Stanford School of Medicine
Surgical Pathology Criteria
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Solitary Fibrous Tumor

Definition

  • Tumor composed of small cells individually separated by thin bands of collagen fibers

Alternate / Historical Names

  • Hemangiopericytoma
  • Localized fibrous tumor
  • Fibrous mesothelioma

Diagnostic Criteria

  • May be grossly circumscribed but frequently infiltrates microscopically
  • Unifying pattern is small cells individually separated by collagen
    • Cells typically small
      • Nuclei dense or vesicular
      • Scant cytoplasm
    • Thin bands of collagen surround and separate individual cells
  • Usually has alternating hypercellular and hypocellular areas
  • Variable architectural patterns
    • Haphazard, patternless
    • Sheets
    • Fascicles
    • Herringbone
    • Perivascular aggregation
    • Storiform
  • Vessels often ectatic, with staghorn appearance
  • Stroma may be myxoid or hyalinized in areas
    • Amianthoid fibers reported in one case
  • Most tumors cytologically bland
    • Metastasis does occur in such tumors but is rare
    • Minimal pleomorphism is not clinically significant
  • CD34 is most sensitive and specific marker
    • Diagnosis can be made in its absence, but should be made cautiously and with consultation
  • Following features predict increased incidence of recurrence and metastasis
    • Significant pleomorphism and atypia
    • High cellularity
    • Mitotic figures >4/10 hpf
    • Atypical mitotic figures
    • Tumor cell necrosis
    • Even one or two of these features may be associated with aggressive behavior
  • SFT with dedifferentiation has been described (Mosquera)
    • Discrete anaplastic component
      • Epithelioid, round cell, spindled, hypercellular patterns
      • Necrosis, cystic degeneration, frequent mitotic figures
      • CD34 positive in half
    • Prognosis reported much worse if over 8 cm diameter
  • Solitary fibrous tumor is considered by many to form a spectrum with hemangiopericytoma
  • Stromal fat may be present, especially in malignant SFT
  • Richard L Kempson MD
    Robert V Rouse MD
    Department of Pathology
    Stanford University School of Medicine
    Stanford CA 94305-5342

    Original posting/updates: 8/10/08, 9/24/09, 11/11/11, 12/29/12

Supplemental studies

Immunohistology

CD34

>90%
bcl2 >90%
CD99 70-90%
Factor XIIIa 80%
Beta catenin 20%
S100 <10%
Smooth muscle actin <10%
Keratin <5%*
Desmin negative
CD117 negative
Calretinin 13%
*One report of 11% focal pos (Barak 2012)

Differential diagnosis

Hemangiopericytoma Solitary Fibrous Tumor
Sheets of cells, usually no collagen separation Bands of collagen separate cells
Staghorn vessels required Staghorn vessels may be present
CD34 50% positive CD34 >90% positive
These two may not always be separable and may perhaps form a spectrum.
They have the same behavior and the same features are predictive of malignancy.

 

Smooth Muscle Tumor Solitary Fibrous Tumor
Spindled cytoplasm Scant cytoplasm
Long fascicular growth pattern No fascicles or short fascicles
Actin positive >95% Actin rare and focal
Desmin variable Desmin negative
CD34 variable, weak CD34 >90% positive

 

Gastrointestinal Stromal Tumor Solitary Fibrous Tumor
Spindled or epithelioid cytoplasm Scant cytoplasm
Skeinoid fibers, if present are irregular, globular and have prominent retraction Ropy collagen
Hemangiopericytoma-like vessels uncommon HPC-like vessels common
CD117 (KIT) 74-95%, DOG1 87-95% positive CD117, DOG1 negative
Actin 30-50% positive Actin rare and focal
CD34 is usually positive in both

 

Nerve Sheath Tumor Solitary Fibrous Tumor
Frequent palisading No palisading
S100 positive in benign tumors S100 <10%
CD34 focal dendritic pattern CD34 extensive

 

Deep Fibrous Histiocytoma Solitary Fibrous Tumor
No bands of collagen separating cells Bands of collagen separate cells
Predominantly storiform Usually patternless
Histiocytic differentiation present No histiocytic differentiation
Usually uniform celllularity Alternating hypocellular and hypercellular areas
CD34 40% positive CD34 >95% positive (negative result favors fibrous histiocytoma)

Clinical

  • Nearly restricted to adults
  • Wide variety of soft tissue and visceral sites
    • Originally described in pleura
  • Size range 0.8 to 26 cm
  • Bland tumors may recur and rarely metastasize
  • Tumors with malignant histologic features more commonly recur and metastasize
  • May be associated with hypoglycemia

Lists

CD34 positive neoplasms (frequent and strong)

Lesions that may demonstrate a prominent hemangiopericytoma-like vascular pattern

Bibliography

  • Kempson RL, Fletcher CDM, Evans HL, Henrickson MR, Sibley RS. Tumors of the Soft Tissues, Atlas of Tumor Pathology, AFIP Third Series, Fascicle 30, 2001
  • Fletcher CDM, Unni KK, Mertens F. Pathology and Genetics of Tumours of Soft Tissue and Bone, World Health Organization Classification of Tumours 2002
  • Weiss SW, Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors, 5th edition, 2008
  • de Saint Aubain Somerhausen N, Rubin BP, Fletcher CD.  Myxoid solitary fibrous tumor: a study of seven cases with emphasis on differential diagnosis.  Mod Pathol 1999 May;12(5):463 71
  • Fukunaga M, Naganuma H, Nikaido T, Harada T, Ushigome S.  Extrapleural solitary fibrous tumor: a report of seven cases.  Mod Pathol 1997 May;10(5):443-50
  • Goodlad JR, Fletcher CD.  Solitary fibrous tumour arising at unusual sites: analysis of a series. Histopathology 1991 Dec;19(6):515-22
  • Mentzel T, Bainbridge TC, Katenkamp D.  Solitary fibrous tumour: clinicopathological, immunohistochemical, and ultrastructural analysis of 12 cases arising in soft tissues, nasal cavity and nasopharynx, urinary bladder and prostate.  Virchows Arch 1997 Jun;430(6):445-53
  • Nielsen GP, O'Connell JX, Dickersin GR, Rosenberg AE.  Solitary fibrous tumor of soft tissue: a report of 15 cases, including 5 malignant examples with light microscopic, immunohistochemical, and ultrastructural data.  Mod Pathol 1997 Oct;10(10):1028-37 
  • Suster S, Nascimento AG, Miettinen M, Sickel JZ, Moran CA.  Solitary fibrous tumors of soft tissue. A clinicopathologic and immunohistochemical study of 12 cases.  Am J Surg Pathol 1995 Nov;19(11):1257-66 
  • Vallat-Decouvelaere AV, Dry SM, Fletcher CD.  Atypical and malignant solitary fibrous tumors in extrathoracic locations: evidence of their comparability to intra-thoracic tumors.  Am J Surg Pathol 1998 Dec;22(12):1501-11.
  • Mosquera JM, Fletcher CD. Expanding the spectrum of malignant progression in solitary fibrous tumors: a study of 8 cases with a discrete anaplastic component--is this dedifferentiated SFT? Am J Surg Pathol. 2009 Sep;33(9):1314-21.
  • Lee JC, Fletcher CD. Malignant fat-forming solitary fibrous tumor (so-called "lipomatous hemangiopericytoma"): clinicopathologic analysis of 14 cases. Am J Surg Pathol. 2011 Aug;35(8):1177-85
  • Barak S, Wang Z, Miettinen M. Immunoreactivity for calretinin and keratins in desmoid fibromatosis and other myofibroblastic tumors: a diagnostic pitfall. Am J Surg Pathol. 2012 Sep;36(9):1404-
  • Collini P, Negri T, Barisella M, Palassini E, Tarantino E, Pastorino U, Gronchi A, Stacchiotti S, Pilotti S. High-grade sarcomatous overgrowth in solitary fibrous tumors: a clinicopathologic study of 10 cases. Am J Surg Pathol. 2012 Aug;36(8):1202-15
 
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