Adult urinary bladder tumors with rabdomyosarcomatous differentiation: Clinical, pathological and immunohistochemical studies

Rhabdomyosarcoma occurs much more commonly in children than in adults in genitourinary tract, in which more than 90% is embryonal, mostly botryoid type. Adult rhabdomyosarcoma is extremely rare [1-7]. Because of its rarity in adults, proper diagnosis and classification can be a challenge. To make this matter more complicated, rhabdomyoblastic differentiation is one of commonly seen heterologous elements in sarcomatoid carcinoma of urinary bladder [7]. Adult rhabdomyosarcoma of urinary bladder can have morphologic features overlapping with small cell carcinoma and poorly differentiated urothelial carcinoma with rhabdomyoblastic differentiation [7]. In this report, we reported three cases of primary rhabdomyosarcomatous tumor of the urinary bladder, two of them were diagnosed as carcinoma with extensive rhabdomyosarcomatous differentiation based on very minor carcinomatous elements identified and one as rhabdomyosarcoma without carcinomatous elements identified in the tissue examined. In addition, we compared the histologic and immunohistochemical features of these urinary bladder tumors with rhabdomyosarcomatous differentiation to that of well characterized bladder small cell carcinoma.The database of the Department of Pathology and Laboratory Medicine of the University of Pennsylvania was searched for bladder rhabdomyosarcoma, carcinoma with rhabdomyosarcomatous differentiation and small cell carcinoma for the period 1987-2010. One case of rhabdomyosarcoma and two cases of poorly differentiated urothelial carcinoma with extensive rhabdomyosarcomatous differentiation were identified, and the medical charts were reviewed and reported. In addition, 8 cases of pure bladder small cell carcinoma and 5 cases of poorly differentiated urothelial carcinoma with areas of small cell carcinoma were retrieved for the study. All specimens were fixed in a 10% neutral-buffered formalin solution and processed routinely. Histologic sections were reviewed and representative blocks of e