Solitary fibrous tumor - clinicopathologic, immunohistochemical and molecular analysis of 28 cases

Molecular genetic analysis of pulmonary benign metastasizing leiomyoma and intravenous leiomyomatosis: a comparative study using whole exome sequencing

OBJECTIVE

Benign Metastasizing Leiomyoma (BML) and Intravenous Leiomyomatosis (IVL) are rare uterine-derived smooth muscle tumors. Although both exhibit histologically benign and similar features, they demonstrate aggressive biological behaviors. Currently, molecular genetic studies on BML and IVL are limited, and no comparative research on their genetic variations has been reported. To investigate the genetic basis underlying their shared aggressive phenotypes, this study employs whole-exome sequencing (WES) to conduct a molecular genetic comparison between the two entities. The aim is to explore potential genetic variations that may reveal common pathological pathways shared by these diseases, thereby enhancing our understanding of the molecular mechanisms driving their invasiveness.

METHODS

A pulmonary BML case and an IVL case underwent analysis, with paraffin-embedded tumor tissues subjected to WES. Mutant genes were screened and comparatively analyzed between the two cases.

RESULTS

WES revealed 15 single nucleotide polymorphism (SNP) genetic mutations in the BML case: HFM1, SCN10A, HEXA, SLC7A14, TEP1, KCNJ12, KCNJ18, DNAJB12, ACOX3, ABCC2, RASA1, ALOX15B, TCIRG1, COL5A3, and MCCC2. In the IVL case, 18 mutant genes were observed: CADPS2, GPSM2, REEP4, KCNJ12, KCNJ18, DUSP15, PDE11A, TCIRG1, KLHL33, PAH, MYO18A, FBLN7, ATP7B, MYO7A, MLKL, LRP10, KRT15, and HEPH. The mutations were consistent across both samples in this case. Shared mutations in BML and IVL cases included TCIRG1, KCNJ12, and KCNJ18.

CONCLUSION

BML and IVL exhibit distinct gene mutations in tumor development, with certain shared mutations.

Mesenchymal Neoplasms of the Kidney and Perinephric Soft Tissue

Mesenchymal neoplasms of the kidney present challenges because they are uncommon, and because perinephric soft tissue biopsies are sometimes submitted as "kidney" masses, causing diagnostic confusion. Here, the author thoroughly reviews mesenchymal neoplasms of the kidney, including metanephric stromal tumor, classic and cellular congenital mesoblastic nephroma, anaplastic sarcoma and clear cell sarcoma of the kidney, malignant rhabdoid tumor, PEComa/angiomyolipoma, and anastomosing hemangioma. The author also discusses perinephric myxoid pseudotumor of fat, as well as diagnostic pitfalls presented by well-differentiated/dedifferentiated liposarcoma and sarcomatoid carcinoma.

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

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

Malignant Extrapleural Solitary Fibrous Tumor

Solitary fibrous tumors (SFTs) are rare spindle cell neoplasms of mesenchymal origin that are most commonly found in the pleura, although they have also been documented in extrapleural locations. SFTs affect males and females in equal distribution, and they typically occur between the fourth and seventh decades of life. Since SFTs are usually benign and asymptomatic, the majority of them are discovered incidentally on computed tomography (CT) or magnetic resonance imaging (MRI) imaging, unless they grow to a size that causes mass effect symptoms on other organs. Nonetheless, imaging is not sufficient to diagnose an SFT, and therefore, biopsy is recommended for further analysis. Advances in immunohistochemistry and molecular diagnostics have identified CD34 and NAB2-STAT6, respectively, as the most consistent markers for SFTs. The risk of SFT metastasis can be determined through the use of a four-variable risk-stratification model developed by Demicco et al., which is based upon the risk factors of patient age, tumor size, mitotic count per 10 high-power fields, and the degree of tumor necrosis. The management of SFTs involves a wide surgical resection of the tumor while preserving surrounding organs and structures. Post-operative surveillance involves imaging the primary tumor site for up to five years due to the risk of local recurrence. At this time, neither radiation therapy nor chemotherapy after resection have yet to show benefit, and therefore, they are not currently recommended. This case report discusses the management of a 68-year-old woman who was diagnosed with a malignant extrapleural SFT in her right medial upper thigh.

An update on selected cutaneous (myo) fibroblastic mesenchymal tumors

Cutaneous (myo)fibroblastic tumors constitute a group of tumors with overlapping clinicopathological features and variable biologic behavior. In the present review we focus on the histomorphology, immunohistochemical profile and molecular background of the following entities: dermatofibrosarcoma protuberans (DFSP), CD34-positive fibroblastic tumor (SCD34FT), myxoinflammatory sarcoma (MIFS), low-grade myofibroblastic sarcoma, solitary fibrous tumor and nodular fasciitis. Although some of these entities typically arise in deep-seated locations, they may occasionally present as cutaneous/superficial tumors and might be challenging to recognize. This review covers in depth the latest advances in molecular diagnostics and immunohistochemical markers that have significantly facilitated the correct classification and diagnosis of these neoplasms.

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

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

Epithelioid and Clear Cell Solitary Fibrous Tumors: Clinicopathologic, Immunohistochemical, and Molecular Genetic Study of 13 Cases

Solitary fibrous tumors (SFTs) are ubiquitous soft tissue neoplasms known for their protean histology and potentially aggressive behavior. Although most cases are composed of a monotonous proliferation of spindle cells, some tumors show unusual cytologic features. We have studied 13 SFTs that were characterized by a predominant population of round epithelioid cells with abundant eosinophilic cytoplasm and clear cell changes. The tumors occurred in 8 women and 5 men, aged 36 to 80 years (mean=63 y), and were located within the orbit (3), lower extremity (3), retroperitoneum (2), abdominal cavity (2), and superficial soft tissues of the neck, pelvis, and pubis (1 each). The tumors measured from 3.5 to 24.5 cm. Using a risk assessment system, 6 cases were stratified as low-risk tumors; 3 of these showed no evidence of recurrence or metastases from 6 to 18 years, and 1 tumor in the orbit recurred and led to the patient's demise. Five cases were of intermediate risk; clinical follow-up showed no evidence of recurrence or metastases from 3 to 4 years in 3 patients, and 1 patient suffered a recurrence 4 years after diagnosis. Two cases were high risk; 1 patient died after 1 year and the second patient experienced local recurrence at 4 years. Immunohistochemical studies showed nuclear positivity for STAT6 in 10 cases. CD34 immunohistochemistry was positive in 11 cases. A NAB2::STAT6 rearrangement was present in all cases. Epithelioid and clear cell SFT should be considered in the differential diagnosis of soft tissue neoplasms with epithelioid and clear cell morphology.

Solitary fibrous tumor of the central nervous system invading and penetrating the skull: A case report

Solitary fibrous tumor (SFT) of the central nervous system is a rare spindle cell tumor of mesenchymal origin. The present study reports the case of a 44-year-old male patient with SFT. Magnetic resonance imaging demonstrated that the majority of the intracranial tumors exhibited uneven low signals on T1-weighted imaging (T1WI) and low mixed signals on T2WI, and there was an enhancement on enhanced scanning. Furthermore, the distal part of the left occipital lobe exhibited hypersignals on T1WI and T2WI, and this was significantly enhanced following enhanced scanning. The lower part of the scalp exhibited low signals on T1WI and high signals on T2WI, and there was no notable enhancement following enhanced scanning. Magnetic resonance spectroscopy demonstrated an elevated choline/creatine peak in the solid part of the tumor. Under the microscope, the tumor exhibited characteristic 'staghorn-shaped' blood vessels. As SFT is difficult to differentially diagnose via imaging, immunohistochemical analysis of CD34, vimentin and signal transducer and activator of transcription 6 was performed for the definitive diagnosis of SFT. Of note, surgical resection was the preferred treatment for SFT; however, due to the rarity of the tumor, subsequent adjuvant therapy and prognosis require further investigation.

Malignant solitary fibrous tumor of maxilla presenting as proptosis: A case report

ABSTRACT

Solitary fibrous tumor (SFT) is a fibroblastic mesenchymal neoplasm that rarely metastasizes. SFTs was first described in relation to pleura. However, occurrence of this tumor type has been reported in other sites like peritoneum, liver, adrenal gland, meninges and oral cavity. In head and neck region, oral cavity is the most common site of involvement. Most of the solitary fibrous tumors are benign and present as an asymptomatic slow growing mass. Surgery remains the mainstay of treatment. Hereby, we describe a case of 71-year-old male with malignant solitary fibrous tumor arising from right maxilla invading the right orbit presenting as proptosis.

The Unique Spectrum of MUTYH Germline Mutations in Colombian Patients with Extracolonic Carcinomas

Background

Protein MUTYH, encoded by the gene MUTYH, is an important mismatch repair enzyme in the base-excision repair pathway of DNA repair. When genetically altered, different neoplastic conditions can arise. One of the widely known syndromes associated with MUTYH mutations is MUTYH-associated polyposis, a form of familial colorectal cancer syndrome. MUTYH may also be a driver in other familial cancer syndromes, as well as breast cancer and spontaneous cancer cases. However, some controversies about the role of these alterations in oncogenesis remain, especially when affected in a heterozygous way. Most available data on MUTYH mutations are on Caucasian patients.

Material and Methods

We analyzed a small cohort of non-Caucasian, Colombian cancer patients with MUTYH germline heterozygous mutations, clinical features suggestive of familial cancer, and extensive genetic studies with no other mutations and without MUTYH-associated polyposis.

Conclusion

With this case series, we intended to provide important data for the understanding of MUTYH as a possible driver of familial cancer, even when only heterozygous mutations are found.

Orbital solitary fibrous tumours: clinicopathological characteristics and recurrence prediction

BACKGROUND

SFTs are thought to have an unpredictable clinical course and currently have no recognized prognostic criterion. Our study aimed to determine the relationship between clinicopathological characteristics and the prognosis of patients with orbital SFTs.

METHODS

The clinicopathological features of these patients were extracted from clinical records. The relationships between these features and prognosis were analysed.

RESULTS

The positive rates of CD34, CD99, Blc2, and STAT6 expression were 90.3%, 90.3%, 83.9%, and 100%, respectively. The tumour recurrence rate was 38.7%. A higher recurrence rate was observed in patients with Ki67 index ≥ 5 (56.25% vs. 20%, P = 0.038).

CONCLUSION

A Ki67 index ≥ 5 was an effective parameter for predicting tumour recurrence of orbital SFTs. Close follow-up is needed for these patients.

A female with solitary fibrous tumor pleura mimicking pulmonary sclerosing pneumocytoma in low resource setting: A case report

Background

Solitary fibrous tumor of pleura (SFTP) is a rare condition. Clinical symptoms and non-specific radiological features in both tumors make preoperative diagnosis difficult to establish.

Case presentation

A Javanese 47-year-old female complained of chest pain and shortness of breath which an X-ray and CT-Scan of the thorax showed giant cell metastases in the lung. Signs and symptoms indicate pulmonary sclerosing pneumocytoma (PSP) and the patient underwent thoracic surgery which was first performed with angiographic embolization. Furthermore, an anatomical pathology analysis was performed with suspected SFTP, supported by the IHC test, which found CD34 (+), EMA (−), and S100 (−). Thoracic surgery followed by radiotherapy and chemotherapy is recommended in SFTP patients.

Discussion

The SFTP and PSP have non-specific clinical symptoms and radiological features. Anatomic pathology and IHC test are definitive diagnostic tools from SFTP and PSP. Establishing a preoperative diagnosis of SFTP and PSP is quite difficult. Surgical resection is the treatment of choice for both.

Conclusion

The comparison of SFTP and PSP can be seen results of the anatomical pathology analysis and IHC test.

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Solitary fibrous tumor of pleura (SFTP) and pulmonary sclerosing pneumocytoma (PSP) are difficult to distinguish in a low-resource setting.

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SFTP and PSP can be differentiated using an immunohistopathology test (cluster of differentiation 34/CD54 was positive).

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Management of SFTP and PSP are both similar to surgery (thoracotomy with a subcostal incision).

A case of a large solitary fibrous tumor in the thigh, displaying NAB2ex4-STAT6ex2 gene fusion

A solitary fibrous tumor (SFT) is documented in several body sites. However, there are few reports on the radiological and corresponding histopathological, including immunohistochemical, features of SFT in the lower extremities. A 58-year-old male presented with a lump in his right thigh of 6 months duration. Plain radiograph revealed a soft tissue lesion in his right thigh, involving the adjacent mid-diaphysis and showing focal cortical thickening and calcification. Magnetic resonance imaging scans displayed two well-defined, T1-isointense and T2 heterogeneously hyperintense lesions, measuring together 15 cm in the intermuscular plane and the juxtacortical location along the mid-diaphyseal region of the right femur. Radiologically, the differential diagnoses considered were undifferentiated pleomorphic sarcoma and synovial sarcoma. Microscopic examination of the core biopsy and the resected tumor revealed a tumor composed of cells with oval to spindle-shaped nuclei in a variably collagenized stroma, including hyalinized blood vessels and focal dystrophic calcification. Mitotic figures were 4/10 high power fields. Immunohistochemically, the tumor cells were positive for CD34, BCL2, and STAT6. Diagnosis of malignant SFT was offered. The tumor displayed NAB2ex4-STAT6ex2 gene fusion on molecular testing. This constitutes a relatively uncommon case report of a large SFT in the thigh, including its radiological and pathological features, confirmed by STAT6 immunostaining. An SFT should be considered in cases of slow-growing, well-defined soft tissue tumors, which are isointense on T1 and heterogeneously hyperintense on T2-weighted sequences, and display calcification and cortical thickening of the adjacent bones. Various differential diagnoses and their treatment-related implications in such cases are discussed herewith.

Solitary Fibrous Tumor of Internal Jugular Vein: An Extremely Rare Entity with Review of Literature

Solitary fibrous tumor (SFT) is an unusual spindle cell neoplasm that commonly arises from pleura. In the last decade, multiple case reports have described its diverse occurrence in extrapleural locations involving almost every anatomic site. Intravascular SFT is extremely rare and has been reported in inferior vena cava and renal vein only, to the best of our knowledge. SFT of the internal jugular vein has never been reported. We present a case of a SFT arising from internal jugular vein with extraluminal exophytic component extending into supraclavicular fossa. It should also be considered as a differential diagnosis for neoplasm arising from the internal jugular vein.

Pulmonary artery intimal sarcoma - A primeval or rediscovered tumor? A report of 14 new cases with literature review

Pulmonary artery sarcomas (PAS) are rare with many being undifferentiated pleomorphic or spindle cell (UPSC) sarcomas with variable atypia. The term pulmonary artery intimal sarcoma (PAIS) was rarely coined in the early literature and sometimes used for luminal sarcomas. With the advent of immunohistochemistry and molecular genetics, many of these UPSC sarcomas were found to frequently overpress MDM2 and/or CDK4 and PDGFRA with genetic alterations in 12q12-15 and 4q12, where the MDM2, CDK4 and PDGFRA genes are located. These recent developments enabled refinement in diagnosis of PAIS. We diagnosed 14 cases of PAIS (6 males and 8 females, mean age 44 years) in 2015 - 2020 in our institution. Six were initially misdiagnosed as thromboembolism and the remaining pulmonary artery tumors. The tumors were pulmonary artery intraluminal polypoid masses with histology of spindle cell sarcomas exhibiting immunohistochemical positivity for MDM2 (100%) and CDK4 (79%) with MDM2 gene amplification (100%). Ten surgically treated patients fared better than four other biopsy only and not surgically treated patients, who died of disease within 5-11 months. PAIS needs to be differentiated from other spindle cell tumors and those exhibiting MDM2 gene amplification, especially dedifferentiated liposarcoma. The use of biopsy to provide diagnostic material poses a sampling error problem and correlation with clinical, radiologic, histologic, immunophenotypic and genotypic features are essential for accurate diagnosis and early surgical intervention of PAIS.

Risk Assessment in Solitary Fibrous Tumor of the Uterine Corpus: Report of a Case and Systematic Review of the Literature

Solitary fibrous tumor (SFT) is an uncommon fibroblastic tumor occurring preferentially in the pleura, with a variable clinical course. SFT can arise also in numerous extrathoracic sites and very rarely in the female genital tract, with only scarce reports of uterine SFT. We reported a new uterine SFT arising in a 45-year-old woman, and we performed a systematic review of SFT cases of the uterine corpus interrogating the electronic databases PubMed, Web of Science, and Scopus. We identified only 13 patients diagnosed with SFT of the uterine corpus, including our one. Complete clinical workout at disease presentation showed no evidence of extrauterine spread in all cases, except for 1 patient who presented with metastatic disease. Tumor recurrences/metastases occurred in a minority of the patients and were poorly related to clinicopathological risk factors and patients stratification based on different scoring systems. Since the long-term clinical behavior of uterine SFT is limited and poorly predictable, extended follow-up is recommended also for all cases arising in the uterine corpus.

Solitary Fibrous Tumor of the Orbit: A Clinicopathologic Study of Two Cases With Review of the Literature

BACKGROUND/AIM

Orbital solitary fibrous tumor (SFT) is a rare lesion among orbital tumors, which can be misdiagnosed as another mesenchymal tumor. In this study we report two cases of orbital SFT, focusing on the imaging and pathological findings of the vascular structure inside the tumor.

CASE REPORT

A 26-year-old woman and 43-year-old man presented with orbital SFT. The pathological findings revealed a patternless growth pattern of the tumor cells and hemangiopericytoma-like vascularity as well as thickened, dilated blood vessels within the tumor tissue. Tumor cells revealed a diffuse strong positivity for cluster of differentiation 34 (CD34) and signal transducer and activator of transcription 6 (STAT6) in both cases, while B-cell lymphoma 2 (bcl-2) and CD99 were positive in one case. Characteristic findings within the tumor were the arterial components, where a variety of STAT6, CD99 and bcl-2-positive smooth muscle cells were intermingled.

CONCLUSION

Histologically, the tumor tissues might be characterized by not only conventional hemangiopericytoma-like vasculature but also dilated arterial vessels, which were shown to be part of the tumor components.

Recurrent Fusion of the GRB2 Associated Binding Protein 1 (GAB1) Gene With ABL Proto-oncogene 1 (ABL1) in Benign Pediatric Soft Tissue Tumors

BACKGROUND/AIM

Fusions of the ABL proto-oncogene 1 gene (ABL1 in 9q34) are common in leukemias but rare in solid tumors. The most notable is the t(9;22)(q34;q11)/BCR-ABL1 coding for a chimeric tyrosine kinase. We herein report an ABL1-fusion in a pediatric tumor.

MATERIALS AND METHODS

G-banding, fluorescence in situ hybridization, reverse transcription polymerase chain reaction and Sanger sequencing were performed on a soft tissue perineurioma found in the left musculus erector spinae of a child.

RESULTS

A der(4)t(4;9)(q31;q34) and a fusion of the GRB2 associated binding protein 1 (GAB1 in 4q31) gene with ABL1 were found. A literature search revealed 3 more cases with similar genetic and clinicopathological characteristics: a soft tissue perineurioma with t(2;9;4)(p23;q34;q31) and ABL1 rearrangement, a soft tissue angiofibroma with a GAB1-ABL1 chimeric gene, and a solitary fibrous tumor carrying a der(4)t(4;9)(q31.1;q34).

CONCLUSION

GAB1-ABL1 is a recurrent fusion gene in benign pediatric tumors.

Lipomatous Solitary Fibrous Tumors Harbor Rare NAB2-STAT6 Fusion Variants and Show Up-Regulation of the Gene PPARG, Encoding for a Regulator of Adipocyte Differentiation

Solitary fibrous tumors (SFTs) harbor activating NAB2-STAT6 gene fusions. Different variants of the NAB2-STAT6 gene fusion have been associated with distinct clinicopathologic features. Lipomatous SFTs are a morphologic variant of SFTs, characterized by a fat-forming tumor component. Our aim was to evaluate NAB2-STAT6 fusion variants and to further study the molecular genetic features in a cohort of lipomatous SFTs. A hybrid-capture-based next-generation sequencing panel was employed to detect NAB2-STAT6 gene fusions at the RNA level. In addition, the RNA expression levels of 507 genes were evaluated using this panel, and were compared with a control cohort of nonlipomatous SFTs. Notably, 5 of 11 (45%) of lipomatous SFTs in the current series harbored the uncommon NAB2 exon 4-STAT6 exon 4 gene fusion variant, which is observed in only 0.9% to 1.4% of nonlipomatous SFTs. Furthermore, lipomatous SFTs displayed significant differences in gene expression compared with their nonlipomatous counterparts, including up-regulation of the gene peroxisome proliferator activated receptor-γ (PPARG). Peroxisome proliferator activated receptor-γ is a nuclear receptor regulating adipocyte differentiation, providing a possible explanation for the fat-forming component in lipomatous SFTs. In summary, the current study provides a possible molecular genetic basis for the distinct morphologic features of lipomatous SFTs.

Solitary fibrous tumor of the adrenal gland – its biological behavior and report of a new case

Introduction

A solitary fibrous tumor (SFT) is an uncommon neoplasm of mesenchymal and probably fibroblastic origin, occurring mainly in the extremities, and pleura. However, a primary involvement of endocrine organs is rare and even exceptional when found in the adrenal gland. Hereby, we describe the 10th report of an adrenal SFT.

Case presentation

A 77-year old man was diagnosed with a lesion in the right adrenal gland during a urologic indicated computed tomography (CT). No symptoms and laboratory anomalies were reported indicating any endocrine activity. Follow up CT-scans showed progressive growth of the nodule for which the patient underwent laparoscopic right adrenalectomy. Histological examination showed a hypercellular spindle cell neoplasm with elongated nuclei and a low mitotic index. The vessels were arranged in a hemangiopericytoma-like pattern with a slight sclerosing appearance. Immunohistochemistry showed a positive staining of neoplastic cells for STAT6, CD-34 and Bcl-2. Translocation analysis using RT-PCR showed no NAB2-STAT6 fusion. The specimen was confirmed as a hypercellular variant of an adrenal SFT.

Discussion

SFT is a rare neoplasm when occurring in the adrenal gland. Differential diagnosis can be broad because of no defined pathognomonic morphological characteristics. However, NAB2-STAT6 gene fusions are considered a molecular hallmark of SFTs. Therefore, STAT6 immunohistochemistry is a valuable diagnostic tool in differentiating between SFT and histologic mimics. After diagnosing SFT, its biological behavior is difficult to predict. SFTs are mostly benign tumors. Nonetheless, a histological benign-appearing SFT can show malignant clinical characteristics impeding assessment of proper follow up. However, malignancy has not been previously reported in any adrenal SFT case report.

A Footprint-Like Intracranial Solitary Fibrous Tumor/Hemangiopericytoma With Extracranial Extension and Acute Intratumoral Hemorrhage

BACKGROUND

Intracranial solitary fibrous tumors/hemangiopericytomas (ISFTs/HPCs) are extremely rare spindle-cell tumors that are mostly benign and derived from mesenchymal tissue. Extracranial metastasis and intratumoral hemorrhage are considered to be special manifestations of malignant tumors, of which extracranial metastases of ISFTs/HPCs have been reported, while tumor hemorrhage has rarely been described. Here, the authors present an interesting case of ISFTs/HPCs with acute intratumoral hemorrhage.

CLINICAL PRESENTATION

A 72-year-old woman underwent brain magnetic resonance imaging (MRI) for recurrent headaches and nausea. The MRI scan showed a footprint-like space-occupying lesion in the bilateral parietooccipital lobe. This lesion had multiple cystic components and invaded the superior sagittal sinus, destroying adjacent cranial bones. While waiting for routine surgery, the patient suddenly developed acute tumor bleeding and then underwent emergency surgery. Postoperatively, the diagnosis of ISFT/HPC was confirmed by pathological and immunohistochemical analysis.

DISCUSSIONS AND CONCLUSIONS

The diagnosis of ISFT/HPC mainly depends on pathological and immunohistochemical results. Malignant cases with cystic necrosis may be prone to acute hemorrhage. Early total surgical excision can provide a good clinical prognosis. Adjuvant radiotherapy is an effective supplement to surgical treatment. Metastasis and recurrence require long-term follow-up monitoring.

Gene Expression in Solitary Fibrous Tumors (SFTs) Correlates with Anatomic Localization and NAB2-STAT6 Gene Fusion Variants

Solitary fibrous tumors (SFTs) harbor recurrent NAB2-STAT6 gene fusions, promoting constitutional up-regulation of oncogenic early growth response 1 (EGR1)-dependent gene expression. SFTs with the most common canonical NAB2 exon 4-STAT6 exon 2 fusion variant are often located in the thorax (pleuropulmonary) and are less cellular with abundant collagen. In contrast, SFTs with NAB2 exon 6-STAT6 exon 16/17 fusion variants typically display a cellular round to ovoid cell morphology and are often located in the deep soft tissue of the retroperitoneum and intra-abdominal pelvic region or in the meninges. Here, we employed next-generation sequencing-based gene expression profiling to identify significant differences in gene expression associated with anatomic localization and NAB2-STAT6 gene fusion variants. SFTs with the NAB2 exon 4-STAT6 exon 2 fusion variant showed a transcriptional signature enriched for genes involved in DNA binding, gene transcription, and nuclear localization, whereas SFTs with the NAB2 exon 6-STAT6 exon 16/17 fusion variants were enriched for genes involved in tyrosine kinase signaling, cell proliferation, and cytoplasmic localization. Specific transcription factor binding motifs were enriched among differentially expressed genes in SFTs with different fusion variants, implicating co-transcription factors in the modification of chimeric NGFI-A binding protein 2 (NAB2)-STAT6-dependent deregulation of EGR1-dependent gene expression. In summary, this study establishes a potential molecular biologic basis for clinicopathologic differences in SFTs with distinct NAB2-STAT6 gene fusion variants.

Management of meningeal solitary fibrous tumors/hemangiopericytoma; surgery alone or surgery plus postoperative radiotherapy?

INTRODUCTION

A meningeal solitary fibrous tumor (SFT), also called hemangiopericytoma, is a rare mesenchymal malignancy. Due to anatomic constrains, even after macroscopic complete surgery with curative intent, the local relapse risk is still relatively high, thus increasing the risk of dedifferentiation and metastatic spread. This study aims to better define the role of postoperative radiotherapy (RT) in meningeal SFTs.

PATIENTS AND METHODS

A retrospective study was performed across seven sarcoma centers. Clinical information was retrieved from all adult patients with meningeal primary localized SFT treated between 1990 and 2018 with surgery alone (S) compared to those that also received postoperative RT (S + RT). Differences in treatment characteristics between subgroups were tested using independent samples t-test for continuous variables and chi-square tests for proportions. Local control (LC) and overall survival (OS) rates were calculated as time from start of treatment until progression or death from any cause. LC and OS in groups receiving S or S + RT were compared using Kaplan-Meier survival curves.

RESULTS

Among a total of 48 patients, 7 (15%) underwent S and 41 (85%) underwent S + RT. Median FU was 65 months. LC was significantly associated with treatment. LC after S at 60 months was 60% versus 90% after S + RT (p = 0.052). Furthermore, R1 resection status was significantly associated with worse LC (HR 4.08, p = 0.038). OS was predominantly associated with the mitotic count (HR 3.10, p = 0.011).

CONCLUSION

This retrospective study, investigating postoperative RT in primary localized meningeal SFT patients, suggests that combining RT to surgery in the management of this patient population may reduce the risk for local failures.

Clinicopathologic and Immunohistochemical Characteristics of Solitary Fibrous Tumor and Its Mimics: A Single-Center Experience

BACKGROUND

Solitary fibrous tumor (SFT) is a fibroblastic tumor that has been originally reported as a pleural tumor but now has been defined as a tumor that can be seen everywhere in the human body. Histopathologically, many of the fibroblastic tumors can mimic SFT, and immunohistochemistry is necessary for differential diagnosis. Several markers have been used, and recently, STAT6 has been introduced as a diagnostic marker. No research study has been reported from Iran.

OBJECTIVES

In this report, we are trying to introduce our experience about the clinicopathologic findings of 35 cases of SFT during the last 10 years from our center with an emphasis on the diagnostic role of STAT6 in this tumor.

PATIENTS AND METHODS

During the last 10 years, we confirmed the diagnosis of 35 cases of SFT in the pathology archives of Shiraz University of Medical Sciences. These 35 cases were considered as cases. All the clinicopathologic findings were also extracted from the clinical charts of the patients. To evaluate the diagnostic role of STAT6, another 35 cases of spindle cell tumors were also extracted from the pathology archives as mimickers of SFT. STAT6 was stained in all of the 70 cases and controls.

RESULTS AND DISCUSSION

Our experience showed that SFT is more common in middle-aged men with a wide age range, although it is very rare in children. It can be present in every location with a wide size range from less than 1 cm to more than 15 cm. The presence of abnormal staghorn vessels is one of the main diagnostic histopathologic characteristics. STAT6 showed a sensitivity and specificity of 91% and 86% in the diagnosis of SFT. Other markers such as CD99, CD34, and BCL2 have also been considered useful in the differential diagnosis of this tumor, although the diagnostic accuracy seems to be lower than STAT6. High mitosis, presence of necrosis, and atypia are important criteria for predicting malignant and aggressive behavior in SFT. Among 35 cases in our study, 17% showed malignant behavior as recurrent or metastatic tumors.

CONCLUSION

Solitary fibrous tumor is a common soft tissue tumor that can be seen everywhere and needs careful histopathologic and immunohistochemical evaluation for the correct diagnosis and prediction of aggressive or benign behavior.

Immunophenotype-Genotype Correlations in Clear Cell Sarcoma of Kidney-An Evaluation of Diagnostic Ancillary Studies

INTRODUCTION

The purpose of this study was to establish a reliable panel of antibodies for immunohistochemical corroboration of a diagnosis of clear cell sarcoma of kidney (CCSK), taking into consideration the various genotypic subsets of CCSK.

METHODS

We conducted full genotypic analysis for evidence of YWHAE-NUTM2, BCOR internal tandem duplication (ITD), and BCOR-CCNB3 in 68 archival cases of CCSK and then immunostained all cases for CCND1, TLE1, and BCOR along with 63 control samples representing tumor types that may enter into the differential diagnosis of CCSK, including 7 congenital mesoblastic nephromas, 2 desmoplastic small round cell tumors, 13 malignant rhabdoid tumors, 9 Ewing sarcomas/primitive neuroectodermal tumor, 5 synovial sarcomas, and 27 Wilms' tumors.

RESULTS

Molecular assays showed that 54 CCSKs harbored a BCOR-ITD, 1 case expressed a YWHAE-NUTM2 fusion transcript while none expressed the BCOR-CCNB3 fusion. The remaining 13 CCSKs were designated "triple-negative" based on the molecular findings. CCND1 showed positive immunoreactivity across all subgroups. TLE1 was positive in 94% of cases, including 1 YWHAE-NUTM2 fusion-positive case. Three BCOR-ITD-positive tumors were TLE1-negative. BCOR immunostaining was most variable among subgroups, with triple-negative tumors showing the weakest staining. In all, 10/68 (15%) tumors did not stain for BCOR, of which 4 were triple-negative (4/13 = 31%) and 6 were BCOR-ITD-positive (6/54 = 11%). The single YWHAE-NUTM2-positive tumor showed strong staining for all 3 markers. No single case was negative for all 3 stains; however, 3 cases showed no reactivity for either BCOR or TLE1 of which 1 was triple-negative and 2 BCOR-ITD-positive.

CONCLUSION

Having completed the first comprehensive evaluation of immunostaining of 68 fully genotyped CCSK tumors, we show herein that there is a rationale for the use of a small panel of antibodies to assist in the diagnosis of CCSK regardless of genotype, and we demonstrate that in combination CCND1, TLE1, and BCOR are compelling markers in aiding CCSK diagnosis.

Orbital solitary fibrous tumors: a multi-centered histopathological and immunohistochemical analysis with radiological description

BACKGROUND

Solitary fibrous tumors (SFT), formerly called hemangiopericytoma, are rare tumors derived from mesenchymal cells originally described in the pleura, but these tumors may affect extraserosal tissues including the lacrimal gland and orbit.

OBJECTIVE

Conduct a multi-centered clinical, radiological and histopathological analysis of 17 orbital SFT cases.

DESIGN

A retrospective case series.

SETTING

Three eye centers in two countries.

PATIENTS AND METHODS

The data collected from the charts of 17 adult patients presenting with tissue diagnosis of orbital hemangiopericytoma or SFT from January 2003 to December 2018 included demographics, clinical imaging and histopathological information including immunohistochemical (IHC) characteristics.

MAIN OUTCOME MEASURES

The demographic characteristics, clinical presentation, and histopathological patterns or variants of SFT were analyzed.

SAMPLE SIZE

17 adult patients.

RESULTS

Mean age was 45 years (range 23-80 years). Male to female ratio was 3:1. The right eye was affected in 12 (70.5%) patients. Commonest presentation was proptosis in 13/17 (76% of patients). Other symptoms were impaired motility (29%) and ptosis (11%). Lesions mostly affected the medial orbit (35%), then orbital apex in 11%. The histopathological classic pattern-less variant was the commonest. One case with aggressive behavior, multiple recurrences and atypical features was encountered. Immunohistochemical (IHC) markers used included CD34 expression in all cases, Bcl-2 expression in 10/11, CD99 in 9/9 and Vimentin in 4/4. STAT6 was used in 2 cases.

CONCLUSIONS

SFTs are rare tumors affecting the orbit in both genders equally in their mid-forties, but showed male predominance in our analysis with a predominant classic histopathological pattern. Tissue diagnosis is essential and requires IHC studies for confirmation.

LIMITATIONS

Sample size is relatively small owing to the rarity of this tumor in the orbit.

CONFLICT OF INTEREST

None.

Aggressive Intraosseous Myofibroma of the Maxilla: Report of a Rare Case and Literature Review

Myofibroma (MF) is a benign mesenchymal myofibroblast-derived tumor, which occurs most frequently in children, and rarely affects the maxilla. We reported a case of an aggressive intraosseous lesion found in the maxilla of a 9-year-old female child. Intraorally, the swelling extended from tooth 12 to 16, causing displacement of teeth 13, 14, and 15. Computed tomography revealed a large osteolytic lesion causing thinning and cortical erosion. Microscopically, the lesion showed a proliferation of spindle-shaped cells, with elongated nuclei and eosinophilic cytoplasm, arranged in interlaced fascicles. The immunohistochemical analysis revealed cytoplasmic positivity for α-SMA and HHF-35, and negativity for desmin, laminin, S-100, β-catenin, and CD34. Ki-67 was positive in 8% of tumor cells. The diagnosis was MF. Herein, we describe an additional case of central MF arising in the maxilla, including clinical, imaging, microscopical, and immunohistochemical features, as well as a review of the literature.

Extrameningeal solitary fibrous tumors-surgery alone or surgery plus perioperative radiotherapy: A retrospective study from the global solitary fibrous tumor initiative in collaboration with the Sarcoma Patients EuroNet

Background

Solitary fibrous tumor (SFT) is a rare mesenchymal malignancy. Although surgery is potentially curative, the local relapse risk is high after marginal resections. Given the lack of prospective clinical trial data, the objective of the current study was to better define the role of perioperative radiotherapy (RT) in various SFT presentations by location.

Methods

This was retrospective study performed across 7 sarcoma centers. Clinical information was retrieved from all adult patients with extrameningeal, primary, localized SFT who were treated between 1990 and 2018 with surgery alone (S) compared with those who also received perioperative RT (S+RT). Differences in treatment characteristics between subgroups were tested using analysis of variance statistics and propensity score matching. Local control and overall survival rates were calculated from the start of treatment until progression or death from any cause.

Results

Of all 549 patients, 428 (78%) underwent S, and 121 (22%) underwent S+RT. The median follow‐up was 52 months. After correction for mitotic count and surgical margins, S+RT was significantly associated with a lower risk of local progression (hazard ratio, 0.19: P = .029), an observation further confirmed by propensity score matching (P = .012); however, this association did not translate into an overall survival benefit.

Conclusions

The results from this retrospective study investigating perioperative RT in patients with primary extrameningeal SFT suggest that combining RT with surgery in the management of this patient population is significantly associated with a reduced risk of local failures, especially in patients who have less favorable resection margins and in those who have tumors with a high mitotic count.

This retrospective study of perioperative radiotherapy in patients with primary extrameningeal solitary fibrous tumors suggests that combining radiotherapy with surgery in the management of this population significantly reduces the risk of local failures, especially in patients who have less favorable resection margins or tumors with a high mitotic count.

Atypical/malignant solitary fibrous tumor of the pancreas with spleen vein invasion: Case report and literature review

INTRODUCTION

Solitary fibrous tumor (SFT) is an uncommon mesenchymal tumor that is most common in the pleura. However, according to previous studies, the SFT of the pancreas is extremely rare; only 20 cases have been reported so far. Here, we conduct a literature review and report the first case of atypical/malignant SFT of the pancreas with spleen vein invasion.

PATIENT CONCERNS

The patient is a 61-year-old Chinese male who presented with 1 week of upper abdominal pain. Abdominal magnetic resonance imaging showed a huge mass (>10 cm) at the distal end of the pancreas, and the mass obstructing the splenic vein.

DIAGNOSIS

Atypical/malignant SFT of the pancreas with splenic vein tumor thrombus.

INTERVENTIONS

The patient underwent laparoscopic distal pancreatectomy with splenectomy procedure to achieve a radical resection, and did not undergo chemotherapy or radiotherapy.

OUTCOMES

Abdominal computed tomography scans were performed at 1 and 4 months after resection, and no signs of recurrence or metastasis were found (. B).(Figure is included in full-text article.) CONCLUSION:: The clinical symptoms of atypical/malignant SFT of the pancreas with spleen vein invasion are not atypical, and imaging feature is lack of specificity. Preoperative diagnosis is difficult, and there is a potential for malignancy. However, due to the paucity of randomized control trials, there is no established, globally accepted treatment strategy, radiation therapy and chemotherapy regimens have not demonstrated global effectiveness, and no standardized treatments have been identified. Therefore, we recommend complete surgical resection and close clinical follow-up.

Solitary fibrous tumors of the head and neck region revisited: a single-institution study of 20 cases and review of the literature

A solitary fibrous tumor (SFT) is a rare, NAB2-STAT6 fusion gene-associated mesenchymal neoplasm. It most commonly arises in the pleural site, but it can occur at many other sites, and rarely also in the head and neck (H&N) region. STFs may show many growth patterns and therefore can be easily mistaken for other more common H&N spindle cell or epithelial lesions. In this study, we present our experience in the diagnosis of 20 cases of SFT in the H&N region and discuss their most notable mimickers. In all cases, STAT6 expression was found positive by immunohistochemistry, and the NAB2-STAT6 fusion was confirmed by next-generation sequencing. Three major fusion variants were detected: NAB2ex2-STAT6int1 (5/20, 25%), NAB2ex6-STAT6ex16 (4/20, 20%), and NAB2ex4-STAT6ex2 (3/20, 15%). Clinical follow-up was available for 16 patients (median follow-up time: 84 months). One patient with a morphologically malignant SFT experienced multiple local recurrences, followed by dissemination into the lungs and meninges. This malignant SFT also displayed an aberrant FLI1 expression, which was not previously reported in SFT cases. We also summarize findings from 200 cases of SFT of the H&N region, which included cases from our study, and from previous studies that reported on the fusion status of the STAT6 gene. The results suggest that metastatic disease developed only in cases with STAT6 variants that included the DNA-binding domain (STAT6-full variants), which contradicts expectations from previous reports and deserves further investigation.

Liver metastasis and local recurrence of meningeal hemangiopericytoma: a case report

This report describes the clinical features, diagnostic and treatment modalities of a 62-year-old female patient with liver metastasis and local recurrence of meningeal hemangiopericytoma (HPC), who presented with the clinical manifestations of memory deterioration, visual reduction and abdominal mass for one month. Skull and abdominal computed tomography (CT), magnetic resonance imaging (MRI) and 18FFluorodeoxyglucose positron emission tomography (FDG-PET)-CT were used for pre-surgery identification. Lesions without FDG uptake and less tumoral viability was observed through FDG-PET-CT, which was characteristic features of HPC before operation. The intraoperative specimens from the liver resection and the calvarium were pathologically examined for further confirming the diagnosis. The patient underwent liver resection and bilateral frontal cerebral convex and parafalx resection as well as intracranial pressure sensor implantation for liver metastasis and local recurrence of HPC respectively. The patient recovered well and no recurrence or distant metastasis was found after 2-year follow-up. Early diagnosis and long-term follow-up are crucial for patients with hepatic metastasis or local recurrence of HPC, and FDG-PET-CT is recommended as an ideal imaging tool. Radical resection of HPC lesions is considered as an optimal treating approach.

Benign schwannoma of posterior mediastinum accompanied by bloody pleural effusion misdiagnosed as solitary fibrous tumor: A case report

Background:

Schwannoma is a peripheral nerve sheath tumor originating from schwann cells. It is the most common neurogenic tumor of the posterior mediastinum. Pleural effusion is a rare presentation of benign schwannoma and it is mainly related to malignant tumors. Histologically, schwannoma as well as solitary fibrous tumor should be considered as a differential diagnosis of spindle cell lesions.

Case presentation:

Here, we report a case of an asymptomatic 61-year-old female misdiagnosed as solitary fibrous tumor of posterior mediastinum which was revealed to have blood stained pleural effusion during the video-assisted thoracic surgery. Eventually pathological study and immunohistochemistry profile of the tumor was reported as benign schwannoma.

Conclusion:

This report indicates that benign schwannoma can be accompanied by bloody pleural effusion and it also emphasizes the role of immunohistochemistry in the diagnosis of biopsy specimen of spindle cell lesions.

Histological and molecular features of solitary fibrous tumor of the extremities: clinical correlation

Solitary fibrous tumor is a rare mesenchymal neoplasm that exhibits a broad spectrum of biological behaviors. Few studies relative to clinical-pathologic features and predictive factors have been reported, all involving a mixed population of tumors occurring at different anatomic sites. In this study, we described a cohort of 41 patients with solitary fibrous tumor of the extremities and evaluated the prognostic role of clinical and histological features, presence of C228T and C250T mutations at the TERT promoter region, and NAB2-STAT6 fusion variants. Patients were stratified according to the latest risk stratification model proposed by Demicco. The two patients with metastasis at presentation were in the high-risk group; the one with metastasis after surgery was classified in the intermediate-risk group. TERT promoter mutations were detected in 9 out of 38 DNA available. All patients with metastasis were characterized by a TERT promoter mutation. TERT promoter mutation was associated with mitoses > 4 per high-power field (p = 0.001), necrosis (p = 0.049), and size > 10 cm (p = 0.031). NAB2-STAT6 fusion variants were detected in 27 out of 41 cases without any prognostic value. In conclusion, we confirmed that the patients with solitary fibrous tumor of the limbs have a better prognosis than other solitary fibrous tumors, with a very low percentage of metastatic events. Besides, our data support an association between TERT promoter mutations and histologically malignant features, suggesting a possible molecular role in stratifying patients into intermediate- to high-risk tumor.

Extremely rare case of intravascular solitary fibrous tumour in the inferior vena cava with review of the literature

BACKGROUND

Solitary fibrous tumour (SFT) is a mesenchymal tumour of fibroblastic type, and it develops in almost any part of the human body. However, according to previous studies, the occurrence of intravascular SFTs is extremely rare.

CASE PRESENTATION

We reported a case of intravascular SFT in a 67-year-old woman who has been experiencing swelling and pain in the right leg for 2 months. Computed tomography venography scan revealed a well-defined mass obstructing the inferior vena cava (IVC). Surgical resection was performed, and histopathologic and immunohistochemical results were consistent with SFT. Further, next-generation sequencing (NGS) analysis was performed, and results revealed two tumour-related gene mutations (deletion of PMS2 and variation of ESR1 [L536P]). The patient did not receive any adjuvant therapy, and no signs of tumour progression were observed during the 6-month follow-up.

CONCLUSION

To the best of our knowledge, this study first presented about SFT arising from the IVC and carried out an NGS analysis to validate the molecular mechanism of such condition.

Molecular changes in solitary fibrous tumor progression

Abstract

Solitary fibrous tumors (SFTs) are NAB2-STAT6 fusion-associated neoplasms. There are several subtypes of NAB2-STAT6 fusions, but their clinical significances are still unclear. Moreover, the mechanisms of malignant progression are also poorly understood. In this study, using 91 SFT cases, we examined whether fusion variants are associated with clinicopathological parameters and also investigated the molecular mechanism of malignant transformation using whole-exome sequencing. We detected variant 1b (NAB2ex4-STAT6ex2) in 51/91 (56%) cases and variants 2a/2b (NAB2ex6-STAT6ex16/17) in 17/91 (19%) cases. The NAB2-STAT6 fusion variant types were significantly associated with their primary site (P < 0.001). In addition, a TERT promoter mutation was detected in 7/73 (10%) cases, and it showed a significant association with malignant SFTs (P = 0.003). To identify molecular changes during malignant progression, we selected an index patient to obtain parallel tissue samples from the primary and metastatic tumors. In the metastatic tissue, 10 unique molecular alterations, including those in TP53 and APAF1, were detected. In vitro functional experiments showed that APAF1 depletion increased the tumor potency of cells expressing NAB2-STAT6 fusion protein under treatment with staurosporine. We found that TP53 immunopositivity (P = 0.006) and loss of APAF1 immunoreactivity (P < 0.001) were significantly associated with malignant SFTs. Our study suggests that dysfunction of TP53 and APAF1 leads to impaired apoptotic function, and eventually contributes toward malignant SFT transformation.

Key messages

We firstly found that the TERT promoter mutation was strongly associated with malignant SFTs (P = 0.003) and the representative 1b (NAB2ex4-STAT6ex2) or 2a (NAB2ex6-STAT6ex16) fusion variants similarly contribute to tumorigenicity.

We also found that TP53 immunopositivity (P = 0.006) and loss of APAF1 immunoreactivity (P < 0.001) were significantly associated with malignant SFTs.

Our study suggests that dysfunction of TP53 and APAF1 leads to impaired apoptotic function, and eventually contributes toward malignant SFT transformation.

Electronic supplementary material

The online version of this article (10.1007/s00109-019-01815-8) contains supplementary material, which is available to authorized users.

Solitary fibrous tumour of the sigmoid colon mesentery

Solitary fibrous tumours (SFTs) are rare tumours arising from mesenchymal tissues. Despite of their more frequent occurrence in the pleura, SFT can present anywhere in the body. Only a few cases have been described arising from the mesentery. Most tumours have a benign nature; however, up to 20% of them can spread, most commonly to liver, lung and bone. Surgical excision including all surrounding tissues remains the treatment of choice; however, there is no consensus regarding the need for adjuvant therapies. We present a 79-year-old man with abdominal pain who was found to have a SFT in the mesentery of the sigmoid colon, treated with en bloc resection. A multidisciplinary team including surgeons, medical and radiation oncologists is recommended in the care of these patients.

Recurrent Sinonasal CD34-Negative Malignant Solitary Fibrous Tumor Diagnosed on STAT6 Immunohistochemistry and NAB2-STAT6 Fusion

A spectrum of mesenchymal neoplasms occur in the sinonasal region. One of these is solitary fibrous tumor (SFT), a translocation-associated neoplasm characterized by NAB2-STAT6 gene fusion. Sinonasal SFTs characteristically display CD34 immunopositivity, which aids in diagnosis. However, a small proportion of SFTs may be negative for CD34, making diagnosis difficult. The availability of STAT6 immunohistochemistry (IHC) has helped to overcome this. Malignant SFTs, characterized by increased cellularity and mitoses > 4 per ten high power fields, are extremely unusual in the sinonasal region, with only ten such cases reported to date. We report a case of a CD34-negative malignant SFT that was diagnosed using STAT6 IHC and confirmed by demonstrating NAB2 ex 4-STAT6 ex 2 fusion, and recurred 8 months after complete excision, to highlight the aggressive nature of this tumor.

Surgical treatment of primary solitary fibrous tumors involving the pelvic ring

The surgical treatment of primary solitary fibrous tumors (SFT) involving the pelvic ring has not been reported previously. In this study, we aimed to evaluate the efficacy of surgical treatment for this disease. From 2009 to 2015, 13 patients underwent tumor resection at our hospital, with an average age of 49.5 years (27–68 years). Four patients underwent en bloc resection, and 9 patients underwent piecemeal resections. A Chi-square test was used to compare the postoperative recurrence rates between the en bloc resection and the piecemeal resection groups (p = 0.68), and no significant difference was found between the benign and malignant solitary fibrous tumor groups (p = 0.44). The 5-year survival rate of the patients in this study was 83.3%, and the 5-year progression-free survival rate was 63.5%. The progression-free survival rate was not significantly different between the en bloc resection and piecemeal resection groups (p = 0.97). Piecemeal resection can also achieve acceptable local control, particularly for patients with sacral tumors, as they may achieve even better postoperative function with sacral nerve preservation. Recurrence and metastasis occur relatively late in the course of this disease. Therefore, long-term follow-up is required.

Extraskeletal Mesenchymal Chondrosarcoma

Extraskeletal mesenchymal chondrosarcoma is a rare soft tissue sarcoma arising from soft tissues, mainly of the lower extremities, meninges, and orbits. It usually presents during the second to third decades of life, and has a slight predominance in females. Histologically, it has a typical biphasic pattern comprising small cells and islands of hyaline cartilage. It can pose a diagnostic challenge in small biopsy specimens where 1 of the 2 components can be absent. The prognosis is extremely variable; survival varies depending on the location of the tumor.

Subperiosteal fibroma of the orbit

Fibromas are benign, well-circumscribed tumors that are characterized as spindle-cell lesions with interlacing fibrous stroma. Here, we describe the clinical presentation, management, and outcome of a patient with an orbital fibroma. To our knowledge, this is the second case report of a biopsy-proven subperiosteal orbital fibroma to date.

Biphenotypic Sinonasal Sarcoma: A Review and Update

Context.—

Biphenotypic sinonasal sarcoma (BSNS) is a rare, slow-growing soft tissue sarcoma of the sinonasal tract, typically presenting with nonspecific obstructive nasal symptoms. Although recurrences are common, no metastases have been reported, and only 1 patient has died of disease thus far. It characteristically demonstrates rearrangements of PAX3 with multiple fusion partners, the most common of which is MAML3.

Objectives.—

To highlight the most important diagnostic features, including morphologic, immunohistochemical, and molecular findings, and to provide comparisons to other entities in the differential diagnosis. We also aim to provide a summary of the clinical features and outcomes in cases reported to date.

Data Sources.—

Recently published literature encompassing BSNS and its synonym, low-grade sinonasal sarcoma with neural and myogenic differentiation.

Conclusions.—

BSNS is a sinonasal tumor that is important to recognize because its biologic behavior differs from most of the entities in the differential diagnosis. The diagnosis can typically be rendered through a combination of morphology, immunohistochemical stains, and ancillary testing for characteristic PAX3 rearrangements.

High p16 Expression Is Associated with Malignancy and Shorter Disease-Free Survival Time in Solitary Fibrous Tumor/Hemangiopericytoma

Objective  Solitary fibrous tumors (SFT) and hemangiopericytomas (HPC) are now classified along a single spectrum of fibroblastic mesenchymal tumors with NAB2-STAT6 fusion. This fusion acts as a driver mutation that constitutively activates EGR1, which is known to be involved in the p16 pathway. Overexpression of p16 is associated with malignancy and worse prognosis in multiple mesenchymal tumors. The authors sought to investigate p16 immunoexpression in association with malignancy and prognosis of SFT/HPC tumors. Design  Twenty-three SFT/HPC tumors (central nervous system [CNS]: 12, non CNS: 11) diagnosed at our institution from 2002 to 2016 were assigned into 3 grades. Data from microarray immunohistochemistry for STAT6, synaptophysin, CD56, chromogranin, SST2A, EGR1, Ki67, and p16, grade and survival were analyzed. Results  CNS SFT/HPCs tend to be malignant (grade 3; 67 vs. 18%, p  = 0.036) and more likely to express synaptophysin (33 vs. 0%, p  = 0.035) than non CNS tumors. Overexpression of p16 (immunopositivity ≥ 50% tumor cells) was associated with malignant (grade 3) tumors, and has a sensitivity of 70% (7/10), and a specificity of 77% (10/13), as a predictive marker for malignancy. SFT/HPC patients with low p16 expression demonstrated significantly longer disease-free survival time (median survival > 113 months) than those with high p16 expression (median survival = 30 months, p  = 0.045). Conclusions  SFT/HPCs in the CNS are more likely to be malignant than the tumors in other sites. High p16 expression is also associated with malignancy and shorter disease-free survival time in SFT/HPC tumors in our study cohort. Clinically, p16 overexpression can be used as predictive marker for malignancy and prognosis and a possible therapeutic target.

Malignant Solitary Fibrous Tumor of the Humerus: A Case Report of an Extremely Rare Primary Bone Tumor

Solitary fibrous tumor (SFT) is a spindle-shaped cell neoplasm originally described in the pleura, but subsequently found in many anatomic sites. Only few cases of primary SFTs in the bone have been previously described in the literature. We present the case of an 86-year-old man with a 1-week history of pain in his left arm. Imaging studies demonstrated a well-defined osteolytic lesion in the proximal humerus measuring 6.1 cm in diameter. Sections showed a round to spindle-shaped cell neoplasm with prominent mitotic activity (28 mitoses per 10 high-power fields) and areas of necrosis, focally surrounding staghorn-shaped vessels. The tumor cells were positive for CD34, CD99, Bcl-2, and STAT6 and negative for smooth muscle actin, epithelial membrane antigen, and cytokeratin AE1/AE3. These findings were consistent with a malignant SFT involving the left humerus. Although extremely rare, SFT should be considered in the differential diagnosis of primary bone tumors. This is the first case report of a primary SFT in a long bone with malignant histological features.