Osteoclast-rich undifferentiated carcinoma of the urinary bladder: an immunohistochemical study.

Osteoclast-rich undifferentiated carcinoma of the urinary tract is a rare tumor which histologically mimicks giant cell tumor of bone. The histogenesis of this tumor has not been clarified yet although its urothelial origin is proposed on the basis of positive reactions of an epithelial marker on mononuclear undifferentiated tumor cells and the existence of foci of a urothelial carcinoma component in some cases. We experienced a case of urinary bladder tumor diagnosed as osteoclastic-rich undifferentiated carcinoma, and performed an immunohistochemical study on the expression of various markers, including stem cell markers to further characterize the tumor properties. Immunohistochemically, CD56, nestin, and Sox2 were expressed in diffusely proliferating mononuclear tumor cells of undifferentiated features, suggesting the stemness properties of these cells. These findings might provide the clue as to the clarification of the pathogenesis of this rare tumor.