Solitary fibrous tumor (SFT) is a distinct spindle cell tumor arising mainly in the pleura, however, SFT of extra-pleural sites had been reported. To our knowledge, five cases of the urinary bladder SFT had been reported. We have recently experienced a case of SFT of the urinary bladder in a 56-year-old man who was admitted to the hospital with a 4-month history of voiding difficulty, frequency, and residual urine sensation. A computerized tormography scan revealed a 12cm sized intravesical mass. The mass was marginally excised under the impression of it being a benign spindle cell tumor by pre-operative needle biopsy. On gross examination, the mass was multinodular, creamy white, and the cut surface was fibrotic with a rubbery consistency. Microscopic examination revealed haphazardly arranged spindle cells with a lace-like deposition of inter- and pericellular collagen. Areas of increased cellularity show nuclear atypia and occasional mitoses (2-3/10HPF). The immunohistochemical staining revealed an intense CD34 and bcl-2 immunoreactivity. Although the exact biologic behavior of these tumors has not been clarified, most of the reported cases have undergone a benign clinical course.
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