Extrapulmonary small cell carcinoma of the bladder.

Among the many sites for primary small cell cancer is the genitourinary system. The majority of cases have been observed in the bladder and prostate. Small cell carcinoma accounts for less than 1% of all bladder tumors. Definitive predisposing factors are unknown; however, small cell carcinoma of the bladder has been associated with cigarette smoking, long-standing cystitis, bladder calculus, and augmented cystoplasty. Contrary to the early theory of derivation from Kulchitsky cells, it is now believed that small cell carcinoma of the bladder originates from the totipotent stem cells present in the submucosa of the bladder wall. A number of chromosomal aberrations have been reported in small cell cancer of the bladder. There are no specific clinical features that differentiate these patients from transitional cell carcinoma of the bladder; however, some patients may have associated paraneoplastic conditions. Diagnosis is established by cystoscopic-assisted biopsy. Like small cell carcinoma of the lung, small cell carcinoma of the bladder has a propensity for early metastases. There is no standard therapy for small cell carcinoma of the bladder and the prognosis is poor; however, patients treated with cisplatin-based chemotherapy regimens seem to have a better prognosis.