Carcinosarcoma of the urinary bladder: a distinct variant characterized by small cell undifferentiated carcinoma with neuroendocrine features.

The clinicopathological features of two carcinosarcomas of the urinary bladder are reported. The tumours occurred in a 64- and a 66-year-old patient presenting with haematuria and both were polypoid. The epithelial component was consistent with small cell undifferentiated carcinoma with neuroendocrine differentiation, whereas the sarcomatous component did not display specific features. The carcinomatous component showed immunohistochemical reactivity for different epithelial markers as well as for chromogranin and neuron specific enolase. Conversely, the sarcomatous cells stained strongly for vimentin and in one case for muscle actin and smooth muscle actin. The differential diagnosis of biphasic tumours of the bladder is discussed and the literature reviewed.