Malignant Solitary Fibrous Tumor of the Urinary Bladder: Clinical and Pathological Challenges of a Rare Tumor

Solitary fibrous tumors (SFT) are rare, usually benign, neoplasms of mesenchymal origin. From just 16 cases reported in the urinary bladder, only two were malignant. We present here an additional case of a 70-year old man with malignant SFT of the urinary bladder with review of the current literature and discussion of the clinical pathology challenges for the diagnosis of these rare tumors. The patient had a family history of bladder cancer, and presented with dysuria, hematuria, and a 3-year history of worsening urinary incontinence. A computed tomography showed a large bladder mass with evidence of invasion into the bladder wall. This was followed by a transurethral resection of the tumor, and histopathological examination revealed a malignant SFT. After a radical cystoprostatectomy was performed, the patient is currently more than one year post-surgery without evidence of recurrence. SFT of the bladder lack distinctive patterns in symptoms, radiological imaging, and patient demographics, which can make the original clinical diagnosis challenging upon presentation. Histopathological examination may also be confused with several benign “spindle cell reactions,” and identification of malignant features including special immunostaining for tissue markers is required.