Small cell neuroendocrine carcinoma of the urinary bladder: report on two cases and review of the literature.

Small cell (Neuroendocrine) carcinoma of the urinary bladder is a rare but highly aggressive malignancy. The neoplastic cells exhibit both neuroendocrine and epithelial differentiation. It is morphologically indistinguishable from the more common pulmonary small cell carcinoma. It can occur either in association with urothelial (transitional cell) carcinoma or in a pure form. Presenting signs and symptoms are non specific. Histologically, it can mimic poorly differentiated urothelial carcinoma and lymphoma. Muscle invasion is almost invariably present at diagnosis and mortality is mainly due to metastases rather than loco regional recurrence. The optimal therapeutic modality is still controversial. In this article, we report on two cases occurring in a pure form and we briefly review the published literature regarding the clinical presentation, morphology, differential diagnosis, prognosis and treatment.