Undifferentiated carcinoma of the renal pelvis with osteoclast-like giant cells: a report of two cases.

Undifferentiated carcinoma with osteoclast-like giant cells arising in the urothelium of the bladder or upper urinary tract is an extremely rare entity. The majority of cases found in the renal pelvis and bladder are associated with either an in situ urothelial malignancy or a conventional high-grade urothelial carcinoma. These malignancies tend to behave poorly with a grim prognosis and course. We report two additional cases of undifferentiated carcinoma with osteoclast-like giant cells of the renal pelvis in two patients disease free 42 and 18 months after surgical treatment, respectively.