Malignant osteoclastoma-like giant cell tumour of the renal pelvis.

We report the fourth case of an osteoclastoma-like giant cell tumour of the renal pelvis. A special feature was that although thorough sampling of the tumour showed an osteoclastoma-like pattern throughout, it was intimately associated with carcinoma in situ change of the adjacent transitional epithelium and this provides further support for the view that these tumours are of epithelial derivation. However, immunohistological and ultrastructural studies failed to reveal epithelial features within the tumour cells and the possible significance of this finding is discussed.