solitary fibrous tumor
Definition: Solitary fibrous tumor is a spindle cell tumor first described in the pleura, but also found in multiple extrathoracic sites including the meninges, orbit, nasal and paranasal sinuses.
Solitary fibrous tumor (SFT) was first described as a pleural-based tumor with an exophytic growth pattern. In addition to pleural- or peritoneal-based locations, SFT has been reported in multiple organs including pancreas, liver, skin, meninges, thyroid and soft tissue.
The tumor is composed of spindle-shaped cells admixed with dense collagen and branching vasculature. Expression of CD34 and CD99 is common, BCL2 is variable, and desmin rare. It has been hypothesized that a pluripotent mesenchymal stem cell is the possible cell of origin for SFT.
Although most SFTs are benign, 10-15% may behave aggressively. Hypercellularity, significant cellular pleomorphism, and more than 4 mitoses per 10 high-power fields are features suggesting aggressive or malignant behavior.
There is no evidence of correlation between karyotype and histology, anatomic location, and clinical outcome. Multiple chromosomal aberrations have been detected in histopathologically benign-appearing SFTs with no evidence of recurrence or metastasis in cases with follow-up data.
Histogenesis
SFT may originate from a unique, perivascular multipotent mesenchyme sharing with its lineage with pericytes, fibroblasts, and infrequently, endothelium.
Consequently, morphological features of SFT may become diversely varied by whether predominantly constituent cells are undifferentiated, pericytic or fibroblastic in nature. (#15909170#)
Solitary fibrous tumour was formerly regarded as a mesothelial or submesothelial lesion involving pleura and peritoneum. This tumor is anatomically ubiquitous and occurs very often in somatic soft tissue.
The large majority of lesions which have been classified as hemangiopericytoma in recent years are, in fact, essentially indistinguishable from solitary fibrous tumour, albeit they are sometimes more diffusely hypercellular.
While it has been recognized for many years that a wide variety of tumours may have a pericytoma-like appearance, leading pathologists to use this diagnostic term less often, the large majority of tumours which have remained in this category show no evidence of pericytic differentiation and, instead, appear to be fibroblastic in nature, further supporting this new name change.
Similarly, so-called lipomatous hemangiopericytoma is now regarded as representing a fat-forming variant of solitary fibrous tumour.
Malignant SFT
Although a small subset of solitary fibrous tumours show overtly malignant features, it is also recognized that these lesions may occasionally give rise to metastatic disease in the absence of any predictive morphological features—in these circumstances, solitary fibrous tumour has been classified into the intermediate (rarely metastasizing) category.
Localization
pleural solitary fibrous tumor (pleural SFT)
extrapleural solitary fibrous tumor
- cavernous sinus (#12808569#)
- cerebellopontine angle (#14707876#)
- oral cavity
- cerebral solitary fibrous tumor
- renal solitary fibrous tumor (#11866209#)
- peripheral nervous solitary fibrous tumor
- thyroid solitary fibrous tumor (#11684960#)
Synopsis
possible glomus tumor-like foci
Immunohistochemistry
vimentin +
CD34 +
BCL2 +
CD99 +
+/- Factor XIIIa
+/- alpha-smooth muscle actin
were less commonly reactive
S-100-
desmin-
CD31-
CD68-
Ultrastructure (#15909170#)
perivascular undifferentiated cells
pericytes
endothelial cells
glomoid foci of myopericytes
Weibel-Palade bodies in capillary endothelium
single and clustered endothelial cells with intracytoplasmic lumen
Variants
malignant progression in solitary fibrous tumor (#19718788#)
dedifferentiated solitary fibrous tumor (#19718788#)
salivary gland heterotopia (#14707876#)
Immunochemistry
CD34+
factor XIIIa F13a+
CD99+
BCL2+
Associations
type I neurofibromatosis (NF1) (#15013617#)
Cytogenetics
isolated tumoral trisomy 21 (#8616788#)
4q13 rearrangements
t(8;12)(p11;q24) (#17175385#)
See also
SFT spectrum (solitary fibrous tumor-hemangiopericytoma spectrum)
References
Expanding the spectrum of malignant progression in solitary fibrous tumors: a study of 8 cases with a discrete anaplastic component—is this dedifferentiated SFT? Mosquera JM, Fletcher CD. Am J Surg Pathol. 2009 Sep;33(9):1314-21. PMID: #19718788#
Torabi A, Lele SM, DiMaio D, Pinnt JC, Hess MM, Nelson M, Bridge JA. Lack of a common or characteristic cytogenetic anomaly in solitary fibrous tumor. Cancer Genet Cytogenet. 2008 Feb;181(1):60-4. PMID: #18262056#
Gengler C, Guillou L. Solitary fibrous tumour and haemangiopericytoma: evolution of a concept. Histopathology. 2006 Jan;48(1):63-74. PMID: #16359538#
The evolving classification of soft tissue tumours: an update based on the new WHO classification. Fletcher CD. Histopathology. 2006 Jan;48(1):3-12. PMID: #16359532#