Carcinosarcomatous malignancy, osteosarcoma and squamous cell carcinoma, in giant cell tumor of the right distal femur.

We report a new type of secondary malignant giant cell tumor of bone, the malignancy of which was assigned to a carcinosarcoma, i.e., osteosarcoma and squamous cell carcinoma. It occurred 25 years after curettage and bone graft surgery under the diagnosis of giant cell tumor of the right distal femur. Although secondary malignant giant cell tumor is known as a sarcoma arising at the site of a previously diagnosed giant cell tumor, this case should be regarded as a new type of secondary malignant giant cell tumor of bone.