Composite adenocarcinoma and carcinoid tumor of urinary bladder.

We present a unique case of primary mixed adenocarcinoma of the urinary bladder consisting of signet-ring cells, glands, and mucinous lakes intimately associated with carcinoid elements. Neuroendocrine differentiation was substantiated with immunohistochemical and ultrastructural studies. The literature on primary carcinoid tumor of the bladder is reviewed.