Surgical Pathology Criteria

Solitary Fibrous Tumor

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)

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