Malignant giant cell tumor of bone: malignant transformation of a benign giant cell tumor treated by surgery.

A case of a giant cell tumor of the right proximal femur that developed malignant change following surgical treatment ("secondary" malignant giant cell tumor) is presented. The patient had a cystic lesion that was initially interpreted as an aneurysmal bone cyst. A local recurrence six months later demonstrated the histological features of typical giant cell tumor. A further recurrence 22 months after the original treatment showed histological malignancy. Death was due to massive local recurrence and to extension of the malignancy to the pleura.