Malignant osteoclast-like giant cell tumor of the kidney.

Osteoclast-like giant cell tumors are rare mesenchymal tumors that typically present in osseous tissue and are remarkable because of their slow growth. We report the sixth documented case of a malignant osteoclast-like giant-cell tumor primary to the kidney of an 81-year-old man with a 5-month history of hematuria. Postnephrectomy analysis of the tumor, including immunohistochemical stains and electron microscopy, confirmed the diagnosis. Although the patient died of unrelated complications, metastatic disease was suspected.