man presented the THBS2::USP6 translocation by RNA sequencing (Archer FusionPlex Sarcoma v2 panel). Further screening of 11 cases of LGMS using fluorescent in situ hybridization (FISH) analysis with a USP6 break-apart probe identified two additional cases. These cases were investigated with RNA-sequencing, and a RRBP1::USP6 translocation was detected in one. The other case was not assessable because of low-quality RNA. Noteworthy, rearranged LGMSs presented distinctive features including variable multinodular/plexiform architecture, prominent vasculature with occasional wall thickening, scattered osteoclast-like multinucleated giant cells, and peripheral lymphoid aggregates.

CONCLUSION

Our findings support the notion that among soft-tissue neoplasms with fibroblastic/myofibroblastic phenotype, USP6 rearrangement is not limited to benign tumours, and warrants further investigation of genetic changes in myofibroblastic sarcomas.

Giant Myxofibrosarcoma in the Lower Limb: An Overview of Diagnostic and Clinical Management

Myxofibrosarcoma (MFS), an aggressive soft tissue sarcoma, is one of the undifferentiated pleomorphic sarcomas; it has a low incidence, affecting people in the sixth to eighth decades of life. It usually involves the extremities and is painless with a slow-growing pattern. Based on the case of a 52-year-old female patient who presented with a painful, massive, rapid-growing, ulcerated tumor of the anterior surface of the left thigh, we performed a literature review regarding the current standard of care for patients with MFS. Computed tomography examination, followed by magnetic resonance imaging and surgical biopsy with histopathological examination, confirmed the diagnosis and the presence of lung and inguinal lymph node metastases. Due to the rapid-growing pattern and the local aggressiveness, our tumor board team recommended emergency excisional surgery, with subsequent reconstructive procedures followed by referral to an oncological center. This review emphasizes the importance of proper and rapid diagnosis, followed by multidisciplinary management, for MFS cases with atypical presentation and distal metastases to improve overall outcomes.

Myofibrosarcoma of Maxilla - Case Report and Review of Literature

Myofibrosarcoma is a distinct mesenchymal malignancy which commonly occurs in head and neck region. It has a high tendency for local recurrence and distant metastasis. 39-year-old male presented with epistaxis, nasal obstruction and left sided complete loss of vision. He underwent functional endoscopic sinus surgery and guided biopsy. MRI scan showed a lesion epicentred in the left maxillary sinus, superiorly extending into the orbit. He underwent Class 4b maxillectomy with neck dissection, tracheostomy and free flap reconstruction. Histopathological examination yielded final diagnosis as myofibrosarcoma of maxilla. The patient was planned for adjuvant radiotherapy and has been disease free for 3 years.

Myofibroblastic sarcoma in breast: a case report and literature review

Myofibroblastic sarcoma is a malignancy in which myofibroblasts are the main component, with a very low incidence. In this study, we report a case of low-grade myofibroblastic sarcoma (LGMS) in the breast. After the diagnosis of LGMS, the patient received a mastectomy. The patient showed no relapse or progression during the follow-up time of 3 months following the operation. LGMS in the breast is extremely rare, and the limited experience with its diagnosis and treatment brings obstacles to doctors. Therefore, this report summarizes the preoperative diagnosis, treatment, and prognosis of breast LGMS through a literature review.

Misdiagnosis of synovial sarcoma - cellular myofibroma with SRF-RELA gene fusion: A case report

BACKGROUND

Cellular myofibroma is a rare subtype of myofibroma that was first described in 2017. Its diagnosis is often challenging because of its relative rarity, lack of known genetic abnormalities, and expression of muscle markers that can be confused with sarcomas that have myogenic differentiation. Currently, scholars have limited knowledge of this disease, and published cases are few. Further accumulation of diagnostic and treatment experiences is required.

CASE SUMMARY

A 16-year-old girl experienced left upper limb swelling for 3 years. She sought medical attention at a local hospital 10 months ago, where magnetic resonance imaging revealed a 5-cm soft tissue mass. Needle biopsy performed at a local hospital resulted in the diagnosis of a spindle cell soft tissue sarcoma. The patient was referred to our hospital for limb salvage surgery with endoprosthetic replacement. She was initially diagnosed with a synovial sarcoma. Consequently, clinical management with chemotherapy was continued for the malignant sarcoma. Our pathology department also performed fluorescence in situ hybridization for result validation, which returned negative for SS18 gene breaks, indicating that it was not a synovial sarcoma. Next-generation sequencing was used to identify the SRF-RELA rearrangement. The final pathological diagnosis was a cellular/myofibroblastic neoplasm with an SRF-RELA gene fusion. The patient had initially received two courses of chemotherapy; however, chemotherapy was discontinued after the final diagnosis.

CONCLUSION

This case was misdiagnosed because of its rare occurrence, benign biological behavior, and pathological similarity to soft tissue sarcoma.

Palmer Nodular Fasciitis Harboring a Novel SREBF1::USP6 Fusion Gene

The diagnosis of low-grade fibroblastic/myofibroblastic tumors of acral sites can be challenging. These tumors encompass a diverse group of neoplasms with a spectrum of biologic potential ranges from benign to overtly malignant. They often demonstrate significant clinical, radiologic, and immunophenotypic overlap, in which the molecular phenotype may play an important diagnostic role to arrive at the final diagnosis. Herein, we report a case of soft tissue mass lesion presented on the palm of an adult patient for four months. Histologically, the tumor consisted of primarily low-grade spindle cells expressing smooth muscle actin. Molecular testing revealed a novel SREBF1::USP6 fusion gene, confirming the final diagnosis of nodular fasciitis and ultimately expanding its molecular profile. This case highlights the diagnostic value of single, cost-effective, targeted molecular panel to arrive at an accurate diagnosis and provide helpful therapeutic information.

Anlotinib in combination with pembrolizumab for low-grade myofibroblastic sarcoma of the pancreas: A case report

BACKGROUND

Low-grade myofibroblastic sarcoma (LGMS) is a rare spindle cell sarcoma especially in the pancreas, with myofibroblastic differentiation. Hitherto, only a few cases have been reported.

CASE SUMMARY

Herein, we report a case involving the discovery of a pancreatic mass detected during a routine physical examination. Subsequent imaging and pathological tests of the patient led to the diagnosis of LGMS of the pancreas. Following surgical intervention, the patient experienced recurrence and metastasis. Conventional treatment is not effective for postoperative recurrent pancreatic LGMS with multiple metastases. After communicating with the patients and their families, informed consent was obtained for the treatment of anlotinib combined with pembrolizumab. Evaluation of imaging and clinical symptoms post-treatment revealed a relatively favorable response to the combination of anlotinib and pembrolizumab.

CONCLUSION

Based on the comprehensive literature review, our report aimed to provide evidence for a better understanding of the disease characteristics, diagnostic criteria, imaging findings, and identification of LGMS. And explore novel treatment strategies for this disease.

Unusual Presentation of Tonsillar Spindle Cell Neoplasm: A Case Report

Spindle cell neoplasm of the tonsil are rare (Minami et al. in Am J Otolaryngol 29(2):123-125, 2008) and can be difficult to diagnose due to their non-specific clinical presentation and histological characteristics (Su et al. in J Chin Med Assoc 69(10):478-483, 2006). Differential diagnoses include lymphoma and squamous cell carcinoma (Hyams in Clin Otolaryngol Allied Sci 3(2):117-126, 1978). Oropharyngeal spindle cell neoplasms were more likely to occur in the tongue base and tonsil (58%) (Gerry et al. in Ann Otol Rhinol Laryngol 123(8):576-583, 2014). In this article, we report a case of tonsillar spindle cell neoplasm which is extremely rare.

A Systematic Review and Illustrative Case Presentation of Low-Grade Myofibroblastic Sarcoma (LGMS) of the Extremities

INTRODUCTION

Low-grade myofibroblastic sarcoma (LGMS) is a rare tumor entity which occurs in the subcutaneous and deep soft tissues; it is less common in the bone with a predilection for the extremities and the head and neck region. As confirming the diagnosis is difficult and treatment strategies are not standardized, we aimed to identify patient and tumor characteristics, and to summarize treatment strategies and their clinical outcomes to guide surgeons.

METHODS

Included were full articles reporting patients with histology of LGMS in the extremities, excluding tumors of the trunk. All patients underwent surgery but with different extend, from marginal to wide resection. Included studies should inform about local recurrence, metastasis, or evidence of disease, depending on the surgical treatment. We conducted a structured search using MEDLINE (via PubMed), Web of Science, EMBASE and Cochrane Central Register of Controlled Trials (CENTRAL) to identify studies on low-grade myofibroblastic sarcoma of the extremities. Study designs like randomized controlled trials, systematic reviews, prospective trials, retrospective studies, and case reports were included. Prospective studies and comparative studies were not available at all. Therefore, meta-analysis was not possible and statistical analysis was purely descriptive.

RESULTS

Of the 789 studies identified from our initial search, 17 studies including 59 cases reported LGMS of the extremities with the surgical treatment and clinical outcome and were therefore analyzed. In addition, we present the rare case and surgical management of a 28-year-old male patient with residual LGMS of the thumb after an initial incomplete resection. The current literature suggests that a wide excision with R0 margins should be considered the standard treatment for LGMS. In cases where surgery leads to significant functional impairment, individual options like free tissue transfer from a donor site have to be considered. Therefore, we also present an illustrative case. For all selected case series and case reports, a high risk of confounding, selection bias, information bias, and reporting bias must be anticipated. Nevertheless, this systematic review provides a comprehensive overview on surgical treatment and clinical outcomes in LGMS surgery of the extremities.

Low-Grade Myofibroblastic Sarcoma on Back with Repeated Localized Recurrence and Regional Metastasis

Low-grade myofibroblastic sarcoma (LGMS) is a rare spindle cell tumor with indolent course. Due to rarity and low-grade histologic features of LGMS, accurate diagnosis is challenging. We report a 63-year-old female patient with a three-month history of a 3.1 cm×2.5 cm sized, firm, skin-colored, painless, protruding left back mass. Initial excisional biopsy was performed and the mass was diagnosed as nodular fasciitis. After 18 months after excision, the mass recurred with pain and grew larger. Considering the clinical manifestations, diagnostic impression was changed as dermatofibrosarcoma protuberans not nodular fasciitis. Second wide excision was performed and the histopathology revealed proliferative atypical spindle cells with moderate nuclear atypia and a distinctive whorling pattern, which is suggestive of low-grade sarcoma. Additional computed tomography and positron emission tomography revealed no metastasis and suspicious residual viable malignant tissue. To remove suspicious residual tumor, third wide excision were performed and the diagnosis confirmed as LGMS. A microscopically clear resection was achieved with deep and lateral safety margin 0.6 cm each. Despite of postoperative radiotherapy with 35 times, recurrence of the tumor and lung metastasis was found after 7 months later. LGMS rarely metastasizes and occurs most commonly in the head and neck region. Thus, we report a rare case of LGMS on back which repeated localized recurrence and regional lung metastasis occurred despite wide excision and adjuvant radiotherapy.

Low-Grade Myofibroblastic Sarcoma of the Oral and Maxillofacial Region: An International Clinicopathologic Study of 13 Cases and Literature Review

Low-grade myofibroblastic sarcoma (LGMS) represents an atypical tumor composed of myofibroblasts with a variety of histological patterns and with a high tendency to local recurrence and a low probability of distant metastases. LGMS has predilection for the head and neck regions, especially the oral cavity. This study aimed to report 13 new cases of LGMS arising in the oral and maxillofacial region. This study included LGMS cases from five oral and maxillofacial pathology laboratories in four different countries (Brazil, Peru, Guatemala, and South Africa). Their clinical, radiographic, histopathological, and immunohistochemical findings were evaluated. In this current international case series, most patients were females with a mean age of 38.7 years, and commonly presenting a nodular lesion in maxilla. Microscopically, all cases showed a neoplasm formed by oval to spindle cells in a fibrous stroma with myxoid and dense areas, some atypical mitoses, and prominent nucleoli. The immunohistochemical panel showed positivity for smooth muscle actin (12 of 13 cases), HHF35 (2 of 4 cases), β-catenin (3 of 5 cases), desmin (3 of 11 cases), and Ki-67 (range from 5 to 50%). H-caldesmon was negative for all cases. The diagnosis of LGMS was confirmed in all cases. LGMS shows predominance in young adults, with a slight predilection for the female sex, and maxillary region. LGMS should be a differential diagnosis of myofibroblastic lesions that show a proliferation of spindle cells in a fibrous stroma with myxoid and dense areas and some atypical mitoses, supporting the diagnosis with a complementary immunohistochemical study. Complete surgical excision with clear margins is the treatment of choice. However, long-term follow-up information is required before definitive conclusions can be drawn regarding the incidence of recurrence and the possibility of metastasis.

Low-grade malignant myofibroblastic sarcoma of the larynx: a case report

Low-grade myofibroblastic sarcoma (LGMS) is a rare malignant mesenchymal tumor derived from myofibroblasts. It is commonly identified in the head and neck, and particularly in the oral cavity, but rarely in the larynx. In this case report, we describe a patient who presented with hoarseness and underwent electronic fiber laryngoscopy, which revealed a neoplasm on the surface of his left vocal cord. The vocal cord tumor was resected under general anesthesia, and a malignant LGMS was diagnosed on postoperative pathologic examination. The results of immunohistochemical staining of the sections for vimentin (diffuse +), actin (partial +), and desmin (-) were consistent with this diagnosis. The patient recovered well after the surgery, and there was no recurrence of the neoplasm.

Risk Factors for Recurrence and the Role of Radiotherapy in Low-grade Myofibroblastic Sarcoma: A Systematic Review

Low-grade myofibroblastic sarcoma (LGMS) is a rare malignancy that commonly occurs in the head and neck region. The role of radiotherapy has been unclear in treating LGMS and the risk factors for recurrence have remained undefined. The objective of this study is to determine risk factors for the recurrence of LGMS in the head and neck as well as the role of radiotherapy in the treatment of LGMS. A comprehensive review of the literature was performed through Pubmed leading to the inclusion of 36 articles after our inclusion and exclusion criteria were applied. Continuous variables were analyzed with a 2-tail unpaired t test. Categorical variables were assessed with the χ 2 test or Fisher exact test. Logistic regression and multivariable logistic regression analysis with 95% CIs were used to obtain odds ratios. LGMS most commonly occurred in the oral cavity (49.2%). Half of all recurrences occurred in the paranasal sinuses/skull base. LGMS occurring at the paranasal sinuses/skull base had a significantly increased risk of recurrence compared with other subsites within the head and neck (odds ratio: -40; 95% CI: 2.190, 762.005; P = 0.013). The average time to recurrence of LGMS was 19.2 months. Adjuvant treatment with radiation did not improve recurrence rates. Sex, tumor size, or bony involvement were not found as risk factors for recurrence. Patients with LGMS of the paranasal sinuses and skull base are at high risk for recurrence and should be monitored closely. The role of adjuvant radiation treatment in these patients remains unclear.

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.

Case Report: Immunotherapy for low-grade myofibroblastic sarcoma of the pharynx

Low-grade myofibroblastic sarcoma (LGMS) characterized by the increased proliferation of myofibroblasts is a rare type of malignant myofibroblastic tumor that frequently occurs in the head and neck region. Presently, there is no consensus regarding the treatment of LGMS. Here, we report a rare case of LGMS of the pharynx in a 40-year-old male admitted to our hospital. The patient underwent resection for a right metastatic lesion and parapharyngeal mass. However, he had recurrence and multiple metastases without a surgical indication. Then the patient received the treatment of anlotinib plus pembrolizumab for 4 cycles, and there was a partial response (PR) to the treatment. Due to the adverse reaction of anlotinib, the patient subsequently received monotherapy of pembrolizumab for 22 cycles and achieved a complete response (CR). As the first case report of the immunotherapy for LGMS, our study highlights that this strategy may be of great significance to the treatment of LGMS.

An update on selected cutaneous (myo) fibroblastic mesenchymal tumors

Cutaneous (myo)fibroblastic tumors constitute a group of tumors with overlapping clinicopathological features and variable biologic behavior. In the present review we focus on the histomorphology, immunohistochemical profile and molecular background of the following entities: dermatofibrosarcoma protuberans (DFSP), CD34-positive fibroblastic tumor (SCD34FT), myxoinflammatory sarcoma (MIFS), low-grade myofibroblastic sarcoma, solitary fibrous tumor and nodular fasciitis. Although some of these entities typically arise in deep-seated locations, they may occasionally present as cutaneous/superficial tumors and might be challenging to recognize. This review covers in depth the latest advances in molecular diagnostics and immunohistochemical markers that have significantly facilitated the correct classification and diagnosis of these neoplasms.

Recurrent Giant Myofibroblastic Sarcoma of Neck in a Teenager: Overcoming Treatment Challenges

Sarcomas are rare tumors arising from a variety of mesenchymal tissues which are even rarer in head and neck region amounting 1% only of the 5% of sarcomas. About 80% of head and neck sarcomas originate in soft tissue while the remaining 20% arise from bone (Cormier and Pollock in J Clin 54:94-109, 2004). One among the commonly presenting variants of sarcomas in head and neck that our patient was diagnosed with is Low grade myofibroblastic sarcoma (LGMS). These even though uncommon have a predilection for head and neck region particularly the tongue (Mentzel et al. in Am J Surg Pathol 22:1228-38, 1998; Cai et al. in Virchows Arch 463:827-36, 2013; Meng et al. in Chin Med J 120:363-9, 2007; Demarosi et al. in Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 108:248-54, 2009). LGMS was reclassified as a distinct entity by the WHO classification of soft tissue tumors in 2002 (Qiu et al. in Oncol Lett 9:619-25, 2015). Oncological resection is the mainstay of treatment. In case of bulky tumor, resection and reconstruction would be challenging. We report a recurrent LGMS of 15-year-old girl who presented with a ginormous soft tissue swelling in her left neck region which made her day-to-day activities strenuous and made her non ambulatory and the line of treatment executed in order to get her back on feet, healthy & free of the debilitating tumor.

Clinical Outcome of Low-Grade Myofibroblastic Sarcoma in Japan: A Multicenter Study from the Japanese Musculoskeletal Oncology Group

This retrospective multicenter study aimed to analyze the clinical features and prognosis of 24 patients diagnosed with LGMS between 2002 and 2019 in the Japanese sarcoma network. Twenty-two cases were surgically treated and two cases were treated with radical radiotherapy (RT). The pathological margin was R0 in 14 cases, R1 in 7 cases, and R2 in 1 case. The best overall response in the two patients who underwent radical RT was one complete response and one partial response. Local relapse occurred in 20.8% of patients. Local relapse-free survival (LRFS) was 91.3% at 2 years and 75.4% at 5 years. In univariate analysis, tumors of 5 cm or more were significantly more likely to cause local relapse (p < 0.01). In terms of the treatment of relapsed tumors, surgery was performed in two cases and radical RT was performed in three cases. None of the patients experienced a second local relapse. Disease-specific survival was 100% at 5 years. A wide excision aimed at the microscopically R0 margin is considered the standard treatment for LGMS. However, RT may be a viable option in unresectable cases or in cases where surgery is expected to cause significant functional impairment.

A unique case of high-grade myofibroblastic sarcoma initially presenting with oral symptoms

High-grade myofibroblastic sarcoma is a rare mesenchymal tumor with a high recurrence and metastatic rate. Few cases of high-grade myofibroblastic sarcomas have been reported. Herein, we report a rare case of undifferentiated, high-grade myofibroblastic sarcoma with an unclear primary site, initially presenting with oral symptoms. High-grade myofibroblastic sarcoma was diagnosed following an excisional biopsy of a gingival tumor. After this excisional biopsy, systemic imaging revealed multiple metastases in the tonsil, lung, liver, kidney, and eye. The patient underwent two cycles of chemotherapy (doxorubicin). During follow-up, the tumor progressed rapidly and metastasized to the skin of the head and neck. The patient expired three months after the initial examination.

NTRK-rearranged spindle cell neoplasms are ubiquitous tumours of myofibroblastic lineage with a distinct methylation class

AIMS

NTRK gene fusions have been described in a wide variety of central nervous system (CNS) and soft tissue tumours, including the provisional tumour type 'spindle cell neoplasm, NTRK-rearranged' (SCN-NTRK), added to the 2020 World Health Organisation Classification of Soft Tissue Tumours. Because of histopathological and molecular overlaps with other soft tissue entities, controversy remains concerning the lineage and terminology of SCN-NTRK.

METHODS AND RESULTS

This study included 16 mesenchymal tumours displaying kinase gene fusions (NTRK fusions and one MET fusion) initially diagnosed as infantile fibrosarcomas (IFS), SCN-NTRK and adult-type fibrosarcomas from the soft tissue, viscera and CNS. We used immunohistochemistry, DNA methylation profiling, whole RNA-sequencing and ultrastructural analysis to characterise them. Unsupervised t-distributed stochastic neighbour embedding analysis showed that 11 cases (two CNS tumours and nine extra-CNS) formed a unique and new methylation cluster, while all tumours but one, initially diagnosed as IFS, clustered in a distinct methylation class. All the tumours except one formed a single cluster within the hierarchical clustering of whole RNA-sequencing data. Tumours from the novel methylation class co-expressed CD34 and S100, had variable histopathological grades and frequently displayed a CDKN2A deletion. Ultrastructural analyses evidenced a myofibroblastic differentiation.

CONCLUSIONS

Our findings confirm that SCN-NTRK share similar features in adults and children and in all locations combine an infiltrative pattern, distinct epigenetic and transcriptomic profiles, and ultrastructural evidence of a myofibroblastic lineage. Further studies may support the use of new terminology to better describe their myofibroblastic nature.

Low-grade myofibroblastic sarcoma of the mandible: A rare tumour of childhood

Low-grade myofibroblastic sarcoma is a rare and indolent tumour of soft tissue. This tumour is relatively common in the head and neck region followed by extremities. Primary low-grade myofibroblastic sarcoma of the mandible is very rarely reported and the occurrence of this tumour in a child is very unusual. A 7-year-old male child presented with a swelling in right angle of mandible. X-ray and computed tomography scan showed a lytic lesion. The lesion was excised and the tissue was sent for histopathological evaluation, which revealed a cellular spindle cell neoplasm arranged in fascicles. The tumour was partly circumscribed and lobulated. On immunohistochemistry (IHC), these tumour cells showed cytoplasmic positivity for vimentin, and smooth muscle actin showed 'tram-track' pattern of positivity. The case was diagnosed as low-grade myofibroblastic sarcoma. There are no definite clinical features or pathognomonic radiological appearances of this tumour that can differentiate this rare tumour from other commonly encountered gnathic bone tumours, such as osteosarcoma, inflammatory myofibroblastic tumour, etc., Histopathological diagnosis coupled with ancillary investigations such as IHC is important to establish a definite diagnosis and rule out the differentials. The exact biological behaviour of this tumour is not known.

Low-Grade Malignant Myofibroblastic Sarcoma of the Larynx: A Case Report and Literature Review

Squamous cell carcinomas predominate in laryngeal malignancies, while spindle cell tumors, typically derived from non-epithelial tissues, are uncommon, accounting for 0.3%-1% of all malignant laryngeal tumors. Low-grade malignant myofibroblastic sarcoma (LGMS) is an extremely rare, atypical myofibroblastic tumor classified as a spindle cell tumor that primarily affects the head and neck region. There have been few reports in the literature regarding the LGMS of the larynx. LGMS of the larynx was discovered during a pathological biopsy. There was no recurrence during the 6-month follow-up after the total laryngectomy.

Transoral Laryngeal Surgery in Low-grade Myofibroblastic Sarcoma of Larynx: A Plausible Treatment Option

The laryngeal tumor type, location and disease extent are essential determinants in deciding the type of surgery and the potential voice and swallowing outcomes. The surgical options available are conservative laryngeal surgeries like transoral laser microsurgery (TLM) or open conservative laryngeal surgery and Total laryngectomy. We report an unusual case of low-grade Myofibroblastic sarcoma of vocal cord which was managed by TLM.

Low-grade myofibroblastic sarcoma of the proximal femur: A case report and literature review

RATIONAL

Low-grade myofibroblastic sarcoma (LGMS) is an atypical type of tumor composed of myofibroblasts. LGMS in the femoral head neck junction is extremely rare and no case treated by hip arthroscopy was reported.

PATIENT CONCERNS

We reported a case of LGMS in the femoral head neck junction treated by hip arthroscopy. A 30-year-old female was admitted to our hospital with discomfort and pain after left hip sprained one year prior. Physical examination revealed swelling of the left hip and magnetic resonance images showed a soft tissue mass in the femoral head neck junction.

DIAGNOSIS

Via microscopy of pathological specimens, spindle cell proliferative lesions, atypia of some cells, and mitotic figures/pathological mitotic figures of some cells were observed. Immunohistochemistry revealed positive for smooth muscle actin, focally positive for CD34 and CD68, while negative for S-100, desmin, and anaplastic lymphoma kinase. The imaging, histomorphological and immunohistochemical features suggested a final diagnosis of LGMS of the proximal femur.

INTERVENTIONS

This patient underwent hip arthroscopy for excision of the soft tissue mass.

OUTCOMES

The clinical and imaging follow-up at 6 months postoperatively showed that surgery had achieved good clinical outcomes.

LESSONS

To the best of our knowledge, this is the first case report of LGMS in the femoral head neck junction treated by hip arthroscopy. Beyond the present case, other 120 cases from 58 literatures (1998-2022) are reviewed and discussed. The age of LGMS patients ranged from 11 months to 77 years and the male-to-female ratio was approximately 1.28:1. The location distribution of previously reported LGMS cases and the present case was as follows: Head&neck (45.90%), trunk (30.33%), and extremity (23.77%). Hip arthroscopic excision of LGMS may achieve relatively good clinical outcomes.

S-100 Immuno-Positive Low Grade Myofibroblastic Sarcoma of Nasal Cavity: A Rare Case Presentation and Review of Literature

Introduction

Myofibroblastic neoplasms comprise a spectrum of benign/malignant neoplasms. Only low-grade malignant forms have been reproducibly characterized as a diagnostic entity in the WHO classification. Low grade myofibroblastic sarcoma (LGMFS) confined to the nasal cavity is extremely rare.

Objective

To review previously reported cases of nasal cavity LGMFS and provide a better insight regarding its clinical and immunohistochemical features.

Data synthesis

A review was performed involving two databases (PubMed and Google Scholar). Four cases of nasal cavity LGMFS were included. The lesion showed no gender or nasal-side predilection. All cases underwent wide excision. None showed distant metastasis while half recurred locally. Histologically, mitotic rate ranged from 1 to 3/10 high-power-field (HPF) and none exhibited spontaneous necrosis. Immuno-expression of calponin, smooth muscle actin (SMA) and vimentin were seen in either all four or three-fourth of cases. Diffuse S-100 expression was a unique finding in present case and not reported previously, that caused a diagnostic dilemma with schwannomas.

Conclusion

LGMFS of nasal cavity is extremely rare. A wide resection is the primary treatment of choice. Adjuvant therapies (chemotherapy or radiotherapy) are of uncertain significance. Distant metastasis is rather unusual. Calponin, SMA and vimentin are highly sensitive immuno-markers. Diffuse S-100 expression is a possible finding. Mitotic rate < 6/10 HPF and absence of spontaneous necrosis are characteristic indolent features differentiating from high grade lesions. Trifecta of clinical and morphological features plus immunohistological phenotype, are sufficient for a definitive diagnosis. Electron microscopy is the most definitive confirmation test, however, should be reserved only for equivocal/atypical immunostaining pattern.

A rare low-grade myofibroblastic sarcoma in lower jaw with the resemblance to benign lesions

Background

Low-grade myofibroblastic sarcoma (LGMS) is a rare solid infiltrative soft tissue tumor with a predilection for the head and neck region.

Case presentation

We report the diagnostic steps of a fast-growing lesion of the lower left jaw in a 45-year-old otherwise healthy woman. A first biopsy and subsequent histopathological examination showed potential differentials of a benign myofibroma, benign nodular fasciitis or an LGMS. This diagnostic overlap was a challenge for the decision of the further treatment approach. The treatment consisted of a segmental en bloc resection of the mandible including the second premolar, first and second molar. Histopathological examination of the resected tumor confirmed an LGMS.

Conclusion

The histopathologic resemblance of LGMS to a range of benign and reactive tumors may lead to misdiagnosis and mistreatment. The rarity of LGMS explains the lack of established treatment protocols. This case shows the importance of adequate clinical decisions, expertise in the histopathology of rare tumors and interdisciplinary exchange to achieve state-of-the-art patient management.

Low-grade myofibroblastic sarcoma of the liver misdiagnosed as cystadenoma: A case report

BACKGROUND

Low-grade myofibroblastic sarcoma (LGMS) is a rare malignant tumor. It has no specific clinical manifestations and commonly occurs in the head and neck, extremities and other body parts, with the liver not as its predisposing site.

CASE SUMMARY

We report a case report of a 58-year-old man with right upper abdominal pain for 11 d. Contrast-enhanced computed tomography (CECT), CE magnetic resonance imaging and CE ultrasound (US) all showed a cystic-solid mass in the right liver. As the initial clinical diagnosis was hepatic cystadenoma, surgical resection was performed, and the postoperative pathology indicated hepatic LGMS. The 3-mo follow-up showed favorable recovery of the patient. However, at 7-mo follow-up, two-dimensional US and CECT showed a suspected metastatic lesion in the right-middle abdomen.

CONCLUSION

Hepatic MS is particularly rare and easily misdiagnosed, more cases will contribute to the understanding and the diagnosis accuracy.

Effective Treatment of Low-Grade Myofibroblastic Sarcoma with Apatinib: A Case Report and Literature Review

Low-grade myofibroblastic sarcoma (LGMS) is a rare, poorly differentiated, malignant tumor. The disease mainly occurs in the head and neck and rarely metastasizes at any age. Currently, there is no consensus regarding the treatment of metastatic LGMS. Here, we report the case of a 45-year-old man who was admitted to our hospital with cough for two weeks and abdominal pain for one week. Preoperative computed tomography revealed a large mass (116×35 mm) in both the lungs and jejunal mass (maximum diameter, 32 mm). The tumor was excised, and immunohistochemical staining was positive for SMA and CD117 and negative for desmin and CD34, indicating a case of LGMS. The patient was effectively treated with apatinib (250 mg/day) after failure of imatinib, liposomal doxorubicin, and ifosfamide. The progression-free survival time was 8.5 months, and the overall survival time was 17 months after treatment with apatinib. No grade 3 or 4 side effects were observed, except hand-foot syndrome. Whole-exome sequencing (WES) and RNA sequencing (RNA-seq) were performed on the patient’s jejunal tumor and para-cancerous tissue samples, and bioinformatics analysis was performed on the results. WES identified five mutations in MKI67, OR2J2, EPPK1, FCGBP, and OR10G4. RNA-seq revealed that 1422 genes were upregulated and 1890 genes were downregulated. The differentially expressed genes were mainly enriched in the phosphatidylinositol 3-kinase (PI3K) signaling pathway, neuroactive ligand-receptor interaction signaling pathway, and cAMP signaling pathway. Our study indicated that apatinib may be a potential novel and effective treatment for LGMS.

Myofibroblastic sarcoma of the oral cavity: a diagnostic dilemma and report of two cases

Introduction: Myofibroblastic sarcoma is designated as a low-grade malignancy, commonly affecting the deep soft tissue of the head and neck. Despite being classified as low-grade, myofibroblastic sarcoma with high-grade features have been reported. Observations: Two such cases affecting the oral cavity, which were diagnosed as different entities upon biopsy, were observed. Case 1 presented as multiple, well-circumscribed soft tissue swellings of the tongue and alveolar mucosa and was diagnosed as synovial sarcoma. Case 2 manifested as a large extensive osseous lesion of the maxilla and was diagnosed as an inflammatory myofibroblastic tumour. Conclusion: Myofibroblastic sarcoma with high-grade features remains a diagnostic dilemma due to its overlapping features with other spectra of fibroblastic/myofibroblastic tumours and lack of consensus regarding its classification as a separate entity. Establishing the definitive diagnosis requires adequate tumour sampling and a systematic clinicopathological approach.

Giant nodular fasciitis originating from the humeral periosteum: A case report

BACKGROUND

Nodular fasciitis (NF) is a self-limiting tumor that mostly occurs in the subcutaneous superficial fascia. NF originating from the appendicular periosteum is extremely rare. A large NF lesion of periosteal origin can be misdiagnosed as a malignant bone tumor and may cause overtreatment.

CASE SUMMARY

A right axillary mass was found in a 46-year-old man and was initially diagnosed intraoperatively as low-grade sarcoma, but later diagnosed as NF after post-resection histopathological evaluation. Furthermore, fluorescence in situ hybridization analysis revealed a USP6 gene rearrangement that confirmed the diagnosis. To the best of our knowledge, this is the first case of NF in the humeral periosteum.

CONCLUSION

NF poses a diagnostic challenge as it is often mistaken for sarcoma. Postoperative histopathological examination of whole sections can be combined with immunohistochemical staining and, if necessary, the diagnosis can be confirmed by molecular detection, and thus help avoid overtreatment.

Management of a Highly Vascular Low-grade Myofibroblastic Sarcoma of the Mandible

An 11-year-old male patient presented with a large, highly vascular, destructive mandibular mass. An intraoral biopsy showed pleomorphic spindle cells arranged in intersecting fascicles, with scattered atypia. A diagnosis of low-grade myofibroblastic sarcoma was made. The lesion was treated with preoperative arterial embolization followed by surgical resection and reconstruction with a fibular osteomyocutaneous free flap. To our knowledge, no reports of highly vascular mandibular low-grade myofibroblastic sarcoma are available in the literature.

Surgical treatment and long-term outcomes of low-grade myofibroblastic sarcoma: a single-center case series of 15 patients

Background

Low-grade myofibroblastic sarcoma (LGMS) is a poorly studied, rare, soft tissue sarcoma. LGMS is characterized by a low malignancy potential, tendency for local recurrence, and low likelihood of distant metastases. However, no studies have reported on the surgical treatment method and its long-term outcomes.

Methods

We included all patients treated for LGMS at our institution between March 2010 and March 2021. Medical charts were retrospectively reviewed to collect demographic information, as well as information about the clinical course, tumor characteristics, and outcomes. Statistical analysis was performed to identify the factors associated with the recurrence rate.

Results

Fifteen patients who underwent surgical treatment were enrolled in this study. There were seven cases in the upper extremities, four in the trunk area, three in the lower extremities, and one in the head and neck area. There were no metastatic cases and two cases of local recurrence.

Conclusions

The incidence of LGMS in the extremities or trunk may be higher than expected based on the current literature. Univariate analysis showed that local tissue invasion and surgical method could be associated with local recurrence. Although further large studies are needed to establish risk factors of local recurrence or extent of resection margins, based on our study, wide local excision under the proper diagnosis is the most important treatment.

Limbal, low-grade myofibroblastic sarcoma: Case report and literature review

Low-grade myofibroblastic sarcoma is a relatively recently-described neoplasm of the myofibroblasts having a predilection for the head and neck region. Ophthalmic involvement is extremely rare. Limbal involvement has not yet been documented in the literature. We describe one such case involving the limbus of a 48-year-old Asian male.

Low-Grade Myofibroblastic Sarcoma of the Oral Cavity: A Report of Three Cases Illustrating an Emerging Disease in Children

Low-grade myofibroblastic sarcoma (LGMS) is a mesenchymal tumor of myofibroblasts that occurs more frequently in adults. A series of three cases is presented to illustrate that LGMS may also occur within the oral cavity in children and adolescents. The first case (Case 1) occurred intra-osseously in the mandible, while the remaining two presented as gingival swellings and were purely restricted to soft tissue (Cases 2 and 3). The intra-osseous lesion arose in a 7-year-old girl, whereas the gingival lesions were observed in a 12-year-old girl (Case 2) and a 13-year-old boy (Case 3). Histopathologically, all cases were composed of spindle shaped cells arranged into long fascicles showing mild to moderate degree of nuclear atypia. Ki-67 (MIB-1) proliferation activity was relatively low, amounting to 3–5% in all cases. Immunohistochemically, all cases showed smooth muscle actin (SMA) positivity in spindle cells, while desmin, beta catenin, cytokeratin, and CD34 were negative, resulting in a diagnosis of LGMS. In conclusion, current series of three cases of LGMSs that occurred in the oral cavity in a child and two adolescent patients is presented to highlight an emerging disease that requires additional data for further characterization.

Low-grade myofibroblastic sarcoma of the levator scapulae muscle: a case report and literature review

BACKGROUND

Low-grade myofibroblastic sarcoma (LGMS) is described as a distinct atypical myofibroblastic tumor often with fibromatosis-like features and predilection for the head and neck, especially the oral cavity and larynx. LGMS arising in the levator scapulae muscle is extremely rare.

CASE PRESENTATION

A 69-year-old woman was admitted to our hospital because she noticed a hard mass in her left neck six months prior. Magnetic resonance images (MRI) showed a soft tissue tumor of the left levator scapulae muscle. A core needle biopsy showed cellular fascicles or a storiform growth pattern of spindle-shaped tumor cells with minimally atypia. Immunohistochemistry revealed focally positive for α-smooth muscle actin (α-SMA), negative for S-100, and a low-grade spindle cell sarcoma was suspected. Following a biopsy, the tumor was resected with a wide surgical margin. Immunohistochemical staining was a positive for vimentin and α-SMA and negative for desmin, CD34, nuclear β-catenin, and h-caldesmon. LGMS diagnosis was determined based on the histopathological findings. The patient was alive with no evidence of disease eight years after the surgery.

CONCLUSIONS

To the best of our knowledge, this is the first case report of LGMS arising in the levator scapulae muscle. In addition to the case report, 48 reports with 103 LGMS cases are reviewed and discussed. In previous reports of LGMS, there were 43 females and 60 males, with a mean age of 43.0 years (range, 2-75). There were 13 (12.6%) patients aged < 18 years, 67 (65.1%) patients aged 18 to 59 years, and 23 (22.3%) patients aged ≥60 years. The average tumor size was 4.4 cm (range: 0.4-22.0). The commonest sites of LGMS was the tongue. Tumor growth patterns were evaluated in 52 cases, and 44 cases (84.6%) showed infiltrative growth patterns. Local recurrence was 26.7%, and distant metastasis was 4.4%. Because of the locally aggressive feature, it is important to diagnose LGMS with biopsy and to excise the tumor with an adequately wide margin.

Primary low-grade myofibroblastic sarcoma: A rare case report of this tumor in the orbit and literature review

Low-grade myofibroblastic sarcoma (LGMS) is an exceedingly rare, malignant tumor with myofibroblastic differentiation. It frequently occurs in the oral cavity and extremities, despite being classified as a distinct entity by the World Health Organization (WHO). Here, we report a rare case of orbital LGMS occurring in an 11-month-old baby with a 3.2 × 2.4 × 2.1 cm mass. LGMS was diagnosed based on the histological and immunohistochemical findings. Previous literature suggests that surgical resection with clear margins is an appropriate method for the treatment of LGMS, and combined adjuvant therapy (local radiotherapy with or without chemotherapy) can improve the prognosis, but further studies are needed.

Evaluation and Management of an Uncommon Tumor of the Larynx: A Case Report and Literature Review of Laryngeal Low-Grade Myofibroblastic Sarcoma

Low-grade myofibroblastic sarcoma (LGMS) of the larynx is an uncommon entity. These mesenchymal tumors of the larynx are rare and account for approximately 0.3% to 1.0% of all neoplasms at this site. We report a rare case of LGMS of the larynx that involved the larynx of a 63-year-old man with a history of hoarseness of voice. The patient was treated with total laryngectomy with partial pharyngectomy without any adjuvant treatment. Histopathologically, the tumor was composed of spindle cells that manifested variable cellular anaplasia and expressed smooth muscle actin (SMA). Our patient is disease-free two years after surgery. The authors emphasize the clinical and histopathological findings and treatment of this case with a literature review. This case is among the few reported cases of LGMS of the larynx. It enlightens the classical clinical findings, histopathology, differential diagnosis, and treatment. Surgical excision with negative margins requires no adjuvant therapy.

Low-Grade Myofibroblastic Sarcoma Demonstrated on 99mTc-MDP Bone Scan and 18F-FDG PET/CT

A 24-year-old woman with left hip pain for 4 months was admitted. Radiographs of the left hip showed a radiolucent lesion in the proximal femur. The lesion demonstrated hypointensity on T1-weighted and high intensity on T2-weighted fat saturated images. Tc-MDP bone scan and F-FDG PET/CT illustrated intense radiotracer accumulation at the osteolytic lesion. Postoperative pathology confirmed a low-grade myofibroblastic sarcoma (LGMS). LGMS is a rare neoplasm, which often occurred in the head and neck region. Our case suggested that LGMS should be considered in the differential diagnosis of proximal femur lesion on Tc-MDP bone scan and F-FDG PET/CT.

Is there a role for chemotherapy and radiation in the treatment of patients with low-grade myofibroblastic sarcoma?

PURPOSE

Low-grade myofibroblastic sarcoma (LGMS) is a rare entity with a predilection for the head and neck. There are still no optimal treatment strategies for patients with LGMS. We retrospectively investigated the efficacies of chemotherapy and radiation treatment for patients with LGMS.

METHODS/PATIENTS

We obtained data from the Surveillance, Epidemiology, and End Result (SEER) database for 96 patients diagnosed with LGMS between 2001 and 2015. We used Kaplan-Meier curves and log-rank tests to estimate overall survival (OS) and Cox proportional hazard regression to identify prognostic factors.

RESULTS

The median age of the patients was 55.0 years. Twenty-two of the patients had LGMS in the head and neck region. Of the 96 patients, 86 (89.6%) received surgical treatment, 28 (29.2%) received radiation treatment, and 20 (10.4%) received chemotherapy. The mean OS was 125.2 [95% confidence interval (CI) 106.3-144.2] months. The 1, 3, 5, and 10-year OS rates were 88%, 77%, 70%, and 59%, respectively. Age greater than 60 years, positive nodal status, and no surgical treatment were independent prognostic factors for patients with LGMS, whereas chemotherapy and radiation treatment were not.

CONCLUSIONS

Surgical resection is the most effective therapy for LGMS. Chemotherapy and radiation had limited effects on survival improvement for patients with LGMS. Therefore, chemotherapy and/or radiation therapy should not be routinely performed in LGMS, especially for those with negative margins after surgery.

Soft Tissue Special Issue: Fibroblastic and Myofibroblastic Neoplasms of the Head and Neck

Fibroblastic and myofibroblastic neoplasms of the head and neck encompass a group of rare tumor types with often overlapping clinicopathologic features that range in biologic potential from benign to overtly malignant. Even neoplasms with no metastatic potential may provide significant therapeutic challenges in this region due to the unique anatomy of the head and neck. This review will cover the following entities, highlighting important clinical aspects of each neoplasm and then focusing on their characteristic histomorphology, immunophenotype, and molecular alterations: nodular and cranial fasciitis, fibrous hamartoma of infancy, nasopharyngeal angiofibroma, nuchal-type and Gardner fibromas, desmoid fibromatosis, dermatofibrosarcoma protuberans and giant cell fibroblastoma, solitary fibrous tumor, inflammatory myofibroblastic tumor, low-grade myofibroblastic sarcoma, infantile fibrosarcoma, low-grade fibromyxoid sarcoma, and sclerosing epithelioid fibrosarcoma. While some of these neoplasms characteristically arise in the head and neck, others are rarely described in this anatomic region and may therefore be particularly difficult to recognize. Distinction between these entities, however, is crucial, particularly as the molecular pathogenetic basis for these neoplasms are being rapidly elucidated, in some instances allowing for targeted therapeutic approaches.

Myofibroblastic sarcoma of the breast. Report of a case induced by radiotherapys

Myofibroblastic sarcoma (MFS) is an uncommon tumor rarely located in the breast. Ionizing radiation is a carcinogen capable of inducing sarcomas through DNA damage. A 42-year-old woman was diagnosed with synchronous bilateral breast infiltrating ductal carcinoma with axillary lymph node metastases on the left side. After modified left radical mastectomy and simple right mastectomy, she underwent postoperative radiation with a total volume dose of 50 Gy that included the thoracic wall and the left axillary-supraclavicular region. After a latency period of 6 years and 4 months, the patient developed an MFS in the area of radiation (mammary upper outer quadrant). To our knowledge, only 11 cases of MFS have been previously published in the breast. The study of the 12 cases including the present one revealed that the ages of the patients ranged from 42 to 86 years (mean 60.3 years). There was a clear difference concerning sex (M:F, 1:5). The average duration of the lesion varied from 1 week to 8 months (mean 3.3 months). The size ranged from 2.2 to 22 cm (average 5.1 cm). The tumors showed frequent mitosis and areas of necrosis. The percentage of recurrences, metastasis, and death due to the tumor was 27.3%, 36.4%, and 27.3% respectively. MFS cases differ from those affecting extramammary regions. They are more common in females and show a greater degree of aggressiveness. Correct diagnosis of mammary MFS requires morphological and immunohistochemical study. We present for the first time a case of MFS of the breast induced by radiotherapy.

Low 68Ga-PSMA PET/CT Uptake in Chronic Intramuscular Nodular Fasciitis

Nodular fasciitis is an uncommon benign mass-forming myofibroblastic proliferation, most frequently found in the upper limbs, with only rare intramuscular cases. We describe herein a case of chronic nodular fasciitis of the left triceps muscle with a low Ga-labeled prostate-specific membrane antigen (PSMA) ligand uptake on PET/CT. Ga-PSMA ligands bind to PSMA-expressing prostate cancer cells, but uptake has also been demonstrated in other solid neoplasms and various benign lesions. Nodular fasciitis should be included in the differential diagnosis of soft tissue lesions with variable Ga-PSMA uptake.

Low-grade Myofibroblastic sarcoma: clinical and imaging findings

Background

Low-grade myofibroblastic sarcoma (LGMS) is a rare type of tumor. Previous research has paid much attention to reporting pathological analyses of LGMS. However, only few systematic clinical and/or radiological studies have been conducted.

Methods

This study recruited 14 cases (8 males and 6 females) of LGMS. X-ray or computer tomography (CT) scan were performed on 11 cases. MRI was performed on 5 cases.

Results

X-Ray and CT scan: Five cases developed LGMS in bones, including 3 cases in the distal femur, 1 in the right shoulder blade, and another 1 in the right inferior ramus. Massive infiltrative and vermiform bone destruction with poorly-circumscribed lesion margins and partial soft tissue masses were observed. The other 9 cases were developed in soft tissues. Out of them, 4 cases presented slightly irregular hyper- or lower-density masses with poorly-circumscribed margins. 2 cases presented massive calcification and ossification. Significant enhancement was observed in 1 case, while no obvious enhancement was seen in the other 2 cases.

MRI: MR images of 5 cases revealed homogeneous iso- or hyper-signal intensity on T1WI and homogeneous or heterogeneous hyper-signal intensity on T2WI. Enhanced MRI revealed homogeneous enhancement in 2 cases and rim enhancement in 1 case.

Conclusions

Our findings show that LGMS is characterized by invasiveness, metastases and calcification. Different radiological tools should be employed to make an accurate diagnosis.

Sinonasal glomangiopericytoma: A clinicopathologic study

Sinonasal glomangiopericytoma (SNGP) is a neoplasm arising in the nasal cavity and paranasal sinuses that shows perivascular myoid differentiation. The diagnosis of SNGP may be diagnostically challenging due to a large number of potential mimics. In the present study, we sought to characterize the histological and molecular features of six cases of SNGP found in prior surgical pathology records over a 15-year period. The average age at diagnosis was 48.5 years (range: 31-78 years), and the male-to-female ratio was 1:1. Imaging studies in all six cases demonstrated avidly enhancing, lobulated soft tissue masses in the nasal cavity, extending into the sinuses and nasopharynx. Histologically, the tumors were unencapsulated and composed of a proliferation of closely packed, bland, and uniform spindle cells growing deep to an intact surface respiratory epithelium. The cells were separated by a distinctive vascular network ranging from capillaries to large vascular spaces. All cases demonstrated strong positivity for smooth muscle actin, cyclin D1, CD99, and β-catenin (100%). Targeted sequencing revealed recurrent CTNNB1 missense mutations in all cases tested. Additionally, TLE1 was positive in all cases which has not been previously reported. No tested cases harbored SS18 translocations. We found that while no single marker resolves immunohistochemical overlap between SNGP and its histologic mimics, an extended immunohistochemical panel that includes β-catenin, cyclin D1, STAT6, smooth muscle actin, pan-cytokeratin cocktails, S100, and SOX10 helps to support the diagnosis of SNGP in diagnostically challenging cases without the need for molecular studies.