Fibrosarcoma of the urinary bladder. Study of a case showing extensive chondroid differentiation.

: A case of primary fibrosarcoma of the urinary bladder showing extensive chondroid differentiation was studied by light microscopy and immunofluorescent microscopy using tissue-specific antibodies against intermediate filaments. The tumor cells were uniformly and positively labeled with vimentin antibodies and were negative for desmin and keratin, thus confirming the nonmuscle mesenchymal origin of the neoplasm. The value of intermediate filament typing in the differential diagnosis of spindle cell tumors of the urinary bladder is discussed, and a review of the literature on the subject is presented. It is postulated that the retained capacity for continued differentiation displayed by this tumor may account for the relatively better prognosis observed for this patient.