Efficacy and toxicity of photon, proton, and carbon ion radiotherapy in the treatment of intracranial solitary fibrous tumor/hemangiopericytoma.

BACKGROUND: Solitary fibrous tumors (SFT) of the central nervous system are rare and treatment options are not well established. The aim of this study was to evaluate the clinical outcomes of radiotherapy (RT) and re-radiotherapy (re-RT) for de novo intracranial SFT and recurrent intracranial SFT. METHODS: This retrospective study analyzed efficacy and toxicity of different RT modalities in patients who received radiotherapy (RT) for intracranial SFT at Heidelberg University Hospital between 2000 and 2020 following initial surgery after de novo diagnosis ("primary group"). We further analyzed the patients of this cohort who suffered from tumor recurrence and received re-RT at our institution ("re-irradiation (re-RT) group"). Median follow-up period was 54.0 months (0-282) in the primary group and 20.5 months (0-72) in the re-RT group. RT modalities included 3D-conformal RT (3D-CRT), intensity-modulated RT (IMRT), stereotactic radiosurgery (SRS), proton RT, and carbon-ion RT (C12-RT). Response rates were analyzed according to RECIST 1.1 criteria. RESULTS: While the primary group consisted of 34 patients (f: 16; m:18), the re-RT group included 12 patients (f: 9; m: 3). Overall response rate (ORR) for the primary group was 38.3% (N = 11), with 32.4% (N = 11) complete remissions (CR) and 5.9% (N = 2) partial remissions (PR). Stable disease (SD) was confirmed in 5.9% (N = 2), while 41.2% (N = 14) experienced progressive disease (PD). 14% (N = 5) were lost to follow up. The re-RT group had 25.0% CR and 17.0% PR with 58.0% PD. The 1-, 3-, and 5-year progression-free survival rates were 100%, 96%, and 86%, respectively, in the primary group, and 81%, 14%, and 14%, respectively, in the re-RT group. Particle irradiation (N = 11) was associated with a lower likelihood of developing a recurrence in the primary setting than photon therapy (N = 18) (OR = 0.038; p = 0.002), as well as doses ≥ 60.0 Gy (N = 15) versus < 60.0 Gy (N = 14) (OR = 0.145; p = 0.027). Risk for tumor recurrence was higher for women than for men (OR = 8.07; p = 0.014) with men having a median PFS of 136.3 months, compared to women with 66.2 months. CONCLUSION: The data suggests RT as an effective treatment option for intracranial SFT, with high LPFS and PFS rates. Radiation doses ≥ 60 Gy could be associated with lower tumor recurrence. Particle therapy may be associated with a lower risk of recurrence in the primary setting, likely due to the feasibility of higher RT-dose application.

Endobronchial solitary fibrous tumors: An enigma for diagnosis.

Solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms constituting less than 2% of all soft tissue tumors. They typically originate in the thoracic cavity, mainly in the pleura, but can also occur in other various sites such as lung parenchyma, pericardium, and bronchus. In this study, a 49-year-old non-smoking female with a history of allergies presented to our pulmonary clinic with a chronic cough. An explorative bronchoscopy revealed an intrabronchial mass in the left superior bronchi, and a 68 Ga-DOTATOC positron emission computed tomography suggested a carcinoid tumor. Subsequent pulmonary segmentectomy unveiled a well-circumscribed polypoid lesion diagnosed as a low-grade bronchus SFT through histopathological and immunohistochemical assessments. The patient was asymptomatic after surgical excision and showed no other lesion during the 6-month follow-up. The endobronchial location of SFT is uncommon, with only a few reported cases in the literature, underscoring the necessity of considering various differential diagnoses, including carcinoid, mucoepidermoid carcinoma, endobronchial pleomorphic adenoma, hamartoma, leiomyoma, and metastasis, depending on location and imaging features. This report underscores the importance of careful histological and immunohistochemical evaluation in understanding and appropriately stratifying the risk associated with polypoid lesions.

Conditional survival analysis and dynamic survival prediction for intracranial solitary-fibrous tumor/hemangiopericytoma.

BACKGROUND: As the form of World Health Organization Central Nervous System (WHO CNS) tumor classifications is updated, there is a lack of research on outcomes for intracranial combined solitary-fibrous tumor and hemangiopericytoma (SFT/HPC). This study aimed to explore conditional survival (CS) pattern and develop a survival prediction tool for intracranial SFT/HPC patients. METHODS: Data of intracranial SFT/HPC patients was gathered from the Surveillance, Epidemiology, and End Results (SEER) program of the National Cancer Institute. The patients were split into training and validation groups at a 7:3 ratio for our analysis. CS is defined as the likelihood of surviving for a specified period of time (y years), given that the patient has survived x years after initial diagnosis. Then, we used this definition of CS to analyze the intracranial SFT/HPC patients. The least absolute shrinkage and selection operator (LASSO) regression and best subset regression (BSR) were employed to identify predictive factors. The Multivariate Cox regression analysis was applied to establish a novel CS-based nomogram, and a risk stratification system was developed using this model. RESULTS: From the SEER database, 401 patients who were diagnosed with intracranial SFT/HPC between 2000 and 2019 were identified. Among them, 280 were included in the training group and 121 were included in the internal validation group for analysis. Our study revealed that in intracranial SFT/HPC, 5-year survival rates saw significant improvement ranging from 78% at initial diagnosis to rates of 83%, 87%, 90%, and 95% with each successive year after surviving for 1-4 years. The LASSO regression and BSR identified patient age, tumor behavior, surgery and radiotherapy as predictors of CS-based nomogram development. A risk stratification system was also successfully constructed to facilitate the identification of high-risk patients. CONCLUSION: The CS pattern of intracranial SFT/HPC patients was outlined, revealing a notable improvement in 5-year survival rates after an added period of survival. Our newly-established CS-based nomogram and risk stratification system can provide a real-time dynamic survival estimation and facilitate the identification of high-risk patients, allowing clinicians to better guide treatment decision for these patients.

Ultrastructural differences between synovial sarcoma and solitary fibrous tumor: comparative study in adult patients from the National Cancer Institute of Mexico.

Synovial sarcoma (SS) and solitary fibrous tumor (SFT) are entities with considerable morphological and immunohistochemical similarities that sometimes show a non-confirmatory profile (TLE1 negative, CD34 and focal or negative STAT6 and lack of specific fusion IHC markers), in which the utility ultrastructure is unknown. A cross-sectional, retrospective, analytical, nonexperimental study was carried out by the Department of Pathology of the National Cancer Institute of Mexico (INCan) e from January 1, 2009 to December 31, 2018. With 17 SFT cases with diffuse or focal CD34 and STAT6 positivity and 18 cases of SS with positive FISH molecular test t(X:18) breakapart were studied by electron microscopy of fresh glutaraldehyde fixed or paraffin-embedded tissue. The ultrastructural findings with a significant difference present in the SS were tandem tight junctions, desmosomes and abundance of dilated rough endoplasmic reticulum (RER) cisternae (p < 0.001, 0.003, and 0.001, respectively); while in the (SFT) the presence of abundant glycogen, basal lamina, long and slender cytoplasmic processes, pinocytic vesicles, hemidesmosomes, and/or dense plaques, collagen skein, and microvilli-like buds (p = 0.028, 0.005, and <0.001 for the last five). We then infer that the five distinctive markers of the SFT are the collagen skeins intermingled with cellular processes in a shape of "squid can," and the pinocytic vesicles as they were not observed in any case of SS. Conversely, tandem junctions were not found in any SFT case. Although the presence of multivesicular buds in the SFT was not significant, it had not been previously described.

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.

A case of fat-forming solitary fibrous tumor that is prone to be confused with liposarcoma.

Fat-forming solitary fibrous tumor is a rare and specific subtype of solitary fibrous tumor. In this case, a mass of 8.3 cm in diameter was found in a 59-year-old male patient's right retroperitoneum, as revealed by abdominal contrast-enhanced computed tomography (CT) images. The tumor exhibited a well-circumscribed nature and histological features characterized by a combination of hemangiopericytomatous vasculature and mature adipose tissue, comprising around 70% of the total tumor composition. Immunohistochemistry staining revealed diffuse positive expression of STAT6 and CD34 in the tumor cells. Based on these findings, the final diagnosis was determined to be a fat-forming solitary fibrous tumor located in the retroperitoneum. It is important to consider other potential differential diagnoses, including angiomyolipoma, dedifferentiated liposarcoma, spindle cell lipoma, and atypical lipomatous tumor/well-differentiated liposarcoma.

Establishment and characterization of a patient-derived solitary fibrous tumor/hemangiopericytoma cell line model.

Solitary fibrous tumor/Hemangiopericytoma (SFT/HPC) is a rare subtype of soft tissue sarcoma harboring NAB2-STAT6 gene fusions. Mechanistic studies and therapeutic development on SFT/HPC are impeded by scarcity and lack of system models. In this study, we established and characterized a novel SFT/HPC patient-derived cell line (PDC), SFT-S1, and screened for potential drug candidates that could be repurposed for the treatment of SFT/HPC. Immunohistochemistry profiles of the PDC was consistent with the patient's tumor sample (CD99+/CD34+/desmin-). RNA sequencing, followed by Sanger sequencing confirmed the pathognomonic NAB2exon3-STAT6exon18 fusion in both the PDC and the original tumor. Transcriptomic data showed strong enrichment for oncogenic pathways (epithelial-mesenchymal transition, FGF, EGR1 and TGFß signaling pathways) in the tumor. Whole genome sequencing identified potentially pathogenic somatic variants such as MAGEA10 and ABCA2. Among a panel of 14 targeted agents screened, dasatinib was identified to be the most potent small molecule inhibitor against the PDC (IC50, 473 nM), followed by osimertinib (IC50, 730 nM) and sunitinib (IC50, 1765 nM). Methylation profiling of the tumor suggests that this specific variant of SFT/HPC could lead to genome-wide hypomethylation. In conclusion, we established a novel PDC model of SFT/HPC with comprehensive characterization of its genomic, epigenomic and transcriptomic landscape, which can facilitate future preclinical studies of SFT/HPC, such as in vitro drug screening and in vivo drug testing.

Clinical outcomes of solitary fibrous tumors and hemangiopericytomas and risk factors related to recurrence and survival based on the 2021 WHO classification of central nervous system tumors.

OBJECTIVE: The authors aimed to explore the clinical outcomes and risk factors related to recurrence of and survival from solitary fibrous tumors (SFTs) and hemangiopericytomas (HPCs) that were reclassified according to the 2021 WHO classification of central nervous system (CNS) tumors. METHODS: The authors retrospectively collected and analyzed the clinical and pathological data of SFTs and HPCs recorded from January 2007 to December 2021. Two neuropathologists reassessed pathological slides and regraded specimens on the basis of the 2021 WHO classification. The prognostic factors related to progression-free survival (PFS) and overall survival (OS) were statistically assessed with univariate and multivariate Cox regression analyses. RESULTS: A total of 146 patients (74 men and 72 women, mean ± SD [range] age 46.1 ± 14.3 [3-78] years) were reviewed, and 86, 35, and 25 patients were reclassified as having grade 1, 2, and 3 SFTs on the basis of the 2021 WHO classification, respectively. The median PFS and OS of the patients with WHO grade 1 SFT were 105 months and 199 months after initial diagnosis; for patients with WHO grade 2 SFT, 77 months and 145 months; and for patients with WHO grade 3 SFT, 44 months and 112 months, respectively. Of the entire cohort, 61 patients experienced local recurrence and 31 died, of whom 27 (87.1%) died of SFT and relevant complications. Ten patients had extracranial metastasis. In multivariate Cox regression analysis, subtotal resection (STR) (HR 4.648, 95% CI 2.601-8.304, p < 0.001), tumor located in the parasagittal or parafalx region (HR 2.105, 95% CI 1.099-4.033, p = 0.025), tumor in the vertebrae (HR 3.352, 95% CI 1.228-9.148, p = 0.018), WHO grade 2 SFT (HR 2.579, 95% CI 1.343-4.953, p = 0.004), and WHO grade 3 SFT (HR 5.814, 95% CI 2.887-11.712, p < 0.001) were significantly associated with shortened PFS, whereas STR (HR 3.217, 95% CI 1.435-7.210, p = 0.005) and WHO grade 3 SFT (HR 3.433, 95% CI 1.324-8.901, p = 0.011) were significantly associated with shortened OS. In univariate analyses, patients who received adjuvant radiotherapy (RT) after STR had longer PFS than patients who did not receive RT. CONCLUSIONS: The 2021 WHO classification of CNS tumors better predicted malignancy with different pathological grades, and in particular WHO grade 3 SFT had worse prognosis. Gross-total resection (GTR) can significantly prolong PFS and OS and should serve as the most important treatment method. Adjuvant RT was helpful for patients who underwent STR but not for patients who underwent GTR.

Historical Misdiagnosis of Recurrent Solitary Fibroma Tumor of the Prostate: A Cases Report and Current Evidence.

BACKGROUND: Solitary fibrous tumors (SFTs) manifest in various anatomical locations but are seldom encountered in the prostate. Despite their rare occurrence in this region, SFTs demonstrate a marked propensity for recurrence. This study elucidates a case of recurrent prostate SFT, previously misdiagnosed, and delineates the salient features and diagnostic criteria pertaining for SFTs. METHODS: Through a meticulous analysis of the patient's antecedent medical records and corroborative diagnostic evaluations, we hypothesized that the presenting pathology was indicative of a prostate SFT. In order to substantiate this supposition, we re-examined archival pathological specimens from the patient. The ensuing pathological assessment validated our conjecture. To address the recurrence, we conducted an open surgical procedure to excise the tumor. Subsequent postoperative pathological evaluations further corroborated the diagnosis of prostate SFT. RESULTS: Upon re-evaluation of the patient's earlier pathological specimens, we discerned that what had been previously classified as a "seminal vesicle tumor" was, in fact, a prostate SFT. During the surgical intervention, it was observed that the prostatic tumor had invaded the bladder, yet there was no seminal vesicle involvement. The tumor dimensions were approximately 7 × 5 × 4 cm, and the margin between the tumor and the surgical resection edge was less than 0.1 cm. The postoperative histological analysis confirmed the diagnosis of recurrent prostate SFT, substantiating our designation of the patient's condition as such. A year-long follow-up revealed no conspicuous signs of tumor recurrence. CONCLUSIONS: Therapeutic intervention for prostate SFT is predominantly surgical. However, given the tumor's marked predisposition for recurrence, the specific mechanisms underlying its etiology and pathogenesis remain enigmatic. Hence, a comprehensive understanding of its pathogenic and recurrent characteristics, coupled with regular postoperative surveillance, is imperative for efficacious treatment and prevention of prostate SFT.

Malignant recurrent orbital solitary fibrous tumor.

Solitary fibrous tumor (SFT) is a rare mesenchymal tumor of fibroblastic origin commonly occurring in pleura. It can occur at many extrapleural sites but is rare in orbit. Most cases are benign and recurrence is not unusual in the head and neck and orbit and is usually due to incomplete surgical excision. However, malignant transformation (MT) in orbital SFT is extremely unusual. We present a case of orbital SFT in adult male who developed recurrence with MT eight years after initial surgical excision. He underwent left orbital exenteration. The recurrent tumor revealed features of malignancy with areas exhibiting morphology typical of SFT. The immunochemistry confirmed the diagnosis of SFT with MT. The patient was given adjuvant radiation and was disease free for the last 18 months. Identification of malignancy in orbital SFT is important for the patient to receive appropriate postoperative treatment, as seen in the present case.

Metastasis of solitary fibrous tumor to the parotid gland diagnosed on aspiration cytology supplemented with immunocytochemistry.

Solitary fibrous tumor (SFT) can occur in varied anatomic locations, most commonly being the extremities-superficial and deep soft tissues, followed by retroperitoneum, visceral organs, and the bone. Head and neck region may harbor a few with a predilection for the orbit and sinonasal tract, oral cavity, and rarely the salivary glands. The parotid gland is most involved among all salivary glands. Overall, SFT in salivary glands is rare and mostly seen as a primary tumor. The occurrence of metastasis to the parotid gland is exceedingly uncommon. We present cytological findings of SFT, metastatic to the parotid gland in a young 31-year-old lady where the diagnosis was confirmed with the help of immunocytochemistry (ICC) on the cell block. The smears were highly cellular and showed predominantly discrete round to oval tumor cells with mild pleomorphism, coarse chromatin, inconspicuous nucleoli, and scanty cytoplasm. Mitosis and focal areas of necrosis were noted. Lymphoglandular bodies were absent ruling out a non-Hodgkin lymphoma. Features were of a poorly differentiated malignant tumor with differentials being sarcoma, myoepithelial carcinoma, and carcinoma ex-pleomorphic adenoma. A panel of ICC was done and positivity for signal transducer and activator of transcription 6 (STAT6) helped in clinching the correct diagnosis of SFT.

Massive solitary fibrous intrathoracic tumor presented as primary lung cancer.

Solitary fibrous tumours (SFT) are rare soft tissue tumours with a primarily benign course. Complete surgical resection is the mainstay treatment. In this case report, a 75-year-old man had a massive intrathoracic SFT which was subsequently surgically resected without complications. Although the clinical presentation and CT features of these tumours can mimic lung cancer, the clinical course is significantly more favourable. Diagnostic examination and surgical treatment of intrathoracic SFT should be considered even in patients with increased post-operative risk.

Solitary fibrous tumor: Two cases report with a focus on the differential diagnosis / Tumor Fibroso Solitário: Relato de dois casos com foco no diagnóstico diferencial

Solitary fibrous tumor (SFT) is a neoplasm of fibroblastic/myofibroblastic origin with intermediate biological behavior. We report here two cases of SFT affecting an unusual anatomical site in 58-year-old and 40-year-old female patients and discuss the differential diagnosis of this lesion. In case 01, the lesion showed the clinical appearance of an asymptomatic "blister" with normal color, rubbery consistency, measuring 0.3 cm, and affected the lower lip; while in case 02, a symptomatic red nodular lesion with a soft consistency and measuring 0.5 cm affected the floor of the mouth. Excisional biopsies were performed. Microscopically, two well-delimited benign neoplasms were observed, exhibiting the proliferation of ovoid to spindle-shaped mesenchymal cells, vascular spaces with staghorn arrangement, and the absence of mitosis figures. Immunohistochemistry was performed in case 01 to assist in the diagnosis. Weak and diffuse immunostaining was observed for α-SMA and intense and diffuse immunopositivity for Bcl-2 and CD34. Based on histopathological and immunohistochemical features, a diagnosis of SFT was rendered in both cases. The low occurrence and nonspecific clinical features of oral SFT may make its clinical diagnosis difficult. Also, morphological and immunohistochemical are essential for differential diagnosis with other mesenchymal neoplasms.(AU)

O tumor fibroso solitário (TFS) é uma neoplasia de origem fibroblástica/miofibroblastica com comportamento biológico intermediário. Nesse artigo relatamos dois casos de TFS afetando sítios anatômicos incomuns em pacientes do sexo feminino de 58 anos e 40 anos e discutir os seus diagnósticos. No caso 01 clinicamente a lesão apresentou um aspecto de "bolha" assintomática, coloração normal da mucosa, consistência borrachoide medindo 0,3 cm, em região de lábio inferior, enquanto que no caso 02, como uma lesão sintomática, vermelha, nodular com consistência mole e medindo 0,5 cm afetando o assoalho bucal. As biópsias excecionais foram realizadas. Microscopicamente, observamos duas lesões neoplásicas bem delimitadas exibindo uma proliferação de células mesenquimais variando de ovoides a fusiformes, vasos sanguíneos em formato de "chifre de veado", com ausência de figuras de mitoses. No caso 01 foi realizado análise imuno-histoquímica para auxiliar no diagnóstico. Foi observado uma marcação fraca e difusa de α-SMA e uma intensa e difusa imunopositividade para o Bcl-2 e CD34.Baseado nos achados histopatológicos e imuno-histoquímicos o diagnóstico de TFS foi estabelecido em ambos os casos. A baixa ocorrência e os achados clínicos inespecíficos do TFS oral podem dificultar o diagnóstico clínico. Além disso, as análises morfológicas e imuno-histoquimicas são essenciais para realização do diagnóstico diferencial com outras neoplasias mesenquimais.(AU)_

Solitary fibrous tumor of the tympanic membrane a case report and systematic review.

PURPOSE: Otological solitary fibrous tumors (SFT) are exceedingly rare. There has been no report of SFT localized to the tympanic membrane. To report on a rare case of solitary fibrous tumor of the tympanic membrane and provide systematic review of the literature pertaining the demographics and pathophysiology of otological SFTs. MATERIALS AND METHODS: This review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) reporting guidelines. A search of PubMed, Google Scholar, and Cochrane Library databases was conducted to identify English-language articles on solitary fibrous tumor of the ear, with emphasis on the tympanic membrane, published through 2022. A combination of Boolean operators and the following keywords were included in the search strategy: "solitary fibrous tumor", "tympanic membrane", and "ear". RESULTS: We found 12 previous reports of solitary fibrous tumors of the ears, none of which were in the tympanic membrane. All cases underwent surgical resection, with or without perioperative embolization, or radiation. There was no evidence of distant diseases in any cases. CONCLUSIONS: In the context of a tympanic membrane mass with associated pain and hearing loss, our findings suggest that solitary fibrous tumor should be included in the differential diagnosis.

A multicentre retrospective study on extra-thoracic solitary fibrous tumour: preoperative MRI findings predict intraoperative findings and postoperative prognosis.

OBJECTIVE: The present study investigated the relationships between the preoperative and operative findings of solitary fibrous tumour (SFT) and between preoperative findings and prognosis. METHODS: We reviewed 50 SFT patients treated at our musculoskeletal oncology hospital group. We analyzed preoperative clinical findings, particularly MRI imaging findings, and intraoperative information as well as the relationship between preoperative findings and outcomes. RESULTS: Mean age was 48.9 years and the mean follow-up was 51.8 months. Prior to surgery, needle biopsy was performed on 27 patients and open biopsy on 14. T2-weighted images showed a high signal intensity in 24 patients and heterogeneous signal intensity in 20. Tumours had polylobular contours in 17 patients and smooth and round contours in 27. Collateral feeding vessels were detected in 22 patients. Gd-enhanced MRI was performed on 23 patients, and showed 15 with homogeneous enhancement and 8 with heterogeneous enhancement. Surgical times were significantly longer in patients with a retroperitoneal origin, a tumour of 10 cm or more, and polylobular-type tumours. Intraoperative blood loss was significantly greater in patients with a retroperitoneal origin and heterogeneous Gd-MRI-enhanced tumours. In histopathological evaluations, surgical margins were positive in 12 patients. Local recurrence was observed in one patient. Distant metastasis was noted in eight patients, four of whom had pulmonary metastases. Positive surgical margins were more common in polylobular-type tumours. Distant metastases were more likely to appear in patients with observable collateral feeding vessels and heterogeneous Gd-MRI enhancement. CONCLUSION: The present results suggest that preoperative clinical findings in SFT patients predict longer surgical times and the risk of increased intraoperative blood loss. Moreover, the risk of a positive surgical margin and postoperative distant metastases may be predicted based on preoperative MRI.

Long-Term Surgical Outcome for Orbital Solitary Fibrous Tumors.

PURPOSE: To report long-term outcomes after surgery for orbital solitary fibrous tumors. METHODS: Retrospective review of patients with orbital solitary fibrous tumor, first seen between 1971 and 2022. Primary excisions were grouped as (A) surgically intact, (B) macroscopic, but with cell spillage, or (C) known incomplete excision. RESULTS: Fifty-nine patients (31 female; 53%) presented at a mean age of 43.0 years (19-82 years), with 5 patients (8.5%) having malignant solitary fibrous tumors. Average follow up was 11.4 years (median 7.8; range 1-43 years). There were 28 of 59 (47%) group A patients with 1 of 28 (3%) having recurrence, 20 of 59 (34%) group B having 6 of 20 (30%) recurrences, and 11 of 59 (19%) group C with 9 of 11 (82%) recurrence ( p < 0.001 for recurrence rate). At a mean of 8.9 (range 1-23.6) years after initial treatment, continued local tumor growth was evident in 16 (27%) patients, with higher-grade recurrence in 3 of 14 (21%) cases. No patient had systemic disease at presentation, but 2 of 59 patients (3%) developed metastases at 22 and 30 years after first treatment. The 10-year progression-free survival was 94% (group A), 60% (group B), and 36% (group C). Tumor disruption or incomplete excision (groups B + C) carries the highest risk of tumor recurrence (hazard ratio 15.0; 95% confidence interval, 1.98-114; p = 0.009), with no correlation to tumor size or histology. CONCLUSIONS: Orbital solitary fibrous tumors have a low recurrence rate with surgically intact excision; piecemeal excision, capsular disruption, or known incomplete resection have a high recurrence rate, which can occur decades later. Baseline postoperative scans is recommended, together with long-term clinical and interval imaging.