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solitary fibrous tumor

Tuesday 14 October 2003

Digital case

- JRC:2671 : Sinonasal solitary fibrous tumor (26 y/o female).
- JRC:2673 : Thyroid Solitary fibrous tumor (49 y/o female).
- JRC:15044 : Thyroid solitary fibrous tumor.

Definition: Solitary fibrous tumor represents a spectrum of mesenchymal tumors, encompassing tumors previously termed hemangiopericytoma, which are classified as having intermediate biological potential (rarely metastasizing) in the 2002 World Health Organization classification scheme.

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#, #14707876#)

Immunochemistry

- CD34+
- factor XIIIa F13a+
- CD99+
- BCL2+

Associations

- type 1 neurofibromatosis (NF1) (#15013617#)

Cytogenetics

- isolated tumoral trisomy 21 (#8616788#)
- 4q13 rearrangements
- t(8;12)(p11;q24) (#17175385#)

Prognosis

While small tumors with low mitotic rates are highly unlikely to metastasize, large tumors ≥15 cm, which occur in patients ≥55 years, with mitotic figures ≥4/10 high-power fields require close follow-up and have a high risk of both metastasis and death. (#22575866#)

See also

- SFT spectrum (solitary fibrous tumor-hemangiopericytoma spectrum)

References

- High-grade Sarcomatous Overgrowth in Solitary Fibrous Tumors: A Clinicopathologic Study of 10 Cases. Collini P, Negri T, Barisella M, Palassini E, Tarantino E, Pastorino U, Gronchi A, Stacchiotti S, Pilotti S. Am J Surg Pathol. 2012 Aug;36(8):1202-15. PMID: #22613995#

- Solitary fibrous tumor: a clinicopathological study of 110 cases and proposed risk assessment model. Demicco EG, Park MS, Araujo DM, Fox PS, Bassett RL, Pollock RE, Lazar AJ, Wang WL. Mod Pathol. 2012 May 11. PMID: #22575866#

- 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#