Osteoclast-like giant cell tumour of the urinary bladder

We report two cases of osteoclast-like giant cell tumour of urinary bladder associated with papillary transitional cell tumours. Both cases were morphologically identical to giant cell tumour of bone. The giant cells stained strongly for acid phosphatase which was resistant to tartrate digestion, a staining reaction typical of osteoclasts. In view of the ability of urinary bladder to induce metaplastic and neoplastic bone, we believe that these tumours may represent extraosseous giant cell tumours of bone.