Carcinosarcoma of the ureter with unusual histologic features.

We report a rare case of carcinosarcoma of the ureter presented as a retroperitoneal tumor. The tumor originated in the ureter as a polypoid protrusion and spread around peri-ureteral, retroperitoneal tissues. The polypoid ureteral tumor was composed of an intra-epithelial carcinoma and a submucosal mesenchymal tumor; the histology of the retroperitoneal tumor in the original site was that of a carcinosarcoma. The bulk of the tumor in the retroperitoneum was composed of blastematous, epithelial and sarcomatous neoplastic cells with foci resembling an incomplete glomeruloid formation, thus mimicking a Wilms' tumor. The lesion appeared to originate from multipotential cells in the mucosal layer of the ureter. Whether or not this tumor has a true nephrogenic property is currently unknown. When a retroperitoneal tumor of the adult resembling a Wilms' tumor is found, one should suspect a possible carcinosarcomatous origin in the ureter.