Background
Solitary fibrous tumor (SFT) was first described in 1870 by Wagner[1] and further established in 1931 by Klemperer and Rabin as a pleural neoplasm.[2] The term hemangiopericytoma (HPC) was first used by Stout and Murray in 1942 to describe a distinct neoplasm of pericytic origin.[3] However, over time, the staghorn-branching vascular pattern representative of HPC was found to be present at least focally in 15% of all soft-tissue tumors and was more of a characteristic histopathologic pattern than a specific clinicopathologic entity.[4]
Today, the diagnosis of HPC is primarily reserved to neuropathologists. The term SFT is favored by soft-tissue pathologists to describe a rare, heterogeneous group of benign and malignant neoplasms along a morphologic continuum.[5]
Three classical clinical forms of SFT are recognized, as follows[5] :
Pleural SFT
Soft-tissue SFT - This variety occurs across a histopathologic spectrum; on one end, a fibrous form is characterized by hyalinized, thick-walled vessels with opened lumina and strong CD34 reactivity, and on the other, a cellular form, representing conventional HPC, has branching, thin-walled vessels and focal or absent CD34 reactivity[4]
Meningeal HPC
Lesions formerly known as HPC have been partitioned into three main groups, as follows:
The first group includes so-called true HPCs; these lesions show clear evidence of myoid and pericytic differentiation and include a subset of sinonasal HPC, subcutaneous infantile myofibromatosis or infantile HPC, and glomangiopericytoma or myopericytoma[4]
The second group includes various lesions with HPC-like features, which are sometimes miscategorized; most notably, the monophasic spindle cell or fibroblastic synovial sarcoma variant can be confused with HPC[6]
The third group includes conventional SFT, a fat-forming SFT or lipomatous HPC, and a giant-cell–rich variant of SFT or giant cell angiofibroma[4]
This article focuses on the cellular variant of conventional SFT, or what was previously termed conventional HPC.
Pathophysiology and Etiology
SFTs are tumors of mesenchymal origin that occur in the extremities. According to the updated classification of soft-tissue tumors published by the World Health Organization in 2013,[7] malignant forms of SFT are defined as hypercellular, mitotically active (>4 mitoses/10 high-power fields), and characterized by cytologic atypia, tumor necrosis, or infiltrative margins. A single-center study by DeVito et al found that malignant SFT, as compared with benign SFT, was associated with larger tumors, elevated mitotic counts, the presence of metastases at diagnosis, and more extensive use of chemotherapy and radiation therapy.[8]
This tumor typically spreads via hematogenous dissemination, primarily to the lungs, but rarely spreads via the lymphatics. Metastatic disease is usually the cause of death. Metastasis appears to be more likely with SFT of extrathoracic origin than with thoracic SFT.[9]
The etiology is unknown.
Epidemiology
Most SFTs occur in adults, with a median age of 45-50 years. SFT is less common in infants and children. Soft-tissue SFTs represent only about 1-2% of all soft-tissue tumors.[5]
Prognosis
Conventional HPCs and SFTs have a better prognosis than some older studies may suggest, in that these studies may have inadvertently included sarcomas with HPC-like features. For patients with a primary tumor who undergo complete resection, 5-year survival is 89-100%. For patients with SFTs of an extremity, the local recurrence rate is 0-6%, and the distant metastasis rate is 0-19%.[6, 10, 11]
Most patients with SFT or HPC have a benign clinical course, but because of the lesion's malignant potential, wide resection and careful long-term follow-up are necessary. Favorable long-term outcomes have been reported in cases of intracranial SFT that required repeat radiosurgery.[12]
History and Physical Examination
A solitary fibrous tumor (SFT) typically presents as a deep, painless enlarging mass in the thigh, axilla, or pelvis. Males and females are equally affected; the median age is 45 years.[5, 6] Patients may exhibit symptoms associated with a local compressive effect on viscera or neurovascular structures. Paraneoplastic syndromes such as hypoglycemia have been described.[13]
Imaging Studies
In addition to a complete physical examination, all patients should undergo local imaging (including intravenous contrast-enhanced magnetic resonance imaging [MRI] and plain radiography), as well as chest radiography or computed tomography (CT).[14] A solitary fibrous tumor (SFT) demonstrates a heterogeneous appearance on MRI, with high signal on T2-weighted series and intermediate to moderately high signal on T1-weighted images.[15] (See the images below.) Cellular SFTs also show rapid initial enhancement on dynamic contrast-enhanced MRI.[16]
View Image | MRI of solitary fibrous tumor demonstrates a deep soft-tissue mass in the anteromedial aspect of the thigh with heterogenous high signal intensity on .... |
View Image | Similar signal intensity as skeletal muscle on precontrast axial T1-weighted fat-suppressed turbo-spin echocardiography. |
View Image | Intense uptake on postcontrast comparison images. |
SFTs are generally well-circumscribed. Small satellite nodules separate from the main lesion are not uncommon, and 12% of patients may present with metastasis or locally recurrent tumors.[6] No distinctive radiologic criteria for malignancy are recognized, other than distant metastasis.
Biopsy
Biopsy should be performed by a musculoskeletal oncologist. If the mass is palpable and accessible, a core needle biopsy may be an alternative to open incisional biopsy. The fibrous nature, potential low cellularity, and usually deep location of the mass may not allow fine-needle aspiration biopsy (FNAB). The biopsy should be placed in line with the incision for definitive tumor resection to allow en-bloc resection of the biopsy tract. Adequate tissue should be acquired to allow for histologic analysis, molecular genetics,[17] and immunohistochemistry (IHC).[18]
Histologic Findings
SFTs must be carefully distinguished from other entities, such as synovial sarcoma and angiosarcoma, which have a worse prognosis and a different treatment course.
The cell of origin for SFTs is controversial.[5] Fibroblasts are elongated, spindle-shaped cells with long processes; on electron microscopy, they are devoid of a basement membrane and demonstrate a prominent rough endoplasmic reticulum. Pericytes also have elongated cell processes and are spindle-shaped. They are contractile and surround capillaries and postcapillary venules. However, few tumors formerly labeled as hemangiopericytomas (HPCs) had actual pericytic differentiation, and most had nonspecific ultrastructural features.[4]
On histology, one can appreciate a staghorn-type branching of vessels, a bland cell morphology, and positive staining for CD34. (See the images below.)
View Image | Histology of solitary fibrous tumor demonstrates a bland cell morphology and staghorn-type branching of vessels on low magnification of hematoxylin an.... |
View Image | Histology of solitary fibrous tumor demonstrates a bland cell morphology and staghorn-type branching of vessels on high magnification of hematoxylin a.... |
View Image | Positive staining for CD34. Image courtesy of Paul E. Wakely, Jr, MD. |
Before the use of IHC, HPC and SFT were commonly confused with synovial sarcoma, particularly monophasic variants. Epithelioid differentiation can help distinguish biphasic synovial sarcomas. Approximately 90% of synovial sarcomas demonstrate the chromosomal translocation t(X;18)(p11.2;q11.2) and the fusion gene SYT-SSX1 or SYT-SSX2, detectable with cytogenetics and reverse transcription polymerase chain reaction (RT-PCR).[17] Nuclear STAT6 immunoreactivity can be helpful in cases where the diagnosis is uncertain.[18]
Staging
SFTs are generally regarded as benign but can demonstrate aggressive behavior even if they appear morphologically benign. Histologic criteria for malignancy include the following[5, 10, 8] :
Cellular pleomorphism
Tumor necrosis
Hemorrhage
Infiltrative margins with surrounding tissues
Hypocellularity
Moderate-to-severe nuclear atypia
Sharply demarcated anaplastic or poorly differentiated foci
High mitotic count (>4 mitoses/10 hpf)
Surgical Therapy
Because even benign-appearing solitary fibrous tumors (SFTs) can be locally recurrent and metastatic, wide resection is recommended for both benign and malignant SFTs. Preoperative vascular studies and arterial embolization should be considered because of the known bleeding risk with resection.[5, 15] Careful exclusion of other diagnoses (eg, synovial sarcoma) is important. Because of the favorable outcome with SFTs, it may be possible to avoid limb-threatening and deforming operations.[6]
No evidence suggests that adjuvant chemotherapy is beneficial. If the SFT appears malignant histologically, adjuvant radiation therapy may be considered. Long-term follow-up is recommended because local and distant relapse is possible, even with benign-appearing tumors.
Author
Vincent Y Ng, MD, Fellow, Musculoskeletal Tumor Surgery, University of Washington Medical Center
Disclosure: Nothing to disclose.
Coauthor(s)
Joel L Mayerson, MD, Associate Professor of Orthopedic Surgery, Director, Musculoskeletal Oncology, Comprehensive Cancer Center, Wexner Medical Center at The Ohio State University; Program Director, Arthur G James Cancer Hospital and Richard J Solove Research Institute; Orthopedic Surgery Residency Co-Director, Bone Tumor Clinic, Nationwide Children's Hospital
Disclosure: Nothing to disclose.
Thomas J Scharschmidt, MD, Assistant Professor of Orthopedics, Division of Musculoskeletal Oncology, Wexner Medical Center at The Ohio State University, The Arthur G James Cancer Hospital and Richard J Solove Research Institute
Disclosure: Nothing to disclose.
Specialty Editors
Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Ian D Dickey, MD, FRCSC, LMCC, Orthopedic Surgeon, Colorado Limb Consultants, Denver Clinic for Extremities at Risk; Medical Director, Denver Sarah Cannon Sarcoma Network; Staff Surgeon, Department of Orthopedics, Presbyterian/St Luke’s Hospital; Adjunct Professor, Department of Chemical and Biological Engineering, University of Maine
Disclosure: Received consulting fee from Stryker Orthopaedics for consulting; Received honoraria from Cadence for speaking and teaching; Received grant/research funds from Wright Medical for research; Received honoraria from Angiotech for speaking and teaching; Received honoraria from Ferring for speaking and teaching.
Chief Editor
Omohodion (Odion) Binitie, MD, Medical Director, Assistant Member, Department of Sarcoma, Section Head, Orthopedics, Adolescent/Young Adult and Pediatric Orthopedic Oncology, Medical Director, Physical Therapy, Speech Therapy, and Rehabilitation Services, Assistant Fellowship Program Director, Musculoskeletal Oncology, Moffitt Cancer Center; Assistant Professor, Department of Oncologic Sciences, Department of Ortho and Sports Medicine, University of South Florida Morsani College of Medicine
Disclosure: Nothing to disclose.
Acknowledgements
Christopher Got University of Medicine and Dentistry of New Jersey-New Jersey Medical School
Disclosure: Nothing to disclose.
Francis Patterson, MD, Assistant Professor, Department of Orthopedics, Division of Musculoskeletal Oncology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School
Francis Patterson is a member of the following medical societies: Alpha Omega Alpha and American Academy of Orthopaedic Surgeons.
Disclosure: Nothing to disclose.
Carin Restivo University of Medicine and Dentistry of New Jersey-New Jersey Medical School
Disclosure: Nothing to disclose.
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