Solitary Fibrous Tumor

Updated: May 06, 2021
  • Author: Vincent Y Ng, MD; Chief Editor: Omohodion (Odion) Binitie, MD  more...
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Overview

Background

Solitary fibrous tumor (SFT) was first described in 1870 by Wagner and further established in 1931 by Klemperer and Rabin as a pleural neoplasm. The term hemangiopericytoma (HPC) was first used by Stout and Murray in 1942 to describe a distinct neoplasm of pericytic origin. 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. [1]

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. [2, 3]

Three classical clinical forms of SFT are recognized, as follows [2] :

  • 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 [1]
  • 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 [1]  
  • 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 [4]
  • 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 [1]  

This article focuses on the cellular variant of conventional SFT, or what was previously termed conventional HPC.

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Pathophysiology and Etiology

SFTs are tumors of mesenchymal origin that occur in the extremities. The 2013 classification of soft-tissue tumors published by the World Health Organization [5]  defined malignant forms of SFT as hypercellular, mitotically active (>4 mitoses/10 high-power fields) lesions 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. [6]

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. [7]  The 2020 WHO classification of soft-tissue tumors listed SFT as an intermediate (rarely metastasizing) tumor. [3]

The etiology is unknown.

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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. [2]

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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%. [4, 8, 9]

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. [10]

Various risk models have been proposed in an effort to predict outcome in patients with SFT. [3]  Demicco et al, in a study comparing five such models designed for soft-tissue and/or pleural SFT—(1) modified Demicco, (2) Pasquali, (3) Salas overall survival (OS), (4) Salas metastasis, and (5) Salas local recurrence (LR)—in 303 patients with extrameningeal SFT found that models (1), (3), and (4) models predicted metastasis and recurrence-free survival and that model (2) correlated best with overall survival. [11]

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