Soft tissue
Fibroblastic / myofibroblastic
Solitary fibrous tumor

Editorial Board Members: Borislav A. Alexiev, M.D., Jose G. Mantilla, M.D.
Josephine K. Dermawan, M.D., Ph.D.
Karen Fritchie, M.D.

Topic Completed: 10 May 2021

Minor changes: 19 July 2021

Copyright: 2003-2021, PathologyOutlines.com, Inc.

PubMed Search: Soft tissue solitary fibrous tumor [title] free full text [sb]

Josephine K. Dermawan, M.D., Ph.D.
Karen Fritchie, M.D.
Page views in 2020: 36,674
Page views in 2021 to date: 32,501
Cite this page: Dermawan JK, Fritchie K. Solitary fibrous tumor. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissuesft.html. Accessed July 31st, 2021.
Definition / general
  • Fibroblastic tumor characterized by haphazardly arranged spindled to ovoid cells, prominent staghorn vasculature and NAB2-STAT6 gene rearrangement
Essential features
  • Haphazard arrangement of spindled to ovoid cells arranged around branching and dilated vasculature within variably collagenous stroma
  • Occurs at any anatomical site with a wide range of histological patterns
  • CD34 usually strong and diffuse but nonspecific
  • STAT6 immunohistochemistry highly sensitive and specific surrogate for NAB2-STAT6 gene fusion (Mod Pathol 2014;27:390)
  • Risk stratification preferred over anatomic staging (Mod Pathol 2017;30:1433)
Terminology
  • Hemangiopericytoma (no longer preferred) (Cancer 1975;36:2232)
  • Giant cell angiofibroma (no longer preferred)
ICD coding
  • ICD-10: D48.1 - neoplasm of uncertain behavior of connective and other soft tissue
Epidemiology
Sites
Pathophysiology
Etiology
  • Unknown
Diagrams / tables

Images hosted on other servers:

Modified 4 variable risk stratification model

Clinical features
  • Symptoms associated with anatomic location
  • Somatic soft tissue tumors present as slow growing, painless mass
  • Abdominopelvic tumors produce symptoms due to organ impingement (Eur Urol 2008;54:1188)
  • Pleural tumors often discovered incidentally but could grow exophytically into lungs
  • Paraneoplastic syndrome (Doege-Potter syndrome) extremely rare; due to IGF2 production by tumor (J Endocr Soc 2019;3:537)
Diagnosis
  • Imaging features are nonspecific and diagnosis is dependent on histologic findings
Radiology description
  • CT: well defined, sometimes lobulated mass that is isodense to skeletal muscle with heterogeneous contrast enhancement (Clin Imaging 2018;48:48)
  • MRI: T1 intermediate and T2 hypointense (cellular / fibrous areas) to hyperintense (myxoid areas) signals (Radiol Clin North Am 2016;54:565)
Radiology images

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Bulky thyroid tumor (CT)

Bulky thyroid tumor (CT)

Huge perineal mass (CT)

Huge perineal mass (CT)

Ischiorectal fossa mass (MRI)

Ischiorectal fossa mass (MRI)

Bladder serosa mass (CT)

Bladder serosa mass (CT)

Prognostic factors
Case reports
Treatment
Clinical images

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Palatal mass causing proptosis

Palatal mass causing proptosis

Huge perineal mass

Huge perineal mass

Gross description
  • Usually unencapsulated but well circumscribed mass, sometimes lobulated
  • Exophytic lesions on serosal surfaces
  • 5 - 15 cm in greatest diameter
  • Gray-white, yellow to red-brown color
  • Fibrous and firm cut surface
  • Cystic, hemorrhagic or myxoid degeneration may be present
  • Tumor necrosis and hemorrhage in malignant tumors
  • Reference: Am J Surg Pathol 1995;19:1257
Gross images

Contributed by Borislav A. Alexiev, M.D. (Case #505)
Fat forming SFT

Fat forming SFT



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Solid white cut surface

Solid white cut surface

Circumscribed lobulated mass

Circumscribed lobulated mass

Central necrosis

Central necrosis

Fleshy nodules

Fleshy nodules

Frozen section description
  • Circumscribed spindled cell tumor
  • Presence of staghorn vasculature helpful but not entirely specific
Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Josephine Dermawan, M.D., Ph.D., Karen Fritchie, M.D.
Ovoid to fusiform cells

Ovoid to fusiform cells

Staghorn vasculature

Staghorn vasculature

Collagenous stroma

Collagenous stroma

High risk solitary fibrous tumor

High risk solitary fibrous tumor

Metastatic solitary fibrous tumor

Metastatic solitary fibrous tumor

Myxoid solitary fibrous tumor

Myxoid solitary fibrous tumor


Lipomatous solitary fibrous tumor

Lipomatous solitary fibrous tumor

Dedifferentiated solitary fibrous tumor

Dedifferentiated solitary fibrous tumor

Diffuse and strong CD34

Diffuse and strong CD34

STAT6

STAT6

STAT6 loss

STAT6 loss

Myogenin

Myogenin




Contributed by Borislav A. Alexiev, M.D. (Case #505)
Fat forming SFT Fat forming SFT Fat forming SFT Fat forming SFT Fat forming SFT Fat forming SFT

Fat forming SFT

Virtual slides

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Solitary fibrous tumor

Solitary fibrous tumor

Cellular solitary fibrous tumor

Cellular solitary fibrous tumor

Lipomatous solitary fibrous tumor

Lipomatous solitary fibrous tumor

Malignant solitary fibrous tumor

Malignant solitary fibrous tumor

Solitary fibrous tumor with necrosis

Solitary fibrous tumor with necrosis

Solitary fibrous tumor

Solitary fibrous tumor

Cytology description
  • Low to moderate cellularity
  • Oval, elongate, rounded or stellate cells with wispy cytoplasm and pink collagenous stroma (Cancer Cytopathol 2018;126:36)
  • High cellularity and nuclear pleomorphism in malignant cases
Cytology images

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Diff-Quik, fine needle aspiration

Diff-Quik, fine needle aspiration

Pap, touch prep

Pap, touch prep

Positive stains
Electron microscopy description
  • Fibroblast-like cells with well developed rough endoplasmic reticulum and surrounded by collagen fibers (Med Mol Morphol 2009;42:239)
Molecular / cytogenetics description
Molecular / cytogenetics images

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Capillary sequencing and RT PCR

Capillary sequencing and RT PCR

Videos

Solitary fibrous tumor

Sample pathology report
  • Soft tissue, pelvis, excision:
    • Solitary fibrous tumor (5.6 cm), completely excised (see comment)
    • Comment: Histologic sections demonstrate a moderately cellular spindled cell tumor in a collagenous stroma with prominent dilated staghorn type vasculature. Mitotic rate is approximately 1 - 2 per 10 high power fields. Overt cytologic atypia and tumor necrosis are not identified. Immunohistochemical studies show that the tumor cells are diffusely and strongly positive for CD34 and STAT6 and are negative for SOX10, S100 and AE1 / AE3, supporting the above diagnosis. According to the 2017 risk stratification criteria by Demicco et al, this should be classified as a low risk solitary fibrous tumor.
Differential diagnosis
Board review style question #1

54 year old woman presents with a 9.6 cm, well circumscribed, firm mass in the deep soft tissue of the thigh. Histologic sections show ovoid to spindled cells arranged haphazardly around prominent thin walled, hyalinized, dilated staghorn type vasculature (see image above). Which of the following is the most sensitive and specific immunohistochemical marker for the diagnosis of this tumor?

  1. Actin
  2. BCL2
  3. CD34
  4. Cytokeratin CAM 5.2
  5. STAT6
Board review style answer #1
Board review style question #2
Which of the following is a favorable prognostic factor for solitary fibrous tumor?

  1. Age < 55 years old
  2. Mitotic rate ≥ 4 per 10 high power fields
  3. TERT promoter mutations
  4. Tumor necrosis
  5. Tumor size ≥ 10 cm
Board review style answer #2
A. Age < 55 years old

Comment Here

Reference: Soft tissue - Solitary fibrous tumor
Board review style question #3
Which of the following is true about the majority of fat forming solitary fibrous tumor cases?

  1. All tumors show reactivity for CD34
  2. Fat forming solitary fibrous tumors usually occur in younger adults, predominantly in females
  3. Multivacuolated lipoblasts are more common in the malignant subset
  4. The imaging findings of fat forming solitary fibrous tumor are specific
  5. The mediastinum is the most commonly affected site
Board review style answer #3
C. Multivacuolated lipoblasts are more common in the malignant subset

Comment Here

Reference: Soft tissue - Solitary fibrous tumor
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