Oat cell carcinoma of urinary bladder.

Oat cell carcinoma of the urinary bladder is extremely uncommon. There have been 52 reported cases in world literature to date. On light microscopic, histochemical, and ultrastructural grounds, these tumors are similar to oat cell carcinoma of the bronchus and other extrapulmonary oat cell carcinomas. Furthermore, they may be grouped together as a clinical entity characterized by an aggressive clinical course with early and extensive metastases, and partial remission with certain chemotherapeutic agents. We report a case of primary small cell carcinoma of the urinary bladder in a forty-two-year-old man and review previous reports with similar histology. The importance of establishing this diagnosis and the optimum forms of therapy are discussed.