STAT6 rabbit monoclonal antibody is a robust diagnostic tool for the distinction of solitary fibrous tumour from its mimics. Pathology. 2014;46:389-395. [PMID: 24977739 DOI: 10.1097/pat.0000000000000122]

NTRK rearranged spindle cell neoplasm of the uterine cervix: a rare case report and literature review

BACKGROUND

Neurotrophic tyrosine receptor kinase (NTRK) rearranged spindle cell neoplasm is an emerging group of molecularly defined rare soft tissue tumors, often presenting with a monotonous spindle cell morphology, infiltrative growth, and co-expression of S-100 and CD34 proteins by immunohistochemistry (IHC). Accurate diagnosis necessitates the combination of morphology, immunohistochemistry, and molecular test results, with next-generation sequencing (NGS) as the gold standard. We present a rare case of NTRK rearranged spindle cell neoplasm of the uterine cervix and review the literature to highlight the current understanding of the diagnosis and treatment of this rare disease.

CASE PRESENTATION

A 49-year-old perimenopausal woman presented with menorrhagia for more than a month. A biopsy of the cervix revealed a cervical spindle cell neoplasm with a tendency to be an isolated fibrous tumor. A total abdominal hysterectomy with bilateral salpingo-oophorectomy was performed and the surgical pathology suggested NTRK rearranged spindle cell neoplasm, while NGS confirmed TFG-NTRK3 fusion gene. Postoperatively, the patient refused larotrectinib maintenance therapy for economic reasons and had no sign of recurrence or metastasis at 31 months of follow-up.

CONCLUSION

We presented the first case of cervical spindle cell neoplasm with TFG-NTRK3 gene rearrangement and retrieved 22 cases of NTRK rearranged spindle cell neoplasm of the uterine cervix from literature. The most prevalent type of gene fusion was TPM3-NTRK1, and almost all cases demonstrated S-100 and CD34 positivity by IHC. Surgery remains the initial treatment of choice and tyrosine receptor kinase (TRK) inhibitors may serve as a promising target therapy for patients with recurred or metastatic disease.

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

INTRODUCTION

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

CASE PRESENTATION

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

CONCLUSIONS

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

CHRNA6 RNA In Situ Hybridization Is a Useful Tool for the Diagnosis of Extraskeletal Myxoid Chondrosarcoma

Extraskeletal myxoid chondrosarcoma (EMC) is an uncommon mesenchymal neoplasm characteristically composed of uniform-appearing round to spindle-shaped cells with eosinophilic cytoplasm and abundant myxoid extracellular matrix. Although the majority of cases harbor a pathognomonic t(9;22) translocation that fuses EWSR1 with the orphan nuclear receptor NR4A3, there are less common variants that partner NR4A3 with TAF15, TCF12, or TFG. By immunohistochemistry, EMC has features of both cartilaginous and neuroendocrine differentiation, as evidenced by inconsistent expression of S100 protein and synaptophysin or INSM1, respectively, in a subset of cases. Given the limitations of available immunohistochemical stains for the diagnosis of EMC, we analyzed genome-wide gene expression microarray data to identify candidate biomarkers based on differential expression in EMC in comparison with other mesenchymal neoplasms. This analysis pointed to CHRNA6 as the gene with the highest relative expression in EMC (96-fold; P = 8.2 × 10-26) and the only gene with >50-fold increased expression in EMC compared with other tumors. Using RNA chromogenic in situ hybridization, we observed strong and diffuse expression of CHRNA6 in 25 cases of EMC, including both EWSR1-rearranged and TAF15-rearranged variants. All examined cases of histologic mimics were negative for CHRNA6 overexpression; however, limited CHRNA6 expression, not reaching a threshold of >5 puncta or 1 aggregate of chromogen in >25% of cells, was observed in 69 of 685 mimics (10.1%), spanning an array of mesenchymal tumors. Taken together, these findings suggest that, with careful interpretation and the use of appropriate thresholds, CHRNA6 RNA chromogenic in situ hybridization is a potentially useful ancillary histologic tool for the diagnosis of EMC.

Giant cell-rich solitary fibrous tumour of the urinary bladder: case report of an unusual histological variant and literature review

BACKGROUND

Giant cell-rich solitary fibrous tumour (GCR-SFT), previously referred to as giant cell angiofibroma, is an uncommon soft tissue tumour that classically occurs in the orbit but very rarely presents in deep organs. Here, we present a case of GCR-SFT occurring in the urinary bladder, which is one of the unusual histological subtypes of SFT.

CASE PRESENTATION

A 56-year-old man was incidentally found to have a mass measuring 4.5 × 4.3 × 4.0 cm located in the left posterior wall of the bladder by computed tomography during a physical examination. The lesion was confirmed as GCR-SFT by pathological examination after laparoscopic radical surgery. Histopathologically, the tumour was a well-circumscribed, nonencapsulated lesion that was composed of bland spindle-ovoid tumour cells alternating with hypocellular and hypercellular areas, staghorn-like vasculatures and scattered large dark-stained multinucleate giant cells lining pseudovascular spaces. The spindle-ovoid cells and multinucleate giant cells showed strong and diffuse expression of CD34 and nuclear STAT6. In addition, the hallmark of the NAB2ex4-STAT6ex5 fusion gene was detected by RT‒PCR. The patient was classified as having a low risk of recurrence or metastasis according to the risk stratification criteria. The patient underwent regular follow-up for 34 months after surgery, and there was no evidence of local recurrence or metastasis.

CONCLUSION

This is the first reported case of GCR-SFT occurring in the urinary bladder with underlying NAB2ex4-STAT6ex5 fusion. Complete surgical excision of the tumour and long-term follow-up are recommended to ensure no local recurrence or metastasis.

Solitary Fibrous Tumor of the Pancreas: Analysis of 9 Cases With Literature Review

Solitary fibrous tumor (SFT) has been increasingly reported in various anatomic sites. However, it is still extremely rare in the pancreas. Herein, we present the first series of primary pancreatic SFTs. Nine cases of primary pancreatic SFTs were analyzed. The mean age was 60 years (36 to 76 y) with no sex predilection. Six tumors were in the head, 3 were in the tail. On imaging studies, tumors were described as a hypervascular mass, 2 revealed cystic areas, and 3 were favored to be neuroendocrine tumors. On biopsy, 2 cases were diagnosed as atypical spindle cell tumor; one was misdiagnosed as suspicious for sarcoma, and another case as metastatic renal cell carcinoma. Two were diagnosed as low-grade sarcoma and low-grade stromal tumor on frozen sections. Grossly, tumors were well-demarcated with a median size of 4 cm (0.9 to 15 cm). Microscopically, they were composed of ovoid to spindle tumor cells with no significant mitotic activity and were arranged in alternating hypercellular and hypocellular areas. Staghorn-like vessels and entrapped pancreatic parenchyma were also detected within all tumors. Tumor cells revealed diffuse/strong nuclear STAT6 expression in 7 of 8, CD34 in 7 of 9, and bcl-2 in 4 of 4 tested cases. One tested tumor harbored NAB2 - STAT6 fusion. Eight patients with available follow-up data were free of disease at a mean follow-up of 76 months (3 to 189 mo). SFT should be considered in the differential diagnoses of mesenchymal neoplasms of the pancreas. Immunohistochemical nuclear STAT6 expression is a characteristic feature of SFT. Primary pancreatic SFTs seem to have favorable biological behavior in our series.

A cell hybridization-based method of generating recombinant rabbit monoclonal antibodies for detecting cytokines

Recombinant rabbit monoclonal antibodies (rabbit rAbs) have shown promise in various biomedical fields. However, it is challenging and costly to generate rabbit rAbs using traditional techniques. Here we describe a convenient and cost-effective method. Using this method, we generated rabbit rAbs against mouse soluble IL-6 receptor α with affinities in the range of 10-9 to 10-12 M. The presented method is suitable for industrial and academic scientists looking to customize rabbit rAbs for their research.

Surgical removal of an unusual huge solitary fibrous tumor in the mediastinum: a case report

BACKGROUND

Intrathoracic Solitary Fibrous Tumors (SFT) mainly arise from the pleura; however, these tumors may also originate from the mediastinum. We present a rare case of posterior SFT extending to several mediastinal sites and with an unusual large size, successfully treated with surgical resection.

CASE PRESENTATION

A 66-year-old female presented with an initial manifestation of ambiguous pain in the chest and dysphagia and later developed pitting edema in both lower extremities and cachexia five months before admission. Chest imaging confirmed a mediastinal mass (17 × 15 × 8 cm) which was surgically removed. Immunohistochemistry confirmed the diagnosis of a solitary fibrous tumor with positive B-cell lymphoma 2, STAT6, and CD99, negative S100 and smooth muscle actin, and low levels of Ki67 (5-7%). The patient's follow-up course was unremarkable.

CONCLUSION

Mediastinal SFTs may grow extremely huge, with the potential to invade multiple adjacent sites. Surgical removal of the tumor remains the mainstay of treatment in these cases.

Expression of neuroendocrine markers in meningeal and extrameningeal solitary fibrous tumors: a potential diagnostic pitfall

Solitary fibrous tumors (SFTs) may show unusual morphologies, and in such circumstances, an unexpected immunoprofile can be misleading. Following an index case of myxoid meningeal SFT with a neuroendocrine immunoprofile, we decided to assess a neuroendocrine profile in SFTs from various locations. The cohort of 9 meningeal and 28 extrameningeal SFTs was evaluated for CNS WHO grade (G1-G3) and 4-tiered Demicco risk stratification. Immunohistochemical detection of synaptophysin, chromogranin, INSM1, CD56, and CD57 was performed in each case and semiquantitatively assessed (0: no expression; 1+: <10% positive; 2+: 11-50%; and 3+: >51%); whole sections (meningeal SFTs) or tissue microarray (extrameningeal SFTs) were used for immunohistochemistry. The cohort included 13 men and 24 women. Meningeal SFTs included 5 WHO G1, 3 WHO G2, and 1 WHO G3 tumors. Extrameningeal SFTs included 21 low-risk, 4 intermediate-risk, and 2 high-risk tumors. INSM1 immunoreactivity was observed in 12 of 37 cases (32%; 8 cases 1+, 3 cases 2+, and 1 case 3+); synaptophysin was positive in 6 of 35 cases (19%; 5 cases 1+ and 1 case 2+); CD56 was positive in 20 of 37 cases (54%; 16 cases 1+, 3 cases 2+, and 1 case 3+); and CD57 was expressed in 14 of 36 cases (39%; 5 cases 1+, 4 cases 2+, and 5 cases 3+). Chromogranin positivity was not observed. No significant association was observed between expression of neuroendocrine markers and tumor grade, Demicco risk group or meningeal and extrameningeal location. Extrapleural SFTs showed a tendency for positivity of INSM1 (P = .014, χ2) and CD57 (P = .017, χ2) compared to pleural SFTs.

GRM1 Immunohistochemistry Distinguishes Chondromyxoid Fibroma From its Histologic Mimics

Chondromyxoid fibroma (CMF) is a rare benign bone neoplasm that manifests histologically as a lobular proliferation of stellate to spindle-shaped cells in a myxoid background, exhibiting morphologic overlap with other cartilaginous and myxoid tumors of bone. CMF is characterized by recurrent genetic rearrangements that place the glutamate receptor gene GRM1 under the regulatory control of a constitutively active promoter, leading to increased gene expression. Here, we explore the diagnostic utility of GRM1 immunohistochemistry as a surrogate marker for GRM1 rearrangement using a commercially available monoclonal antibody in a study of 230 tumors, including 30 CMF cases represented by 35 specimens. GRM1 was positive by immunohistochemistry in 97% of CMF specimens (34/35), exhibiting moderate to strong staining in more than 50% of neoplastic cells; staining was diffuse (>95% of cells) in 25 specimens (71%). Among the 9 CMF specimens with documented exposure to acid decalcification, 4 (44%) exhibited diffuse immunoreactivity (>95%) for GRM1, whereas all 15 CMF specimens (100%) with lack of exposure to decalcification reagents were diffusely immunoreactive ( P =0.003). High GRM1 expression at the RNA level was previously observed by quantitative reverse transcription polymerase chain reaction in 9 CMF cases that were also positive by immunohistochemistry; low GRM1 expression was observed by quantitative reverse transcription polymerase chain reaction in the single case of CMF that was negative by immunohistochemistry. GRM1 immunohistochemistry was negative (<5%) in histologic mimics of CMF, including conventional chondrosarcoma, enchondroma, chondroblastoma, clear cell chondrosarcoma, giant cell tumor of the bone, fibrous dysplasia, chondroblastic osteosarcoma, myoepithelial tumor, primary aneurysmal bone cyst, brown tumor, phosphaturic mesenchymal tumor, CMF-like osteosarcoma, and extraskeletal myxoid chondrosarcoma. These results indicate that GRM1 immunohistochemistry may have utility in distinguishing CMF from its histologic mimics.

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.

Management of Myxofibrosarcoma and Undifferentiated Pleomorphic Sarcoma

Undifferentiated pleomorphic sarcoma (UPS) and myxofibrosarcoma (MFS) are genomically complex tumors commonly diagnosed in the extremities or trunk of elderly patients. They likely represent a spectrum of disease differentiated by myxoid stroma and curvilinear vessels observed in MFS but not in UPS. Limb-sparing surgery is the standard of care although the infiltrative nature of MFS mandates wider resection margins than are necessary for UPS. UPS are conversely associated with high risks of distal recurrence, often prompting recommendations for adjuvant chemotherapy. In both histologies, anthracycline-based therapies or gemcitabine and docetaxel are used to manage advanced disease; immunotherapy may be of benefit in a subset of patients.

Solitary Fibrous Tumor With Extensive Epithelial Inclusions

OBJECTIVES

Solitary fibrous tumor (SFT) harboring extensive epithelial inclusions is rare and can stimulate a biphasic neoplasm composed of epithelial and stromal elements.

METHODS

Three cases of SFT with extensive epithelial inclusions were retrieved. H&E stain, immunohistochemical stain, and targeted next-generation sequencing were performed.

RESULTS

There were two male patients and one female patient aged 54, 32, and 68 years. All tumors were located in abdominopelvic sites involving the kidney (case 1), omentum (case 2), and prostate (case 3), respectively. Microscopically, all tumors were circumscribed and composed of a background of SFT admixed with randomly embedded glands or cysts, organizing sometimes in a phyllodes-like architecture. The covered epithelium displayed a range of morphologies from simple cystic to stratified and to complex papillary proliferation. Immunohistochemically, both STAT6 and CD34 were expressed in the spindle cells but not in the epithelial inclusions. RNA sequencing revealed fusions involving NAB2~STAT6 in all cases. DNA sequencing demonstrated TERT c.-124C>T mutation in case 1. Prognostic stratification scores were intermediate in case 1 and low in cases 2 and 3.

CONCLUSIONS

SFT with extensive epithelial inclusions represents a rare but potentially underrecognized variant of SFT and shows compatible molecular features with conventional SFT.

Case Report: Molecular Characterization of Aggressive Malignant Retroperitoneal Solitary Fibrous Tumor: A Case Study

Solitary fibrous tumors (SFT) are mesenchymal neoplasms with a favorable prognosis usually originating from the visceral pleura. Rarely, they may occur at various extrapleural sites and show malignant behavior coupled with dedifferentiation. NAB2-STAT6 fusion gene and STAT6 nuclear expression are biomarkers for diagnosis of SFT in addition to CD34, Bcl-2, and CD99. Furthermore, several reports have shown specific NAB2-STAT6 fusion variants and loss of STAT6 protein expression are associated with malignancy. We report a rare case of retroperitoneal SFT which rapidly progressed to death within 35 days after admission. Autopsy found a primary tumor containing both benign and malignant histologies, with multiple metastatic sites similar to the malignant, dedifferentiated tumor. STAT6 was detected in the primary differentiated tumor but not in the primary dedifferentiated tumor or lung/liver metastases. However, the NAB2-STAT6 fusion gene (NAB2ex6/STAT6ex16 variant) was detected in the primary tumor and lung/liver metastases. Intriguingly, fusion gene expression at the transcriptional level was downregulated in the dedifferentiated tumors compared to the differentiated tumor. We further performed target DNA sequencing and found gene mutations in TP53, FLT3, and AR in the dedifferentiated tumors, with TP53 mutations especially found among them. We demonstrate that downregulation of NAB2-STAT6 fusion gene at the transcriptional level is associated with malignant SFT for the first time. Moreover, the present study supports the idea that TP53 mutations promote malignancy in SFTs.

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

Solitary fibrous tumors (SFTs) usually occur in the pleura and account for two-thirds of all cases; however, SFTs occurring in the prostate are extremely rare. Approximately 25 cases have been reported in the literature to date. This study reports the case of a 43-year-old man referred to our hospital with the chief complaint of a pelvic tumor after careful examination. The tumor marker levels were within normal limits. T2-weighted magnetic resonance imaging revealed a tumor, demonstrating primarily low signal intensity. It showed a capsule-like rim at the left lobe of the prostate, suggesting that the tumor was partially invading the rectal wall. Histopathological examination of needle-core biopsies showed spindle cell neoplasm with small and fusiform cells, strongly expressing signal transducer and activator of transcription 6 (STAT6) with a ramifying vascular network. Therefore, the clinical diagnosis of the patient was SFT of the prostate and robot-assisted radical prostatectomy was performed. Histopathological examination revealed that the tumor was composed of spindle cells with patternless and staghorn patterns. Immunohistochemical analysis showed a strong expression of STAT6. Furthermore, the tumor was partially positive for CD34. Therefore, the patient was diagnosed with SFT of the prostate. Two years after the initial diagnosis, the patient was alive with normal erectile function, continence status, and no evidence of the disease.

Undifferentiated and dedifferentiated soft tissue neoplasms: Immunohistochemical surrogates for differential diagnosis

Undifferentiated soft tissue sarcomas (USTS) are described in the current World Health Organization Classification of Soft Tissue and Bone Tumours as those showing no identifiable line of differentiation when analyzed by presently available technologies. This is a markedly heterogeneous group, and the diagnosis of USTS remains one of exclusion. USTS can be divided into four morphologic subgroups: pleomorphic, spindle cell, round cell and epithelioid undifferentiated sarcomas, with this combined group accounting for up to 20% of all soft tissue sarcomas. As molecular advances enable the stratification of emerging genetic subsets within USTS, particularly within undifferentiated round cell sarcomas, other groups, particularly the category of undifferentiated pleomorphic sarcomas (UPS), still remain difficult to substratify and represent heterogeneous collections of neoplasms often representing the common morphologic endpoints of a variety of malignant tumors of various (mesenchymal and non-mesenchymal) lineages. However, recent molecular developments have also enabled the identification and correct classification of many tumors from various lines of differentiation that would previously have been bracketed under 'UPS'. This includes pleomorphic neoplasms and dedifferentiated neoplasms (the latter typically manifesting with an undifferentiated pleomorphic morphology) of mesenchymal (e.g. solitary fibrous tumor and gastrointestinal stromal tumor) and non-mesenchymal (e.g. melanoma and carcinoma) origin. The precise categorization of 'pleomorphic' or 'undifferentiated' neoplasms is critical for prognostication, as, for example, dedifferentiated liposarcoma typically behaves less aggressively than other pleomorphic sarcomas, and for management, including the potential for targeted therapies based on underlying recurrent molecular features. In this review we focus on undifferentiated and dedifferentiated pleomorphic and spindle cell neoplasms, summarizing their key genetic, morphologic and immunophenotypic features in the routine diagnostic setting, and the use of immunohistochemistry in their principal differential diagnosis, and highlight new developments and entities in the group of undifferentiated and dedifferentiated soft tissue sarcomas.

PDGFB RNA in situ hybridization for the diagnosis of dermatofibrosarcoma protuberans

Dermatofibrosarcoma protuberans (DFSP) is a spindle cell neoplasm of the skin and superficial soft tissue with a tendency for locally aggressive behavior; metastatic potential coincides with fibrosarcomatous transformation. The vast majority of DFSPs harbor the t(17;22) translocation resulting in a COL1A1-PDGFB fusion that drives autocrine growth stimulation via PDGFB overexpression. Here, we examined the utility of PDGFB RNA chromogenic in situ hybridization (CISH) for the diagnosis of DFSP. A total of 337 tumors represented in whole tissue sections and tissue microarrays, including 37 cases of DFSP and 300 histologically similar spindle cell tumors, were subjected to PDGFB RNA CISH using commercially available probes. PDGFB overexpression was observed by light microscopy in 24 of 26 conventional DFSPs (92%) and 11 of 11 fibrosarcomatous DFSPs (100%). One of two DFSPs negative for PDGFB by RNA CISH was found to harbor an uncommon alternative rearrangement involving PDGFD. All examined cases of histologic mimics were negative for PDGFB overexpression; limited PDGFB expression, not reaching an empirical threshold of greater than 5 puncta or one aggregate of chromogen in more than 25% of cells, was observed in 7 of 300 mimics (2.3%), including desmoplastic melanoma, malignant peripheral nerve sheath tumor, angiosarcoma, and pleomorphic dermal sarcoma. Vascular PDGFB expression was seen in several tumor types. We conclude that PDGFB RNA CISH, with careful interpretation and the use of appropriate thresholds, may serve as a surrogate marker of PDGFB rearrangement and a useful ancillary tool for the diagnosis of DFSP.

Solitary Fibrous Tumors of the Chest: An Analysis of Fifty Patients

Background

A solitary fibrous tumor of the chest (SFTC) is a subtype of solitary fibrous tumor (SFT) with a low incidence rate. The purpose of this study is to analyze the diagnosis and treatment of SFTC and the difference between benign and malignant solitary fibrous tumor of the pleura (SFTP) to improve the understanding of this rare disease.

Methods

A retrospective analysis of fifty patients with SFTC (33 cases in the pleura and 17 in the lung) was performed. Clinical and imaging characteristics, pathological features, and treatment follow-up outcomes were analyzed.

Results

The common symptoms of the 50 patients included a cough, expectoration, chest tightness, fever, and chest pain. Space occupying lesions were found via plain computed tomography (CT) and enhanced CT was used for enhancement of the tumors. It was also found that 18 cases had necrosis, and 5 cases had calcification. The histopathology results showed that frequent nuclear division, obvious morphological variation, necrosis, and the high expression of Ki-67 cells are markers of malignant SFTC. There were significant differences in age, chest tightness, necrotic foci in CT, and expression of Ki-67 between the benign and malignant SFTP cases. All the patients who received treatment were given an excellent prognosis.

Conclusion

A combination of enhanced CT, histopathology, and immunohistochemistry can be used for the accurate diagnosis of SFTC. Advanced age, chest tightness, necrotic foci in CT, and a high Ki-67 index were more likely to be malignant SFTP. Operation and radiofrequency ablation can provide favorable outcomes for both benign and malignant SFTC.

STAT6 Expression in Solitary Fibrous Tumor and Histologic Mimics: a Single Institution Experience

STAT6 stain has proved to be a good surrogate marker for the genetic alteration (NAB2-STAT6 gene fusion) in solitary fibrous tumor (SFT). This study aims to validate the use of STAT6 rabbit monoclonal antibody in differentiating SFT from its histologic mimics. Forty-five cases of SFT and 110 cases from 9 other spindle cell tumors were collected for STAT6 immunostaining. Positive nuclear STAT6 staining was present in all 45 SFT cases (100% sensitivity). No nuclear staining was identified in other spindle cell neoplasms (0/13, dedifferentiated liposarcoma; 0/17, synovial sarcoma; 0/16, malignant peripheral nerve sheath tumors; 0/25, undifferentiated pleomorphic sarcoma; 0/10, dermatofibrosarcoma protuberans; 0/9, low-grade fibromyxoid sarcoma; 0/6, angiofibroma; 0/5, deep fibromatosis; 0/9, gastrointestinal tumor). The STAT6 staining in SFT was usually diffuse (5+ in 19 cases; 4+ in 17 cases) and strong (40 cases). Monoclonal STAT6 stain is highly sensitive and specific for SFTs and particularly useful in the diagnosis of difficult SFT cases.

Solitary Fibrous Tumor of the Orbit: A Case Series With Clinicopathologic Correlation and Evaluation of STAT6 as a Diagnostic Marker

PURPOSE

To retrospectively describe the clinical characteristics, management, and outcomes of a series of patients with solitary fibrous tumor (SFT) of the orbit and to evaluate signal transducer and activator of transcription 6 (STAT6) as a diagnostic marker.

METHODS

Review of a retrospective, noncomparative, consecutive series of patients treated at a single institution with a histopathologic diagnosis of SFT. Demographic, clinical, and imaging data were collected, and paraffin-embedded tissue sections were stained to evaluate for the presence of STAT6 and other pertinent markers.

RESULTS

Twenty-one patients were identified. Most presented with painless progressive proptosis or eyelid swelling for less than 6 months. Imaging revealed well-circumscribed, firm, variably vascular contrast-enhancing lesions with low to medium reflectivity on ultrasound. Four tumors were histopathologically malignant. All tumors were primarily excised, and 1 patient required exenteration. Two patients were treated with adjuvant radiation therapy. Six patients had recurrent disease of which 3 underwent repeat excision, and 2 were observed. No metastatic disease or attributable deaths were observed. All lesions with available tissue stained positively for both CD34 and STAT6.

CONCLUSION

This is the largest single institution case series of orbital SFT with clinicopathologic correlation and the largest series to confirm the presence of STAT6 in orbital lesions. The management of SFT remains challenging due to unpredictable tumor behavior, and complete excision is the generally recommended treatment. It remains unclear whether a subset of asymptomatic patients with histopathologically benign disease can be durably observed without negative sequelae.

Dumbbell-shaped solitary fibrous tumor in the parapharyngeal space: A case report

BACKGROUND

Solitary fibrous tumors (SFTs) occurring in the parapharyngeal space are rare, and their final diagnosis depends on pathological and immunohistochemical analyses. Once the tumor is diagnosed, complete resection and regular postoperative follow-up are required.

CASE SUMMARY

A 40-year-old male patient with a right parotid gland mass discovered 8 years ago was admitted to hospital. The mass showed no tenderness or local skin redness. Imaging was carried out as the patient had stable vital signs and showed that the mass was a dumbbell-shaped tumor comprising a superficial tumor approximately 5 cm long and 3 cm wide in size that compressed the right parotid gland and a deep tumor located in the right parapharyngeal space approximately 4.5 cm long and 2.5 cm wide in size. Both tumors were connected in the middle. Prior to surgery, the tumors were considered to be parapharyngeal schwannomas. During surgical dissection, the tumors were found to be smooth and tough, without obvious adhesion to the surrounding tissues. The tumors were revealed to be a SFT following postoperative pathological analysis.

CONCLUSION

SFTs in the parapharyngeal space are rarely reported, and complete resection of such tumor is recommended. Adjuvant chemoradiotherapy is used in patients with extensive tumor invasion to lower the recurrence rate. Postoperative long-term follow-up is required.

DDIT3 Immunohistochemistry Is a Useful Tool for the Diagnosis of Myxoid Liposarcoma

Myxoid liposarcoma is a malignant adipogenic neoplasm characterized by prominent arborizing capillaries, occasional lipoblasts, and primitive-appearing spindle cells in a myxoid background. A recurrent translocation in myxoid liposarcoma results in an oncoprotein consisting of full-length DDIT3 (CHOP) fused to an N-terminal segment of either FUS (TLS) or, less often, EWSR1. Here, we explore the diagnostic significance of DDIT3 expression in myxoid liposarcoma using a mouse monoclonal antibody recognizing an epitope in the N-terminal region. Studying a total of 300 tumors, we find diffuse, moderate-to-strong nuclear-localized anti-DDIT3 immunoreactivity in all 46 cases of myxoid liposarcoma representing 36 unique tumors, including 6 cases with high-grade (round cell) morphology. DDIT3 immunohistochemistry also highlighted a distinctive vasculocentric growth pattern in 7 myxoid liposarcomas treated with neoadjuvant radiation. In contrast, the vast majority of other examined lipomatous and myxoid neoplasms exhibited no DDIT3 expression; limited, weak immunoreactivity in <10% of cells was infrequently observed in dedifferentiated liposarcoma (6/39, 15%), solitary fibrous tumor (3/12, 25%), pleomorphic liposarcoma (1/15, 7%), and high-grade myxofibrosarcoma (2/17, 12%). Although this minimal DDIT3 expression did not correlate with DDIT3 amplification or myxoid liposarcoma-like morphology in dedifferentiated liposarcoma, there was evidence among sarcomas (excluding myxoid liposarcoma) of a relationship between expression and exposure to neoadjuvant radiation or cytotoxic chemotherapy. The constellation of findings indicates that DDIT3 immunohistochemistry may have utility in the evaluation of myxoid and lipomatous neoplasms to support the diagnosis of myxoid liposarcoma.

Endoscopic resection of solitary fibrous tumor of the ethmoid: Case report review of the literature

INTRODUCTION

Solitary fibrous tumour (SFT), as are benign neoplasms of fibroblastic cells. Nasosinusal localisation is exremely rare, difficult to diagnose and to manage.

CASE REPORT

We report a rare case of Solitary fibrous tumour in the nasal cavity in a 47-year-old- woman, with complete surgical resection.

DISCUSSION

SFTs are of mesenchymal origin, mainly from serous membranes. The head and neck region is affected with a percentage ranging from 5 to 27%. On the other hand, LTS unusually affects the nasal tract (NTS). Because of this rarity and its variable morphological appearance, it is difficult to distinguish TNS from other mesenchymal lesions.

CONCLUSION

Although there are no standard clinical guidelines, the preferred treatment for FLS is radical surgical resection.

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.

Primary cutaneous synovial sarcoma-Sometimes the hoof beats are zebras

Synovial sarcoma accounts for 5% to 10% of soft tissue sarcoma and it typically presents as a deep soft tissue mass. Primary cutaneous presentation is exceptionally rare, with only isolated case reports. We report a case of primary cutaneous synovial sarcoma in a 58-year-old woman that presented as a nodule involving the left occipital scalp. A complete radiologic evaluation of the patient failed to reveal any other mass lesion. Histologic sections showed a densely cellular, diffuse spindle cell proliferation within the subcutis. The lesion was composed of uniform, plump spindled cells with nuclei and vesicular chromatin, arranged in haphazard fascicles. There was admixed hemorrhage and a hemangiopericytoma-like vasculature. Immunohistochemically, the spindled cells showed focal strong positivity for cytokeratin (CK) OSCAR, CK5/6, CK34BE12, and pan-CK. Fluorescence in situ hybridization was positive for a rearrangement of SYT (SS18), confirming the diagnosis of monophasic synovial sarcoma. Synovial sarcoma should be considered in the differential diagnosis of monomorphous spindle cell tumors, especially if the tumors have a hemangiopericytoma-like vasculature or express keratins. In such cases, confirmatory molecular testing should be performed to confirm the diagnosis.

Two Cases of STAT6-Positive, Primary Conjunctival Giant Cell-Rich Solitary Fibrous Tumour (Giant Cell Angiofibroma) with Some Unusual Histological Features

An 84-year-old male presented with a history of a slowly growing lesion beneath the right lower lid. Examination showed a right-sided mass in the inferior bulbar conjunctiva, measuring approximately 10 × 6 mm. The lesion was excised and showed a giant cell-rich solitary fibrous tumour (GCR-SFT) with pseudo-vascular spaces with benign cytology, with STAT6, expressed in the spindle, ovoid, and tumour giant cells. A second case, a 26-year-old white female, presented with a 12-month history of a gradually expanding lesion in left inferior bulbar conjunctiva. Examination showed a well-defined, dome-shaped pink fleshy mass of 10 × 7 × 2 mm, on the inferior bulbar conjunctiva and abutting the inferior fornix. Excision followed by histology showed a similar appearance to the first case except that the multinucleate giant cells closely resembled Touton giant cells and did not show the rather hyperchromatic crowded nuclei of the giant cells observed in the first case. No pseudo-vascular spaces were identified. The tumour cells, including the Touton-like multinucleate giant cells, displayed nuclear positivity for STAT6. An unexpected feature was the presence of a Melan A- and Sox10-positive population amongst the GCR-SFT, postulated to be a subepithelial melanocytic nevus colliding with the GCR-SFT.

Extrapleural solitary fibrous tumor of the thyroid gland: A case report and review of literature

BACKGROUND

Solitary fibrous tumor (SFT) is an uncommon mesenchymal neoplasm that arises from the pleura. A few SFTs have also been described in extrapleural sites. However, SFT of the thyroid gland is rare. Here, we report a case of extrapleural SFT on the thyroid gland, in addition to a literature review.

CASE SUMMARY

A 59-year-old man visited our hospital in July 2017 complaining of a large mass in his neck. His thyroid function test results, including antibody levels, were within the normal limits. Ultrasonography showed a 4.7 cm × 4.0 cm × 3.2 cm solitary mass of intermediate suspicion in the left thyroid lobe. A fine-needle aspiration biopsy was subsequently performed. The pathologist reported a benign follicular lesion. However, the size of this nodule increased to 5.5 cm × 5.0 cm × 3.4 cm by April 2018. After a multidisciplinary discussion, a left lobectomy was performed in May 2018. The specimen showed a well-demarcated, partly encapsulated, soft nodule of whitish and tan/brown color on the cut surface. Light microscopy revealed high cellularity with moderate cytologic atypia. The mitotic count was 5/10 high-power fields. There was no tumor necrosis or lymphovascular invasion. The tumor was CD34-positive and signal transducer and activator of transcription 6-positive. Neither thyroid transcription factor-1 nor cytokeratin expression was detected. The Ki-67 showed intermediate proliferative activity. The final diagnosis was extrapleural SFT of the thyroid gland with a clear resection margin. The patient was discharged without complication three days after the surgery.

CONCLUSION

In the literature, extrapleural SFT of the thyroid gland has been reported to behave indolently with the capacity for recurrence and rare metastasis, although surgical resection is the treatment of choice. Understanding this disease entity is important for accurate diagnosis and proper management.

Cervical Myxoid Solitary Fibrous Tumor: Report of an Unusual Variant and a Brief Overview of the Literature

We present a 49 year old female with a diagnostically challenging myxoid solitary fibrous tumor arising in the soft tissue of the neck. The tumor was diffusely positive for CD34 and STAT6 on immunohistochemistry.

What's new in nerve sheath tumors

Peripheral nerve sheath tumors are commonly encountered and frequently pose challenges to the pathologist and the clinician. This review discusses the wide range of entities with an emphasis on new discoveries in the past decade. Clinical, histologic, immunohistochemical, and pathogenetic findings are discussed with an emphasis on clinical implications and differential diagnosis.

Superficial Solitary Fibrous Tumor: A Series of 26 Cases

While superficial (cutaneous/subcutaneous) solitary fibrous tumor (SFT) have been described, definitive diagnosis is difficult due to overlapping features with other tumors. We describe the largest series to date of superficial SFT. For inclusion, SFT had to arise in dermis or subcutis. Twenty-six cases were identified. Patients ranged from 16 to 80 years (mean, 47 y) with a marked female predominance (19 F; 7 M). Tumors involved the head (11), thigh (7), back (3), shoulder (2), upper arm (1), ankle (1), and great toe (1). Mean size was 2.9 cm (range, 1.0 to 7.0 cm). The majority (n=19) had typical histologic features (cellular SFT) with irregular fascicles of spindled cells, staghorn-like blood vessels, and variable amounts of collagen. Necrosis was evident in 3 cases (all <25%). Mitotic activity ranged from 0 to 10 mitotic figures/10 high-power fields (mean, 2 mitotic figures/10 high-power fields). Seventeen of the 18 were positive for STAT6, whereas 21/22 expressed CD34. All were low risk (23/23) by proposed criteria (Demicco and colleagues), including 2 cases with malignant histology. Three could not be risk stratified due to lack of information on tumor size. Follow-up, available on 7 cases, showed no recurrence/metastasis (mean follow-up, 100 mo; range, 2 to 241 mo). Cutaneous SFT are more common in women and most often involve the head. They are usually low risk by proposed criteria and appear to behave in an indolent manner, though larger studies are needed to confirm this. Recognition that SFT may present as a superficial mass will avoid misclassification as other CD34-positive neoplasms that frequently arise in the skin and subcutaneous tissue.

Update on Lipomatous Tumors with Emphasis on Emerging Entities, Unusual Anatomic Sites, and Variant Histologic Patterns

This article reviews the histologic patterns of spindle cell/pleomorphic lipoma, well-differentiated liposarcoma, and dedifferentiated liposarcoma in the context of both usual and atypical anatomic presentation. The utility of molecular and immunohistochemical diagnostic modalities to distinguish these entities is described. In addition, more recently described and controversial entities, including atypical spindle cell lipomatous tumor and anisometric cell lipoma, are discussed.

Solitary fibrous tumor in the liver: case report and literature review

Background

Solitary fibrous tumors (SFTs) are uncommon mesenchymal neoplasms that present most commonly at intrathoracic sites. SFTs of the liver are rare, with only a few having been reported in the English-language literature. We report a rare case of a hepatic SFT and literature review.

Case presentation

A 49-year-old woman underwent surgery for a cranial hemangiopericytoma two decades previously. She currently presented with malaise. Abdominal computed tomography (CT) showed a huge, sharply demarcated mass in the anterior segment of the liver. Tumor marker levels were within the normal range. Following central bisegmentectomy of the liver, histological examination of the specimen revealed that the tumor was composed of spindle and fibroblast-like cells with collagenous stroma. Immunohistochemically, the spindle cells were negative for CD34 but positive for STAT6. The NAB2–STAT6 fusion gene was detected by the reverse transcription polymerase chain reaction. A diagnosis of SFT was thus confirmed histopathologically and genetically.

Conclusions

The SFT of the liver is an uncommon finding. Because there are no specific imaging features, it is difficult to diagnose the hepatic SFT preoperatively. We consider that careful surgical resection and postoperative follow-up are necessary for hepatic SFTs.

Thyroid Gland Solitary Fibrous Tumor: Report of 3 Cases and a Comprehensive Review of the Literature

Solitary fibrous tumors of the thyroid gland are exceptionally rare. In order to further characterize the clinical and pathologic features of solitary fibrous tumor arising at this anatomic site, three cases of thyroid gland solitary fibrous tumor were analyzed in conjunction with 35 cases compiled from the English literature. Thyroid gland solitary fibrous tumors showed an equal sex distribution with a mean age at presentation of 54.4 years (range, 28-88 years). The patients typically presented with an asymptomatic, slow growing neck mass. 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. Two previous reported tumors were considered to be histologically malignant on the basis of increased mitotic activity, profound pleomorphism and tumor necrosis. Immunohistochemically, the tumor cells are variably positive with CD34, bcl-2, and CD99. STAT6 immunohistochemistry, performed on the current cases, demonstrated a strong, diffuse nuclear expression in all tumors. Among 26 patients with available follow up data (mean 47.3 months), one developed local recurrence and distant metastasis. Solitary fibrous tumors occurring in the thyroid gland are uncommon, but can be reliably diagnosed based on the presence of characteristic morphologic features as well as immunohistochemical expression of STAT6 and CD34. The majority of thyroid gland solitary fibrous tumors have exhibited an indolent clinical course, however experience is limited. The rare potential for aggressive clinical behavior requires clinical surveillance.

Rare Occurrence of an Intraocular Choroidal Solitary Fibrous Tumor/Hemangiopericytoma

Purpose

Tumors previously diagnosed as solitary fibrous tumors (SFT) and hemangiopericytomas (HPC) are characterized by the NAB2-STAT6 fusion gene, leading to nuclear STAT6 expression, and are now considered part of one SFT/HPC tumor entity by the 2016 World Health Organization Classification of Tumors of the Central Nervous System. We present the first primary choroidal SFT/HPC with the diagnosis confirmed by STAT6 expression.

Procedures

A 51-year-old man underwent enucleation for a choroidal mass, which revealed a spindle cell neoplasm involving the optic nerve, without extrascleral extension. Immunohistochemical stains for S-100, melan-A, tyrosinase, and HMB45 were all negative; however, detection of monosomy 3 by FISH favored a choroidal spindle cell melanoma. Four years later, he presented with hepatic metastases of a spindle cell tumor, and a year later with an epithelioid malignancy involving the calvarium.

Results

The calvarial tumor showed nuclear STAT6 immunoreactivity, supporting the diagnosis of SFT/HPC. Retrospectively, the choroidal and hepatic masses were also found to demonstrate nuclear STAT6 expression, supporting the diagnosis of a primary choroidal SFT/HPC with metachronous metastases to the liver and calvarium.

Conclusions

This case highlights the significance of considering SFT/HPC in the diagnosis of intraocular spindle cell tumors and the importance of STAT6 immunohistochemistry in the evaluation of such tumors.

Limited biopsies of soft tissue tumors: the contemporary role of immunohistochemistry and molecular diagnostics

Diagnosing soft tissue tumors is challenging, even on ample incisional biopsies or resection specimens. There are more than 100 distinct types of soft tissue neoplasms, including more than 80 benign and intermediate mesenchymal tumors and around 40 soft tissue sarcomas. Accurate diagnosis relies first upon recognition of characteristic histologic and cytologic features, including architecture, stromal characteristics, vascular patterns, and dominant cytology; these features may not be represented or apparent in limited core needle biopsy or fine needle aspiration specimens. Once a differential diagnosis is established, application of immunohistochemistry and cytogenetic or molecular diagnostic assays (especially fluorescence in situ hybridization) is used in an attempt to reach a specific diagnosis. In recent years, the diagnostic armamentarium for soft tissue tumors has expanded dramatically, following the discovery of molecular alterations that underlie the pathogenesis of soft tissue tumors. These include new diagnostic immunohistochemical markers that serve as useful surrogates for molecular genetic alterations. Availability of such markers has improved our ability to render accurate and specific diagnoses based on limited biopsy samples. In this review, examples of recently developed markers for the diagnosis of selected soft tissue tumor types will be discussed, including solitary fibrous tumor (STAT6), malignant peripheral nerve sheath tumor (H3K27me3), epithelioid hemangioendothelioma (CAMTA1), dedifferentiated liposarcoma (MDM2), and CIC-DUX4 sarcoma (WT1 and ETV4).

Solitary fibrous tumor

Solitary fibrous tumor (SFT) is a rare tumor of mesenchymal origin that account for less than 2% of all soft tissue masses. Initially identified in the pleura, SFT has been identified in multiple anatomic locations and can arise anywhere in the body. The varying histologic features along with non-specific means of identification have led SFT to be associated with several different names. Over the last several decades, sustained advances through research and technology have led to more reliable methods for differentiating this distinct soft tissue tumor. Advances specifically in immunohistochemistry and molecular diagnostics have identified CD34 as the most consistent marker in SFT, however even this lacks specificity to conclusively narrow down the broad differential for exact identification. More recently the discovery of the NAB2-STAT6 fusion gene has led to more precise diagnosis of SFT. Like many other soft tissue tumors, surgical management is the mainstay of treatment for SFT with emphasis on obtaining tumor-negative margins. Radiation therapy and chemotherapy regimens have not demonstrated global effectiveness, and thus no standardized treatments have been identified. Given the rarity of SFT and current supportive evidence for therapies, management should be focused on tumor extirpation. Nonetheless, individualized therapy, determined within a multidisciplinary setting should be considered.

A novel group of spindle cell tumors defined by S100 and CD34 co-expression shows recurrent fusions involving RAF1, BRAF, and NTRK1/2 genes

Tumors characterized by co-expression of S100 and CD34, in the absence of SOX10, remain difficult to classify. Triggered by a few index cases with monomorphic cytomorphology and distinctive stromal and perivascular hyalinization, immunopositivity for S100 and CD34, and RAF1 and NTRK1 fusions, the authors undertook a systematic review of tumors with similar features. Most of the cases selected were previously diagnosed as low-grade malignant peripheral nerve sheath tumors, while others were deemed unclassified. The tumors were studied with targeted RNA sequencing and/or FISH. A total of 25 cases (15 adults and 10 children) with kinase fusions were identified, including 8 cases involving RAF1, 2 BRAF, 14 NTRK1, and 1 NTRK2 gene rearrangements. Most tumors showed a monomorphic spindle cell proliferation with stromal and perivascular keloidal collagen, in a patternless architecture, with only occasional scattered pleomorphic or multinucleated cells. Most cases showed low cellularity, a low mitotic count, and absence of necrosis. Although a subset showed overlap with lipofibromatosis-like neural tumors, the study group showed distinctive hyalinization and overt malignant features, such as highly cellular fascicular growth and primitive appearance. All tumors showed co-expression of S100 and CD34, ranging from focal to diffuse. SOX10 was negative in all cases. NTRK1 immunohistochemistry showed high levels of expression in all tumors with NTRK1 gene rearrangements. H3K27me3 expression performed in a subset of cases was retained. These findings together with the recurrent gene fusions in RAF1, BRAF, and NTRK1/2 kinases suggest a distinct molecular tumor subtype with consistent S100 and CD34 immunoreactivity.

Solitary Fibrous Tumors in Pediatric Patients: A Rare and Potentially Overdiagnosed Neoplasm, Confirmed by STAT6 Immunohistochemistry

Pathological diagnosis of solitary fibrous tumor (SFT) in the pediatric population is challenging, as it occurs uncommonly in this age-group and resembles other spindle cell neoplasms. SFT contains a NAB2-STAT6 fusion gene, which can be reliably detected using STAT6 immunohistochemistry. Positive staining is highly sensitive and specific. We sought to investigate the utility of STAT6 immunohistochemistry, to show how commonly SFT was historically recognized at 3 academic pediatric institutions, to reclassify them when appropriate, and to demonstrate features of major mimics of SFT. Our series included cases with a previous diagnosis of SFT or for which SFT was among key considerations, from 3 major academic pediatric hospitals seen over the past 30 years. Of 18 tumors identified, only 3 tumors from 2 patients demonstrated positive STAT6 staining as well as the typical histology and immunophenotype seen in SFT. The remaining 15 tumors were reclassified based on morphology, additional immunohistochemistry and fluorescence in situ hybridization as desmoid-type fibromatosis (3 tumors), nerve sheath/neural tumors (3 tumors), low-grade fibromyxoid sarcoma, medallion-like dermal fibroma, poorly differentiated Sertoli cell tumor, nodular/proliferative fasciitis, calcifying fibrous tumor, aneurysmal bone cyst of soft tissue, STAT6-negative SFT with adipocytic differentiation, undifferentiated small round blue cell tumor, and scar (1 tumor each). Our study confirms that SFT is rare in the pediatric population and that it is potentially overdiagnosed. STAT6 immunohistochemistry is recommended to confirm the diagnosis of SFT in the pediatric population.

Grading of meningeal solitary fibrous tumors/hemangiopericytomas: analysis of the prognostic value of the Marseille Grading System in a cohort of 132 patients

The finding that meningeal solitary fibrous tumors (SFTs) and meningeal hemangiopericytomas (HPCs) are both characterized by NAB2-STAT6 gene fusion has pushed their inclusion in the WHO 2016 Classification of tumors of the central nervous system (CNS) as different manifestations of the same entity. Given that the clinical behavior of the CNS SFT/HPC spectrum ranges from benign to malignant, it is presently unclear whether the grading criteria are still adequate. Here, we present the results of a study that analyzed the prognostic value of an updated version of the Marseille Grading System (MGS) in a retrospectively assembled cohort of 132 primary meningeal SFTs/HPCs with nuclear overexpression of STAT6. The median patient follow-up was 64 months (range 4-274 months); 73 cases (55%) were MGS I, 50 cases (38%) MGS II and 9 cases (7%) were MGS III. Progression-free survival (PFS) and disease-specific survival (DSS) were investigated using univariate analysis: the prognostic factors for PFS included MGS, extent of surgery, radiotherapy, chemotherapy and mitotic activity ≥5/10 high-power field (HPF). Moreover, MGS, radiotherapy, mitotic activity ≥5/10 HPF, and necrosis were the prognostic factors measured for DSS. In multivariate analysis, extent of surgery, mitotic activity ≥5/10 HPF, MGS I and MGS III were the independent prognostic factors measured for PFS while necrosis, MGS III and radiotherapy were the independent prognostic factors for DSS. In conclusion, our results show that assessing the malignancy risk of SFT/HPC should not rely on one single criterion like mitotic activity. Therefore, MGS is useful as it combines the value of different criteria. In particular, the combination of a high mitotic activity and necrosis (MGS III) indicates a particularly poor prognosis.

Telomerase promoter mutations and copy number alterations in solitary fibrous tumours

AIMS

Solitary fibrous tumour (SFT) is an infrequently metastasising mesenchymal tumour defined by the NAB2-STAT6 fusion gene. Activating mutations in the telomerase reverse transcriptase (hTERT) gene promoter has been reported to associate with adverse patient outcome in SFTs.

METHODS

We analysed the hTERT gene for promoter mutations and copy number alterations in 43 primary extrameningeal SFTs (9 malignant and 34 benign tumours according to WHO 2013 criteria), six local recurrences and three metastatic lesions.

RESULTS

Activating -124 C>T (n=12) or -148 C>T (n=2) mutations were found in 33% of the tumours and associated with older age (P=0.006), necrosis (P=0.009), higher mitotic rate (P=0.003), nuclear atypia (P=0.002), malignant histological diagnosis (P=0.04) and worse progression-free survival (P=0.023). We also observed frequent (24%) hTERT promoter mutations in histologically benign tumours without metastasis (mean follow-up >9 years), and in 14%-18% of low-risk SFTs as determined by three risk-stratification models. Mutations were seen in 2/6 metastatic tumours and metastatic lesions. hTERT copy number gain was seen in 11/28 hTERT promoter wild-type cases.

CONCLUSIONS

Activating hTERT promoter mutations associate with aggressive histopathological features, indicating a role in tumour progression. Given the comparatively high prevalence of hTERT promoter mutations in low-risk and non-metastasising lesions, further studies are required to clarify the prognostic value of hTERT promoter analysis before implementing the analysis in clinical diagnostics.

Malignant Solitary Fibrous Tumor Metastatic to Widely Invasive Hurthle Cell Thyroid Carcinoma: A Distinct Tumor-to-Tumor Metastasis

We illustrate a case of synchronous malignant solitary fibrous tumor of the thoracic cavity, and widely invasive thyroid Hurthle cell carcinoma. The Hurthle cell carcinoma was found to harbor distinct areas of malignant solitary fibrous tumor. This is a unique case of tumor-to-tumor metastasis that, to the best of our knowledge, has not been previously reported.

Mesenchymal tumors of the prostate

Mesenchymal tumors of the prostate are rare but often cause considerable diagnostic difficulty when encountered. These may be either benign or malignant and can arise within the prostate gland or in adjacent tissues. This review covers prostatic stromal proliferations (prostatic stromal tumor of uncertain malignant potential and stromal sarcoma), solitary fibrous tumor, myofibroblastic proliferations, smooth muscle neoplasms (leiomyoma and leiomyosarcoma), gastrointestinal stromal tumor, schwannoma, rhabdomyosarcoma, sarcomatoid carcinoma, postradiation sarcoma, and mixed epithelial stromal tumor of the seminal vesicle. Differential diagnostic considerations are emphasized, including descriptions of helpful histological and/or clinical clues and the use of adjuvant diagnostic techniques.

Sinonasal Tract Solitary Fibrous Tumor: A Clinicopathologic Study of Six Cases with a Comprehensive Review of the Literature

Solitary fibrous tumors (SFTs) are well recognized in the head and neck region, but rarely arise in the sinonasal tract (SNT). Six primary SNT SFTs were identified in the files of Southern California Permanente Medical Group between 2006 and 2017. The patients included five males and one female ranging in age from 33 to 72 years (mean 52 years), most of whom presented clinically with nasal obstruction. Three tumors involved the nasal cavity alone, one involved the paranasal sinuses, and two involved both the nasal cavity and paranasal sinuses. Histologically, the tumors were characterized by a variably cellular proliferation of cytologically bland spindle cells within a collagenous stroma with prominent interspersed branching vessels. Mitotic activity was low (range 0-2 per 10 high power fields) and there was no evidence of pleomorphism or tumor necrosis. Surface ulceration was noted. By immunohistochemistry, the lesional cells were positive for CD34, STAT6 and bcl-2. Clinical follow up information was available for all patients (range 32-102 months; mean 72 months). There were no recurrences or metastases and all were alive with no evidence of disease at last follow-up. SFTs rarely affect the SNT, but should be considered in the differential diagnosis of SNT mesenchymal lesions. Immunohistochemical expression of STAT6 can aid in diagnosis and separation of SFT from other spindle cell lesions occurring at this anatomic site. In combination with cases reported in the literature, primary SNT SFT behave in an indolent manner with conservative treatment.

Scrotum solitary fibrous tumor: A case report and review of literature

BACKGROUND

A solitary fibrous tumor (SFT) is a rare clinical tumor, often manifesting as solitary nodules. It is a rare condition that occurs in the scrotum. Currently, no study has reported this condition.

CASE SUMMARY

We reported a case of an SFT in a 77-year-old man, and discuss its diagnosis, differential diagnosis, and treatment. Clinical and histopathological features, as well as the EnVision 2-step method, were used to diagnosis the SFT. The results of imaging tests and surgery indicated that the SFT was located in the right scrotum with 2 connected tumor nodules and a clear perimeter. The larger one was 11.0 cm × 9.3 cm × 8.1 cm, and the smaller one was 3.1 cm × 2.0 cm × 2.0 cm. Pathological results indicated that in both tumor nodules, tumor cells were spindle-shaped with unclear cell boundaries. The nucleus was vacuolated with mild to moderate atypia. In the larger tumor nodule, there were many thin-walled blood vessels with vasodilation or branching. In the smaller tumor nodule, rich blood vessels were found, mostly with fibrous degeneration of the thick walls of blood vessels, and more collagen-like tissue in the interstitial layers. Immunohistochemical results demonstrated diffuse, strongly positive expression of CD34, CD99, Vim, and Bcl-2 markers. The expression of the new fusion gene, NAB2-STAT6, as an alternative tool specifically confirmed the diagnosis of SFT. This patient underwent lump resection without further treatment. The patient is alive after 18-month follow-up.

CONCLUSION

This case was diagnosed as a SFT according to its histopathological features, immunophenotype. The patient is still alive at 18 months follow-up after the lump resection.

FNA cytology of solitary fibrous tumors and the diagnostic value of STAT6 immunocytochemistry

BACKGROUND

Solitary fibrous tumors (SFTs) are rare mesenchymal tumors commonly located in the pleura, soft tissues, or meninges and are characterized by the NGFI-A-binding protein 2 (NAB2)-signal transducer and activator of transcription 6 (STAT6) fusion gene. Recent studies have indicated that nuclear STAT6 immunohistochemistry is a specific marker for SFTs.

METHODS

The authors reviewed fine-needle aspiration (FNA) specimens from extracranial SFTs diagnosed at their institution between 1993 and 2017. Histologic blocks and available formalin-fixed smears of FNA specimens from SFTs were investigated for STAT6 immunoreactivity using a monoclonal antibody. STAT6 immunocytochemistry was also investigated in schwannomas and spindle cell lipomas. Cytopathologic and clinical characteristics were described.

RESULTS

Nineteen benign and 9 malignant SFTs were identified. Both benign and malignant SFTs had a female predominance (female-to-male ratio, 2.8:1 and 1.25, respectively). Localization varied, and approximately one-half of the extrapleural tumors were located in the extremities and frequently were intramuscular. Benign and malignant primary tumors had limited differences in cytologic presentation, the most notable feature being nuclear pleomorphism. Cytomorphologic features included low-to-moderate cellularity of mixed oval, elongated, round, and stellate cells with pink collagenous stroma and hypercellular clusters with infrequent atypia. In metastatic SFTs, the cytopathology was suggestive of sarcoma. Immunohistochemistry revealed nuclear STAT6 immunoreactivity in SFTs (n = 5) with cytoplasmic reactivity in cytologic mimickers.

CONCLUSIONS

Benign and malignant SFTs have common cytopathologic features, and the ability to distinguish between them is limited. Nuclear STAT6 immunoreactivity is a valuable cytologic marker for SFTs. Cancer Cytopathol 2018;126:36-43. © 2017 American Cancer Society.