Solitary fibrous tumor with neuroendocrine and squamous dedifferentiation: a potential diagnostic pitfall

Dedifferentiated Solitary Fibrous Tumor: A Clinicopathologic, Immunohistochemical, and Molecular Characterization of 25 Cases

Dedifferentiated solitary fibrous tumor (DDSFT) is a rare and clinically aggressive malignancy with a poor prognosis. It represents the progression of solitary fibrous tumor to a high-grade, morphologically nondistinctive sarcoma. This study characterizes the clinicopathologic and molecular features of 25 DDSFT. The study cohort comprised 13 males and 12 females with a median age of 63 years (range 31 to 84). Tumors were most common in the pelvic cavity (8/25), thoracic cavity (6/25), and trunk (4/25). Histologically, DDSFT demonstrated remarkably variable morphology, including pleomorphic, epithelioid, spindle cell, and round cell features. Heterologous elements were present in 4/25 (16%). Immunohistochemical expression of STAT6 was completely lost in 8/22 (36%) tumors. Targeted DNA sequencing demonstrated that in most tumors (10/13; 77%), the NAB2::STAT6 fusion variant resulted in a truncated STAT6 (STAT6-TAD) in the fusion protein. Recurrent secondary alterations involved TP53 (10/14; 71%), TERT (8/14; 57%), and RB1 (3/14; 21%). Statistical analysis of the study cohort and 55 cases reported in the literature demonstrated that complete loss of STAT6 in DDSFT is associated with shorter disease-specific survival (HR 12.69, P=0.023).

Targeted RNA sequencing in diagnostically challenging head and neck carcinomas identifies novel MON2::STAT6, NFATC2::NUTM2B, POC5::RAF1, and NSD3::NCOA2 gene fusions

AIMS

Although molecular tests developed for a growing list of oncogenic alterations have significantly aided in the classification of head and neck carcinomas, tumours in which prototypical histologic and immunophenotypic features are lacking or only partially developed continue to pose diagnostic challenges. Searching for known diagnostic and therapeutic targets by clinical next-generation sequencing (NGS) assays can often lead to new discoveries.

METHODS AND RESULTS

We present our institutional experience in applying targeted RNA NGS in 36 head and neck carcinomas that were morphologically difficult to classify between 2016 and 2023. The patients ranged in age from 5 to 83 years (median, 64), with the majority of tumors occurring in the major salivary glands and the sinonasal tract. Overall, seven (19%) cases showed unusual gene rearrangements, including five novel alterations: MON2::STAT6 in a hard palate adenocarcinoma with mucinous features, POC5::RAF1 in apocrine intraductal carcinoma of the lacrimal gland, EWSR1::CDADC1 fusion in a basaloid carcinoma of the submandibular gland, NFATC2::NUTM2B in myoepithelial carcinoma, and NSD3::NCOA2 fusion in a peculiar high-grade carcinoma with a peritheliomatous growth pattern, and focal myogenic differentiation. Potential therapeutic actionability was identified in three cases (RAF1 and FGFR2 fusions).

CONCLUSION

These findings broaden the current spectrum of gene rearrangements in head and neck carcinomas and support the utility of clinical NGS in identifying unusual, actionable alterations in diagnostically challenging cases.

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.

A rare case of dedifferentiated intracranial solitary fibrous tumor with chondrosarcomatous differentiation

This report details a rare case of a 30-year-old female presenting with neurological symptoms, including headaches, seizures, and left-sided weakness. Imaging revealed a mass in the right parafalcine region of her brain. Surgical resection identified a tumor with two distinct components. The first component exhibited characteristics of a classic solitary fibrous tumor (SFT) with typical fibroblastic cells and branching blood vessels. The second component showed high-grade sarcoma with chondrosarcomatous differentiation, a rare feature in SFT. Immunohistochemistry confirmed dedifferentiation with decreased STAT6 expression in the sarcomatous areas compared to the conventional SFT. This case highlights the challenges of managing dedifferentiated SFTs, especially in the brain, where surgical limitations increase risks. Despite the rarity of this presentation, it emphasizes the importance of recognizing this variant for appropriate diagnosis and management.

Solitary fibrous tumor of the central nervous system with epithelioid neuroendocrine "Transdedifferentiation": A case report and review of the literatures

Solitary fibrous tumors (SFTs) of the central nervous system (CNS) are rare mesenchymal tumors characterized by a fusion of the NGFI-A-binding protein 2 (NAB2) gene and the signal transducer and activator of transcription 6 (STAT6) gene, immunohistochemically resulting in nuclear expression of STAT6 - an immunohistochemical hallmark essential for diagnosis, as outlined in the fifth edition of the World Health Organization Classification of Tumors. Dedifferentiation, where low-grade tumors transform into high-grade forms, has been observed in SFTs, with documented cases involving sarcomatous or rarely epithelial transformations. We report the first case of a CNS SFT exhibiting "transdedifferentiation" into epithelioid neuroendocrine differentiation. A 36-year-old woman presented with worsening frontal headaches and vision deterioration due to an 8.2-cm frontal tumor with skull erosion. Histologically, the tumor consisted of predominantly high-grade undifferentiated epithelioid round cells that expressed STAT6, along with multifocal synaptophysin and chromogranin A positivity, and occasional cytokeratin and claudin-4 reactivity, resembling large cell neuroendocrine carcinoma. A minor bland spindle cell component with STAT 6 immunoreactivity was also noted. This case highlights the rare occurrence of neuroendocrine "transdedifferentiation" in CNS SFTs. This case highlights the importance of recognizing dedifferentiation in CSF SFTs, which often correlates with aggressive tumor behavior and poor prognosis. Given the rarity of neuroendocrine "transdedifferentiation," this case adds valuable insight into the diverse dedifferentiation patterns seen in CNS SFTs, emphasizing the need for accurate diagnosis to guide appropriate treatment strategies.

Thoracic solitary fibrous tumors with small cell features: A clinicopathological and immunohistochemical analysis of 5 cases

Five cases of thoracic solitary fibrous tumor (SFT) with small cell features are presented mimicking a neuroendocrine neoplasm. The patients were four men and one woman aged 43 to 74 years who presented with symptoms of chest pain, cough, dyspnea or hemoptysis. Two tumors were intrapulmonary neoplasms, while three were pleural-based. Grossly, the tumors ranged in size from 4 to 6 cm and were white and solid; in two tumors necrosis was apparent. Histologically, they were characterized by a cellular proliferation composed of small cells with round nuclei and inconspicuous nucleoli. The cellular proliferation in some areas had a subtle nested pattern, while in other areas the tumor showed extensive sclerosis and small vessel proliferation. Cellular pleomorphism was not marked and the mitotic activity varied from 1 to 5 mitotic figures per 10 high power fields. Microscopically, necrosis was observed in two cases and focally present in one. Immunohistochemical stains showed tumors cells universally negative for pancytokeratin; in the two pulmonary cases, focal staining for synaptophysin, CD56, and INSM1 was observed. The unexpected lack of expression of pancytokeratin led to additional analysis revealing positive staining with CD34 and STAT6 confirming a diagnosis of SFT. Clinical follow-up showed tumor recurrence in one patient while three patients remained alive and well after a period of 12 to 20 months. The current cases highlight an unusual variant of SFT that may be confused with other small cell tumor entities, such as neuroendocrine or neuroectodermal tumors, especially when originating in the thoracic cavity.

Intracranial solitary fibrous tumour with rhabdomyosarcomatous differentiation: A diagnostic challenge of a rare presentation

INTRODUCTION AND IMPORTANCE

Solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms, initially described in the pleura but capable of arising in various anatomical locations, including the central nervous system. Dedifferentiation, characterized by the transformation of a low-grade tumor into a high-grade sarcoma, is an uncommon phenomenon in SFTs, especially in the intracranial region.

CASE PRESENTATION

A 31-year-old male visited the neurology outpatient department with complaints of frequent headaches, seizures, speech difficulties, and weakness on the left side of his body. MRI was done which showed a relatively well defined T1 isointense and T2 hypointense extra-axial mass lesion in the right frontal lobe. Histopathological analysis confirmed the diagnosis of dedifferentiated SFT, marked by distinct fibroblastic differentiation and areas of high-grade sarcomatous transformation (rhabdomyosarcoma). Immunohistochemically, areas with fibroblastic differentiation showed strong and diffuse positivity for CD99, STAT6, vimentin and focal BCL-2 High-grade sarcomatous area was positive for vimentin, desmin and Myo-D1 and was negative for GFAP, EMA, PR, S-100, SMA and CD-34. It also showed focal positivity for STAT-6. The final diagnosis of intracranial solitary fibrous tumor with rhabdomyosarcomatous differentiation was made. At 2 months of follow-up, the patient is doing well.

CLINICAL DISCUSSION

Given the rarity of dedifferentiation in intracranial SFTs, there is limited consensus on optimal management strategies. En bloc resection remains the primary treatment approach, though the unpredictable behaviour of dedifferentiated SFTs complicates prognosis. This case underscores the importance of integrating clinical, radiological, and pathological findings for accurate diagnosis and discusses the need for further research into effective therapeutic options for dedifferentiated SFTs, particularly in challenging intracranial cases.

CONCLUSION

This case report presents a unique instance of an intracranial dedifferentiated SFT with rhabdomyosarcomatous dedifferentiation, highlighting the significant diagnostic challenges posed by this rare entity.

Systemic metastasis in malignant solitary fibrous tumor of the liver: two case reports and literature review

Solitary fibrous tumor of the liver (SFTL) is an exceptionally rare mesenchymal tumor, with only 117 cases reported in the literature. While most SFTs are benign, some exhibit malignant behavior, including local recurrence and metastasis. This report presents two cases of SFTL with systemic metastases, both involving prior intracranial tumors. The first case, a 52-year-old woman, discovered a liver mass incidentally during a routine physical exam. Subsequent investigations revealed potential bone metastasis, and biopsy confirmed SFT. She received two TACE procedures, anlotinib targeted therapy, and radiotherapy for the iliac bone lesion, resulting in stable disease with reduction in lesion size. The second case, a 46-year-old man, presented with multiple liver, pelvic, and lung lesions following pelvic tumor resection, with pathology confirming SFT. He was treated with long-term anlotinib therapy, CyberKnife for hepatic, lung, and pelvic lesions, and radiofrequency ablation for hepatic lesions. Postoperative recovery was uneventful, with no tumor progression on follow-up. SFTL presents with atypical clinical and imaging features, and diagnosis requires pathological and genetic confirmation. Radical resection is preferred for solitary tumors, while comprehensive treatment, including surgery and long-term follow-up, is essential for cases with recurrence or metastasis.

Solitary Fibrous Tumor of the Masticator Space with Unusual Extension: a Case Report

Background: We present the case of a patient with solitary fibrous tumor of the masticator space with unusual extension. Case presentation: A 43-year-old woman presented with a painless mass with intraoral extension on the right cheek. The B-scan sonograph and magnetic resonance imaging revealed the extension of the tumor. The biopsy performed under local anesthesia raised the suspicion of a solitary fibrous tumor. Tumor excision included a preoperative tumor embolization. The surgical removal of the tumor included a partial parotidectomy on the right side, insertion of masseteric and temporalis muscle, resection of the middle part of the zygomatic bone and stabilization of the bone with a plate, mobilization of the tumor from the maxillary sinus and the pterygopalatine fossa through an endoscopic approach and an approach via partial resection of the anterior wall of the maxillary sinus after identifying and sparing the infraorbital nerve. Ôhe histological findings confirmed the diagnosis of solitary fibrous tumor. The patient's treatment completed with radiation therapy, and 2.5 years later, there was recurrence in the right temporal area. Conclusion:To our knowledge, this is the second reported case of solitary fibrous tumor arising in the masticator space and the only case with extension intraorally and in the paranasal sinuses. Tumor embolization and complete surgical excision are the most frequently recommended treatments.

Solitary Fibrous Tumor of the Masticator Space with Unusual Extension: a Case Report

Background: We present the case of a patient with solitary fibrous tumor of the masticator space with unusual extension. Case presentation: A 43-year-old woman presented with a painless mass with intraoral extension on the right cheek. The B-scan sonograph and magnetic resonance imaging revealed the extension of the tumor. The biopsy performed under local anesthesia raised the suspicion of a solitary fibrous tumor. Tumor excision included a preoperative tumor embolization. The surgical removal of the tumor included a partial parotidectomy on the right side, insertion of masseteric and temporalis muscle, resection of the middle part of the zygomatic bone and stabilization of the bone with a plate, mobilization of the tumor from the maxillary sinus and the pterygopalatine fossa through an endoscopic approach and an approach via partial resection of the anterior wall of the maxillary sinus after identifying and sparing the infraorbital nerve. Ôhe histological findings confirmed the diagnosis of solitary fibrous tumor. The patient's treatment completed with radiation therapy, and 2.5 years later, there was recurrence in the right temporal area. Conclusion:To our knowledge, this is the second reported case of solitary fibrous tumor arising in the masticator space and the only case with extension intraorally and in the paranasal sinuses. Tumor embolization and complete surgical excision are the most frequently recommended treatments.

Exploring Solitary Fibrous Tumors at a Tertiary Cancer Center: Clinicopathological and Immunomorphologic Profile

Background Solitary fibrous tumor (SFT) is a distinct fibroblastic tumor that can occur at any anatomical site and can manifest a variety of histopathological features. NAB2-STAT6 gene fusion has recently emerged as a sensitive and specific molecular marker and its surrogate on immunohistochemistry, STAT6 has also displayed considerable efficacy. Nevertheless, its histologic diversity can result in diagnostic challenges, especially when classic features are not apparent. Methods A retrospective study was conducted at a tertiary cancer centre in North India over 3 years to document the clinicopathologic and immunomorphologic profile of SFTs. Immunohistochemical analysis of BCOR and p53 were gauged additionally and patients were stratified according to Modified Demicco and Salas criteria for risk of metastasis. Results Sixteen patients of SFT were identified, affecting middle-aged men and women equally. Though lung/pleura are known to be involved commonly, SFT affects other sites such as the kidney, brain, buccal mucosa, liver, and penis as well. The majority endured localized disease while a lesser number suffered locoregional/distant spread. Two patients revealed features of a malignant profile. Risk stratification according to the Modified Demicco and Salas criteria evinced comparable results. No discernible relationship however was highlighted between the immunohistochemical expression of BCOR, p53, and any significant SFT parameter. Conclusion Although SFTs are very rare substantially benign mesenchymal neoplasms, pathologists must be conversant with their histological diversity and be vigilant of their malignant attributes. The worth of STAT6 immunohistochemistry for precise diagnosis and long-term studies for delineating clinical behavior cannot be overemphasized.

Spindle Cell Tumors of the Sinonasal Tract: A Diagnostic Update with Focus on Ancillary Workup

Spindle cell neoplasms arising in the head and neck may be challenging to recognize due to their relative rarity. While underlying molecular alterations are increasingly elucidated, testing for these features may not be readily available. In most cases, combinations of key morphologic features and diagnostic immunohistochemical markers can be used to replace molecular diagnostics. Conversely, some molecular alterations and expression of their surrogate biomarkers are not specific for any one entity, and it is important to recognize these to avoid diagnostic pitfalls. In this review, we discuss both old and new spindle cell tumors of the sinonasal tract, with an emphasis on histologic features and clinically relevant immunohistochemical markers serving as surrogate markers for underlying genomic alterations.

Solitary fibrous tumor: Can the new Huang risk stratification system for orbital tumors improve prognostic accuracy in other tumor locations?

Solitary fibrous tumors (SFTs) are known for their heterogeneous morphology, characterized by a variety of cell shapes and different growth patterns. They can also arise in various anatomical locations, most commonly in extremities and deep soft tissues. Despite this diversity in morphology and location, all SFTs share a common molecular signature involving the NAB2::STAT6 gene fusion. Due to their unpredictable clinical behavior, establishing prognostic factors is crucial. This study aims to evaluate an orbital risk stratification system (RSS) proposed by Huang et al. for use in extraorbital SFTs using a database of 97 cases. The Huang model takes into consideration tumor size, mitotic figures, Ki-67 index, and dominant constituent cell (DCC) as key variables. Survival analysis confirmed the model's predictive value, with higher-risk scores being associated with poorer outcomes. However, in contrast to the orbital SFTs studied by Huang et al., our study did not find a correlation between tumor size and recurrence in extraorbital cases. While the Huang model performs slightly better than other RSS, it falls short on achieving statistical significance in distinguishing recurrence risk groups in extraorbital locations. In conclusion, this study validates the Huang RSS for use in extraorbital SFTs and underscores the importance of considering DCC, mitotic count, and Ki-67 together. However, we found that including tumor size in this model did not improve prognostic significance in extraorbital SFTs. Despite the benefits of this additional RSS, vigilant monitoring remains essential, even in cases classified as low-risk due to the inherent unpredictability of SFT clinical outcomes.

Solitary fibrous tumor developing in the right retroperitoneal space

Solitary fibrous tumor (SFT) is a rare mesenchymal tumor that is quite aggressive and prone to recurrence and metastasis. Most SFTs are benign, but the identification of the histological features that define the dedifferentiation of SFTs can predict the aggressiveness of the tumor and the presence of a reserved prognosis. We present a rare case of conventional SFTs with features of malignancy and highlight the diagnostic and therapeutic difficulties related to this case. Computed tomography aspect suggested a possible gastrointestinal stromal tumor. Surgical intervention was performed through median laparotomy and a tumor of approximately 15∕12 cm was found, developed from the level of the right retroperitoneal space, and pushing anteriorly the ascending colon, cecum, and terminal ileum. The immunohistochemical aspect correlated with the histopathological one suggests a SFT most likely malignant. In conclusion, the early diagnosis of SFTs is essential in establishing an appropriate treatment. Immunohistochemistry is indispensable in establishing the diagnosis of SFTs.

A Low Grade Nasopharyngeal sarcoma With FUS::NACC1 Fusion and Immunohistochemical Evidence of Epithelial Differentiation: Expanding the Clinicopathologic Spectrum of an Emerging Entity

BACKGROUND

RNA sequencing of unclassified soft tissue tumors has allowed for definition of multiple new entities. Antonescu et al. recently reported three case of low grade sarcoma with recurrent EWSR1/FUS::NACC1 fusion and distinctive storiform architecture that were suggestive of a novel tumor type.

METHODS

Here, we present a case of an additional sarcoma with FUS::NACC1 fusion that arose in the head and neck and showed immunohistochemical evidence of epithelial differentiation.

RESULTS

A 41 year old woman presented with throat and inner ear pain and was found to have a nasopharyngeal mass. Biopsy highlighted a spindle cell neoplasm composed of bland cells arranged in a tight storiform pattern. On immunohistochemistry, the tumor cells were focally positive for S100 in a fibrillary pattern but were also positive for high molecular weight cytokeratin, p40, and CD34. RNA sequencing demonstrated a FUS::NACC1 fusion. The patient remains free of disease 2 years after surgical resection.

CONCLUSION

These findings confirm the previously-reported recurrent storiform histology in sarcomas with EWSR1/FUS::NACC1 fusion while simultaneously expanding the immunohistochemical spectrum of this entity to include overt epithelial differentiation. With involvement of a head and neck mucosal site, these findings also expand the differential diagnosis to include multiple mesenchymal entities including spindle cell squamous cell carcinoma. Further recognition of this emerging entity via expanded RNA sequencing panels will be necessary to determine the prevalence of these unique features.

Primary neuroendocrine tumors and primary neuroendocrine carcinomas of the liver: a proposal for a multidiscipline definition

Primary hepatic neuroendocrine tumors and primary hepatic neuroendocrine carcinomas are rare and pose challenges for both diagnosis and for determining whether the tumor is primary to the liver versus metastatic disease. The lack of a uniform definition for primary hepatic neuroendocrine neoplasms is also a limitation to understanding and treating these rare tumors. Recently, there have been significant histological advances in the diagnosis and classification of neuroendocrine tumors in general, as well as significant advances in imaging for neuroendocrine neoplasms, all of which are important for their treatment. This article presents a multiple disciplinary definition and proposed guidelines for diagnosing a neuroendocrine tumor/neuroendocrine carcinomas as being primary to the liver.

Teratocarcinosarcoma-Like and Adamantinoma-Like Head and Neck Neoplasms Harboring NAB2::STAT6: Unusual Variants of Solitary Fibrous Tumor or Novel Tumor Entities?

The archetypal solitary fibrous tumor (SFT) features fibroblastic cells with varying cellularity without any particular architectural arrangement in a collagenous matrix, with staghorn vessels, CD34 and STAT6 expression, and NAB2::STAT6. To date, this fusion is thought to be specific for SFT. With more routine use of fusion gene panels, the histologic diversity of NAB2::STAT6-positive tumors is increasingly appreciated. Here we present four head and neck tumors harboring NAB2::STAT6 but exhibiting remarkably unusual morphologic features for SFT. All cases were pulled from the authors' consultation files. Immunohistochemistry was performed, along with targeted RNA sequencing in all cases, plus DNA next-generation sequencing on two. The cases arose in the nasal cavity (n = 2), retromolar trigone (n = 1) and parapharynx (n = 1), in patients ranging from 39 to 54 (mean, 44). Both nasal cases were biphasic, with a variably cellular collagenized stroma that resembled SFT but also interspersed malignant epithelial and neuroepithelial nests. One of the nasal cases also exhibited overt rhabdomyoblastic differentiation within both components. The two non-nasal cases were comprised of plump, epithelioid cells that were diffusely positive for pan-cytokeratin. One of these cases had prominent cystic change lined by overtly squamous epithelium. STAT6 immunostaining was positive in all cases, although the epithelial/neuroepithelial nests in the sinonasal cases were negative. All cases were confirmed to harbor NAB2::STAT6 by RNA sequencing. The two sinonasal cases were also found to harbor oncogenic mutations. The presented cases highlight a much broader histologic diversity than previously known for neoplasms with NAB2::STAT6. The biphasic nasal cases closely resemble teratocarcinosarcoma, while the epithelioid, cytokeratin-positive cases could be conceptualized as "adamantinoma-like," to borrow terminology already in use for Ewing sarcomas with complex epithelial differentiation. To identify similar cases, pathologists should have a low threshold for using STAT6 immunohistochemistry on any difficult-to-characterize head and neck tumor.

Misleading Morphologic and Phenotypic Features (Transdifferentiation) in Solitary Fibrous Tumor of the Head and Neck: Report of 3 Cases and Review of the Literature

Solitary fibrous tumor (SFT) is a rare fibroblastic neoplasm with potentially malignant behavior that may develop in any anatomic site and may involve the head and neck (H&N) region as well. Although typical SFT has a relatively characteristic morphology, its morphologic spectrum is extraordinarily broad and also includes rare cases with dedifferentiation or transdifferentiation which result in aberrant morphologic and/or immunohistochemical features. However, since virtually all cases are molecularly characterized by NAB2::STAT6 gene fusions, molecular genetic methods or STAT6 immunohistochemistry can be effectively used in confirming the diagnosis. Herein, we report 3 diagnostically challenging H&N SFT cases with an unusual morphology and/or phenotypes closely mimicking other well-known H&N entities. The tumors originated in the oral minor salivary glands, the base of the tongue, and sinonasal tract and closely resembled hyalinizing clear cell carcinoma of the salivary gland, adenocarcinoma not otherwise specified and biphenotypic sinonasal sarcoma, respectively. All cases were positive for cytokeratins, variably expressed S100 protein, showed diffuse nuclear STAT6 positivity, and harbored NAB2::STAT6 gene fusions.

Transcatheter arterial embolization of malignant pelvic solitary fibrous tumor: case report and literature review

Pelvic malignant solitary fibrous tumor (SFT) is a relatively rare disease, and literature on radical resection with transcatheter arterial embolization of pelvic SFT is lacking. In this work, we report on a 55-year-old man with a presacral mass who was hospitalized at our department. Computed tomography and magnetic resonance imaging indicated pelvic space-occupying lesions that were 12 cm × 10 cm in size and pelvic lesions that were not clearly demarcated from the right posterior wall of the bladder and the right ureter. This result suggested severe secondary hydronephrosis of the right renal pelvis. The patient underwent transcatheter iliac arterial embolization. Radical tumor resection was performed, and the results of pathological examination confirmed the diagnosis of malignant pelvic SFT. There was no SFT recurrence in this patient at 1-year follow-up. Herein, we report on the treatment of a patient with malignant pelvic SFT, a rare condition, who underwent successful radical resection after transcatheter arterial embolization. Transcatheter arterial embolization can block the blood supply of the SFT as much as possible and improve the possibility of tumor resection. In the future, pelvic SFTs can be considered improving the resection rate by transcatheter arterial embolization before surgery.

Cytopathological characteristics of solitary fibrous tumour involving the pancreas by fine needle aspiration: Making an accurate preoperative diagnosis in an uncommon location

BACKGROUND

Solitary fibrous tumour (SFT) is a unique mesenchymal neoplasm with classic features on histology and is characterised by the NAB2-STAT6 gene fusion. There are rare reports of SFTs with pancreatic involvement and only two cases in the literature reporting its features by preoperative fine needle aspiration (FNA). Herein, we characterise the cytomorphological features of four SFTs involving the pancreas by FNA to establish a preoperative diagnostic approach.

METHODS

The anatomic pathology archives of two academic medical centres were searched to identify patients with a pancreatic FNA cytology specimen and a confirmed diagnosis of SFT by surgical resection. The clinical history, pathological diagnosis, cytomorphological findings, and results of immunohistochemistry (IHC) were reviewed.

RESULTS

Four SFTs were identified from four patients with a median age of 59 years. The morphological features were variable but most frequently showed a bland spindled-to-epithelioid proliferation in fragments and single cells with small, oval, elongated, and hypochromatic nuclei in a haphazard arrangement with or without dense collagen. One tumour presented with a concurrent metastasis and showed a pure epithelioid component with necrosis and enlarged, hyperchromatic nuclei with conspicuous nucleoli and scattered mitoses. IHC was necessary for all diagnoses which were confirmed by surgical resection.

CONCLUSIONS

SFTs with pancreatic involvement are rare, and non-specific features and tumour heterogeneity can pose a diagnostic challenge on FNA; however, IHC can be used to make a definitive diagnosis. As a result, FNA is a simple, safe, cost-effective, and accurate approach that can be used to diagnose SFT in the pancreas.

Solitary Fibrous Tumor: Integration of Clinical, Morphologic, Immunohistochemical and Molecular Findings in Risk Stratification and Classification May Better Predict Patient outcome

Although solitary fibrous tumors (SFTs) have an unpredictable evolution, some specific clinicopathologic factors have been associated with the final outcome. We retrieved clinical, pathological and molecular data of 97 patients with a histological diagnosis of SFT and Signal transducer and activator of transcription 6 (STAT6) positivity. We retrospectively studied the pathological factors predictive of recurrence/metastasis and compared them with the clinical outcome. A wide immunohistochemical study and molecular analysis to detect NAB2/STAT6 gene fusion, tumor protein-53 (TP53) and/or (telomerase reverse transcriptase) TERT promotor mutation were performed. The risk of metastasis was calculated using the Demicco risk stratification system (RSS). The results were combined and examined to assess the accuracy of risk stratification and classification. The most common location was in non-extremities; 66% were located in soft tissue or subcutaneous areas and 92.8% in deep locations. On microscopic analysis, 38.1% of tumors revealed hypercellularity with a predominant patternless and/or hemangiopericytic growth pattern; 13.4% had ≥4 mitoses/10HPF; 16.5% showed necrosis, and almost half the tumors showed at least focal myxoid areas. Dedifferentiation was observed in three tumors. Immunomarker expression in SFTs was as follows: CD34 92.9%, CD99 57.1%, Bcl2 67.9%, neuroendocrine markers (at least 1) 25.7%, Desmin 14.3%, CK(AE1/AE3) 3%, Apoptotic Protease Activating Factor (APAF-1) 87% and finally Ki-67 ≥ 10% in 14.4%. The NAB2/STAT6 gene fusion was detected in 50 tumors. After a median follow-up of 90 months, 9.3% recurred, 11.3% metastasized, 10.3% died of disease and 76.2% were free of disease. TERT mutations were detected in 40.6% of the SFTs; the TP53 mutation was detected in 17%, and only 9.3% showed both mutations. According to the Demicco RSS, 6.1%, 11.3% and 82.4% of the tumors were classified as high, intermediate or low-risk of metastasis, respectively. All high-risk tumors had ≥4 mitoses/10HPF, necrosis, Ki-67 ≥ 10, HTER and/or TP53 mutation and poor evolution. The intermediate risk SFTs with worse evolution displayed the HTER mutation. Almost all low-risk tumors had a favorable evolution, although four showed at least one adverse factor (Ki-67 ≥ 10, ≥4 mitoses/10HPF or high tumor size) and had a worse evolution. An integration of clinical, morphologic, immunohistochemical and molecular findings may improve risk stratification and classification and better predict patient outcome. The unfavorable course seems to be more frequent in high-risk SFTs, although it is not exceptional in low-risk SFTs either; hence, a long-term follow-up is required independently of the assigned risk stratification score. The inclusion of molecular findings in risk stratification systems could improve the precision in the classification of SFTs, especially those of intermediate risk. Future studies will be required to determine the most effective way to incorporate molecular analyses into RSS on SFTs. The coexistence of several adverse factors such as ≥4 mitoses/10HPF, necrosis, Ki-67 ≥ 10%, mutations in HTER and/or p53 may suggest a closer clinical follow-up regardless of the histological appearance of the tumor.

Solitary fibrous tumor of thoracic cavity, extra-thoracic sites and central nervous system: Clinicopathologic features and association with local recurrence and metastasis

Published risk stratification models of solitary fibrous tumor (SFT) have been associated with distant metastases outside the central nervous system (CNS), but have not been studied for tumors occurring in the CNS. In a retrospective review, we identified 72 cases of solitary fibrous tumor or hemangiopericytoma (HPC) diagnosed between January 2011 and December 2020 at our institution. The tumors involved the central nervous system (N = 17), thoracic cavity (N = 28), and extrathoracic sites (N = 27). The risk of local recurrence, distant metastasis, or death at 5 years was 57% (95% CI 23%, 76%) in the CNS, 24% (95% CI 2%, 41%) in the thoracic cavity, and 13% (95% CI 0%, 25%) in extrathoracic sites. By contrast, the risk of distant metastasis or death at 5 years was 13% (95% CI 0%, 29%) in CNS primaries, 5% (95% CI 0%, 14%) in thoracic primaries, and 14% (95% CI 0%, 27%) in extrathoracic primaries. Using the published 3- and 4-variable risk stratification models by Demicco et al., we retrospectively assessed our cases for risk of local recurrence, distant metastasis, and death. For tumors outside the CNS, we show that three- and four-variable risk stratification models were associated with recurrence-free survival in addition to the previously known association with distant metastasis (all P < 0.05). In contrast, inside the CNS, we show that neither risk model is a significantly associated with clinical behavior, and that WHO grade is likely the best available prognostic tool, though none of the differences were significant. The lack of significant differences can be likely explained by the younger median age (47 years vs 61 years) and smaller median tumor size (3.5 cm vs 5.6 cm), downgrading the risk stratification scores in CNS compared to non-CNS primaries. In conclusion, existing risk stratification models of SFT are not associated with clinical behavior for tumors arising inside the CNS, but are associated with local recurrence in addition to distant metastasis outside the CNS.

Pelvic cavity malignant solitary fibrous tumor with dedifferentiation and multifocal cytokeratin expression

Pelvic cavity small-sized malignant solitary fibrous tumors are rare. Surgeons easily misjudge these tumors as benign lesions, and they are usually resected by laparoscopic surgery. When accompanied by dedifferentiation, malignant solitary fibrous tumors are difficult to diagnose by pathologists. Here, we describe a challenging case. A 47-year-old man was accidentally found to have a pelvic mass after three months. Surgeons assumed a diagnosis of a benign tumor according to the Computed Tomography and Ultrasonography reports. The patient underwent laparoscopic surgery to resect the tumor. After the operation, the patient was diagnosed as having a malignant solitary fibrous tumor with dedifferentiation. The patient had a recurrence one year later. This pelvic cavity malignant solitary fibrous tumor was a rare case because of its dedifferentiation and cytokeratin expression. The expression of cytokeratin and the absence of vimentin and CD34 were pitfalls to diagnosis. In this case, there was still a high amount of malignancy despite the small size of the tumor. Clinical image and pathologic multidisciplinary analysis and core needle biopsies before surgery had a great effect on diagnosis and therapy of this disease. The case is a cautionary tale not only for pathologists but also for surgeons.

The many faces of solitary fibrous tumor; diversity of histological features, differential diagnosis and role of molecular studies and surrogate markers in avoiding misdiagnosis and predicting the behavior

Background

Solitary Fibrous Tumor (SFT) is a distinct soft tissue neoplasm associated with NAB2-STAT6 gene fusion. It can involve a number of anatomic sites and exhibits a wide spectrum of histological features.

Main body

Apart from diversity in morphological features seen even in conventional SFT, two histologic variants (fat-forming and giant cell-rich) are also recognized. In addition, a malignant form and dedifferentiation are well recognized. Owing to diverse histological features and involvement of diverse anatomic locations, SFT can mimic other soft tissue neoplasms of different lineages including schwannoma, spindle cell lipoma, dermatofibrosarcoma protuberans, liposarcoma, gastrointestinal stromal tumor (GIST), malignant peripheral nerve sheath tumor (MPNST), and synovial sarcoma. SFT is classified as an intermediate (rarely metastasizing) tumor according to World Health Organization Classification of Tumors of Soft tissue and Bone, 5th edition. The management and prognosis of SFT differs from its malignant mimics and correct diagnosis is therefore important. Although SFT expresses a distinct immunohistochemical (IHC) profile, the classic histomorphological and IHC profile is not seen in all cases and diagnosis can be challenging. NAB2-STAT6 gene fusion has recently emerged as a sensitive and specific molecular marker and its IHC surrogate marker signal transducer and activator of transcription 6 (STAT6) has also shown significant sensitivity and specificity. However, few recent studies have reported STAT6 expression in other soft tissue neoplasms.

Conclusion

This review will focus on describing the diversity of histological features of SFT, differential diagnoses and discussing the features helpful in distinguishing SFT from its histological mimics.

A dedifferentiated intracranial solitary fibrous tumor with osteosarcoma components: rapid tumor progression and lethal clinical course

Solitary fibrous tumor/hemangiopericytoma is a mesenchymal tumor that originates from a common NAB2-STAT6 fusion gene and is known to very rarely demonstrate dedifferentiation in the pattern of local recurrence or distant metastasis. Here we describe for the first time a rare case of intracranial dedifferentiated solitary fibrous tumor/hemangiopericytoma with osteosarcoma components that developed in an 84-year-old man after frequent gamma knife radiosurgery over a 14-year period. We performed tumor-debulking and gamma knife radiosurgery, but unfortunately the patient died shortly after the development of dedifferentiation. There is no established treatment for dedifferentiated cases due to the rare histology and limited published data, and therefore further accumulation of histological and genetic profiles is necessary to develop novel target gene therapies.

Controversial issues in soft tissue solitary fibrous tumors: A pathological and molecular review

The clinical evolution of solitary fibrous tumor (SFT) remains unclear. Although various clinical, morphological and molecular criteria may indicate increased risk of malignancy, some SFT can still progress despite having a clearly benign appearance. Various risk stratification systems have been proposed, but unfortunately they are not sufficient to precisely determine the malignant potential. In this review, we discuss current knowledge on SFT, focusing on the following controversial issues: (i) the diverse morphologic spectrum: 'the great simulator;' (ii) malignant transformation or dedifferentiation; (iii) current risk stratification systems; and (iv) molecular factors associated with clinical evolution. The morphological spectrum of SFT and the list of differential diagnoses continue to expand. Both have increased considerably since the first descriptions of specific molecular alterations. A classification of malignant SFT should not be based on histology alone. The correlation of all pathological and molecular factors is recommended; its inclusion in risk stratification systems may help to improve diagnosis and prognosis.

Spinal solitary fibrous tumor of the neck: Next-generation sequencing-based analysis of genomic aberrations

A solitary fibrous tumor (SFT) is a rare neoplasm with recurrent NAB2-STAT6 gene fusion. An SFT may develop almost anywhere throughout the body, including the head and neck region, and is characterized by a broad spectrum of malignancy. Here we present a case involving a 57-year-old male with a dumbbell-shaped SFT in the cervical spine that mimicked schwannoma. Repeated fine-needle aspiration cytology failed to establish a definitive diagnosis. Given that the tumor size increased significantly over a 10-month period, open biopsy was then performed. Though the biopsy result was inconclusive, a nonepithelial tumor, including sclerosing epithelioid fibrosarcoma or ossifying fibromyxoid tumor, was suspected. The tumor was then completely removed together with adjacent parts of C2 and C3 vertebrae and left vertebral artery via combined anterior and posterior approaches. Histologically, the tumor consisted of round cells with prominent stromal hyalinization and was immunohistochemically positive for STAT6, CD34, and cytokeratin. Finally, Todai OncoPanel, a next-generation sequencing-based molecular profiling system using formalin-fixed paraffin-embedded samples, demonstrated fusion transcript in which NAB2 exon 6 was fused to STAT6 exon 16 supporting the diagnosis of SFT, while whole-exome sequencing analysis detected no somatic mutations which were known to be oncogenic.

Solitary fibrous tumor: a case series identifying pathological adverse factors-implications for risk stratification and classification

Solitary fibrous tumors (SFTs) are a rare type of mesenchymal lesion in which specific clinicopathologic factors have been related to patient outcome. We collected clinical, pathological, and molecular data of 28 patients with histologically confirmed SFT having at least one pathological factor associated with aggressive behavior. Molecular analysis to detect NAB2/STAT6 gene fusion, TP53, and/or TERT promoter mutation was performed. We analyzed the pathological factors predictive of recurrence/metastasis and compared with clinical outcome. The risk of metastasis was calculated using four previously described scoring systems. Histopathologically, all tumors revealed hypercellularity, 11 had ≥ 4 mitoses/10 HPF, and 12 showed necrosis. Dedifferentiation was observed in three tumors. STAT6 was positive in all cases. Desmin, p16, INSM1, and HTER immunoexpressions were detected in 14, 18, 21, and 46% of the SFT, respectively. The NAB2/STAT6 gene fusion was detected in 16 tumors. After a median follow-up of 34 months, 32.0% recurred, 32.1% metastasized, and 35.7% died of disease. TERT mutations were detected in almost half the tumors. Tumors with TP53 mutations or with TP53 and TERT promoter mutations were almost always classified as high risk, and the patients developed metastases and/or died of disease. Tumors with intermediate-risk and TERT mutation had a worse evolution. SFTs with adverse pathological parameters were not always related with a poor outcome, thus confirming the unpredictable clinical behavior of SFT. The inclusion of molecular factors (TP53 and TERT promoter status) may provide new prognostic indicators for future risk stratification systems, especially in the intermediate-risk group.

A dedifferentiated solitary fibrous tumor of the parotid gland: a case report with Cytopathologic findings and review of the literature

Background

Solitary fibrous tumor (SFT) is a ubiquitous mesenchymal neoplasm but it rarely occurs in the parotid gland. The histological features are variable, with the majority having spindle cell morphology and non-specific branching (staghorn) ecstatic vascular pattern. SFT ranges from benign to overtly malignant. Dedifferentiation within SFTs represents an abrupt transition from a well-differentiated component to a high-grade area, the latter most often including poorly differentiated epithelioid/round cell or high-grade spindle cell morphology. To the best of our knowledge, dedifferentiated SFT in the parotid gland has not been previously reported.

Case presentation

A 33-year-old woman presented with a soft tissue tumor in the right parotid gland that had been present for 6 months. Fine needle aspiration (FNA) cytology indicated epithelioid morphology in the dedifferentiated component of the tumor, along with metachromatic myxoid matrix. The tumor was initially interpreted as a salivary gland neoplasm of uncertain malignant potential (SUMP).Right partial parotidectomy was performed, and microscopic examination of the resected specimen revealed a malignant spindle cell tumor with a central epithelioid/anaplastic component. The tumor cells were diffusely positive for CD34, STAT-6 and FLI-1, and negative for pan-cytokeratin, CAM5.2, p63, S100 protein, CD31, SMA, and calponin.ERG and Ki67 immunostaining showed an accentuated nuclear staining pattern in the central dedifferentiated area. There was no overexpression of p53 or p16. The patient is currently undergoing regular follow-up and is 11 months postresection with no evidence of recurrence or distant metastasis.

Conclusions

Unlike the typical spindle cell morphology of conventional SFTs, malignant SFTs can show areas of dedifferentiation mimicking an epithelial neoplasm. FNA of dedifferentiated SFTs of the parotid gland may show, a combination of atypical epithelioid cells and metachromatic myxoid/collagenous matrix, which is a less emphasized cytological feature of SFT and may lead to misdiagnosis as a more common parotid gland epithelial neoplasm.

Clinicopathological characteristics of angiofibroma of soft tissue: report of three cases

Angiofibroma of soft tissue (AFST) is a recently-reported, rare, fibrovascular soft tissue neoplasm that commonly develops in the lower extremities of middle-aged women. Here, we report three cases located in the right temporal lobe of a woman, the left popliteal fossa of a female, and the right lower limb of a male patient, respectively, the former of which is first reported in the light of a literature review owing to its anatomical location. Histological and immunohistochemical features were consistent with the diagnosis of AFST. The two female patients have been individually followed up for 20 and 16 months after surgical resection without any local recurrences or any metastases. Meanwhile, we reviewed the clinicopathological characteristics of 81 AFST to further characterize this tumor. In addition, AFST is a benign tumor that should be considered in the differential diagnosis of a solitary fibrous tumor, a low-grade fibromyxoid sarcoma, and low-grade myxofibrosarcoma, to avoid being misdiagnosed as malignant.