Solitary fibrous tumor of the lung: diagnostic challenges and surgical management.

A rare case of a giant pulmonary solitary fibrous tumor: Diagnostic and therapeutic challenges in the absence of malignancy.

Late recurrence of renal solitary fibrous tumour in the contralateral kidney

Introduction- Solitary fibrous tumor (SFT) is a rare, ubiquitous mesenchymal tumor with a yearly incidence of one new case per million. It affects adults between the ages of 20 and 70 years. The metastatic risk is about 35-45%, including abdominal cavity (31%), limbs (29%), pleura (22%), trunk (11%), and other sites including the head and neck (7%). We present a unique case report of a 69-year-old with SFT that metastasized to infrequent anatomical sites. Case Presentation- A 69-year-old woman presented to the ER with syncope along with two episodes of vomiting. CT of the head and neck revealed bilateral carotid artery stenosis, which probably caused the syncope; it coincidentally revealed bilateral pulmonary nodules in the apical lungs. CT of the chest confirmed innumerable bilateral pulmonary nodules (Figure 1) across multilobar segments and a left lower lobe versus posterior mediastinal mass lesion. CT of the abdomen demonstrated a large, necrotic mass measuring 7.2 cm in the left lower lobe of the lung and a lesion in the left liver lobe, measuring about 2.3 cm in its largest diameter. The patient presented to pulmonology with dry cough, exertional dyspnea, decreased exercise tolerance, and unintentional weight loss. She was not a known smoker. PET scan showed multiple metabolically active lesions – 1) left lung base, 2) numerous pulmonary nodules, 3) a 2.6 cm right thyroid lobe nodule, and 4) left hepatic lobe mass. Specimen from CT-guided percutaneous left lung biopsy was positive for STAT6 and CD34 and negative for AE1/AE3, cytokeratin, CD31, S100, and desmin. Core biopsy was primarily hypocellular, with areas of hypercellularity consisting of short-spindled cells. Beta-catenin immunostaining showed a membranous expression pattern with no mitotic figures, consistent with a solitary fibrous tumor. Chest imaging showed growing pulmonary nodules in the background of worsening symptoms. Histopathology confirmed the spread of metastatic solitary fibrous tumor to the lungs, liver, thyroid, and left level IV lymph nodes. The patient was started on Pazopanib, a tyrosine kinase inhibitor associated with VEGFR, PDGFR, and Kit receptor. Her clinical course was complicated by prolonged hospitalization for pulmonary embolism, respiratory failure, and stroke, causing a significant decline in functional status and placement in a facility. Discussion- SFTs may be localized or metastatic. While surgical resection is the cornerstone for localized SFT, chemotherapy is used to tackle advanced disease. Our one-in-a-million case report underscores the importance of further research into treatment strategies to improve clinical outcomes.

Secondary hypertrophic osteoarthropathy associated with solitary fibrous tumor of the lung

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

59. Dedifferentiated solitary fibrous tumour arising from the bladder: A case report

Non-central nervous system hemangiopericytoma (HPC) and solitary fibrous tumor (SFT) are considered by pathologists as two variants of a single tumor entity now subsumed under the entity SFT. Recent detection of frequent NAB2-STAT6 fusions in both, HPC and SFT, provided additional support for this view. On the other hand, current neuropathological practice still distinguishes between HPC and SFT. The present study set out to identify genes involved in the formation of meningeal HPC. We performed exome sequencing and detected the NAB2-STAT6 fusion in DNA of 8/10 meningeal HPC thereby providing evidence of close relationship of these tumors with peripheral SFT. Due to the considerable effort required for exome sequencing, we sought to explore surrogate markers for the NAB2-STAT6 fusion protein. We adopted the Duolink proximity ligation assay and demonstrated the presence of NAB2-STAT6 fusion protein in 17/17 HPC and the absence in 15/15 meningiomas. More practical, presence of the NAB2-STAT6 fusion protein resulted in a strong nuclear signal in STAT6 immunohistochemistry. The nuclear reallocation of STAT6 was detected in 35/37 meningeal HPC and 25/25 meningeal SFT but not in 87 meningiomas representing the most important differential diagnosis. Tissues not harboring the NAB2-STAT6 fusion protein presented with nuclear expression of NAB2 and cytoplasmic expression of STAT6 proteins. In conclusion, we provide strong evidence for meningeal HPC and SFT to constitute variants of a single entity which is defined by NAB2-STAT6 fusion. In addition, we demonstrate that this fusion can be rapidly detected by STAT6 immunohistochemistry which shows a consistent nuclear reallocation. This immunohistochemical assay may prove valuable for the differentiation of HPC and SFT from other mesenchymal neoplasms.

Solitary fibrous tumor (SFT) is an uncommon fibroblastic neoplasm. Although histologic characteristics and frequent CD34 expression allow for an accurate diagnosis in the majority of SFT cases, a wide histologic spectrum and an occasional unexpected immunophenotype may pose diagnostic challenges. Molecular analyses have discovered that almost all SFTs harbor an NAB2-STAT6 fusion gene, which is considered specific to this tumor type. Recent studies have suggested that STAT6 immunohistochemistry is a reliable surrogate for detection of the fusion gene. Our aim was to validate these findings by examining a large number of SFT cases and a broad array of 30 different types of non-SFT tumors. A total of 49 SFTs with a range of histologic characteristics and 159 benign or malignant tumors that can mimic SFTs were retrieved and stained for STAT6. All 49 SFTs (100%) showed STAT6 expression that was restricted in the nucleus, mostly in a diffuse and strong manner, irrespective of the tumor sites and histologic patterns. The staining was uniform in most cases but was heterogenous in about 20% of the cases in which zonal staining attenuation was observed, likely reflecting variability in fixation or tissue ischemia. In contrast, only 4 non-SFT tumors (2.5%) exhibited weak nuclear STAT6 expression, whereas the remaining 155 cases showed no staining or often weak reactivity in both the cytoplasm and the nucleus. Therefore, nuclear STAT6 immunoreactivity is a highly sensitive and specific marker of SFTs and can be helpful when diagnosis is inconclusive by conventional methods.

Recurring Rare Liver Tumor Presenting With Hypoglycemia

This 49-year-old woman with a 1-year history of deteriorating quadriparesis visited our clinic in November 1999. She required a cane to walk and presented with a large elastic mass in the neck posteriorly. Neurological examination showed exaggerated deep tendon reflexes in the upper and lower extremities bilaterally as well as positive Hoffmann and Babinski reflexes bilaterally. Sensory disturbance and diffuse muscle weakness (Grades 2/5 on the right side and 4/5 on the left) below C-5 were also present. Magnetic resonance (MR) imaging revealed an 8� 5 � 8–cm extradural tumor (Fig. 1). Angiography demonstrated an intense hypervascular tumor fed by the bilateral ascending cervical and vertebral arteries. Following embolization, we resected the tumor, first separating the posterior extraspinal portion of the tumor in the muscular layer from surrounding tissues and excising it at the surface of the laminae, where severe bleeding was encountered. After hemostasis, we conducted a C2–5 laminectomy, and completely removed the tumor. The bilateral facet joints remained intact during laminectomy, making fusion unnecessary. The tumor had a gray pseudocapsule and was easily separated from the dura mater. Histological examination was compatible with a solitary fibrous tumor (Fig. 2). At 1-year follow-up examination, the patient suffered no neck pain or neurological deficits except for slightly exaggerated lower-extremity deep tendon reflexes. Radiography revealed no cervical instability or malalignment. No residual or recurrent tumor was found on MR imaging. Solitary fibrous tumors were first differentiated from diffuse mesothelioma by Klemperer and Rabin.4 These lesions are most commonly found in the visceral pleura but are considered to arise from mesenchymal rather than mesothelial tissue. Those occurring in the spinal canal are so rare that only 12 cases have been reported to date. 1–3,5,6 Of these, four harbored tumors in the cervical and thoracic spine and three in the lumbar spine. On the axial plane, tumors were intradural–extramedullary in seven, extradural in four, and intramedullary in one. Diagnosis of solitary fibrous tumors is based on characteristic pathological findings. Because CD34 staining, however, is also positive in other tumors such as hemangioma, fibroma, and epithelioma, the final diagnosis should be made on the basis of hematoxylin and eosin and CD34 staining together. Solitary fibrous tumors of the spine are usually benign, and marginal resection is considered to be sufficient. One case in which the tumor recurred after partial resection has been reported, indicating that complete resection and careful follow-up examination are mandatory. 2

Solitary fibrous tumor involving the pancreas: report of the cytologic features and first report of a primary pancreatic solitary fibrous tumor diagnosed by fine-needle aspiration biopsy

e23522 Background: Solitary fibrous tumors (SFTs) are fibroblastic tumors which carry a characteristic NAB2::STAT6 gene rearrangement. SFTs represent a heterogenous group that may arise in multiple locations and have variable risk of progression. Despite a consistent oncogenic driver, there is little biological data explaining this variability. Recently, the German Cancer Research Network (DKFZ) have modified their brain tumor methylation classifier for use in sarcomas. We subjected solitary fibrous tumors diagnosed at our institution to a validated, in-house sarcoma methylation array classifier modeled after that of the DKFZ in order to assess for differences in methylation patterns that may account for biological or clinical variances. Methods: Twenty-eight primary site SFTs from 2011-2021 were subjected to the sarcoma methylation classifier. Histologic diagnosis was confirmed by STAT6 immunohistochemistry or by the presence of the NAB2::STAT6 fusion. The methylation classifier was run on the Illumina iScan platform and the resulting IDAT files were analyzed via a custom bioinformatics pipeline. The sarcoma classifier was trained using the same samples and normalization strategies used by the DKFZ group and validated using the same publicly available samples. Results: Methylation data for each tumor was collected, given a classification score, and visualized by t-distributed stochastic neighbor embedding (t-SNE). We noted three distinct groups of SFTs on the t-SNE plot. Group 1 was comprised of all eight intracranial SFTs and were correctly classified as SFT (classifier score ≥0.9). Group 2 contained nine pleural-based tumors and one SFT each from the mediastinum and bladder wall. Classification was successful in only seven of eleven tumors. Group 3 SFTs predominantly arose in the soft tissues or bone (two pelvis, four extremity, and one mediastinum) and all failed accurate classification. Finally, two orbital SFTs stratified separately from all groups on t-SNE plot but did achieve an appropriate classification. There were no significant differences in grade or risk stratification among the three groups. Conclusions: Our preliminary data show differential clustering based on tumor location, suggesting biological differences between intracranial, pleural/visceral, and connective tissue locations. These results highlight the heterogeneity of these tumors and the inadequacy of the current methylation classification scheme for SFT. Future directions will include analysis of additional cases, gene expression patterns, and outcome data.

Solitary fibrous tumour (SFT) is uncommonly found in the salivary glands and is a rare group of spindle-cell tumours. A review of literature revealed only 40 reported cases of SFT of major salivary glands over a 15-year period from 2004 to 2018. SFTs of the salivary glands are usually benign, although rarely, can be aggressive and may sometimes recur after initial resection. Histology and Immunohistochemistry are the most important criteria to distinguish SFT from other head and neck tumours. SFTs strongly stain for CD34 and hence is the most frequently used stain for diagnosis. All reported SFT cases with available information on immunohistochemical stains were positive for CD34. Recently, immunohistochemistry for STAT6 has been introduced as a surrogate diagnostic marker for SFT that is highly sensitive and specific. We report a case of a 51-year-old Chinese gentleman who presents with a 3-month history of a left parotid tumour that required a subtotal parotidectomy for complete excision. It was diagnosed as SFT based on histology and immunohistochemical features. He was followed-up for 3 months post-operatively with no clinical evidence of recurrence. This case proposes that, although rare, SFT should be considered in the differential diagnosis of soft-tissue tumors in the major salivary glands. An awareness of this rare entity will help clinicians and pathologists better manage similar patients in the future.

Solitary fibrous tumor (SFT) is a rare spindle cell neoplasm showing fibroblastic differentiation, initially observed in the pleura, but now currently recognized to develop in any extrapleuric location 1,2. In the female genital tract, SFTs are extremely rare and have a predilection for the vulva, vagina and cervix 2,3. There are very few cases of ovarian SFTs having been reported in the literature. Malignant SFTs of the ovary are exceedingly rare neoplasms characterized by their mesenchymal origin and distinctive histopathological features. First identified as a separate entity in soft tissues, SFTs of the ovary represent a diagnostic and therapeutic challenge due to their rarity and overlapping characteristics with other ovarian neoplasms. These tumors are generally considered benign, but their malignant variants can exhibit aggressive behavior, including metastasis and recurrence. The pathogenesis of SFTs is associated with molecular abnormalities, particularly NAB2-STAT6 gene fusions 4, which play a crucial role in diagnosis and may have prognostic implications. Our case of ovarian malignant SFT showed an unusual pattern of dedifferentiation. The conventional SFT component displays a pattern less architecture, uniform fibroblastic morphology, prominent branching vessels, and is diffusely positive for CD34 and STAT6. However, there is an abrupt transition to a pleomorphic, high mitotic rate component with fascicular spindle cell morphology resembling a smooth muscle neoplasm. This dedifferentiated area is positive for SMA and desmin but negative for CD34 and STAT6 and includes focal ossification. Stains for MDM2, CDK4, and caldesmon are negative. The case is notable for its atypical progression, as most dedifferentiated SFTs transition directly from a benign-appearing SFT to a high-grade component without signs of malignancy in the conventional SFT region.

We aimed to report a case of orbital solitary fibrous tumour (SFT) in a child and to review the relevant literature. We describe an SFT in a 13-year-old boy with a 1-month history of painless proptosis in the left eye. Magnetic resonance imaging revealed a well circumscribed mass filling most of the left intraconal orbit. The lesion was excised and histopathological examination revealed a malignant SFT. Postoperative follow-up for 18 months was uneventful. Malignant SFT of the orbit should be included in the differential diagnosis of paediatric orbital tumours. Complete surgical excision remains the preferred method of management and the longterm prognosis is guarded.