Comparison of published risk models for prediction of outcome in patients with extrameningeal solitary fibrous tumour

Solitary fibrous tumor occurring at unusual sites: A clinico-pathological series of 31 cases with emphasis on its wide morphological spectrum

Solitary fibrous tumor (SFT) is a relatively rare mesenchymal fibroblastic tumor occurring most commonly in adults with no gender predilection. Although the pathological diagnosis of SFT is usually straightforward, some difficulties may occasionally arise mainly due to the wide morphological spectrum exhibited by this tumor. In the present paper we aimed to evaluate the unusual clinicopathological features in a series of 31 SFTs arising from parenchymal organs, superficial soft tissues and deep soft tissues. Our results emphasize that SFTs may occur anywhere, including unusual sites such as periosteum of the thoracic spine, mesorectal tissue, hepatic hilum, paravescial space, kidney and breast. Moreover, a wide morphological spectrum was observed in tumors included in our series. The most striking morphological features observed included: extensive lipomatous component, myxoid stromal changes, epithelioid cell component, metaplastic mature bone, neurofibroma-like, myxofibrosarcoma-like and pseudoalveolar-like areas. Additionally, multinucleated giant cells and sarcomatous dedifferentiation were also identified. Our paper emphasizes that SFT may occur in unusual anatomical locations and exhibits a wide morphological spectrum. Pathologists must be aware of these features to avoid confusion with other benign and malignant neoplasms that may show overlapping morphological features.

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.

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.

Risk factors for recurrent disease after resection of solitary fibrous tumor: a systematic review

Introduction

Solitary fibrous tumor (SFT) is a rare soft tissue tumor found at any site of the body. The treatment of choice is surgical resection, though 10%-30% of patients experience recurrent disease. Multiple risk factors and risk stratification systems have been investigated to predict which patients are at risk of recurrence. The main goal of this systematic review is to create an up-to-date systematic overview of risk factors and risk stratification systems predicting recurrence for patients with surgically resected SFT within torso and extremities.

Method

We prepared the review following the updated Prisma guidelines for systematic reviews (PRISMA-P). Pubmed, Embase, Cochrane Library, WHO international trial registry platform and ClinicalTrials.gov were systematically searched up to December 2022. All English studies describing risk factors for recurrence after resected SFT were included. We excluded SFT in the central nervous system and the oto-rhino-laryngology region.

Results

Eighty-one retrospective studies were identified. Different risk factors including age, symptoms, sex, resection margins, anatomic location, mitotic index, pleomorphism, hypercellularity, necrosis, size, dedifferentiation, CD-34 expression, Ki67 index and TP53-expression, APAF1-inactivation, TERT promoter mutation and NAB2::STAT6 fusion variants were investigated in a narrative manner. We found that high mitotic index, Ki67 index and presence of necrosis increased the risk of recurrence after surgically resected SFT, whereas other factors had more varying prognostic value. We also summarized the currently available different risk stratification systems, and found eight different systems with a varying degree of ability to stratify patients into low, intermediate or high recurrence risk.

Conclusion

Mitotic index, necrosis and Ki67 index are the most solid risk factors for recurrence. TERT promoter mutation seems a promising component in future risk stratification models. The Demicco risk stratification system is the most validated and widely used, however the G-score model may appear to be superior due to longer follow-up time.

Systematic Review Registration

CRD42023421358.

Prognostic analysis of extrameningeal solitary fibrous tumor using the modified Demicco model: a clinicopathologic study of 111 Chinese cases

Introduction

Solitary fibrous tumor (SFT) represents a fibroblastic neoplasm exhibiting NAB2::STAT6 gene rearrangement, displaying diverse clinical manifestations, spanning from benign to malignant. To predict prognosis, the modified (four-variable) Demicco (mDemicco) model was introduced. This investigation aims to authenticate the mDemicco risk model's precision in Asian patients while investigating the clinicopathological and molecular factors linked to the prognosis of extrameningeal SFTs.

Methods

Clinicopathological data from 111 extrameningeal SFT cases in East China, covering the period from 2010 to 2020, were thoroughly analyzed. The tumors were classified using the mDemicco model. Immunohistochemical evaluation of P16 and P53, molecular detection of TP53 and TERT promoter mutation, and fluorescence in situ hybridization for CDKN2A gene alterations were performed. Statistical methods were utilized to assess the associations between clinicopathological or molecular factors and prognosis.

Results

Histologically, only one parameter, the mitotic count, exhibited a statistical correlation with progression-free survival (PFS) and overall survival (OS). During the Kaplan-Meier analysis, the variation in PFS among the different risk groups exhibited a notable trend towards statistical significance. Nevertheless, 3 out of 74 patients classified as low-risk SFTs and 7 out of 21 patients classified as intermediate-risk exhibited disease progression. Among the 5 patients with TP53 mutations and/or mutant-type P53 immunophenotype, 3 experienced disease progression, including 2 intermediate-risk patients. Additionally, among the 4 patients with TERT promoter mutations who were followed up, 3 showed progression, including 2 intermediate-risk patients. Moreover, it was observed that hemizygous loss of CDKN2A was detected in more than 30% of one case, yet the patient exhibited a favorable survival outcome.

Conclusion

The mDemicco risk model exhibits certain limitations when dealing with smaller tumor sizes, younger age groups, and occurrences of malignant and dedifferentiated SFTs. Furthermore, molecular factors, such as TP53 or TERT promoter mutations, may identify intermediate-risk SFTs with poorer prognoses.

Diagnostics and Treatment of Extrameningeal Solitary Fibrous Tumors

Solitary fibrous tumors (SFT) are rare mesenchymal neoplasms that account for less than 2% of all soft tissue masses. In the latest WHO 2020 Classification of Soft Tissue Tumors, extrameningeal SFT was listed as intermediate (rarely metastasizing) or malignant neoplasms. Due to the lack of characteristic clinical features, their diagnosis and treatment remain challenging. The pathogenesis of SFT is often associated with the presence of fusions of the NAB2-STAT6 gene on the 12q13 chromosome. Cytoplasmic CD34 positive staining is considerably characteristic for most SFTs; less frequently, factor XII, vimentin, bcl-2, and CD99 are present. A key factor in the diagnosis is the prevalent nuclear location of STAT6 expression. Radical resection is the mainstay of localized SFTs. In the case of unresectable disease, only radiotherapy or radio-chemotherapy may significantly ensure long-term local control of primary and metastatic lesions. To date, no practical guidelines have been published for the treatment of advanced or metastatic disease. Classical anthracycline-based chemotherapy is applicable. The latest studies suggest that antiangiogenic therapies should be considered after first-line treatment. Other drugs, such as imatinib, figitumumab, axitinib, and eribulin, are also being tested. Definitive radiotherapy appears to be a promising therapeutic modality. Since standards for the treatment of advanced and metastatic diseases are not available, further investigation of novel agents is necessary.

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.

Long-Term Surgical Outcome for Orbital Solitary Fibrous Tumors

PURPOSE

To report long-term outcomes after surgery for orbital solitary fibrous tumors.

METHODS

Retrospective review of patients with orbital solitary fibrous tumor, first seen between 1971 and 2022. Primary excisions were grouped as (A) surgically intact, (B) macroscopic, but with cell spillage, or (C) known incomplete excision.

RESULTS

Fifty-nine patients (31 female; 53%) presented at a mean age of 43.0 years (19-82 years), with 5 patients (8.5%) having malignant solitary fibrous tumors. Average follow up was 11.4 years (median 7.8; range 1-43 years). There were 28 of 59 (47%) group A patients with 1 of 28 (3%) having recurrence, 20 of 59 (34%) group B having 6 of 20 (30%) recurrences, and 11 of 59 (19%) group C with 9 of 11 (82%) recurrence ( p < 0.001 for recurrence rate). At a mean of 8.9 (range 1-23.6) years after initial treatment, continued local tumor growth was evident in 16 (27%) patients, with higher-grade recurrence in 3 of 14 (21%) cases. No patient had systemic disease at presentation, but 2 of 59 patients (3%) developed metastases at 22 and 30 years after first treatment. The 10-year progression-free survival was 94% (group A), 60% (group B), and 36% (group C). Tumor disruption or incomplete excision (groups B + C) carries the highest risk of tumor recurrence (hazard ratio 15.0; 95% confidence interval, 1.98-114; p = 0.009), with no correlation to tumor size or histology.

CONCLUSIONS

Orbital solitary fibrous tumors have a low recurrence rate with surgically intact excision; piecemeal excision, capsular disruption, or known incomplete resection have a high recurrence rate, which can occur decades later. Baseline postoperative scans is recommended, together with long-term clinical and interval imaging.

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.

A giant breast malignant solitary fibrous tumor: A rare case report and brief review

Solitary fibrous tumors (SFTs), which were first identified in the pleura and later at multiple anatomical locations, are rare mesenchymal neoplasms. The characteristics of SFTs include well-circumscribed margins, intense vascularity and a relatively indolent clinical course. SFTs originating from the breast are rare. To the best of our knowledge, only 33 cases of breast SFTs, including five malignant tumors, have been reported to date. In the present study, a rare case of complete resection of a giant malignant SFT is reported. A 48-year-old female patient who visited Weifang People's Hospital (Weifang, China) had a 2-year history of a right palpable breast lesion. The patient reported no other symptoms, such as skin changes or nipple discharge. An ultrasound examination revealed a giant, well-circumscribed, heterogeneous and hypoechoic lesion with central and peripheral blood flow. Owing to the large size of the lesion, mammography and magnetic resonance imaging were not feasible. Core needle biology showed that the lesion was a malignant spindle cell tumor. Following this, mastectomy and sentinel lymph node biopsy were performed. The sentinel lymph nodes exhibited metastasis. A definitive diagnosis of malignant SFT was made by microscopic examination with immunohistochemistry. The treatment strategy for benign breast SFTs should be complete surgical excision, whereas for malignant SFTs, it should include radical resection along with radiotherapy and chemotherapy. Owing to the indolent nature and late recurrence and metastasis of malignant breast SFTs, regular patient follow-up for a longer duration is essential.

Evaluation of Alternative Risk Stratification Systems in a Large Series of Solitary Fibrous Tumors with Molecular Findings and Ki-67 Index Data: Do They Improve Risk Assessment?

The clinical evolution of solitary fibrous tumors (SFTs) is often uncertain and several risk stratification systems (RSS) have been proposed. The Demicco et al. RSS is the most frequently implemented. In this study we aim to validate two alternative RSS (Sugita et al. and G-Score) using results for the Demicco RSS from a previous study of 97 SFTs. In addition, we aim to determine whether reclassified cases had any distinctive molecular features. As the Sugita et al. system substitutes mitotic count with Ki-67 index we also investigated whether Ki-67 results for tissue microarrays are comparable to those obtained using whole tissue sections. In the present study we detected that many cases classified by Demicco RSS as low-risk were reclassified as intermediate risk using the new system (G-score RSS). Kaplan-Meier survival plots for G-Score RSS showed that the low-risk and intermediate-risk SFTs had a similar evolution that contrasted with the more aggressive high-risk group. Moreover, the similar evolution in both low and intermediate-risk groups occurred despite the G-score system being stricter in classifying low-risk tumors. We observed that Sugita RSS does not provide any better risk stratification in comparison with the Demicco RSS, and testing both RSS in our series produced similar Kaplan-Meier survival data. We found some discordant results when comparing whole sections and the corresponding tissue microarrays samples, finding the hotspot areas easier to locate in whole sections. Forty-one SFTs with initial low-risk assigned by the Demicco RSS were reclassified as intermediate-risk by G-score finding both TP53 and HTER mutations in four cases, only HTER mutation in 11 cases, and only TP53 mutation in 2 cases. All six cases of SFT classified as high-risk by both the Demicco and G-score RSS suffered recurrence/metastasis, and half showed both TP53 and HTER mutations. Five SFTs were categorized as low-risk by both Demicco and G-score, of which 4 cases revealed HTER mutation. Regarding the outcome of these 5 patients, two were lost to follow-up, and one of the remaining three patients suffered recurrence. We believe that although the presence of both TP53 and HTER mutations may confer or be related to poor evolution, the isolated presence of HTER mutation alone would not necessarily be related to poor outcome. The G-score RSS more accurately identified low-risk patients than the other two risk models evaluated in the present series. Late recurrence/metastasis may occasionally be observed even in low-risk SFTs categorized by stricter classification systems such as the G-score RSS. These findings support the possibility that additional, as yet unknown factors may influence the clinical evolution of SFTs. In conclusion, given the possibility of late recurrence, long-term follow-up is recommended for all SFT patients, even in cases classified as low risk by the stricter G-score system. An integration of clinical, radiological, pathological, and molecular findings may improve SFT risk stratification and better predict patient outcome.

Validation of a novel risk score to predict early and late recurrence in solitary fibrous tumour

BACKGROUND

Current risk models in solitary fibrous tumour (SFT) were developed using cohorts with short follow-up and cannot reliably identify low-risk patients. We recently developed a novel risk model (G-score) to account for both early and late recurrences. Here, we aimed to validate the G-score in a large international cohort with long-term follow-up.

METHODS

Data were collected from nine sarcoma referral centres worldwide. Recurrence-free interval (RFi) was the primary endpoint.

RESULTS

The cohort comprised 318 patients with localised extrameningeal SFTs. Disease recurrence occurred in 96 patients (33%). The estimated 5-year RFi rate was 72%, and the 10-year RFi rate was 52%. G-score precisely predicted recurrence risk with estimated 10-year RFi rate of 84% in low risk, 54% in intermediate risk and 36% in high risk (p < 0.001; C-index 0.691). The mDemicco (p < 0.001; C-index 0.749) and SalasOS (p < 0.001; C-index 0.674) models also predicted RFi but identified low-risk patients less accurate with 10-year RFi rates of 72% and 70%, respectively.

CONCLUSIONS

G-score is a highly significant predictor of early and late recurrence in SFT and is superior to other models to predict patients at low risk of relapse. A less intensive follow-up schedule could be considered for patients at low recurrence risk according to G-score.

Giant Paratesticular Liposarcoma: Molecular Characterization and Management Principles with a Review of the Literature

Paratesticular liposarcomas are extremely rare malignant tumors originating from fat tissues, with an often-challenging diagnosis. We present here the case of a 76-year-old man with a giant paratesticular liposarcoma, initially misdiagnosed as a scrotal hernia. After two years, the progressively enlarging mass underwent surgical resection, and a diagnosis of well-differentiated liposarcoma (lipoma-like subtype) was made. Post-operative treatments were not indicated, and the patient remains relapse free. Next generation sequencing performed on the neoplastic tissue showed co-amplification of MDM2 and CDK4. These alterations are molecular hallmarks of well-differentiated liposarcomas and corroborate the histological diagnosis. Clinical and molecular features of the presented case are in line with the majority of previously published experiences. In conclusion, the presence of a liposarcoma should be taken into account during the diagnostic workup of scrotal masses, in order to minimize the rate of misdiagnosis and improper management. Molecular analysis may support histological characterization of these rare entities and potentially disclose novel therapeutic targets.

Low to Intermediate (Borderline) Grade Breast Spindle Cell Lesions on Needle Biopsy: Diagnostic Approach and Clinical Management

Spindle cell proliferations of the breast are a heterogeneous group of lesions ranging from benign or reactive lesions to aggressive malignant neoplasms. Diagnosis on core biopsy can be particularly challenging as lesions displaying different lineages associated with variable outcomes share overlapping morphologies (scar vs. fibromatosis-like metaplastic carcinoma) whereas individual entities can exhibit a large variety of appearances (myofibroblastoma). In this review, lesions are grouped into lineage, when possible, including those showing fibroblastic/myofibroblastic differentiation, ranging from entities that require no additional management, such as scar and nodular fasciitis, to those with unpredictable clinical outcomes such as fibromatosis and solitary fibrous tumor or locally aggressive behavior such as dermatofibrosarcoma protuberans. The review of low-grade vascular lesions includes atypical vascular lesion and low-grade angiosarcoma. Also discussed are various adipocytic lesions ranging from lipoma to liposarcoma, and rare smooth muscle and neural entities more commonly encountered in locations outside the breast, such as leiomyoma, neurofibroma, schwannoma, or granular cell tumor. Optimal histological evaluation of these entities merges clinical and radiologic data with morphology and ancillary testing. We present our approach to immunohistochemical and other ancillary testing and highlight issues in pathology correlation with imaging. Recent updates in the management of breast spindle cell lesions are addressed. In a well-sampled lesion with radiographic concordance, the core biopsy diagnosis reliably guides management and we advocate the inclusion of management recommendations in the pathology report. Precise characterization using up to date guidelines is important to identify a subset of patients who may safely avoid unnecessary surgical procedures. A multidisciplinary approach with close collaboration with our clinical colleagues is emphasized.

A Case Report of Rare Sacral Solitary Fibrous Tumor

Huge primary epidural solitary fibrous tumors in the sacrum are a rare clinical entity. The purpose of this article is to present our experience in treating such large and complex neoplasms in a 31-year-old woman. The patient complained of constant nocturnal bilateral hip and lower back pain and unilateral radicular symptoms (numbness, paresthesias) in the left S1/S2 dermatomal distribution. Diagnostic imaging, biopsy, preoperative endovascular embolization, two-staged tumor resection, and lumbosacroiliac fusion were performed. The treatment resolved the patient’s neurological symptoms and resulted in overall good postoperative functionality. The patient has been in remission for more than five years despite her refusal of adjuvant radiotherapy.

Toward Better Understanding and Management of Solitary Fibrous Tumor

Solitary fibrous tumor (SFT) comprises a histologic spectrum of soft tissue neoplasms that are characterized by the unique NAB2-STAT6 gene fusion. Changes in diagnostic terminology and site-specific classification over the past few decades have resulted in a disjointed literature. Complete surgical excision with preservation of function remains the mainstay of treatment. New risk stratification systems including risk factors such as mitotic rate, age, tumor size, and presence of necrosis, among others, can be used to predict risk of recurrence or metastasis. Long-term follow-up after surgical resection is recommended. The clinical manifestations, diagnosis, management, and prognosis of SFT are reviewed here.

Solitary Fibrous Tumors of the Female Genital Tract: A Study of 27 Cases Emphasizing Nonvulvar Locations, Variant Histology, and Prognostic Factors

We report 27 solitary fibrous tumors of the female genital tract emphasizing nonvulvar locations, variant histology, and prognostic factors. The patients ranged from 25 to 78 years (most were over 40), and tumors occurred in the vulva (7), vagina (2), cervix (2), corpus (6), fallopian tube/paratubal soft tissue (5), and ovary (5). They ranged from 1.5 to 39 (mean=10.5) cm and were typically solid, but 4 were predominantly cystic. All had a haphazard arrangement of spindled to ovoid cells, with most demonstrating alternating cellular and hypocellular areas and prominent vessels, but 13 lacked hypocellular areas, and 7 had focal diffuse growth with inconspicuous vasculature. Other patterns included corded (8), fascicular (5), trabecular (1), and nested (1). Microcysts (6), myxoid background (8), hyalinization (8), lipomatous differentiation (2), and multinucleated cells (6) were also present, and 10 tumors had necrosis. Vasculature included thin-walled branching "staghorn" (27), thick-walled (7), and hyalinized vessels (5) or dilated anastomosing vascular channels (3). Nuclear atypia ranged from mild (19), moderate (7), to severe (1), and mitoses from 0 to 24/10 HPF (mean=4). STAT6 was positive in all 25 tumors tested. One tumor showed dedifferentiation; the remainder were classified as benign (19) or malignant (7) based on mitotic rate (univariate stratification model) and as low risk (14), intermediate risk (8), or high risk (4) based on the Demicco multivariate risk stratification score. Follow-up (median=23 mo) was available for 16 patients. Six tumors recurred (2 intermediate risk, 3 high risk, and the dedifferentiated tumor), 5 in the abdomen; the dedifferentiated tumor metastasized to the lung. Multivariate risk stratification was superior to univariate classification, as 5 "benign" tumors were reclassified as intermediate risk using the multivariate model; of these, 2 recurred, and 1 patient died of disease. Upper female genital tract tumors occurred in older patients, were larger, and more frequently classified as high risk compared with those of the lower tract. A trend toward increased cellularity was also seen in the upper tract tumors. Only size (P=0.04), necrosis (P=0.04), and Demicco score (P=0.01) independently correlated with recurrence. Female genital tract solitary fibrous tumors demonstrate a wide range of variant morphologies and occur in diverse sites in addition to the vulva. Tumors were often misdiagnosed as other neoplasms; thus, awareness of solitary fibrous tumors occurring at these sites is crucial in prompting staining for STAT6 to establish this diagnosis. The Demicco risk stratification system effectively predicts behavior.

Evaluation of NAB2-STAT6 Fusion Variants and Other Molecular Alterations as Prognostic Biomarkers in a Case Series of 83 Solitary Fibrous Tumors

Simple Summary

A solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm that can arise at any body location. Local or distant recurrences occur in a significant proportion of cases, but these recurrences are difficult to predict using clinical or pathological features. A specific genetic alteration, the gene fusion NAB2-STAT6, is considered to be the defining driver mutation, and different fusion variants seem to account for specific clinical and pathological features, but their prognostic value remains controversial. We inspected a series of 83 SFTs with a high rate of recurrence to evaluate the clinical significance of several potential biomarkers in addition to gene fusion. Our findings confirm previous observations and uncover novel associations of molecular alterations with clinical features, adding additional evidence for their potential application as molecular biomarkers that are helpful to predict the course of the disease.

Abstract

Risk stratification of solitary fibrous tumor (SFT) patients based on clinicopathological features has limited efficacy, especially in predicting late relapse or metastasis. The hallmark alteration of SFT is the gene fusion NAB2-STAT6, whose prognostic value remains controversial. As biological knowledge of this entity has increased in recent years, new molecular alterations have emerged that could be helpful to refine current risk models. Here, we evaluated NAB2-STAT6 fusion variants and other molecular alterations in a series of 83 SFTs that are enriched in progressing cases. Gene fusion variants were identified by targeted RNA-seq in the whole series, whereas TERT promoter (pTERT) mutations were inspected by Sanger sequencing in a subset of 18 cases. Immunohistochemical assays were performed to assess BCOR and NTRK expression as well as P53 mutation status in 45, 44, and 44 cases, respectively. While confirming the associations of gene fusion variants with clinicopathological parameters, our results do not prove their prognostic value. Pan-TRK immunoexpresion correlated with recurrence/progression, P53 staining associated with higher mitotic counts, and pTERT mutations were enriched in cases with fatal outcome. An intriguing correlation was found for BCOR protein expression with gene fusion variants, size, and tumor location.

Molecular description of meningeal solitary fibrous tumors/hemangiopericytomas compared to meningiomas: two completely separate entities

INTRODUCTION

Meningeal solitary fibrous tumors (SFT), like all SFT, are defined by NAB2-STAT6 fusion and share clinicopathologic similarities with meningiomas, the most frequent meningeal tumors. Our aim is to establish the molecular identity of meningeal SFT and seek molecular prognostic factors.

METHODS

RNA sequencing and whole exome sequencing were performed in STAT6-positive SFT and grade 2-3 meningiomas, and data concerning other soft tissues tumors was obtained from the local database. Uniform manifold approximation and projection, individual gene expression and Gene Set Enrichment Analysis were performed.

RESULTS

RNA clustering shows that SFT share a common molecular signature, different from any other type of tumoral tissue. Meningeal SFT aggregate with other SFT, with no clinical or histological subgroup. Comparison of genes expressions suggests significant over-expressions of ZIC2, ZIC3, ZIC5, GABBR2, TP53 in CNS-SFT. The pathogenic TP53 c.743G>T variant, previously undescribed in SFT, was found in one sample of meningeal SFT during malignant progression.

CONCLUSIONS

Meningeal SFT are molecular counterparts of extra-meningeal SFT, completely separate from meningiomas. They might develop from the same tissues and benefit from the same treatments as SFT.

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.

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.

Mesenchymal tumours of the gastrointestinal tract

Mesenchymal tumours represent a heterogenous group of neoplasms encopassing benign, intermediate malignancy, and malignant entities. Sarcomas account for approximately 1% of human malignancies. In consideration of their rarity as well as of intrinsic complexity, diagnostic accuracy represents a major challenge. Traditionally, mesenchymal tumours are regarded as lesions the occurrence of which is mostly limited to somatic soft tissues. However, the occurrence of soft tissue tumours at visceral sites represent a well recognized event, and the GI-tract ranks among the most frequently involved visceral location. There exist entities such as gastrointestinal stromal tumours (GIST) and malignant gastointestinal neuroectodermal tumors that exhibit exquisite tropism for the GI-tract. This review will focus also on other relevant clinico-pathologic entities in which occurrence at visceral location is not at all negligible.

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.

CD34-negative Solitary Fibrous Tumor: A Clinicopathologic Study of 25 Cases and Comparison With Their CD34-positive Counterparts

CD34-negative solitary fibrous tumors (SFTs) are rare and have not been comprehensively studied. We retrospectively reviewed all cases of SFT confirmed with STAT6 immunohistochemistry and/or STAT6 gene fusion between 2013 and 2020 and collected pertinent clinicopathologic parameters. Of a total of 244 cases, 25 (10%) lacked CD34 expression by immunohistochemistry. Compared with CD34-positive SFT, CD34-negative SFT are more likely to arise in the head and neck area (32% vs. 24%, P=0.02) and present as metastatic disease (28% vs. 1%, P<0.0001). A significantly higher percentage of CD34-negative SFT exhibit high-grade cytologic atypia (hypercellularity, round cell or anaplastic morphology, nuclear pleomorphism, etc.) (48% vs. 22%, P=0.0073). There are no significant differences in the distributions of age, sex, tumor size, mitotic count, tumor necrosis, or risk stratification between CD34-negative and CD34-positive SFT. In addition, only 56% of CD34-negative SFT display a typical hemangiopericytoma-like vascular pattern. Special histologic features among CD34-negative SFT include prominent alternating hypercellular or fibrous and hypocellular myxoid areas with curvilinear vessels mimicking low-grade fibromyxoid sarcoma, pulmonary edema-like microcystic changes, and prominent amianthoid collagen fibers. In conclusion, compared with their CD34-positive counterparts, CD34-negative SFT is more likely to present as metastatic disease, show high-grade nuclear atypia, and lack the characteristic hemangiopericytoma-like vasculature, posing a unique diagnostic challenge. The use of STAT6 immunohistochemistry and/or molecular studies may be prudent in soft tissue tumors that appear CD34 negative and lack conventional SFT histopathologic characteristics.

A novel risk score to predict early and late recurrence in solitary fibrous tumour

AIMS

Solitary fibrous tumours (SFTs) are rare mesenchymal neoplasms with recurrence rates of 10-30%. Current risk stratification systems for extrameningeal SFTs are based on cohorts with limited follow-up and are not suitable for prediction of late recurrences. In this study we aimed to develop a prognostic model accounting for both early and late recurrences using a relatively large patient cohort with long-term follow-up.

METHODS AND RESULTS

Clinicopathological factors were analysed in a cohort of 100 extrameningeal, STAT6-positive SFTs. Median follow-up for overall survival (OS) and recurrence-free interval (RFi) were 121 and 84 months, respectively. Disease relapse occurred in 31% of patients and median time to recurrence was 63 months. In univariate analysis mitotic count, necrosis, male gender and presence of severe atypia and pleomorphism were associated with inferior RFi. Mitotic count, necrosis and male gender were independent predictors of recurrence in multivariate analysis. Previously published risk models were also statistically associated with RFi in our cohort, but failed to reliably identify low-risk patients due to poor prediction of late recurrences. A novel risk score based on mitotic count, necrosis and gender was able to stratify patients into low-, intermediate- and high-risk groups for both early and late recurrences.

CONCLUSIONS

In this cohort of patients with extrameningeal SFT and long-term follow-up mitotic count, necrosis and gender were independent prognostic markers of recurrence. We propose a novel risk score based on these factors and accounting for late recurrences, which should be validated in external cohorts with sufficient follow-up time.

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.

Aggressive Behavior Predictors in Solitary Fibrous Tumor: Demographic, Clinical, and Histopathologic Characteristics of 81 Cases

BACKGROUND

Solitary fibrous tumor (SFT) is a rare mesenchymal tumor with an intermediate tendency to metastasize. Meningeal hemangiopericytoma (HPC), arising in the meningeal membranes, also is considered an SFT. Although SFT is assumed to show an unpredictable behavior, the authors defined some factors associated with its aggressive behavior.

METHODS

This retrospective study was based on the medical records of 81 SFT patients treated surgically, with the median follow-up period of 59 months. The patients were assigned to three histopathologic groups based on the 2016 WHO classification: group 1 (SFT, 29 patients), group 2 (cellular SFT/hemangiopericytoma [HPC], 27 patients), and group 3 (malignant SFT/anaplastic HPC, 25 patients).

RESULTS

The SFT histopathologic classification was associated with distant metastasis (DM) (p = 0.007). The multivariate analysis showed that cellular SFT had an independent impact on DM (odds ratio [OR] = 25.42; p = 0.006). Tumor diameter larger than 7.25 cm was correlated with DM (p = 0.010) and the patient's disease-specific death (DSD) (p = 0.007). A 1-cm increase in tumor diameter enhanced the likelihood of metastasis by 1.26 (OR = 1.26; 95% confidence interval [CI], 1.05-1.53). Tumors originating from the central nervous system (CNS) showed a greater tendency toward local recurrence (LR) (p = 0.039) and DM (p = 0.05). Radiotherapy had no association with LR, DM, or DSD. The 10-year disease-specific survival rate was 82.7%.

CONCLUSIONS

Tumor size and histopathologic diagnosis are the predictors of SFT's aggressive behavior. Cellular SFTs behave as aggressively as the malignant form of the tumor. A SFT grading based on SFT cellularity would contribute to anticipation of its aggressive behavior.

Clinical Outcomes of Patients with Metastatic Solitary Fibrous Tumors: A Japanese Musculoskeletal Oncology Group (JMOG) Multiinstitutional Study

BACKGROUND

Although the unpredictable malignant behavior of solitary fibrous tumors (SFTs) has been recognized, the clinical features and prognosis of metastatic SFTs have not been well documented due to the extreme rarity of these cases. The aim of this study is to investigate the clinical features, prognostic factors, and optimal management of patients with metastatic SFTs.

PATIENTS AND METHODS

Sixty patients with metastatic SFT were retrospectively reviewed. Univariate and multivariate analyses were performed to identify the factors associated with survival. Time to next treatment (TNT) was used to evaluate the effects of various chemotherapy regimens.

RESULTS

A total of 34 male and 26 female patients (median age 55 years, range, 23-87 years) were included in the study. The median follow-up period after metastasis was 32 months (range 1-126 months). Tumor location and local recurrence were correlated with late metastasis. The 3- and 5-year overall survival rates were 72.7% and 49.2%, respectively. Primary tumor location, number of metastases, and metastasectomy were significantly associated with survival. Metastasectomy was the only significant variable on multivariate analysis. The TNT was significantly different among the various regimens.

CONCLUSIONS

Patients with metastatic SFTs had relatively longer survival periods compared with those with other metastatic soft-tissue sarcomas. Tumor location and number of metastases was associated with survival. Surgical resection of the metastatic lesions offers the best chance of survival, however further studies are warranted to define patients who would benefit from metastasectomy, and the most effective chemotherapeutic regimen for patients with metastatic SFTs remains unknown.

The 2020 WHO Classification of Soft Tissue Tumours: news and perspectives

Mesenchymal tumours represent one of the most challenging field of diagnostic pathology and refinement of classification schemes plays a key role in improving the quality of pathologic diagnosis and, as a consequence, of therapeutic options. The recent publication of the new WHO classification of Soft Tissue Tumours and Bone represents a major step toward improved standardization of diagnosis. Importantly, the 2020 WHO classification has been opened to expert clinicians that have further contributed to underline the key value of pathologic diagnosis as a rationale for proper treatment. Several relevant advances have been introduced. In the attempt to improve the prediction of clinical behaviour of solitary fibrous tumour, a risk assessment scheme has been implemented. NTRK-rearranged soft tissue tumours are now listed as an "emerging entity" also in consideration of the recent therapeutic developments in terms of NTRK inhibition. This decision has been source of a passionate debate regarding the definition of "tumour entity" as well as the consequences of a "pathology agnostic" approach to precision oncology. In consideration of their distinct clinicopathologic features, undifferentiated round cell sarcomas are now kept separate from Ewing sarcoma and subclassified, according to the underlying gene rearrangements, into three main subgroups (CIC, BCLR and not ETS fused sarcomas) Importantly, In order to avoid potential confusion, tumour entities such as gastrointestinal stroma tumours are addressed homogenously across the different WHO fascicles. Pathologic diagnosis represents the integration of morphologic, immunohistochemical and molecular characteristics and is a key element of clinical decision making. The WHO classification is as a key instrument to promote multidisciplinarity, stimulating pathologists, geneticists and clinicians to join efforts aimed to translate novel pathologic findings into more effective treatments.

Solitary fibrous tumor of bone developing lung metastases on long-term follow-up

Solitary fibrous tumors are rare mesenchymal neoplasms of fibroblastic or myofibroblastic origin. Primary solitary fibrous tumors arising in bone are extremely rare and rarely metastasize. We present a case of solitary fibrous tumor where the diagnosis was delayed due to a failure to recognize the subtle, lytic lesion underlying a fracture of the left humerus. The patient underwent proximal humeral replacement and was followed closely with imaging of humerus and chest. A small lung metastasis was found on CT scan 38 months later and was resected. Two additional small metastases were found and resected 62 months after initial tumor resection. The purpose of this case report is both to highlight the radiologic challenges which can lead to overlooking a lytic lesion underlying a fracture and to show the importance of long-term follow-up in patients with solitary fibrous tumor.

Intracranial malignant solitary fibrous tumor metastasized to the chest wall: A case report and review of literature

BACKGROUND

Solitary fibrous tumor (SFT) is a rare fibroblastic mesenchymal neoplasm that affects spindle cell soft tissues with broad-spectrum biological behavior; it is predominantly benign, and rarely metastasizes. SFT occurs mainly in the tissue structure of the serosa in the pleura and the thorax, and can be found throughout the body, though extra-thoracic localization, including the cephalic region, is un-common. We reported the first case of intracranial malignant SFT metastasized to the chest wall.

CASE SUMMARY

An 81-year-old Japanese man was referred to our hospital due to progressive gait disturbance and appetite loss. His medical history included partial resection due to brain tumor, four times, and 50-Gray radiation therapy at another hospital, starting when he was 74 years old. An unenhanced head computed tomography (CT) scan revealed an 8 cm × 5.1 cm × 6.5 cm mixed-density mass at the left frontal lobe, accompanying a midline shift, and an unenhanced chest-abdomen CT scan revealed a 6 cm × 4.1 cm × 6.5 cm low-density mass in the left chest wall. A CT-guided percutaneous lung biopsy was performed, and the pathological findings were SFT corresponding to brain tumor. Finally, the correct diagnosis of his brain tumor in history of past illness revealed to be SFT, and the unremovable tumor, namely present brain lesions enlarged and metastasized to the chest wall. We established a definitive diagnosis of intracranial malignant SFT metastasized to the chest wall. We notified him and his family of the disease, and offered palliative care. He passed away on the 29^th hospital day.

CONCLUSION

This case suggests the need for careful, detailed examination, and careful follow-up when encountering patients presenting with a mass.

Malignant solitary fibrous tumour of the prostate: four cases emphasising significant histological and immunophenotypical overlap with sarcomatoid carcinoma

Solitary fibrous tumour (SFT) is well-described in the urinary tract, but malignant examples are rare. We studied our experience with high grade malignant SFT of the prostate to address the degree of histological and immunophenotypical overlap with sarcomatoid carcinoma and prostatic stromal sarcoma. Four cases were identified from the surgical pathology consultation archives. All available H&E stained sections were reviewed. Immunostains for STAT6, CAM5.2, NKX3.1, PAX-8, GATA3, high molecular weight cytokeratin (34BE12), p40, and p63 were performed on available material. Each case was evaluated by three separate SFT prognostic risk models based on clinicopathological features, and for features of 'dedifferentiated SFT'. The patient's ages were 49, 55, 69, and 73 years. Three presented with symptoms of benign prostatic hyperplasia and one with haematuria. Tumour sizes were 5, 9, 13, and 13 cm. Mitotic rate ranged from 6 to 20 mitoses per 10 high power fields, and two cases showed abrupt transition from conventional SFT to areas with marked nuclear pleomorphism/anaplasia (i.e., 'de-differentiation'). Immunophenotypically, all four cases had strong and diffuse nuclear reactivity for STAT6. For other markers, three of three had both focal PR and GATA3 nuclear expression (up to 30% of cells). One case with 'dedifferentiated' features showed expression of multiple epithelial markers, including EMA (focal), high molecular weight cytokeratin (focal), p63, and p40. In summary, malignant SFT may rarely occur in the prostate and may closely mimic sarcomatoid carcinoma or prostatic stromal sarcoma, both histologically and immunophenotypically. Consideration of the diagnostic possibility of malignant SFT, recognition of unexpected GATA3 and PR expression, and utilisation of monoclonal STAT6 immunohistochemistry facilitate appropriate diagnosis at this unusual anatomical site.

Orbit Solitary Fibrous Tumor: A Proposed Risk Prediction Model Based on a Case Series and Comprehensive Literature Review

Solitary fibrous tumors (SFTs) of the orbit are rare. In order to further characterize the clinical and pathologic features of solitary fibrous tumor arising at this anatomic site, 12 cases of orbital SFTs were analyzed in conjunction with a review of 263 cases reported from the English literature in order to develop a risk prediction model. SFTs of the orbit were equally distributed between males (n = 5) and females (n = 7) with a mean patient age of 46.8 years (median 44.5 years; range 18-76 years) at initial diagnosis. The patients typically presented with swelling or mass around the orbit, with proptosis (n = 10), ptosis (n = 5), and visual changes (n = 6). Tumors were orbital (n = 10) or upper eyelid (n = 2). Mean tumor size was 2.5 cm (median 2.6 cm). Microscopically, the tumors were characterized by cytologically bland spindle cells with patternless growth, hypocellular and hypercellular areas, variable amounts of collagen, and ectatic, branching blood vessels. By immunohistochemistry, all cases had a strong nuclear STAT6 expression. All patients were initially managed with excision or biopsy, three with presurgical embolization. The two patients with biopsy only had persistent disease (mean 37.2 months), but a third patient developed distant bone metastasis at 86.9 months. Overall mean follow-up was 73.1 months: 9 patients are alive or dead without disease (mean 77.9 months), two patients with persistent disease, and one patient with metastatic disease at last follow-up (102 months). Incorporating cases sufficiently reported in the literature, a risk prediction model based on age > 45 years, tumor size > 3 cm, tumor necrosis, mitoses of > 4/2 mm², moderate to high cellularity, and moderate to severe pleomorphism allows for risk stratification for the development of local recurrence and distant metastasis. In conclusion, orbital SFTs are rare, but can be reliably diagnosed based on the presence of characteristic morphologic features and STAT6 immunohistochemistry. Orbital tumors tend to show a higher frequency of local recurrence than distant metastasis, which can be predicted by a risk stratification model unique to orbital tumors. With late disease common, long term clinical follow-up is recommended.

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.