Pure primary small cell carcinoma of urinary bladder: A rare diagnostic entity.

Small cell carcinoma of the bladder is a rare, aggressive, poorly differentiated neuroendocrine neoplasm accounting for only 0.3-0.7% of all bladder tumors. Since the tumor is very rare, pathogenesis is uncertain. Small cell carcinomas of the urinary bladder are mixed with classic urothelial carcinomas or adenocarcinomas of the bladder in 68% cases, making pure primary small cell carcinoma even a rarer entity. The unknown etiology and natural history of small cell carcinoma of the urinary bladder represent a challenge both to the pathologist and urologists for its diagnosis and treatment, respectively.