Gene expression profiling of solitary fibrous tumors

The role of molecular pathology in soft tissue tumor diagnosis: what the radiologist needs to know

For both general radiologists and those specializing in soft tissue sarcoma imaging, understanding the importance and basic concepts of molecular pathology is becoming increasingly relevant to current clinical practice. As molecular research identifies the most fundamental causes and markers of disease, diagnostic testing is increasingly focused on the cell nucleus and its genetic material. Identifying molecular abnormalities, such as mutations, deletions, and amplifications, has advanced our ability to diagnose genetic diseases, including a variety of cancers. Over the past two decades, molecular pathology has rapidly evolved, enhancing our understanding of sarcoma pathogenesis, diagnosis, and classification. This progress forms the foundation of the 2020 WHO classification of soft tissue and bone tumors. This article will highlight cases where molecular diagnostics are crucial for the definitive classification and diagnosis of select soft tissue tumors, with MRI correlation and key teaching points.

Molecular pathways and therapeutic strategies in dermatofibrosarcoma protuberans (DFSP): unravelling the tumor's genetic landscape

Dermatofibrosarcoma Protuberans (DFSP) is a rare soft tissue sarcoma distinguished by its infiltrative growth pattern and recurrence potential. Understanding the molecular characteristics of DFSP is essential for enhancing its diagnosis, prognosis, and treatment strategies. The paper provides an overview of DFSP, highlighting the significance of its molecular understanding. The gene expression profiling has uncovered unique molecular signatures in DFSP, highlighting its heterogeneity and potential therapeutic targets. The Platelet-Derived Growth Factor Receptors (PDGFRs) and Fibroblast Growth Factor Receptors (FGFRs) signaling pathways play essential roles in the progression and development of DFSP. The abnormal activation of these pathways presents opportunities for therapeutic interventions. Several emerging therapies, i.e., immunotherapies, immunomodulatory strategies, and immune checkpoint inhibitors, offer promising alternatives to surgical resection. In DFSP management, combination strategies, including rational combination therapies, aim to exploit the synergistic effects and overcome resistance. The article consisting future perspectives and challenges includes the discovery of prognostic and predictive biomarkers to improve risk stratification and treatment selection. Preclinical models, such as Patient-derived xenografts (PDX) and genetically engineered mouse models, help study the biology of DFSP and evaluate therapeutic interventions. The manuscript also covers small-molecule inhibitors, clinical trials, immune checkpoint inhibitors for DFSP treatment, combination therapies, rational therapies, and resistance mechanisms, which are unique and not broadly covered in recent pieces of literature. See also the graphical abstract(Fig. 1).

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.

Solitary fibrous tumor with IGF-II-induced non-islet cell tumor hypoglycemia: a case report and molecular characterization by next-generation sequencing

Background

Non-islet cell tumor-induced hypoglycemia (NICTH) is a rare, life-threatening medical condition caused by excessive insulin-like growth factor II (IGF-II) secretion from tumors of most commonly mesenchymal origin. Using next-generation sequencing, we have characterized the genome and transcriptome of the resected IGF-II-secreting solitary fibrous tumor from a patient with severe hypoglycemia accompanied by hypoglycemia unawareness.

Case presentation

A 69-year-old male patient presenting with abdominal discomfort was examined using computer tomography, revealing a large lesion at the lesser pelvis extending above the umbilicus. As no bone and lymph node metastases were detected, the patient was scheduled for laparotomy. Before surgery, the patient presented with symptoms of severe hypoglycemia. Suppressed C-peptide levels and subsequent hypokalemia indicated a possible case of NICTH. The patient was treated with methylprednisolone (8 mg) to assess hypoglycemia. After the surgery, mild hypoglycemia was present for the postoperative period, and no radiological recurrences were observed 3 and 12 months after discharge. Histopathological examination results were consistent with the diagnosis of malignant solitary fibrous tumor (SFT). Overexpression of IGF-II was confirmed by both immunohistochemistry and RNA sequencing. Further NGS analysis revealed an SFT characteristic alteration-NAB2-STAT6 fusion. Additionally, three deleterious missense variants were detected in oncogenes BIRC6, KIT, and POLQ, and one homozygous in-frame deletion in the RBM10 tumor suppressor gene.

Conclusion

While the NAB2-STAT6 fusions are well characterized, the mutational landscape of SFTs remains understudied. This study reports the importance of NGS to characterize SFTs as we detected four coding variants in genes (BIRC6, KIT, POLQ, and RBM10) associated with tumorigenesis that could potentially contribute to the overall pathogenesis of SFT.

ASPSCR1::TFE3 orchestrates the angiogenic program of alveolar soft part sarcoma

Alveolar soft part sarcoma (ASPS) is a soft part malignancy affecting adolescents and young adults. ASPS is characterized by a highly integrated vascular network, and its high metastatic potential indicates the importance of ASPS's prominent angiogenic activity. Here, we find that the expression of ASPSCR1::TFE3, the fusion transcription factor causatively associated with ASPS, is dispensable for in vitro tumor maintenance; however, it is required for in vivo tumor development via angiogenesis. ASPSCR1::TFE3 is frequently associated with super-enhancers (SEs) upon its DNA binding, and the loss of its expression induces SE-distribution dynamic modification related to genes belonging to the angiogenesis pathway. Using epigenomic CRISPR/dCas9 screening, we identify Pdgfb, Rab27a, Sytl2, and Vwf as critical targets associated with reduced enhancer activities due to the ASPSCR1::TFE3 loss. Upregulation of Rab27a and Sytl2 promotes angiogenic factor-trafficking to facilitate ASPS vascular network construction. ASPSCR1::TFE3 thus orchestrates higher ordered angiogenesis via modulating the SE activity.

The Recent Advances in Molecular Diagnosis of Soft Tissue Tumors

Soft tissue tumors are rare mesenchymal tumors with divergent differentiation. The diagnosis of soft tissue tumors is challenging for pathologists owing to the diversity of tumor types and histological overlap among the tumor entities. Present-day understanding of the molecular pathogenesis of soft tissue tumors has rapidly increased with the development of molecular genetic techniques (e.g., next-generation sequencing). Additionally, immunohistochemical markers that serve as surrogate markers for recurrent translocations in soft tissue tumors have been developed. This review aims to provide an update on recently described molecular findings and relevant novel immunohistochemical markers in selected soft tissue tumors.

Trabectedin Is Active against Two Novel, Patient-Derived Solitary Fibrous Pleural Tumor Cell Lines and Synergizes with Ponatinib

Solitary fibrous tumor of the pleura (SFT) is a rare disease. Besides surgery combined with radiotherapy in nondisseminated stages, curative options are currently absent. Out of fourteen primo-cell cultures, established from surgical SFT specimens, two showed stable in vitro growth. Both cell models harbored the characteristic NAB2-STAT6 fusion and were further investigated by different preclinical methods assessing cell viability, clone formation, and protein regulation upon single-drug treatment or in response to selected treatment combinations. Both fusion-positive cell models showed-in line with the clinical experience and the literature-a low to moderate response to most of the tested cytotoxic and targeted agents. However, the multi-tyrosine kinase inhibitors ponatinib and dasatinib, as well as the anti-sarcoma compound trabectedin, revealed promising activity against SFT growth. Furthermore, both cell models spontaneously presented strong FGFR downstream signaling targetable by ponatinib. Most interestingly, the combination of either ponatinib or dasatinib with trabectedin showed synergistic effects. In conclusion, this study identified novel trabectedin-based treatment combinations with clinically approved tyrosine kinase inhibitors, using two newly established NAB2-STAT6 fusion-positive cell models. These findings can be the basis for anti-SFT drug repurposing approaches in this rare and therapy-refractory disease.

Cytomorphological Spectrum of Solitary Fibrous Tumor: Revisited

BACKGROUND

Solitary fibrous tumor (SFT) is a tumor of mesenchymal origin. Its diagnosis on cytology is challenging, owing to variation in cellularity, sparsely distributed cellular and stromal components and inapparent vasculature. The cytomorphologic findings have been rarely described in literature with a few case reports and occasional case series. We present the cytomorphologic features of SFT with special emphasis on immunochemical findings.

MATERIALS AND METHODS

We present cytological data from eight cases of histopathologically proven SFTs. The cytomorphologic features, immunochemical markers and differential diagnostic entities on fine needle aspiration cytology (FNAC) arediscussed.

RESULTS

FNA was performed at different anatomical sites. Cytology smears showed variable cellularity with tumor cells arranged in loose clusters and as singly scattered cells. Interlacing fascicles with palisading of cells was noted. The cells were predominantly spindle to elongated, having moderate cytoplasm with elongated wavy nuclei. These nuclei had fine to coarse chromatin, with inconspicuous to prominent nucleoli. There was prominent metachromatically staining, amorphous to fibrillary, collagenous to myxoid matrix materialassociated with tumor cells. Other findings included intranuclear pseudo-inclusions, multinucleated giant cells and atypical mitoses. Cytological diagnosis offered varied from 'spindle cell neoplasm' to 'spindle cell sarcoma' or 'suggestive of sarcoma'.Immunocytochemistry (ICC) done on cell block sections showed positivity for STAT6, CD34 and Bcl-2.

CONCLUSION

Cytological diagnosis of SFT can be challenging. A prudent search for characteristic cytomorphological features is of diagnostic help. The cytomorphology should be interpreted with caution with appropriate ICC panel including STAT6 and CD34.

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.

Aberrant expression of thyroid transcription factor-1 in meningeal solitary fibrous tumor/hemangiopericytoma

Meningeal solitary fibrous tumor (SFT) and hemangiopericytoma (HPC) were categorized as the same entity in the World Health Organization (WHO) 2016 classification of tumors of the central nervous system (CNS). Although NAB2-STAT6 fusion protein can be used to distinguish most of SFT/HPC from the other sarcomas, additional biomarkers were requested to separate meningeal SFT/HPC from meningioma and the molecular pathological difference between meningeal SFT/HPC and extra-CNS SFT/HPC still remains unclear. In this study, we evaluated the expression of TTF-1 in 67 meningeal SFT/HPC, 62 extra-CNS SFT/HPC and 201 meningiomas samples with immunohistochemistry (IHC) assays. The results showed that TTF-1 was detected in 23 of 67 (34.3%) meningeal SFT/HPC, 3 retroperitoneum SFT/HPC and none of meningiomas. Meanwhile, the copy number variation and mRNA expression of TTF-1 were measured by real-time quantitative PCR (qPCR) in meningeal SFT/HPC. These results demonstrated that TTF-1 protein expression level was significantly correlated with its transcription level, but independently related to the gene copy number variant. In conclusion, our study suggested that a large proportion of meningeal SFT/HPC was positive to TTF-1, while very few extra CNS SFT/HPC cases and no meningiomas were stained. So TTF-1 has value as an auxiliary diagnostic marker for meningeal SFT/HPC.

Histopathological findings and immunohistochemical expression of the stem cell markers CD44, ALDH1, Bmi-1, and Nanog in oral solitary fibrous tumors

OBJECTIVES

The aim of this study was to evaluate the histomorphologic presentation and the expression of stem cell-related markers in a series of oral solitary fibrous tumors (SFTs).

STUDY DESIGN

Histopathological variables and the expression of the standard stem cell markers CD34 and CD99, used for SFT diagnosis, as well as STAT6 were evaluated in 13 oral SFTs. The expression of the cancer stem cell markers CD44, ALDH1, Bmi-1, and Nanog and the tumor suppressor gene p16^Ink4a were also investigated.

RESULTS

The majority of oral SFTs were circumscribed and characterized by a proliferation of spindle cells arranged in a hyalinized stroma. Only 2 oral SFTs showed >4 mitoses/10 high-power fields. Hypercellularity as well as nuclear and cellular pleomorphism were classified as low and moderate in most of the oral SFTs. All oral SFTs were positive for CD34, STAT6, CD44, ALDH1, Bmi-1, and p16^Ink4a. CD99 and Nanog expression was observed in 11 and 10 oral SFT cases, respectively.

CONCLUSION

We suggest that STAT6 and ALDH1 have relevant diagnostic value. The expression of CD44, ALDH1, Bmi-1, and Nanog, which is observed in cancer stem cells, may confer advantages to oral SFT cells.

[What's new in the management of meningeal solitary fibrous tumor/hemangiopericytoma?]

Meningeal fibrous solitary tumors/hemangiopericytoma are rare and aggressive mesenchymal neoplasms considered as sarcomas. They represent less than 1% of intracranial tumors and derive from the pericytes of Zimmerman which permit capillary contraction. They tend to occur more often in males in the fifth decade. They are often revealed by intracranial hypertension. Some scannographic and MRI characteristics permit to distinguish meningeal fibrous solitary tumor/hemangiopericytoma from other meningeal tumors. Meningeal hemangiopericytoma and fibrous solitary tumors were considered as different entities until 2016. Following the discovery of an identical genetic event, the locus 12q13 chromosome inversion leading to a NAB2-STAT6 fusion with nuclear immunoreactivity for STAT6 protein, the 2016 WHO classification defines these tumors as a single entity. Meningeal fibrous solitary tumors/hemangiopericytoma have a high recurrence rate. Long-term recurrences may occur. Local relapses are more frequent than extracranial metastasis. A multimodal management is recommended to treat a localized disease. It involves a complete resection followed by adjuvant radiotherapy. When local recurrences occur, surgery or stereotactic radiosurgery permit sometimes a local control. Metastatic disease has a poor prognostic and a weak chimiosensitivity. Targeted therapies, like pazopanib, are a hopeful option.

A novel DNA-binding motif in prostate tumor overexpressed-1 (PTOV1) required for the expression of ALDH1A1 and CCNG2 in cancer cells

PTOV1 is a transcription and translation regulator and a promoter of cancer progression. Its overexpression in prostate cancer induces transcription of drug resistance and self-renewal genes, and docetaxel resistance. Here we studied PTOV1 ability to directly activate the transcription of ALDH1A1 and CCNG2 by binding to specific promoter sequences. Chromatin immunoprecipitation and electrophoretic mobility shift assays identified a DNA-binding motif inside the PTOV-A domain with similarities to known AT-hooks that specifically interacts with ALDH1A1 and CCNG2 promoters. Mutation of this AT-hook-like sequence significantly decreased the expression of ALDH1A1 and CCNG2 promoted by PTOV1. Immunohistochemistry revealed the association of PTOV1 with mitotic chromosomes in high grade prostate, colon, bladder, and breast carcinomas. Overexpression of PTOV1, ALDH1A1, and CCNG2 significantly correlated with poor prognosis in prostate carcinomas and with shorter relapse-free survival in colon carcinoma. The previously described interaction with translation complexes and its direct binding to ALDH1A1 and CCNG2 promoters found here reveal the PTOV1 capacity to modulate the expression of critical genes at multiple levels in aggressive cancers. Remarkably, the AT-hook motifs in PTOV1 open possibilities for selective targeting its nuclear and/or cytoplasmic activities.

In Vivo Expansion of Cancer Stemness Affords Novel Cancer Stem Cell Targets: Malignant Rhabdoid Tumor as an Example

Cancer stem cell (CSC) identification relies on transplantation assays of cell subpopulations sorted from fresh tumor samples. Here, we attempt to bypass limitations of abundant tumor source and predetermined immune selection by in vivo propagating patient-derived xenografts (PDX) from human malignant rhabdoid tumor (MRT), a rare and lethal pediatric neoplasm, to an advanced state in which most cells behave as CSCs. Stemness is then probed by comparative transcriptomics of serial PDXs generating a gene signature of epithelial to mesenchymal transition, invasion/motility, metastasis, and self-renewal, pinpointing putative MRT CSC markers. The relevance of these putative CSC molecules is analyzed by sorting tumorigenic fractions from early-passaged PDX according to one such molecule, deciphering expression in archived primary tumors, and testing the effects of CSC molecule inhibition on MRT growth. Using this platform, we identify ALDH1 and lysyl oxidase (LOX) as relevant targets and provide a larger framework for target and drug discovery in rare pediatric cancers.

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Human malignant rhabdoid tumor (MRT) can be propagated in vivo as tumor xenografts

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Long-term propagated PDX enrich for CSC frequency with no need for immune selection

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Distinct gene signature in stem-like MRT xenografts reveals putative CSC biomarkers

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Screening of putative CSC biomarkers allows identification of therapeutic targets

Molecular profiling of sarcomas: new vistas for precision medicine

Sarcoma is a large and heterogeneous group of malignant mesenchymal neoplasms with significant histological overlap. Accurate diagnosis can be challenging yet important for selecting the appropriate treatment approach and prognosis. The currently torrid pace of new genomic discoveries aids our classification and diagnosis of sarcomas, understanding of pathogenesis, development of new medications, and identification of alterations that predict prognosis and response to therapy. Unfortunately, demonstrating effective targets for precision oncology has been elusive in most sarcoma types. The list of potential targets greatly outnumbers the list of available inhibitors at the present time. This review will discuss the role of molecular profiling in sarcomas in general with emphasis on selected entities with particular clinical relevance.

Solitary fibrous tumour of the genitourinary tract: a clinicopathological study of 11 cases and their association with the NAB2-STAT6 fusion gene

AIMS

To characterise clinicopathological features and clinical outcomes of the genitourinary tract solitary fibrous tumours, incorporating NAB2-STAT6 gene fusion status.

METHODS

The presence of the molecular hallmark NAB2-STAT6 gene fusion and for the defining fusion partner product STAT6 was assessed in 11 cases of the genitourinary tract solitary fibrous tumours. NAB2-STAT6 gene fusion analysis was performed using a break-apart fluorescence in situ hybridisation (FISH) probe using a probe cocktail with Bacterial artificial chromosome (BAC) clones for STAT6 and NAB2.

RESULTS

Eleven solitary fibrous tumours were diagnosed in eight male patients and three female patients with a mean age of 46 years (range: 11-64 years). Four of the tumours had malignant histological features, and three were considered moderate risk for metastasis. With a mean follow-up time of 61 months, 1 recurred locally and 2 presented at distant metastatic sites. Using a break-apart FISH probe cocktail, we found the NAB2-STAT6 gene fusion and nuclear STAT6 expression in 58% and 91% of cases, respectively. However, the NAB2-STAT6 fusion status was not correlated with STAT6 expression or useful in discriminating between malignant histological features or subsequent clinical outcomes in the genitourinary solitary fibrous tumours.

CONCLUSIONS

A subset of solitary fibrous tumours of the genitourinary tract behaved aggressively. Using a break-apart FISH probe cocktail, we found the NAB2-STAT6 gene fusion in 64% of cases. However, the NAB2-STAT6 fusion status was not correlated with STAT6 expression or useful in discriminating between low-risk or high-risk tumours and subsequent clinical outcomes.

The Current Status of Solitary Fibrous Tumor: Diagnostic Features, Variants, and Genetics

Solitary fibrous tumor (SFT) is a fibroblastic mesenchymal tumor originally described in the pleura but now shown at almost every anatomic site. Histopathologically, SFT is characteristically a circumscribed neoplasm composed of variably cellular and patternless distributions of bland spindle and ovoid cells within prominent collagenous stroma and shows diffuse expression of CD34, but it has a broad spectrum of both morphology and of biologic behavior. Many different names (particularly hemangiopericytoma) were previously used in the course of our understanding of this neoplasm but are now subsumed under the term "SFT," and the putative cell of origin was debated. However, it is now recognized that SFT is a translocation-associated neoplasm, consistently associated with NAB2-STAT6 gene fusions arising from recurrent intrachromosomal rearrangements on chromosome 12q, and this translocation is a likely major contributor to its pathogenesis. While most SFT with classical morphologic features behave in an indolent manner and those with overtly malignant histologic features tend to be aggressive neoplasms that behave as high-grade sarcomas, the behavior of SFT is unpredictable, and it is important to be aware of the propensity for aggressive behavior in a minority of histologically classical SFT and to ensure adequate clinical follow-up. Surgical excision remains the treatment gold standard; while radiotherapy and conventional chemotherapeutic agents have only shown limited efficacy, further understanding of the molecular events underlying tumorigenesis may allow the development of novel targeted treatments. We review SFT, discussing the morphologic spectrum and variants, including malignant and dedifferentiated subtypes, clinicopathological aspects, recent molecular genetic findings, and the differential diagnosis.

A GRIA2 and PAX8-positive renal solitary fibrous tumor with NAB2-STAT6 gene fusion

Solitary fibrous tumor (SFT) is a rare neoplasm composed of mesenchymal-derived spindle cells. Although SFT occurs anywhere in the body, they most frequently affects the thoracic region. Here, we reported an extremely rare case of an extrathoracic SFT occurring primarily in the kidney. To our knowledge, little information has been described on the immunohistochemistry (IHC) and genetics of renal SFT.

A 41-year old Japanese female came to our hospital for further examination of a left kidney mass detected incidentally with ultrasound. Extensive investigation of the tumor, including physical, laboratory, and image examinations led to a clinical diagnosis of renal cancer (cT1aN0M0), which were in most parts imbedded in the lower polar parenchyma. The patient underwent laparoscopic radical nephrectomy. The mass was diagnosed pathologically as SFT originating from the kidney, but not as renal carcinoma. Microscopically, the tumor was composed of spindle-shape cells distributed variably in dense collagenous stroma and had a focal hemangiopericytomatous staghorn-like vascular pattern. Mitotic figures, atypical structures, necrosis and hemorrhage were not identified. No adjuvant therapies were given postoperatively. The patient has been free of tumor recurrence for 25 months since the surgery. IHC revealed that the tumor diffusely expressed CD34, CD99, Bcl2, PAX8, NAB2, STAT6, and GRIA2. The tumor stained negatively for desmin, S-100, c-Kit, CK-AE1/AE3, CDK4 and MDM2. A NAB2-SATA6 gene fusion was detected in tumor cells by reverse transcription-polymerase chain reaction, direct sequencing, and an in situ proximity ligation brightfield assay. The gene fusion occurred as an 831 bp truncation of exon 2 in NAB2 connected to the beginning of exon 3 in STAT6. We have reported a case of GRIA2 and PAX8-positive SFT occurring primarily in the kidney with such NAB2-STAT6 gene fusion for the first time. Diffuse expression of PAX8 in the tumor might present with a renal origin. Reportedly, benign histology of SFT cannot necessarily predict favorable clinical prognosis. Genetic alterations recently identified in SFT could possibly refer to risk stratification for tumor recurrence. However, malignant preponderance of extrathoracic SFT over thoracic SFT remains unexplained so far. Long-term follow-up after surgery should be performed in the present case.

Immunohistochemical evaluation of stem cell markers and signal transducer and activator of transcription 6 (STAT6) in solitary fibrous tumors

Solitary fibrous tumors (SFT) are fibroblastic, ubiquitous mesenchymal tumors. Although several SFT studies have been conducted, the cell of origin of SFT remains controversial and reliable diagnostic markers are needed for SFT identification for proper prognosis and therapeutics. To analyze the immunophenotype of SFT for the identification of specific diagnostic markers and the cell of origin of this tumor, we performed an immunohistochemical study of stem cell markers [aldehyde dehydrogenase 1 (ALDH1), CD29, CD44, CD133, and nestin] and signal transducer and activator of transcription 6 (STAT6) in 18 cases of SFT. The results demonstrated that ALDH1 was present in 16 cases (16/18), STAT6 in 13 cases (13/18), CD44 in 8 cases (8/18), and CD29 in 1 case (1/18), whereas CD133 and nestin were absent in all cases (0/18). Our results indicate that combination with ALDH1 and STAT6 can improve the diagnostic value of CD34 for SFT. The immunohistochemical findings for stem cell surface markers indicate that SFT may originate from stem cells and that ALDH1 plays an important role in the development of SFT.

Immunophenotype Heterogeneity in Nasal Glomangiopericytoma

Nasal glomangiopericytoma is rare. The immunophenotype is heterogeneous, more frequently smooth-muscle-actin and CD34-positive. We report expression patterns for several vascular-related proteins such as CD99, CD146, Bcl2, and WT1 as well as for treatment-related proteins such as mTOR and EGFR in a nasal glomangiopericytoma. The patient (woman, 86 years) presented with a left nasal tumefaction. The resected specimen (1.5-cm) showed a glomangiopericytoma. Tumor cells expressed smooth-muscle-actin, CD31, CD34, and progesterone receptor. They also expressed the vascular-cell-related proteins Bcl2, CD99, CD146, and WT1, as well as mTOR and EGFR. Nasal glomangiopericytomas show immunohistochemical heterogeneity for vascular-related markers, suggesting a possible extensive pericytic differentiation. The expression of potential targets for drug treatments such as mTOR and EGFR may impact on the clinical follow-up of these tumors occurring at advanced ages, which may require complex surgery.