Giant-cell tumor-like proliferation associated with a papillary transitional cell carcinoma of the renal pelvis.

A 56-year-old man with painless hematuria was found to have a papillary transitional cell carcinoma of the renal pelvis with an accompanying nodule composed of multinucleated and mononuclear cells, resembling a giant cell tumor of bone. The nodule was well demarcated from the carcinoma and most likely represents a response to hemorrhage into a cystic cavity. A classification composed of four groups is proposed for extraosseous tumors having features resembling giant cell tumors of bone. This grouping should help in predicting prognosis and avoid the overdiagnosis of sarcoma or undifferentiated carcinoma.