Expression of fibroblast activation protein in intrathoracic solitary fibrous tumor.

PURPOSE: Fibroblast activation protein (FAP) is a serine integral membrane protease, the expression of which has been confirmed in various cancer types. Solitary fibrous tumors of the pleura (SFTP) are rare mesenchymal fibroblastic neoplasms. We present a case of 18F-labeled FAP inhibitor ([18F]FAPI-74) PET imaging and its correlation with histological FAP expression and review an SFTP series at our institution in relation to the extent of FAP expression. METHODS: This retrospective study included 13 patients who underwent surgery between March 2011 and December 2022 at our institute. One of the patients also underwent [18F]FAPI-74 PET imaging. We semi-quantitatively evaluated FAP expression in SFTPs using immunohistochemical staining and H-scores. RESULTS: Nine of the 13 patients were male, with a median age of 64 years (range, 28-79 years). The median tumor size was 6.6 cm (1.1, 16 cm). In the pathological findings, expression levels of Ki67 were 1-5% in 12 of 13 cases. Furthermore, FAP expression was observed in all patients, and the median H-score was 160 (range, 10-280). The H-score of FAP expression in two of the 13 patients was low (10 in both), and that in two of the 13 patients was high (240 and 280). The SUVmax value of [18F]FAPI-74 PET was 3.57 in a patient in whom the H-score of FAP expression was 180. CONCLUSIONS: SFTPs expressed FAP to varying degrees in different patients and the [18F]FAPI-74 PET results in one patient reflected FAP expression in the tumor tissue.

Intense PSMA Uptake in Solitary Fibrous Tumor of the Seminal Vesicle.

ABSTRACT: Solitary fibrous tumor arising from the seminal vesicle is very rare. We describe 18 F-PSMA-1007 PET/CT findings in a case of prostate adenocarcinoma with a solitary fibrous tumor of the left seminal vesicle. The solitary fibrous tumor showed intense 18 F-PSMA-1007 uptake mimicking metastatic prostate adenocarcinoma. This case indicates that solitary fibrous tumor may cause false-positive result when using PSMA PET in staging of prostate cancer.

Comprehensive analysis reveals potential therapeutic targets and an integrated risk stratification model for solitary fibrous tumors.

Solitary fibrous tumors (SFTs) are rare mesenchymal tumors with unpredictable evolution and with a recurrence or metastasis rate of 10-40%. Current medical treatments for relapsed SFTs remain ineffective. Here, we identify potential therapeutic targets and risk factors, including IDH1 p.R132S, high PD-L1 expression, and predominant macrophage infiltration, suggesting the potential benefits of combinational immune therapy and targeted therapy for SFTs. An integrated risk model incorporating mitotic count, density of Ki-67+ cells and CD163+ cells, MTOR mutation is developed, applying a discovery cohort of 101 primary non-CNS patients with negative tumor margins (NTM) and validated in three independent cohorts of 210 SFTs with the same criteria, and in 36 primary CNS SFTs with NTM. Compared with the existing models, our model shows significantly improved efficacy in identifying high-risk primary non-CNS and CNS SFTs with NTM for tumor progression.Our findings hold promise for advancing therapeutic strategies and refining risk prediction in SFTs.

Solitary Fibrous Tumors of the Lung: A Clinicopathological Analysis of 52 Cases.

OBJECTIVE: To explore the clinicopathological features of solitary fibrous tumors (SFTs) of the lung. METHODS: We collected the clinical data of 52 patients with SFTs of the lung confirmed by pathology, and summarized the clinical, radiological, and morphological features, the immunophenotypes, and the prognosis of SFTs. RESULTS: Fifty-two cases of SFTs of the lung were enrolled in this study, including 51 cases of borderline and 1 case of malignancy, 22 males and 30 females. The average onset age was 52.7 years. The lower lobe of the left lung was the preferred site of SFTs, accounting for 30.77% (16/52). Chest CT showed regular and well-demarcated soft tissue density mass, and the tumor size of most cases (46/52, 88.46%) was 1-10 cm. Morphological features: The distribution of tumor cells showed sparse and dense areas. Tumor cells were spindle-shaped, in whorls or hemangiopericytoma-like conformation. Atypia, mitotic figures, and necrosis were found. Immunohistochemistry showed positive expression of CD34, STAT6, Vimentin, BCL2, and CD99. Ki-67 was ≤ 5% in borderline SFTs and >20% in a malignant SFT. CONCLUSIONS: Solitary fibrous tumors of the lung occur more frequently in middle-aged and elderly people, and there is no significant difference in gender. The lower lobe of the left lung is the preferred site of SFTs. The size of most SFTs is 1-10 cm. Chest CT shows morphologically regular and well-demarcated soft tissue density mass. Pathologically, SFTs of the lung are mostly borderline and occasionally malignant. Immunohistochemistry shows the positive expression of CD34, STAT6, Vimentin, BCL2, and CD99.

Orbital solitary fibrous tumours: clinicopathological characteristics and recurrence prediction.

BACKGROUND: SFTs are thought to have an unpredictable clinical course and currently have no recognized prognostic criterion. Our study aimed to determine the relationship between clinicopathological characteristics and the prognosis of patients with orbital SFTs. METHODS: The clinicopathological features of these patients were extracted from clinical records. The relationships between these features and prognosis were analysed. RESULTS: The positive rates of CD34, CD99, Blc2, and STAT6 expression were 90.3%, 90.3%, 83.9%, and 100%, respectively. The tumour recurrence rate was 38.7%. A higher recurrence rate was observed in patients with Ki67 index ≥ 5 (56.25% vs. 20%, P = 0.038). CONCLUSION: A Ki67 index ≥ 5 was an effective parameter for predicting tumour recurrence of orbital SFTs. Close follow-up is needed for these patients.

ISG15 as a prognostic biomarker in solitary fibrous tumour.

BACKGROUND: Solitary fibrous tumour (SFT) is a rare mesenchymal malignancy that lacks robust prognostic and predictive biomarkers. Interferon-stimulated gene 15 (ISG15) is a ubiquitin-like modifier, associated with tumour progression, and with poor survival of SFT patients, as previous published by our group. Here, we describe the role of ISG15 in the biology of this rare tumour. METHODS: ISG15 expression was assessed by immunohistochemistry in tissue microarrays from SFT patients and tested for correlation with progression-free survival and overall survival (OS). The effects of ISG15 knockdown or induction were investigated for cancer stem cell (CSC) characteristics and for drug sensitivity in unique in vitro models of SFT. RESULTS: The prognostic value of ISG15 for OS was validated at protein level in malignant SFT patients, prospectively treated with pazopanib and enrolled in GEIS-32 trial. In SFT in vitro models, ISG15 knockdown lead to a decrease in the expression of CSC-related genes, including SOX2, NANOG, ALDH1A1, ABCB1 and ABCC1. Likewise, ISG15 downregulation decreased the clonogenic/ tumoursphere-forming ability of SFT cells, while enhancing apoptotic cell death after doxorubicin, pazopanib or trabectedin treatment in 3D cell cultures. The regulation of CSC-related genes by ISG15 was confirmed after inducing its expression with interferon-ß1; ISG15 induction upregulated 1.28- to 451-fold the expression of CSC-associated genes. CONCLUSIONS: ISG15 is a prognostic factor in malignant SFT, regulating the expression of CSC-related genes and CSCs maintenance. Our results suggest that ISG15 could be a novel therapeutic target in SFT, which could improve the efficacy of the currently available treatments.

Solitary fibrous tumor arising from the buccal mucosa: diagnostic challenge of a rare entity.

A solitary fibrous tumor (SFT) is an uncommon mesenchymal tumor characterized by spindle cell proliferation that rarely affects the oral cavity. The clinical and histopathologic features of an oral SFT are described for the benefit of dental practitioners who may encounter one of these rare cases. A 25-year-old man presented with a slow-growing swelling in the left buccal mucosa. A painless, exophytic, and well-circumscribed submucosal lesion was detected, and an excisional biopsy was performed. The biopsy specimen was submitted for histologic and immunohistochemical staining and subsequent microscopic analysis. The histopathologic examination revealed variable cellularity areas that included spindle- and star-shaped cell proliferation. These cells were immersed in a collagenized stroma containing branching vessels with a staghorn arrangement. According to immunohistochemical analysis, the tumor was characterized by STAT6, CD34, ß-catenin, and Bcl-2 expression. Diagnosis of oral SFTs is challenging given that their microscopic characteristics can mimic those of malignant mesenchymal neoplasms.

Cutaneous solitary fibrous tumor: Report of three cases with review of histopathological mimics.

Solitary fibrous tumor (SFT) is a relatively uncommon spindle cell mesenchymal neoplasm that is most often based on the pleura but may rarely arise in extrapleural locations, including the skin. Herein, we describe three cases of cutaneous SFTs. SFT is characterized by epithelioid and spindle cells arranged in random patterns with focal prominent stromal collagen and pericytomatous vessels. Immunohistochemical evaluation is required for definitive distinction of SFT from other benign and malignant cutaneous spindle cell neoplasms. Although aggressive biologic behavior is uncommon, accurate diagnosis of it is required for prognostication and counseling. CD34, bcl-2, and CD99 stains are positive in SFT, but not specific. STAT6 is the most sensitive and specific immunohistochemical marker to confirm diagnosis of SFT.

Clinicopathologic Features of Retroperitoneal Malignant Solitary Fibrous Tumors.

We aimed to explore the clinicopathologic and histologic characteristics, as well as the (differential) diagnosis of retroperitoneal malignant solitary fibrous tumors (RMSFTs) in this study. Nine cases of RMSFTs were recruited and identified by an experienced pathologist from the Pathology Department of Beijing Shijitan Hospital. Clinical information was extracted from medical records and obtained by phone calls. A systematic review of published literature on RMSFTs was conducted using PubMed. A pre-specified search strategy was adopted using the key words "solitary fibrous tumor" and "retroperitoneum." Case reports and literature published in the China Academic Journals (CNKI) and WAN FANG databases were also included. In total, 58 patients (33 males and 25 females) were included; their age ranged from 17 to 83 years, with a median age of 52 years. The tumor size ranged from 4 to 36 cm, and most patients had abdominal masses and pain. Of these patients, 56 underwent surgical resection, and two patients died and underwent an autopsy. All patients were followed up for up to 288 months (with a median follow-up of 36 months). RMSFTs are extremely rare. Their diagnosis mainly relies on the histological morphology and the expression profiles of a panel of pathologic molecules measured by immunohistochemistry. Diagnosis of RMSFTs is usually based on the expression of biomarkers such as vimentin, CD34, Bcl-2, CD99, and STAT6. Differential diagnosis includes spindle-shaped cell tumors, such as schwannoma, gastrointestinal stromal tumors, dermatofibrosarcoma protuberans, synovial sarcoma, malignant peripheral nerve sheath tumors, and fibrosarcoma. RMSFTs are prone to recur and even metastasize. Complete resection remains a major treatment, and close follow-up is highly recommended.

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.

Cytopathology of solitary fibrous tumor: a series of 34 cases.

INTRODUCTION: Solitary fibrous tumor (SFT), a fibroblastic neoplasm characterized by a specific genetic alteration (NAB2-STAT6 fusion) and relatively specific immunohistochemical profile (STAT6/CD34 positivity), is seldom the subject of cytopathology data. We report our experience with scrape smears and fine-needle aspiration (FNA) biopsies of SFT in a large patient cohort. MATERIALS AND METHODS: A search was made of our cytopathology and surgical pathology databases for cases diagnosed as solitary fibrous tumor (SFT). FNA biopsy smears, imprint smears, and cell blocks were performed and examined using standard technique. RESULTS: Thirty-four cases from 30 patients (M:F = 1.1:1; age range: 24-86 years, x = 58 years) met inclusion criteria for this study. All patients had prior or subsequent tissue confirmation of SFT. Twenty-seven (79%) specimens were FNAs, and 7 (21%) were scrape smears. Most cases (29, 85%) represented primary tumors, 4 (12%) were metastatic deposits, and 1 (3.5%) was a locally recurrent neoplasm. Sites included: pleura/lung 9 (26%), head/neck 8 (24%), lower extremity 7 (21%), trunk 4 (12%), intra-abdominal 3 (9%), upper extremity 2 (7%), and mediastinum 1 (4%). Mean tumor size was 7.2 cm (range: 1.5-19 cm). Three (9%) cases were diagnosed specifically as SFT. Remaining diagnoses were spindle cell neoplasm/proliferation 14 (41%), nondiagnostic 5 (15%), specific type of sarcoma 3 (9%), malignant round cell tumor 2 (6%), sarcoma 2 (6%), malignant tumor 2 (6%) and single cases of melanoma, pleomorphic adenoma, and mesenchymal tumor. Immunohistochemical (IHC) testing was performed in 7 of 27 (26%) cell blocks. CONCLUSION: SFT FNA cytopathology is morphologically ambiguous, overlapping with a broad array of other spindle cell proliferations. A specific diagnosis is only possible with added staining of STAT6 coupled with a set of other IHC markers.

STAT6: A review of a signaling pathway implicated in various diseases with a special emphasis in its usefulness in pathology.

Signal Transducer and Activator of Transcription 6 (STAT6), belonging to a family of seven similar members is primarily stimulated by interleukin(IL)-4 and IL-13, and acts as a T helper type 2 (Th2)-inducing factor. Thus, it is implicated in the pathophysiology of various allergic conditions, such as asthma, atopic dermatitis, eosinophilic esophagitis and food allergies, but also in tumor microenvironment regulation. Furthermore, certain forms of lymphomas, notably the Hodgkin lymphoma group, the primary mediastinal and primary central nervous system lymphoma, as well as some follicular and T cell lymphomas are associated with dysregulation of the STAT6 pathway. STAT6 immunohistochemical expression also serves as a surrogate marker in the diagnosis of solitary fibrous tumor, despite not directly responsible for the tumorigenic effect. These pathophysiological implications of the STAT6 pathway, its diagnostic or prognostic role in pathology, as well its immunohistochemical detection with different antibodies will be discussed in this review.

Clinical and molecular implications of NAB2-STAT6 fusion variants in solitary fibrous tumour.

Solitary fibrous tumour (SFT) is a mesenchymal neoplasm characterised by pathognomonic NAB2-STAT6 gene fusions. The clinical implications and prognostic value of different fusion variants has not been clarified. In the current study, we explore the clinicopathological, prognostic and molecular differences between tumours with different fusions. Thirty-nine patients with localised, extrameningeal SFT were included, of whom 20 developed distant recurrence and 19 were without recurrence after long term follow-up. Capture-based RNA sequencing identified 12 breakpoint variants, which were categorised into two groups based on the STAT6 domain composition in the predicted chimeric proteins. Twenty-one of 34 (62%) sequenced tumours had fusions with most of the STAT6 domains intact and were classified as STAT6-Full. Thirteen tumours (38%) contained only the transactivation domain of STAT6 and were classified as STAT6-TAD. Tumours with STAT6-TAD fusions had a higher mitotic count (p=0.016) and were associated with inferior recurrence-free interval (p=0.004) and overall survival (p=0.012). Estimated 10-year recurrence-free survival was 25% for patients with STAT6-TAD tumours compared to 78% for the STAT6-Full group. Distinct transcriptional signatures between the fusion groups were identified, including higher expression of FGF2 in the STAT6-TAD group and IGF2, EGR2, PDGFRB, STAT6 and several extracellular matrix genes in STAT6-Full tumours. In summary, we demonstrate that NAB2-STAT6 fusion variants are associated with distinct clinicopathological and molecular characteristics and have prognostic significance in extrameningeal SFT.

Programmed Death Ligand 1 and Immune Cell Infiltrates in Solitary Fibrous Tumors of the Pleura.

BACKGROUND: Approximately 10% to 15% of patients with solitary fibrous tumors of the pleura (SFTP) have recurrence after resection. Many are not candidates for reresection and lack effective treatments. We explored the expression of programmed death ligand 1 (PD-L1) as a biomarker for candidacy for treatment with immune checkpoint inhibitors. METHODS: We reviewed the medical records of 52 patients with primary SFTP and 5 with recurrent SFTP. We performed immunohistochemistry on tumor tissue to determine the expression of PD-L1 and infiltration by cluster of differentiation 8 (CD8)-positive immune cells. RESULTS: Any PD-L1 expression was observed in 11 primary SFTP (21.2%). Overall, PD-L1 expression level was less than 1% in 10 patients (19.2%) and greater than 1% in 1 (1.9%). Tumor infiltration by CD8-positive immune cells was absent or rare in 13 patients (25%), less than 5% in 31 (59.6%), and 5% to 25% in 8 (15.4%). There were no associations between PD-L1 expression or immune cell infiltrates and known risk factors for recurrence or a prognostic risk score classification. Time to recurrence was strongly associated with the risk score classification (P < .001), but it was not associated with PD-L1 expression (P = .296) or immune cell infiltrates (P = .619). In recurrent SFTP, PD-L1 was expressed in 4 of 10 tumors (40%; all <1% expression). There was no correlation in PD-L1 expression between primary and recurrent SFTP samples. CONCLUSIONS: A small subset of SFTP express PD-L1 at low levels (<1%) but exhibit colocalization of CD8-positive immune cells suggesting an inducible expression mechanism. The role of PD-L1 merits exploration in the clinical setting in patients with advanced SFTP when alternative treatments or clinical trials are considered.

RNA expression profiling reveals PRAME, a potential immunotherapy target, is frequently expressed in solitary fibrous tumors.

Solitary fibrous tumors are a type of translocation-associated sarcoma with up to 30% rates of metastasis and poor response to conventional chemotherapy. Other translocation-associated sarcomas have been shown to display elevated expression of various cancer-testis antigens which may render them susceptible to immunotherapy strategies such as cancer vaccines and adoptive T-cell therapy. After an RNA sequencing assay brought the cancer-testis antigen Preferentially Expressed Antigen In Melanoma (PRAME) to our attention as possibly being upregulated in aggressive TERT promoter-mutated solitary fibrous tumors, we used tissue microarrays to asses PRAME expression in a large series of previously characterized solitary fibrous tumors, with correlation to various clinicopathologic features, as well as with tumor-infiltrating macrophages and the associated signal regulatory protein α (SIRPα)-CD47 regulatory checkpoint. We found that PRAME was expressed in 165/180 solitary fibrous tumors, with high expression seen in 58%, irrespective of TERT promoter status. Elevated PRAME expression was more frequent in primary intrathoracic solitary fibrous tumors and correlated with older age at primary diagnosis. Elevated PRAME was also associated with features suggestive of immune evasion, including lower numbers of antigen-presenting CD163+ and CD68+ macrophages, and expression of the "don't eat me" receptor CD47 on tumor cells. Taken together, these features suggest that strategies targeting PRAME with or without concomitant SIRPα-CD47 axis inhibition may represent a potential future therapeutic option in aggressive solitary fibrous tumor.

Intracranial anaplastic solitary fibrous tumor/hemangiopericytoma: immunohistochemical markers for definitive diagnosis.

Intracranial anaplastic hemangiopericytoma (AHPC) is a rare and malignant subset of solitary fibrous tumor/hemangiopericytoma (SFT/HPC) as per the WHO 2016 Classification of Tumors of the Central Nervous System. AHPC portends a poor prognosis and is associated with higher rates of recurrence/metastasis in comparison with SFT/HPC. Accordingly, it is critical to continue to define the clinical course of patients with AHPC and in so doing further refine clinicopathologic/immunohistochemical (IHC) criteria needed for definitive diagnosis. Herein, we describe clinical/histological characteristics of six patients with AHPC. In addition, we reviewed and analyzed the expression of various IHC markers reported within the literature (i.e., a total of 354 intracranial SFT/HPCs and 460 meningiomas). Histologically, tumors from our six patients were characterized by a staghorn-like vascular pattern, mitotic cells, and strong nuclear atypia. Immunohistochemically, all tumors displayed positive nuclear staining for STAT6; other markers, including CD34 and Bcl-2, were expressed only in three patients. Analysis of IHC expression patterns for SFT/HPC and meningioma within the literature revealed that nuclear expression of STAT6 had the highest specificity (100%) for SFT/HPC, followed by ALDH1 (97.2%) and CD34 (93.6%). Of note, SSTR2A (95.2%) and EMA (85%) displayed a high specificity for meningioma. Anaplastic SFT/HPC is a tumor with poor prognosis that is associated with higher rates of recurrence and metastasis in comparison with SFT/HPC. Given that anaplastic SFT/HPC requires more aggressive treatment than meningioma despite of a similar presentation on imaging, it is crucial to be able to distinguish between these tumors.

Clinicopathological features to distinguish malignant solitary fibrous tumors of the prostate from prostatic stromal tumors.

Mesenchymal tumors of the prostate are rare but encompass a wide differential diagnosis. In our study, we aimed to investigate the clinicopathological features that can be used to differentiate malignant solitary fibrous tumors (mSFTs) occurring in the prostate from prostatic stromal tumors. A total of 15 patients with mesenchymal tumors of the prostate were identified in Nanjing Drum Tower Hospital from 2009 to 2019, including 3 mSFTs, 9 stromal tumors of uncertain malignant potential (STUMPs), and 3 prostatic stromal sarcomas (PSSs). Immunohistochemical stains for signal transducer and activator of transcription 6 (STAT6), aldehyde dehydrogenase 1 (ALDH1), CD34, desmin, smooth muscle actin (SMA), progesterone receptor (PR), CD117, and cytokeratin (CK) were performed on representative sections from each tumor, and the clinical features, histology, and immunophenotype of these three groups were analyzed. There was no significant difference in mean patient age of patients diagnosed with mSFTs, STUMPs, and PSSs. mSFTs and PSSs showed significantly increased tumor size (p < 0.05), Ki-67 proliferation index (p < 0.0001), and mitotic activity (p < 0.05) when compared with STUMPs. mSFTs showed significantly higher expression of STAT6 compared with both PSSs and STUMPs (p < 0.0001, p < 0.0001). PR showed significantly more expression in STUMPs than in mSFTs or PSSs (p < 0.0001, p < 0.0001). Desmin and SMA showed significantly more expression in STUMPs than in mSFTs (p < 0.05). ALDH1, CD117, CK, and CD34 showed no significant difference in staining between mSFTs, STUMPs, and PSSs. Therefore, a limited panel of STAT6, PR, and Ki-67 may be useful in distinguishing between mSFTs, STUMPs, and PSSs.

Extraordinarily long-inactive solitary fibrous tumor transformed to produce big insulin-like growth factor-2, leading to hypoglycemia and rapid liposarcoma growth: a case report.

BACKGROUND: A high-molecular-weight form of insulin-like growth factor-2 (IGF-2), known as "big" IGF-2, is occasionally produced by various tumor types, leading to hypoglycemia. Although solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm, it has been estimated that 4-6% of SFT patients develop hypoglycemia due to circulating big IGF-2. The mean time elapsed from tumor detection until the onset of hypoglycemia is reportedly less than one year (8.5 ± 1.9 months). CASE PRESENTATION: A 68-year-old man was hospitalized for exacerbation of recurring hypoglycemic episodes. He had been diagnosed with an SFT 17 years before the onset of hypoglycemia, and the SFT had already been very large at that time. The tumor, which was non-resectable and refractory to chemotherapies, had slowly increased in size since the initial diagnosis. Half a year before the hypoglycemic episodes manifested, another tumor, adjacent to the left kidney, was newly identified. Fluorodeoxyglucose positron emission tomography-computed tomography scanning, revealed the left peri-renal tumor to show much higher fluorodeoxyglucose uptake than the preexisting SFT, suggesting that it was unlikely to be a metastasis from the SFT. Abundant serum big IGF-2 was detected by western immunoblot analysis, indicating it to be the cause of the hypoglycemia. Since the 17 years between SFT detection and the onset of IGF-2-induced hypoglycemia was an extremely long period as compared with those in previous reports, we initially suspected that the new, peri-renal tumor had produced big IGF-2, but transcatheter arterial embolization of its feeding arteries did not suppress hypoglycemia. Notably, by measuring the tumor volume doubling time, the peri-renal tumor growth was shown to be markedly accelerated in parallel with exacerbation of the hypoglycemia. The patient died of heart failure 21 months after the onset of hypoglycemia. Unexpectedly, autopsy revealed that big IGF-2 had been produced only by the preexisting SFT, not the peri-renal tumor, and that the peri-renal tumor was a dedifferentiated liposarcoma. CONCLUSIONS: We should keep in mind that even a long-inactive SFT can undergo transformation to produce big IGF-2, which then acts on both insulin and IGF-1 receptors, possibly leading to both hypoglycemia and the development/growth of another tumor, respectively.

Perigastric solitary fibrous tumor (SFT) diagnosed on fine needle aspiration: A case report and review of literature.

Solitary fibrous tumor (SFT) is a mesenchymal tumor initially described in the pleura. When the tumor is located in the pleura and the classic histologic findings are present, the diagnosis of SFT can be straightforward. However, the cytologic diagnosis of perigastric SFT can be challenging due its rarity with only one cytology case report. Another confounding factor is its potential mimicry with other perigastric/gastric mesenchymal tumors. Herein, we report a case of perigastric SFT diagnosed on cytology in conjunction with immunohistochemical stains. The patient is a 79-year-old woman who presented with an enlarging perigastric mass on computerized tomography scan which was highly concerning for a saccular aneurysm. Endoscopic ultrasound (EUS) revealed a 6.6 cm hypoechoic lesion abutting the stomach. An EUS-guided fine needle aspiration was performed. The smears showed singly scattered to clusters of bland spindle cells with scant cytoplasm dispersed in a bloody background. The cell block showed similar spindle cells focally supported by a collagenized stroma. Immunohistochemical stains performed on the cell block showed the tumor cells were positive for CD34, BCL2, and STAT6 and negative for CD117, DOG1, CD31, ERG-ENDO, AE1/AE3, S-100, desmin, and synaptophysin, supporting the diagnosis of solitary fibrous tumor.