Small cell carcinoma with skeletal muscle differentiation of urinary bladder

Reported herein is a case of small cell carcinoma (SCC) with skeletal muscle differentiation of urinary bladder in a 76-year-old woman presenting macrohematuria. Ultrasonography and CT detected a mass at the anterior wall of the urinary bladder, and total cystectomy followed. The tumor consisted of solid growth of small round cells with high nucleocytoplasmic ratio admixed with rhabdoid cells with eosinophilic cytoplasmic inclusions, invading the perivesical tissue. On immunohistochemistry the tumor cells were diffusely positive for neural markers and CD99, and sporadically for skeletal muscle markers. Fluorescence in situ hybridization showed no translocation of EWS. The patient died from massive recurrence in the pelvis 4 months after operation. This rare tumor indicates a potential of myoid differentiation in SCC of the urinary bladder and differential diagnosis from primitive neuroectodermal tumor is important because the treatment is different.