American Urological Association - Solitary Fibrous Tumor
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Solitary Fibrous Tumor

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  • Originally described in pleura and other serosal surfaces, later also described in somatic tissues and visceral organs including prostate.
  • Considered as same spectrum with hemangiopericytoma (cellular SFT).
  • Exceedingly rare, only a handful was reported.
  • Patients are 21 to 75 years old (mean 58 years) and most present with obstructive symptoms and abnormal DRE.
  • Gross: tumor is well circumscribed, solid, firm or rubbery, with white-tan nodular cut surface.
  • Histology:
    • Characteristically shows spindle cells with scant cytoplasm admixed with thick "ropey" collagen in a haphazard (patternless) pattern.
    • Degree of cellularity varies with hypo- and hypercellular areas (image A).
    • Vessels are abundant with characteristic larger staghorn vessels (image B).
  • Immunohistochemistry: CD34+, CD99+ and Bcl-2+.
  • Larger tumors (>10 cm) with increase mitosis, pleomorphism, infiltrative borders and necrosis are considered malignant.
  • (So far) has favorable outcome even those considered to be histologically malignant.
  • DDX: other spindle cell lesions of the prostate such as stroma-predominant BPH (nodules multiple with spindle cells following small vessels), stromal tumors, smooth muscle tumor (actin+), sarcomatoid carcinoma (keratin+) and GIST (c-kit+).