Malignant Transformation of Fibrous Dysplasia

A 34-year-old man developed a spindle-cell sarcoma originating in a preexisting lesion of monostotic fibrous dysplasia. A review of the literature reveals 83 cases of a malignant degeneration in fibrous dysplasia; osteosarcoma was the most common type of tumor. The next most common were fibrosarcoma and chondrosarcoma. The malignant tumor usually developed in the third or fourth decade of life. The most frequent anatomic sites were the craniofacial bones, the femur, and the tibia. Twenty-three of the 83 cases were treated with local radiation. In fibrous dysplasia, any abrupt alteration in the clinical course, manifested by pain and swelling, raises the possibility of malignant degeneration.