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
- Cells typically small
- 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
- Discrete anaplastic component
- Solitary fibrous tumor is considered by many to form a spectrum with hemangiopericytoma
- Stromal fat may be present, especially in malignant SFT
- Ranges from mature fat to lipoblasts to areas resembling atypical lipomatous tumors (Lee 2011)
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
