Nuclear expression of STAT6 distinguishes solitary fibrous tumor from histologic mimics

Solitary fibrous tumor in the pterygopalatine fossa: a rare case report and literature review

INTRODUCTION

Solitary fibrous tumor is a rare spindle cell tumor that may occur in various parts of the body. No documented case of solitary fibrous tumor has been reported in pterygopalatine fossa.

CASE REPORT

A 25-year-old male complained of right facial numbness for 20 days. Computed tomography of the paranasal sinuses demonstrated a well-circumscribed lesion centered in the right pterygopalatine fossa. On magnetic resonance imaging the lesion was homogenously isointense to muscle on T1 weighted imaging (T1WI) and slightly hyperintense to muscle on T2 weighted (T2WI). The intro-operative frozen pathology reveals a benign spindle cell tumor. The tumor was removed successfully via transnasal combined with Caldwell-Luc approach without complications. However, the final pathology combined with immunohistochemistry confirmed the diagnosis of solitary fibrous tumor. No further radiotherapy is performed post-operation. After half a year follow up, there is no recurrence.

CONCLUSION

For the tumor in the pterygopalatine fossa, the possibility of solitary fibrous tumor should be considered and radical endoscopic resection should be the preferred treatment approach.

When Is It Important to Sequence Sarcomas and Other Mesenchymal Neoplasms? A Practical Guide to Molecular Testing

The increasingly widespread availability of next-generation sequencing has led to its incorporation as a diagnostic tool in pathology and a modality for identifying targetable alterations. However, sequencing is still a somewhat expensive and time-consuming. Here, we discuss tumor types for which (1) molecular testing is not generally indicated, (2) surrogate immunohistochemical markers have rendered molecular testing unnecessary, or (3) sequencing is important for diagnostic and therapeutic purposes. We also provide a practical framework to assist in decision-making for molecular testing of both classified and unclassified mesenchymal neoplasms, reflecting our practice in a tertiary sarcoma referral center.

Comprehensive Clinicopathological and Multiomics Characterization of Dermatofibrosarcoma Protuberans Revealed PDGFD Fusion as Distinct Molecular Subtype with Better Survival

Dermatofibrosarcoma protuberans (DFSP) is a locally aggressive superficial mesenchymal neoplasm characterized by COL1A1::PDGFB fusion. Recently, PDGFD has been identified as a less common fusion partner. However, the clinicopathological and molecular differences between PDGFD and PDGFB fusion DFSP remain largely unknown. In this study of 363 DFSPs, we found 10 cases with PDGFD fusion, including two with a previously undescribed partner involving the EMILIN1 gene. Multi-omics analysis showed distinct transcriptomics, epigenomics, and copy number features for PDGFD fusion DFSP versus PDGFB fusion DFSP. PDGFD fusion DFSP had higher PDGFD expression and virtually no PDGFB expression. Both clustered into the DFSP epigenomic cluster but formed a distinct sub-cluster with differential methylation affecting fibroblast migration genes. Copy number analysis revealed that PDGFD fusion DFSP formed a distinct subgroup with a generally copy number neutral profile and better survival compared to PDGFB fusion DFSP that was dominated by amplification at translocation sites in chromosomes 17 and 22. Pooled analysis of 39 cases (incorporating 29 from the literature) revealed that PDGFD fusion DFSP was more common in females (71.8% vs. 42.4%, p <0.001), occurred at a lower age (Median 37 vs. 45, p < 0.01), and had a higher chance of occurrence at the breast (25.6% vs. 2.3%; p < 0.001). PDGFD fusion DFSP also tended to centre predominantly in the subcutis (63.6% vs. 30%; p < 0.001), had a circumscribed border (50% vs. 19.2%, p < 0.001), was smaller in size (3 cm vs. 3.5 cm, p = 0.017), and had a lower mitotic count (Median 1 vs. 3 per 10 h.p.f., p = 0.03). Overall, our study provided detailed multi-omics characterization of PDGFD fusion DFSP with significant clinico-pathological and diagnostic implications.

A Rare Case of Solitary Fibrous Tumor Involving the Nasolacrimal Duct System in a 12-Year-Old Female: A Case Report and Review of the Literature

The authors report the youngest case of solitary fibrous tumor (SFT) with extensive involvement of the nasolacrimal duct system and discuss current literature regarding this tumor type. A 12-year-old female presented with a 6-month history of an enlarging right medial orbit mass. CT orbits revealed a well-circumscribed, enhancing lesion adjacent to the right nasolacrimal system. Pathology confirmed SFT (1.2 × 1.1 × 1.1 cm) with spindle cell morphology and a mitotic rate of 5 per 10 high power fields. Immunohistochemistry (IHC) was positive for CD-34 and signal transducer and activator of transcription 6 and negative for S-100, consistent with SFT. Next-generation sequencing confirmed NGFI-A-binding protein 2::signal transducer and activator of transcription 6 gene fusion. To the authors' knowledge, only 17 cases of SFT involving the lacrimal sac have been reported, of which, the average age was 43.5 years. Notably, SFTs with a high mitotic rate carry a heightened risk of malignant transformation. Given this patient's mitotic rate of 5 per 10 high power fields, positive surgical margins, and young age, close follow-up is imperative.

Solitary Fibrous Tumor of the Paranasal Sinuses with Intracranial Extension: A Rare Case Report and Review of the Literature

Solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms that were initially identified in the pleura. SFTs in the nasal or paranasal sinuses are especially rare. Most SFTs exhibit indolent behavior, with a low local recurrence rate. A 39-year-old man complained of bilateral nasal congestion, hyposmia, and occasional right eye tears six months prior to hospitalization. Based on MRI and CT imaging, a total gross surgical resection was achieved. Subsequently, postsurgical histopathological examinations were conducted. Under the microscope, pathological mitotic bodies were visible (<5 mitoses per 2 mm2). The immunohistochemical staining results revealed that tumor cells were positive for CD34, BCL-2, STAT-6, and Ki-67 (<5%) but negative for EMA, S-100, PR, GFAP, and SMA. Based on these findings, the patient was diagnosed with SFT.

A Rare Case of Myxoid Solitary Fibrous Tumor of the Upper Lip: The Key Role of STAT6 in Diagnosis

A solitary fibrous tumor (SFT) is an uncommon spindle cell mesenchymal neoplasm that most commonly arises in the pleura. SFTs have been shown to arise in various internal organs but are not typically discovered cutaneously. The diagnosis of SFT requires an integrated approach since SFT can mimic a variety of benign and malignant tumors, both clinically and histologically. To further complicate the histological diagnosis, there are different morphological variants of SFT. Therefore, immunohistochemical markers such as signal transducer and activator of transcription 6 (STAT6) can be utilized for SFT diagnosis due to their high specificity and sensitivity, as nuclear expression of STAT6 is a distinguishing feature of SFT and helps differentiate it from histological mimickers. A correct diagnosis is imperative for proper treatment and management. In this report, we present a 74-year-old healthy man with a growing painless mass on his upper lip for several years. Biopsy results confirmed the diagnosis of SFT with myxoid variation, and the patient underwent a successful excision of the lesion. Our case emphasizes the importance of a multidisciplinary approach and the utilization of immunohistochemical staining when diagnosing superficial tumors.

Mesenchymal Neoplasms of the Bladder and Male Genital Tract, including the Perineum and Scrotum

Mesenchymal neoplasms of the bladder and male genital tract are uncommonly encountered in routine diagnostic practice and present diagnostic challenges. Here, I systematically survey mesenchymal tumors at each body site, including the spermatic cord, scrotum, and perineum. I provide a detailed overview of tumor types that specifically or most commonly occur in the bladder and male genital tract, including pseudosarcomatous myofibroblastic neoplasm of the bladder, proliferative funiculitis, paratesticular sclerosing rhabdomyoma, penile myointimoma, and so-called prostatic stromal tumors.

Primary sarcomas of the bladder and prostate: A genomic landscape study

Primary sarcomas of the bladder and prostate are exceedingly rare, often highly aggressive and account for less than 1 % of all malignant tumors of these organs. In this landscape study, we searched for genomic biomarkers that could aid in either treatment selection or further classification of these tumors. 18 (0.2 %) bladder sarcomas were identified from 11,193 bladder cancers and 11 (0.6 %) prostate sarcomas were identified from 19,057 prostate cancers that underwent hybrid capture-based comprehensive genomic profiling (CGP) to assess all classes of genomic alterations (GA). The bladder sarcomas included 12 leiomyosarcomas, 3 rhabdomyosarcomas and 3 high-grade undifferentiated sarcomas. The sarcomas of the prostate featured 9 primary prostatic stromal sarcomas, 1 leiomyosarcoma and 1 rhabdomyosarcoma. The most frequent gene alterations were in TP53, RB1 and ATRX. Bladder sarcomas were also found to have more than 2-fold more genetic alterations than compared to prostatic sarcomas.

Mesenchymal Tumors of the Liver: An Update Review

Hepatic mesenchymal tumors (HMTs) are non-epithelial benign and malignant tumors with or without specific mesenchymal cell differentiation. They are relatively uncommon. Except for mesenchymal hamartoma, calcified nested stromal-epithelial tumor, and embryonal sarcoma, most mesenchymal lesions are not specific to the liver. Pathologists face challenges in diagnosing HMTs due to their diverse morphologies and phenotypic variations. Accurate diagnosis is critical for directing appropriate patient care and predicting outcomes. This review focuses on mesenchymal tumors with a relative predilection for the liver, including vascular and non-vascular mesenchymal neoplasms. It provides a thorough and up-to-date overview, concentrating on clinical and pathological features, differential diagnosis, and diagnostic approaches.

Solitary fibrous tumors: radiologic features with clinical and histopathologic correlation

Objective

Solitary fibrous tumor (SFT) is an uncommon mesenchymal neoplasm that exhibits a broad spectrum of biological behaviors. Few studies relative to clinical-pathologic features and radiologic manifestations of SFTs have been reported. This study aimed to correlate the radiologic findings of SFTs with the clinical and histopathologic features.

Methods

The clinical, surgical, and histopathologic records; and CT or MR images in 38 pathologically proved cases of SFTs were retrospectively evaluated.

Results

All tumors were seen as oval (n=18) or irregular (n=20), well-defined (n=36) or ill-defined (n=2) masses with a mean size of 11.0 cm. On CT images, most tumors showed a heterogeneous density on precontrast image, and the mean density of the tumor parenchyma was 40.7 hounsfield units. Intratumoral calcification was seen in 6 tumors. After contrast media administration, most tumors showed moderate to marked enhancement (n=34). Multiple intratumoral vessels were seen in 23 tumors. Collateral feeding vessels were seen in 19 tumors. On MR images, all 6 tumors showed a low signal intensity on T1 weighted images and high signal intensity with separate foci of hypointensity on T2 weighted images, as well as significantly imhomogeneous enhancement after contrast administration.

Conclusion

The presence of a large, well-defined, highly vascular soft tissue tumor with map-like enhancement and prominent collateral feeding vessels should alert the radiologist to the possible diagnosis of SFT. Diagnostic imaging coupled with clinicopathologic analysis allows accurate localization, identification, and resection of SFTs.

A Rare Case of Solitary Fibrous Tumor of the Breast in a Healthy 40-Year-Old Woman

Solitary fibrous tumor (SFT) is a rare neoplasm of mesenchymal origin that is primarily found in the lungs but can be found in other locations such as the retroperitoneum, deep soft tissues of the proximal extremities, abdominal cavity, head, and neck. Moreover, SFTs found in the breast are extremely rare and, oftentimes, are found incidentally during screening mammography. Our case presents an exceptionally rare occurrence of a SFT in the breast of a 40-year-old woman. This rarity is underscored by its classification as a SFT and its unusual location within the breast tissue as well as this patient's young age. This case emphasizes the importance of a thorough evaluation with both imaging and histopathology for diagnosing SFTs. It also addresses the potential difficulties that may arise during this process, especially for radiologists who may have limited experience encountering SFTs.

A Rare Case of a Malignant Epithelioid Neoplasm With an Underlying Novel EWSR1::ZBT44 Fusion, Identified on Next-Generation Sequencing (NGS)

The clinicopathological spectrum of undifferentiated round cell sarcomas of bone and soft tissues is expanding after the 5th edition of the WHO classification. A 23-year-old male patient presented with a lump in his left thigh of 3 months' duration. Radiological examination revealed a well-defined, solid-cystic lobulated, soft tissue lesion in the proximal medial region of his left thigh, measuring 7.7 cm in the largest dimension. The referring diagnosis was an epithelioid sarcoma. Histopathological review of the tumor sections revealed a cellular tumor composed of malignant epithelioid to focally "rhabdoid-like" cells in a variable hyalinized and myxoid stroma with geographic areas of necrosis. In addition, there were areas reminiscent of hemangiopericytomatous vasculature. By immunohistochemistry, the tumor cells were diffusely positive for CD34, focally and distinctly for pan keratin (AE1/AE3). INI1/SMARCB1 and SMARCA4 (BRG1) were diffusely positive (normal). Next-generation sequencing with a wide sarcoma panel revealed EWSR1exon8::ZBT44exon4 fusion. The present example constitutes the first malignant epithelioid tumor with a hemangiopericytomatous growth pattern, exhibiting this rare fusion. The differential diagnoses of this tumor and their corresponding immunohistochemical profile are discussed. This example highlights the value of NGS in unraveling rare fusions and in differentiating these tumors from their several mimics.

NAB2::STAT6 Rearranged Carcinoma of the Parotid Gland with Sebaceous Differentiation: A Case Report

PURPOSE

The NAB2::STAT6 fusion is predominantly associated with solitary fibrous tumors (SFTs) and is utilized in diagnosing SFTs through nuclear STAT6 protein overexpression. Recent studies expanded the phenotypic spectrum of NAB2::STAT6 rearranged neoplasms, including adamantinoma-like and teratocarcinosarcoma-like phenotypes. We report a case of a NAB2::STAT6 rearranged epithelial tumor exhibiting sebaceous differentiation in the parotid gland.

METHODS

Fine-needle aspiration (FNA), histopathology, immunohistochemistry, and molecular studies of this case were described.

RESULTS

Fine-needle aspiration (FNA) revealed atypical basaloid cells, suggesting primary salivary gland carcinoma or metastasis. Histological examination showed basaloid-squamous cells with a monomorphic appearance containing foci of sebaceous differentiation, expressing pancytokeratin, p40, and androgen receptor, while CD34 staining was negative. Molecular studies identified a NAB2::STAT6 fusion, along with an AKT1 mutation.

CONCLUSION

This case further expands the phenotypic spectrum of NAB2::STAT6 rearranged neoplasms and emphasizes comprehensive histopathological and molecular analysis in challenging head and neck tumors. It suggests STAT6 immunohistochemistry as a potential screening tool for head and neck tumors resembling sebaceous carcinoma, myoepithelial tumors, or GLI1-altered neoplasms.

SS18-SSX Expression and Clinicopathologic Profiles in a Contemporary Cohort of Primary Paratesticular Synovial Sarcoma: A Series of Fourteen Patients

Synovial sarcoma (SS) is a rare genitourinary malignancy with a specific SS18::SSX 1/2 gene fusion in majority of the instances. The paratesticular location of this neoplasm is extremely rare and only 4 cases are reported in the literature. Herein, we describe the clinicopathologic features and molecular profile of paratesticular SS in the largest case series to date and to the best of our knowledge, and the only series to use novel SS18-SSX antibody for immunohistochemistry. Clinicopathologic, immunohistochemical (IHC), molecular, treatment, and follow-up data of the patients were analyzed. There were 14 patients, ranging from 15 to 47 years (mean: 30 y). The tumor size ranged from 4​​​​​​ to 15 cm. The tumors were unilateral, solid, and homogeneous tan-white with monomorphic spindle cell histology. All 14 tumors expressed SS18-SSX and TLE1 IHC and harbored SS18 rearrangement. In addition, the tumor with multifocal SS18-SSX expression had lower break-apart signals in the FISH assay (38% of the tumor cells; range: 29% to 85%). Radical orchiectomy was performed in all 14 patients and adjuvant chemotherapy was administered in 9 patients. Follow-up was available in 9 patients. The follow-up duration ranged from 5 to 24 months (median=10 mo). Four patients died of metastatic disease (range: 5 to 16 mo) and 2 patients who are alive had metastatic disease at the last follow-up. Based on our experience with the largest series to date and aggregate of the published data, paratesticular SS has a poor prognosis despite aggressive therapy. Owing to its rarity, the differential diagnosis is wide and requires a systematic approach for ruling out key morphologic mimics aided with SS18-SSX IHC and molecular confirmation because this distinction carries important therapeutic and prognostic implications. Due to the excellent concordance of SS18-SSX IHC results with FISH results as observed in our study, we would like to suggest inclusion of SS18-SSX in the diagnostic immunohistochemistry panel of all spindle cell sarcomas where synovial sarcoma is considered as a morphologic differential. SS18-SSX-positive staining may be used as a surrogate for FISH assay in a resource-limited setting where molecular assay is not available. Furthermore, IHC has a fairly shorter turn-around-time, is less complex, and of low cost.

Solitary fibrous tumor of the bladder: A rare cause of bladder outlet obstruction in an adult male

Introduction

Solitary fibrous bladder tumors are extremely uncommon, with only a few cases reported. These fibroblastic mesenchymal neoplasms are typically benign, indolent, and slow growing.

Case presentation

A 44-year-old male patient with obstructive uropathy was referred to our unit for workup. Ultrasonography and MRI of the pelvis showed a large, well-circumscribed bladder mass, also visualized cystoscopically. This mass was excised en bloc using the Pfannenstiel approach. Histopathological and immunohistochemical analyses revealed a solitary fibrous tumor.

Conclusion

The management of SFTs can be challenging due to the lack of established guidelines. Hence, we offered our patient long-term follow-up. Twelve months postoperatively, no recurrence or metastases were found on the follow-up imaging.

Solitary Fibrous Tumor of the Pleura: Surgical Treatment and Recurrence

BACKGROUND

 Solitary fibrous tumors of the pleura (SFTPs) are primary pleural tumors originating from the mesenchymal tissue. Surgical treatment was the first choice for management of SFTPs. There were no defined guidelines for the follow-up of these tumors and the postoperative therapy due to the rarity of these tumors.

METHODS

 We conducted a retrospective, multicenter study from two high-volume centers in Italy. Data of patients diagnosed with pleural solitary fibrous tumors between January 2003 and October 2022 were prospectively recorded and retrospectively analyzed. The aim of this study was to identify predictive prognostic factors and the correlation between tumor characteristics and recurrence.

RESULTS

 In all, 107 patients undergoing R0 surgical resection of pleural solitary fibrous tumor were included in the study. Patients were divided in two groups: benign and malignant. All the patients were treated with surgery with the aim to obtain R0 resection. Lung resection was necessary when the tumor adhered strongly to the lung parenchyma or infiltrated it. Twenty of the 107 patients had tumor recurrence. At a multivariate analysis, histological characteristics (high mitotic index) and maximum standardized uptake values (maxSUV) were related to recurrence. The mean disease-free survival (DFS) was 143.3 ± 6.1 months.

CONCLUSION

 In our experience, histological features of malignancy and maxSUV are significantly related to recurrence, which can occur even years after the first diagnosis. Surgical excision with negative surgical margins results in good long-term outcomes. After surgery, a long-term and strict follow-up should be done, in order to detect recurrence early. R0 of the recurrence is associated with long-term survival.

Diagnostic and Predictive Immunocytochemistry in Head and Neck Lesions

BACKGROUND

The application of immunocytochemistry (ICC) as a diagnostic and predictive tool in the workup of head and neck lesions has followed the changes and progresses in the surgical pathology evaluation. The contribution of ICC has shown a significant role in head and neck cytology, demonstrating as its contribution can support the diagnosis of many lesions. Furthermore, its role has been evolving as an important adjuvant tool in targeted therapies. An additional useful role is defined by the recent introduction of ICC markers related to genetic alterations, which has opened the door to the adoption of a surrogate for molecular evaluation also on cytological material.

SUMMARY

The current review article analyzes the role of ICC in the field of head and neck cytology, showing that it might represent a valid diagnostic tool in difficult cases. The review will include all the different head and neck lesions, demonstrating how we could rely on organ-specific ICC markers but also on ICC markers able to discriminate between benign and malignant lesions.

KEY MESSAGES

The role of ICC represents a valid additional tool in the management of several difficult lesions, especially when morphology alone is not able to make a conclusive diagnosis. The support of ICC is likely to support the morphological findings leading to the definition of the diagnosis and the most appropriate management.

Primary Intraosseous Solitary Fibrous Tumor of the Mandible: Report of a Diagnostically Challenging Case with NAB2::STAT6 Fusion and Review of the Literature

INTRODUCTION

Solitary fibrous tumor (SFT) represents an uncommon mesenchymal neoplasm affecting primarily the extremities and deep soft tissues with, overall, benign but locally aggressive biologic behavior and an underlying pathognomonic NAB2::STAT6 fusion. Intraosseous SFTs are infrequent, and involvement of the jawbones is exceedingly rare.

CASE PRESENTATION

A 54-year-old woman presented with an asymptomatic, well-demarcated, multilocular radiolucency of the left posterior mandible featuring focally irregular borders, root resorption and lingual cortex perforation. The lesion had shown progressive growth over a 6-year period. Microscopically, a proliferation of predominantly ovoid and spindle-shaped cells with indistinct cell membrane borders, elongated, plump or tapered, hyperchromatic nuclei, and lightly eosinophilic cytoplasm was noted. Marked cytologic atypia, pleomorphism and mitoses were absent. A secondary population of epithelioid cells exhibiting ovoid or elongated vesicular nuclei, and abundant, pale eosinophilic or vacuolated cytoplasm was also present. The supporting stroma was densely fibrous with areas of marked hyalinization and variably-sized, ramifying, thin-walled vessels. By immunohistochemistry, lesional cells were strongly and diffusely positive for STAT6 and CD99, and focally immunoreactive for MDM2 and SATB2. Ki-67 was expressed in less than 5% of lesional cells, while most interspersed epithelioid cells were positive for the histiocyte marker, CD163. Molecular analysis disclosed a NAB2::STAT6 fusion confirming the diagnosis of SFT. The patient underwent segmental mandibulectomy.

CONCLUSIONS

Herein, we report the first case of primary intraosseous SFT of the mandible with complete documentation of its characteristic immunohistochemical and molecular features. Diagnosis of such unusual presentations may be further complicated by the challenging histomorphologic diversity of SFT.

Detection of GRM1 gene rearrangements in chondromyxoid fibroma: a comparison of fluorescence in-situ hybridisation, RNA sequencing and immunohistochemical analysis

AIMS

Chondromyxoid fibroma (CMF) is a rare, benign bone tumour which arises primarily in young adults and is occasionally diagnostically challenging. Glutamate metabotropic receptor 1 (GRM1) gene encodes a metabotropic glutamate receptor and was recently shown to be up-regulated in chondromyxoid fibroma through gene fusion and promoter swapping. The aim of this study was to interrogate cases of CMF for the presence of GRM1 gene rearrangements, gene fusions and GRM1 protein overexpression.

METHODS AND RESULTS

Selected cases were subjected to testing by fluorescent in-situ hybridisation (FISH) with a GRM1 break-apart probe, a targeted RNA sequencing method and immunohistochemical study with an antibody to GRM1 protein. Two cases were subjected to whole transcriptomic sequencing. In 13 of 13 cases, GRM1 protein overexpression was detected by immunohistochemistry using the GRM1 antibody. Of the 12 cases successfully tested by FISH, nine of 12 showed GRM1 rearrangements by break-apart probe assay. Targeted RNA sequencing analysis did not detect gene fusions in any of the eight cases tested, but there was an increase in GRM1 mRNA expression in all eight cases. Two cases subjected to whole transcriptomic sequencing (WTS) showed elevated GRM1 expression and no gene fusions.

CONCLUSION

GRM1 gene rearrangements can be detected using FISH break-apart probes in approximately 75% of cases, and immunohistochemical detection of GRM1 protein over-expression is a sensitive diagnostic method. The gene fusion was not detected by targeted RNA sequencing, due most probably to the complexity of fusion mechanism, and is not yet a reliable method for confirming a diagnosis of CMF in the clinical setting.

Advances in the molecular biology of the solitary fibrous tumor and potential impact on clinical applications

Solitary fibrous tumor (SFT) is a rare fibroblastic mesenchymal neoplasm. The current classification has merged SFT and hemangiopericytoma (HPC) into the same tumor entity, while the risk stratification models have been developed to compensate for clinical prediction. Typically, slow-growing and asymptomatic, SFT can occur in various anatomical sites, most commonly in the pleura. Histologically, SFT consists of spindle to oval cells with minimal patterned growth, surrounded by stromal collagen and unique vascular patterns. Molecularly, SFT is defined by the fusion of NGFI-A-binding protein 2 (NAB2) and signal transducer and activator of transcription 6 (STAT6) genes as NAB2-STAT6. This fusion transforms NAB2 into a transcriptional activator, activating early growth response 1 (EGR1) and contributing to SFT pathogenesis and development. There are several fusion variants of NAB2-STAT6 in tumor tissues, with the most frequent ones being NAB2ex4-STAT6ex2 and NAB2ex6-STAT6ex16/ex17. Diagnostic methods play a crucial role in SFT clinical practice and basic research, including RT-PCR, next-generation sequencing (NGS), FISH, immunohistochemistry (IHC), and Western blot analysis, each with distinct capabilities and limitations. Traditional treatment strategies of SFT encompass surgical resection, radiation therapy, and chemotherapy, while emerging management regimes include antiangiogenic agents, immunotherapy, RNA-targeting technologies, and potential targeted drugs. This review provides an update on SFT's clinical and molecular aspects, diagnostic methods, and potential therapies.

Spindle Cell Neoplasms Unique to the Sinonasal Tract

The spindle cell neoplasms include sinonasal tract angiofibroma (STA), glomangiopericytoma (GPC), and biphenotypic sinonasal sarcoma (BSNS). These entities share some clinical, histomorphologic, immunohistochemical, and even molecular characteristics. Nevertheless, there are features that are unique to each tumor type. STA shows heavily collagenized and vascular stroma, with apparent relationship to underlying hormonal changes. GPC consistently exhibits monomorphic, ovoid cytologic appearance with the constant feature of Beta-catenin nuclear accumulation by IHC. Lastly, BSNS is a deceptively bland and neural-like neoplasm featuring consistent co-expression of S100 and smooth muscle markers with specific genetic rearrangements serving to uniquely characterize this entity.

Case report: A case of giant malignant solitary fibrous tumor of the pleura with Doege-Potter's syndrome and review of the literature

The solitary fibrous tumor of the pleura (SFTP) is a rare intrathoracic neoplasm that commonly originates from the subpleural mesenchymal cells of the visceral pleura and accounts for less than 5% of all pleural tumors. We reported a case of a 54-year-old man with a two-week history of hypoglycemia, a six-month history of productive cough and fatigue, and chronic right chest pain. Radiological techniques revealed a giant intra-thoracic mass with hypervascularization, and pathological staining was carried out to make a definitive diagnosis of SFTP. Interventional embolization was conducted to block the main feeding vessels before the surgery, and an anterolateral thoracotomy combined with a transverse sternotomy was performed to achieve a complete resection, which demonstrates significant potential for further application in patients with unilateral giant SFTP. The postoperative course was uneventful, with no signs of hypoglycemia observed during the follow-up. Additionally, we reviewed and prospected the research progress on SFTP. The aim of this study is to enhance clinicians' understanding of SFTP through our case and to provide a detailed review of the current research.

Case report: A rare case of malignant solitary fibrous tumor within the joint cavity with review of the literature

Solitary fibrous tumors (SFTs) are classified as fibroblastic/myofibroblastic tumors that originate from CD34-positive dendritic cells and usually occur in the pleura. In this paper, we describe a case of SFT within the joint cavity of the left knee. A 60-year-old man was admitted to hospital due to swelling in the left knee for the past 8 months without relevant trauma history. X-ray, computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography-computed tomography (PET-CT) presented a large, ill-circumscribed, hypervascular, and highly enhanced mass with eccentric calcification and peripheral, intra-lesional vessels. Subsequently, the patient underwent surgical resection. Postoperative pathology confirmed the neoplastic cells to be positive for CD34, Bcl-2, and SATA6, therefore was finally diagnosed as malignant SFT. The patient developed bone metastases within 1 year after surgery. SFT in the joint cavity is rare, and it is difficult to make a preoperative diagnosis.

Solitary fibrous tumors of the oral and maxillofacial region: a case series from a single-center

BACKGROUND

Solitary fibrous tumor (SFT) is a rare mesenchymal lesion that has a wide anatomic distribution. However, this lesion rarely occurs in the oral or maxillofacial region.

METHODS

A retrospective review was performed to evaluate the clinical symptoms, radiological images, pathology and immunohistochemistry results of 9 patients with SFTs treated between January 2015 to April 2024 in our institute. Surgical tumor resection was administered to all patients. Follow-up for these patients spanned until the conclusion of April 2024.

RESULTS

The series contained 3 males and 6 females, with the mean age 50.6 years (range: 25 to 73 years). The tumors were distributed at six different sites, including the tongue, submandibular region, cheek, sublingual gland, mandible, and hard palate. Clinically, the mass grew gradually and usually without obvious clinical symptoms. On imaging examination, the boundaries of all the tumors were clear, except for one patient with a mandibular tumor. Surgical excision was performed in all patients. Histological characteristics and positive immunostaining for STAT6, CD99, CD34 and Bcl-2 were the most important criteria for a final diagnosis. All tumors were positive for CD34 and Bcl-2. Only one tumor was negative for STAT6. While CD99 was negative in one case and weakly positive in two cases. All patients had no local recurrence during the follow-up period ranging from 1 to 100 months (mean 41.4 months).

CONCLUSIONS

Benign SFTs occurring in the oral and maxillofacial region are rare, and surgery is the primary treatment for this tumor. It usually presents as a distinctly bordered heterogeneous mass on imaging. The tumors can compress surrounding bone tissue leading to bone resorption, and in rare cases, it may exhibit invasive resorption. SFTs should be included in the differential diagnosis of lesions in the oral and maxillofacial region.

Solitary Fibrous Tumor of the Larynx: A Case Report and Brief Literature Review

Solitary fibrous tumors (SFTs) are a rare type of soft tissue tumor first identified as arising from pleura and usually arising in the thoracic cavity. The incidence of SFTs arising in the head and neck region is much lower, accounting for about 7% of SFT cases. Involvement of the larynx specifically is exceedingly rare and can have inconspicuous presentations, making them challenging to diagnose. This case report represents a patient with a history of urothelial cancer and obstructive sleep apnea who was ultimately found to have a fibrous tumor of the larynx, which was confirmed by histopathology and immunohistochemistry and treated with transoral microsurgical resection. This case report aims to shed light on an infrequently documented location of a solitary laryngeal fibrous tumor and a unique clinical presentation of this rare pathology and its successful surgical management.

Solitary fibrous tumor of the gallbladder: a case report

BACKGROUND

Primary solitary fibrous tumors (SFTs) of the gallbladder are rare. Here, we report the case of a patient who underwent surgical treatment for a primary SFT originating in the gallbladder.

CASE PRESENTATION

A 48-mm gallbladder tumor was detected in a 70-year-old man using abdominal ultrasonography at a primary hospital, and he was subsequently referred to our department. A 50-mm enhanced tumor in the gallbladder was identified using computed tomography. Magnetic resonance imaging revealed a smooth-marginated tumor with hyperintensity on T2-weighted imaging. 18F-Fluorodeoxyglucose positron emission tomography confirmed high-level fluorodeoxyglucose uptake in the gallbladder tumor in the early phase without increasing uptake in the later phase. Surgical resection was planned to evaluate the tumor diagnosis. Initially, we performed open cholecystectomy with wedge resection of the gallbladder bed. Intraoperative pathological examination suggested gallbladder cancer; therefore, we performed radical surgery, including resection of the common bile duct, extended radical lymphadenectomy, and choledochojejunostomy. Ultimately, the final pathological examination revealed an SFT originating from the gallbladder with a negative surgical margin. Postoperatively, the patient developed bile leakage that was treated with tube drainage. The patient recovered satisfactorily and was discharged on postoperative day 20. At 24 months postoperatively, the patient was in good general condition without recurrence.

CONCLUSIONS

We report a rare case of a primary SFT originating in the gallbladder. Clinicians should be aware that SFT can be found in the gallbladder, and when it is difficult to make a preoperative diagnosis, surgical treatment should be considered.

Case Report: Successful Treatment of Solitary Fibrous Tumor with Selective Internal Radiation Therapy (SIRT)

Background: This case report details the innovative use of selective internal radiation therapy (SIRT) with Yttrium-90 resin microspheres to treat a 73-year-old woman with a solitary fibrous tumor (SFT), a rare and challenging tumor type. SFTs often present significant treatment difficulties, especially in cases of recurrence or metastasis, as systemic therapies typically show limited effectiveness. This report explores SIRT as an alternative therapeutic approach for SFTs with liver metastasis. Methods: The patient initially presented with a pelvic mass, which was surgically resected. However, metastatic disease later developed in the liver. After experiencing severe side effects from targeted therapy with sunitinib, the patient was selected for treatment with SIRT as an alternative. Results: Following the SIRT intervention, the patient demonstrated a substantial reduction in tumor size and significant relief from symptoms. This outcome suggests SIRT's effectiveness as a targeted treatment for metastatic SFT. Conclusions: To our knowledge, and based on an extensive literature review, this is the first reported instance of treating SFT with SIRT. This case provides new insights into SIRT's potential as a therapeutic strategy, particularly for patients for whom conventional treatments are either ineffective or intolerable. The success observed here underscores SIRT's potential as a less invasive, locally targeted treatment option, offering hope for similar cases.

Orbital solitary fibrous tumor

INTRODUCTION

Solitary fibrous tumor (SFT) is a rare borderline mesenchymal tumor typically arising in the pleura and involving the orbit as its most common extra-pleural location.

CASE DESCRIPTION

We herein describe two cases of orbital SFT arising in both a 69-year-old woman presenting with progressive proptosis of the left eye and a 49-year-old woman presenting with binocular diplopia. The diagnoses relied on histopathological analysis of biopsy samples. Because of the poor local prognosis, we decided to perform an orbital exenteration in the first case. In the second case, a complete resection surgery was performed.

CONCLUSION

SFT presents classics histological features and immunohistochemical markers that are essential to the diagnosis. SFT is classified as a benign tumor, but in some cases, it can show aggressive behavior with the potential for local tissue invasion and, more scarcely, distant metastasis. This is why complete resection remains the treatment of choice for SFT.

[Molecular testing in mesenchymal neoplasms: What, when, and how to test? : A review with a special focus on the value of next-generation immunochemistry as a substitute for molecular testing]

With the widespread use of diverse modern molecular testing tools, the last two decades have seen significant advances in the classification of soft tissue neoplasms. Specifically, numerous molecularly defined new entities have been introduced and many established older entities have received more insightful molecular studies that have developed their classification further. The discrepant therapeutic and prognostic implications of this evolving complexity of the nosology of neoplastic diseases make the precise subtyping of soft tissue neoplasms unavoidable. However, these rapid developments of the modern diagnostic molecular pathology did not only offer efficient solutions to many complex classification issues, but they were accompanied by similarly complex and diverse emerging problems. Most importantly, these advances have not only challenged the historical dogma of some phenotypes that were once considered specific, but they also have questioned the value of diagnostic immunohistochemistry compared to emerging modern diagnostic molecular tools. Moreover, the central question of when to test, what to test, and how to test became more confusing. This review addresses the major molecular categories in soft tissue neoplasms, their characteristics, and the criteria to be used for selecting the most appropriate molecular diagnostic tool to be used in individual cases with a special focus on the value of next generation immunohistochemistry as a substitute for molecular testing.

Solitary fibrous tumor of the prostate with accompanying low-grade prostate cancer

We present the rare case of a 51-year-old male diagnosed with a solitary fibrous tumor (SFT) of the prostate, along with a concurrent low-grade prostate adenocarcinoma (Gleason score 3 + 3, Grade Group 1). The diagnosis was confirmed by positive immunohistochemical markers, including CD34, BCL2, and STAT6, and molecular analysis showing a NAB2-STAT6 fusion. Following successful surgical management and the simultaneous diagnosis of a pulmonary relapse from a prior thyroid carcinoma, the patient remains under clinical surveillance. This is particularly significant given the patient's history of multiple tumors, including Hodgkin's lymphoma, papillary thyroid carcinoma, prostate cancer, and SFT.

Epithelioid solitary fibrous tumors from CNS and soft tissues: an unusual morphologic variant

BACKGROUND

Solitary fibroous tumors (SFTs) are distinctive soft tissue tumors characterized by rearrangements of NAB2-STAT6 gene, which are associated with thin-walled, branching, "staghorn"-shaped vessels. SFTs are originally classified as a type of hemangiopericytoma (HPC). Classical SFTs are composed of spindle to ovoid cells arranged haphazardly or in fascicles. Rarely, SFTs exhibit unusual morphological variants such as fat formation, giant cells, dedifferentiation, or epithelioid variant. The epithelioid cell variant, which is composed almost entirely of epithelioid cells and arranged in solid or nest patterns, is extremely rare and frequently malignant.

CASE PRESENTATION

In this study, we reported three cases of epithelioid SFTs (ESFTs) located in extrathoracic sites (right lateral ventricle, right lumbar, left pelvis). All the subjects in this study were elderly, with a predominance of female patients, accounting for two out of the three cases, and only one case involved a male patient. The tumor cells were entirely composed of epithelioid cells and exhibited positive for CD34 and STAT-6 markers. Ultimately, the majority of cases (two out of three) were diagnosed as malignant SFTs.

CONCLUSION

This study aims to enhance the awareness of ESFTs. In these cases, irrespective of the onset location, the arrangement patterns of tumor cells, such as papillary structures and the morphology of epithelial-like cells, conspicuously lack the hallmark histological characteristics of Solitary Fibrous Tumors (SFTs). Consequently, it requires differential diagnosis from a plethora of malignant neoplasms. Moreover, the elevated malignancy level of this cohort of cases poses substantial diagnostic challenges to pathologists, compounding the complexity of accurate interpretation.

Clinical outcomes of patients undergoing reoperation with solitary fibrous tumors/hemangiopericytomas and malignant progression of tumors

OBJECTIVE

The purpose of this study was to analyze the clinical outcomes and malignant progression of tumors in patients who underwent reoperation for recurrent solitary fibrous tumors (SFTs) and hemangiopericytomas (HPCs).

METHODS

We identified 48 patients who underwent reoperation because of tumor recurrence at Tangdu Hospital between January 2010 and December 2021 and analyzed the clinical outcomes, namely, the rate of gross total resection (GTR), progression-free survival (PFS), overall survival (OS), malignant progression of tumors and radiotherapy. The survival curves for each group were plotted using the Kaplan‒Meier method and compared using log-rank tests.

RESULTS

Of the 48 patients (25 men and 23 women, mean age 49.5 ± 14.3 years), 25 experienced a second recurrence or metastasis, 15 of whom underwent a third surgery, and the remaining 10 patients who did not undergo surgery ultimately died after tumor progression. The median time (95% CI) to tumor recurrence was 40.0 (32.3-47.7) months after reoperation, with 3-, 5- and 10-year PFS rates of 54.6%, 29.5% and 14.8%, respectively. The median (95% CI) survival time was 70.0 (46.6-93.4) months, with 3-, 5- and 10-year survival rates of 67.9%, 55.1% and 36.7%, respectively. Among the 48 patients who underwent reoperation, 27 (56.3%) achieved GTR, and 21 (43.8%) achieved STR. Twelve patients in the GTR group (12/27, 44.4%) received radiotherapy after surgery, and 18 patients in the STR group (18/21, 85.7%) received radiotherapy. Of the 48 recurrent SFTs, 24 were classified as WHO grade 1, 14 were classified as WHO grade 2, and 10 were classified as WHO grade 3 based on 2021 WHO classification after the primary operation. After reoperation, 9 tumors developed malignant progression, including 4 WHO grade 1 tumors progressing to WHO grade 2 tumors, 1 WHO grade 1 tumor progressing to a WHO grade 3 tumor and 4 WHO grade 2 tumors progressing to WHO grade 3 tumors.

CONCLUSIONS

GTR after reoperation was associated with better PFS and OS compared to STR. However, the PFS after the third surgery was significantly shorter than that after the second surgery, and the rate of GTR also decreased. Malignant progression may occur after second or third tumor recurrence. Furthermore, compared with WHO grade 1 SFTs, WHO grade 2 and grade 3 SFTs significantly decreased PFS, but OS did not differ among the three groups. Radiotherapy did not prolong PFS or OS in patients who underwent reoperation.

Solitary fibrous tumor of deep parotid gland preoperatively classified as salivary gland neoplasm of uncertain malignant potential by the Milan system for reporting salivary gland cytopathology: A common diagnosis for a rare entity

Solitary fibrous tumor (SFT) is a rare fibroblastic tumor with spindle cell morphology, which is characterized by a prominent branching vasculature and a NAB2-STAT6 gene rearrangement. SFT may occur in any anatomical site and may involve salivary glands, including the parotid gland. We present a young female with a primary parotid SFT diagnosed as "neoplasm-Salivary gland neoplasm of uncertain malignant potential (SUMP)" per the Milan system for reporting salivary gland cytopathology by fine-needle aspiration (FNA) with surgical pathology follow-up. Cytomorphology of SFT is diverse and overlaps with more common entities causing a diagnostic challenge. Non-diagnostic FNA results are not uncommon. Thankfully, the majority of SFTs involving the salivary gland can be identified as "neoplasm" on FNA. The Neoplasm-SUMP subcategory is considered for the majority of cases, which would warrant a diagnostic excision with clear surgical margins, which is also curative in most cases. The Neoplasm-SUMP also perfectly encompasses the neoplastic behavior of SFT, which runs on a scale from indolent to malignant.

Different Shades of Desmoid-Type Fibromatosis (DTF): Detection of Noval Mutations in the Clinicopathologic Analysis of 32 Cases

BACKGROUND

Desmoid-type fibromatosis (DTF) is a locally aggressive myofibroblastic/fibroblastic neoplasm with a high risk of local recurrence. It has a variety of histologic features that might confuse diagnosis, especially when detected during core needle biopsy. The Wnt/β-catenin pathway is strongly linked to the pathogenesis of DT fibromatosis.

METHOD

This study examined 33 desmoid-type fibromatoses (DTFs) from 32 patients, analyzing its clinical characteristics, histologic patterns, occurrence rates, relationship with clinical outcomes, immunohistochemical and molecular findings.

RESULTS

The DTFs exhibit a range of 1 to 7 histologic patterns per tumor, including conventional, hypercellular, myxoid, hyalinized/hypocellular, staghorn/hemangiopericytomatous blood vessels pattern, nodular fasciitis-like, and keloid-like morphology. No substantial association was found between the existence of different histologic patterns and the clinical outcome. All thirty-three (100%) samples of DTF had a variable percentage of cells that were nuclear positive for β-catenin. An NGS analysis detected novel non-CTNNB1 mutations in two DTFs, including BCL10, MPL, and RBM10 gene mutations.

CONCLUSIONS

This study reveals a diverse morphology of DTFs that could result in misdiagnosis. Therefore, surgical pathologists must comprehend this thoroughly. Also, the importance of the newly identified non-CTNNB1 gene mutations is still unclear. More research and analyses are needed to completely grasp the clinical implications of these mutations.

Pulmonary Cytopathology: Current and Future Impact of Microscopy and Immunohistochemistry

With the advancement of tissue procurement techniques, in-depth knowledge of morphology is crucial for cytopathologists to diagnose neoplastic and nonneoplastic lung diseases optimally. Cytopathologists must also be well versed in immunohistochemistry/immunocytochemistry markers and their interpretation for an accurate diagnosis.

Non-IgG4-Related Fibrosing Mediastinitis Diagnosed on Core Needle Biopsy and Treated with Steroids: A Case Study and Review of the Differential Diagnoses

OBJECTIVES

This study aimed to investigate the histological characteristics and treatment efficacy of non-immunoglobulin G4-related fibrosing mediastinitis and discuss differential diagnoses for this rare entity.

METHODS

We present a case study of non-immunoglobulin G4-related fibrosing mediastinitis diagnosed on core biopsy and treated with steroids. A total of four 18-gauge core needle biopsy specimens were obtained for surgical pathology. Analysis of the patient's medical history, radiological characteristics of fibrosing mediastinitis, histological features, immunohistochemistry results, the differential diagnosis and treatment efficacy of different types of fibrosing mediastinitis was performed.

RESULTS

This report describes a unique presentation of fibrosing mediastinitis (syncope and weight loss) that was concerning for malignancy. Histological, laboratory and radiographical studies confirmed the diagnosis of non-immunoglobulin G4-related fibrosing mediastinitis. The patient received corticosteroid treatment which showed marked improvement after 1 month of treatment.

CONCLUSIONS

Fibrosing mediastinitis is an extremely uncommon entity with unknown pathogenesis, and it is more important to rule out malignancy and infection than to delineate between fibrosing mediastinitis and IgG4-related disease. In doing this, we may reasonably initiate a trial of corticosteroids which may prove beneficial, as in this patient. More studies on the pathogenesis of fibrosing mediastinitis are necessary to guide better directed treatments.

Pathogenetic and molecular classifications of soft tissue and bone tumors: A 2024 update

Soft tissue and bone tumors comprise a wide category of neoplasms. Their diversity frequently raises diagnostic challenges, and therapeutic options are continuously developing. The therapeutic success rate and long-term prognosis of patients have improved substantially due to new advances in immunohistochemical and molecular biology techniques. A fundamental contribution to these achievements has been the study of the tumor microenvironment and the reclassification of new entities with the updating of the molecular pathogenesis in the revised 5th edition of the Classification of Soft Tissue Tumors, edited by the World Health Organization. The proposed molecular diagnostic techniques include the well-known in situ hybridization and polymerase chain reaction methods, but new techniques such as copy-number arrays, multiplex probes, single-nucleotide polymorphism, and sequencing are also proposed. This review aims to synthesize the most recent pathogenetic and molecular classifications of soft tissue and bone tumors, considering the major impact of these diagnostic tools, which are becoming indispensable in clinicopathological practice.

Solitary Fibrous Tumor of Breast and Axilla: Clinicopathological Profile of Five Tumors With Comparison of Risk Stratification Models

Introduction: Solitary fibrous tumor (SFT) is a fibroblastic tumor with malignant potential that is underpinned by a recurrent inv12(q13q13)-derived NAB2::STAT6 fusion. Breast and axilla are uncommon locations for this entity. Methods: Records of two academic institutions were electronically searched for breast and axillary SFTs. Clinical and pathologic data were reviewed. Literature review for breast or axillary SFTs was performed. Present study and previously reported tumors were stratified using five SFT risk models: original and modified Demicco metastatic risk, Salas local recurrence risk, Salas metastatic risk, and Thompson local recurrence risk. Results: Five patients with breast or axillary SFT were identified. Median age was 49 years, and median follow-up (available for four patients) was 82 months. Three patients showed no evidence of disease, and one developed recurrence. Literature review identified 58 patients with breast or axillary SFT. Median age was 54 years, and median follow-up (available for 35 patients) was 24 months. Thirty-one patients showed no evidence of disease, three developed recurrence, and one developed metastasis. Original and modified Demicco models and Thompson model showed the highest sensitivity; original and modified Demicco models and Salas metastatic risk model demonstrated the highest specificity. Kaplan-Meier models were used to assess recurrence-free probability (RFP). Original and modified Demicco models predicted RFP when stratified by "low risk" and "moderate/intermediate and high risk" tumor, though sample size was small. Conclusions: While many SFTs of breast and axilla remain indolent, a subset may develop recurrence and rarely metastasize. The modified Demicco risk model demonstrated optimal performance characteristics.

Primary Omentum Malignant Hemangiopericytoma Present with Acute Abdomen

The greater omentum primary malignant tumors are rare, with less than 50 cases reported. Malignant hemangiopericytomas constitute only four of these cases. The common clinical manifestations of a malignant omental tumor are abdominal mass and pain. We report on a woman 38 years old who came to the hospital's emergency department with a finding consisting of intestinal obstruction (abdominal pain, constipation, abdominal distention, and vomiting), and during a clinical examination a mass was discovered in the lower half of her abdomen. She had been experiencing these symptoms for three days before her arrival. During a clinical examination, a large size, hard mobile mass was discovered in the lower half of her abdomen. The patient underwent an abdominal CT scan which indicated the presence of a sizable, soft tissue mass located within the abdominal and pelvic region, exerting pressure on the small bowel loops, with mild free ascites. Due to the patient's acute abdomen, an exploration laparotomy was performed, revealing a large mass in the omentum measuring 20×20×10 cm and weighing 3 kg. The mass, along with the omentum, was completely removed, and histopathology confirmed a malignant hemangiopericytoma.

Immunotherapy for Solitary Fibrous Tumor (Hemangiopericytoma): A Unique Treatment Approach for a Rare Central Nervous System Tumor

INTRODUCTION

Solitary fibrous tumors (SFTs) of the central nervous system represent a unique entity with limited data on best treatment practices.

CASE REPORT

Here, we present a case of multiply recurrent central nervous system SFT treated with radiation and immunotherapy. Immunotherapy was chosen based on mutations of genes encoding DNA repair enzymes detected through next-generation sequencing of the tumor, DNA polymerase epsilon catalytic subunit ( POLE ) and mutL homolog 1. The use of radiation and immunotherapy led to slight shrinkage and no recurrence of the tumor for over 2 years.

CONCLUSION

The presence of somatic DNA repair enzyme gene mutations in SFT may suggest a benefit from a combination of radiotherapy and immunotherapy. This may serve as a biomarker for guiding management in patients with this rare tumor.

Oral solitary fibrous tumors: A collaborative clinicopathologic study of 19 cases

OBJECTIVE

To report the clinicopathologic features of 19 oral solitary fibrous tumors (SFTs).

METHODS

Clinical data were collected from the records of seven pathology services. All cases were re-evaluated by HE staining and confirmed by immunohistochemistry.

RESULTS

The series comprised 11 females (57.9%) and 8 males (42.1%), with a mean age of 47.3 ± 14.7 years (range: 22-71 years) and a 1.3:1 female-to-male ratio. Most tumors affected the buccal mucosa (n = 7; 36.8%) and presented clinically as an asymptomatic solitary submucosal well-circumscribed nodule with coloration similar to the oral mucosa. Morphologically, most SFTs (n = 10; 52.6%) exhibited a classic hybrid pattern characterized by a well-circumscribed proliferation of densely cellular areas alternating with hypocellular areas in a variably collagenous vascular stroma. Remnants of accessory salivary glands were observed in two cases (n = 2; 10.5%). All tumors were positive for STAT6 and CD34 (n = 19; 100%). Outcome information was available from 6 patients (31.6%), with clinical follow-up ranging from 6 to 24 months (mean ± SD, 9.5 ± 6.8 months), and none developed local recurrence.

CONCLUSIONS

Oral SFTs are rare and often clinically misdiagnosed. Pathologists should consider SFT in the differential diagnosis of oral spindle cell tumors. Accurate diagnosis requires careful morphological evaluation supported by immunohistochemical analysis.

Solitary fibrous tumor within the mesorectum: literature review based on a case report of resection by transanal minimally invasive surgery (TAMIS)

PURPOSE

Solitary fibrous tumors (SFT) are a rare entity of in majority benign neoplasms. Nevertheless, up to 20% of cases show a malignant tendency with local infiltration or metastasis. Commonly arising in the thoracic cavity, only few cases of SFT of the mesorectal tissue have been reported in the literature. Complete surgical resection, classically by posterior approach, is the treatment of choice. The purpose of this review is to demonstrate the safety and suitability of transanal minimally invasive surgery (TAMIS) as a surgical approach for the resection of benign pararectal solid tumors.

METHODS

We report the case of a 52-year-old man who was diagnosed incidentally with SFT of the distal mesorectum. Resection by TAMIS was performed. Based on this case, we describe the steps and potential benefits of this procedure and provide a comprehensive review of the literature.

RESULTS

Histopathology confirms the completely resected SFT. After uneventful postoperative course and discharge on day four, follow-up was recommended by a multidisciplinary board by clinical examination and MRI, which showed a well-healed scar and no recurrence up to 3 years after resection.

CONCLUSION

SFT of the mesorectum is a very rare entity. To our knowledge, this is the first report on a TAMIS resection for SFT, demonstrated as a safe approach for complete resection of benign pararectal solid tumors.

Solitary fibrous tumor of the adrenal gland: a case report and review of the literature

Solitary fibrous tumor (SFT) is a rare mesenchymal tumor, probably of fibroblastic origin, mainly in the extremities and pleura. Primary SFT of the adrenal gland is clinically more rare. Here, we report the case of a 47-year-old woman who detected a left adrenal mass on physical examination, without any symptoms, and no laboratory abnormalities. A computed tomography (CT) examination of the adrenal gland suggested a round-like soft tissue density shadow in the left adrenal area. An unenhanced scan showed uneven density of the mass, with a scattered circular-like cystic low-density shadow inside, and an enhanced scan showed obvious uneven enhancement. We considered it to be adrenal pheochromocytoma. Ultimately, the patient was treated with laparoscopic left adrenalectomy. A pathological examination suggested an adrenal SFT. We reviewed previous case reports of adrenal SFTs and summarized the clinical characteristics of adrenal SFT combined with the relevant literature. For adrenal tumors with uneven low-density shadow and uneven CT enhancement features, we should consider the differential diagnosis of adrenal SFT.

Solitary fibrous tumor occurring in the colon as submucosal mesenchymal lesion: report of two cases and review of the literature

Solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm most often arising from the pleura and rarely in extra-pleural locations, including the gastrointestinal tract. We describe two cases of a SFT presenting as submucosal colonic lesion and review the literature on this lesion. One submucosal lesion was localized in the cecum and was 10 mm in size. The second lesion presented as a 17 mm submucosal rectal lesion. Both lesions presented as well-circumscribed submucosal lesions arranged in short fascicles, blending with abundant collagenous stroma. In both cases, the spindle cells were positive for CD34, STAT6 and CD99, and molecular studies showed NAB2:STAT6 fusion supporting the diagnosis of SFT. Both patients are alive and well 10 and 5 years post-excision, respectively. In conclusion, SFT can occur in the colon as a submucosal lesion and should be included in the differential diagnosis of colonic mesenchymal lesions.

Solitary Fibrous Tumor of the Kidney With Pure Round Cell Features: A Case Report With Review of Literature

Solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm known to occur at various soft tissue and visceral locations. Kidney is a rarely reported site for these tumors. Most of the SFTs described in the kidney exhibit a classical CD34-positive patternless spindle cell histology. Focal round cell morphology is seldom reported. Herein, we describe a 48-year-old male patient with renal SFT. This tumor had pure round cell morphology with a CD34-/STAT6+ immunophenotype. Fluorescent in situ hybridization and a multiplexed sequencing assay performed on an Illumina® HiSeq 4000 platform revealed NAB2 and STAT6 gene rearrangement. Renal tumors with round cell morphology are diagnostically challenging and SFT is not often considered in the differential diagnosis of a round cell tumor of the kidney. Moreover, a CD34-negative profile can be rather confounding while diagnosing such lesions. In such scenarios, a strong nuclear STAT6 immunostaining is extremely helpful in clinching the diagnosis. SFT should always be considered in the differential diagnosis of round cell tumors of the kidney due to significant diagnostic and therapeutic implications.

GLI1 Coamplification in Well-Differentiated/Dedifferentiated Liposarcomas: Clinicopathologic and Molecular Analysis of 92 Cases

GLI1(12q13.3) amplification is identified in a subset of mesenchymal neoplasms with a distinct nested round cell/epithelioid phenotype. MDM2 and CDK4 genes are situated along the oncogenic 12q13-15 segment, amplification of which defines well-differentiated liposarcoma (WDLPS)/dedifferentiated liposarcoma (DDLPS). The 12q amplicon can occasionally include GLI1, a gene in close proximity to CDK4. We hereby describe the first cohort of GLI1/MDM2/CDK4 coamplified WD/DDLPS. The departmental database was queried retrospectively for all cases of WD/DDLPS having undergone next-generation (MSK-IMPACT) sequencing with confirmed MDM2, CDK4, and GLI1 coamplification. Clinicopathologic data was obtained from a review of the medical chart and available histologic material. Four hundred eighty-six WD/DDLPS cases underwent DNA sequencing, 92 (19%) of which harbored amplification of the GLI1 locus in addition to that of MDM2 and CDK4. These included primary tumors (n = 60), local recurrences (n = 29), and metastases (n = 3). Primary tumors were most frequently retroperitoneal (47/60, 78%), mediastinal (4/60, 7%), and paratesticular (3/60, 5%). Average age was 63 years, with a male:female ratio of 3:2. The cohort was comprised of DDLPS (86/92 [93%], 6 of which were WDLPS with early dedifferentiation) and WDLPS without any longitudinal evidence of dedifferentiation (6/92, 7%). One-fifth (13/86, 17%) of DDLPS cases showed no evidence of a well-differentiated component in any of the primary, recurrent, or metastatic specimens. Dedifferentiated areas mostly showed high-grade undifferentiated pleomorphic sarcoma-like (26/86,30%) and high-grade myxofibrosarcoma-like (13/86,16%) morphologies. A disproportionately increased incidence of meningothelial whorls with/without osseous metaplasia was observed as the predominant pattern in 16/86 (19%) cases, and GLI1-altered morphology as described was identified in a total of 10/86 (12%) tumors. JUN (1p32.1), also implicated in the pathogenesis of WD/DDLPS, was coamplified with all 3 of MDM2, CDK4, and GLI1 in 7/91 (8%) cases. Additional loci along chromosomal arms 1p and 6q, including TNFAIP3, LATS1, and ESR1, were also amplified in a subset of cases. In this large-scale cohort of GLI1 coamplified WD/DDLPS, we elucidate uniquely recurrent features including meningothelial whorl-like and GLI-altered morphology in dedifferentiated areas. Assessment of tumor location (retroperitoneal or mediastinal), identification of a well-differentiated liposarcoma component, and coamplification of other spatially discrete genomic segments (1p and 6q) might aid in distinction from tumors with true driver GLI1 alterations.

Nonmesothelial Spindle Cell Tumors of Pleura and Pericardium

Spindle cell lesions of the pleura and pericardium are rare. Distinction from sarcomatoid mesothelioma, which has a range of morphologic patterns, can be difficult, but accurate diagnosis matters. This article provides practical guidance for the diagnosis of pleural spindle cell neoplasms, focusing on primary lesions.

Intracranial Solitary Fibrous Tumor: A Case of a 21-Year-Old Male With Olfactory Hallucination

Meningeal solitary fibrous tumors (SFTs) are a rare central nervous system neoplastic process, resulting in frequent misdiagnosis as meningioma prior to pathologic analysis. Appropriate diagnosis is essential to lowering morbidity and mortality, as Grade II or III SFTs are aggressive neoplasms that possess metastatic potential. The existing data may suggest that intracranial SFTs primarily afflict those in their fourth through sixth decades of life. However, we present the case of a patient outside this demographic presenting with symptoms that we were unable to identify in any prior reports. A 21-year-old male in the United States Navy presented to the emergency department (ED) with a two-month history of progressive headaches, leading to nausea and emesis. The patient also endorsed a daily incidence of the same olfactory hallucination followed by several minutes of palpitations, flushing, and dizziness. His neurologic exam was unremarkable, but imaging in the ED revealed a large mass abutting the right medial sphenoid wing. The radiographic appearance of the mass with a dural tail led to a preoperative diagnosis of meningioma. However, pathologic analysis following gross total resection identified the mass as an SFT. A brief literature review complementary to this case underscored the high variability of intracranial SFT case presentations with a relative scarcity of epidemiologic data due to rarity. This review identified that it was common to initially diagnose SFTs as meningioma, similar to this particular case. This emphasizes the importance of an appropriate pathologic diagnosis. This case adds to the existing literature as anecdotal evidence of SFT occurring in a young patient and a unique symptom profile most notable for olfactory hallucination and dysautonomia as features of focal seizure.