[Malignant change in fibrous dysplasia (author's transl)].

Report on 2 cases of poly-ostotic fibrous dysplasia combined with pigmented areas of the skin with secondary fibrosarcoma of the ulna or femur. They are analysed together with 49 cases published so far. The average age at the time of malignancy being diagnosed was 34.4 years. The average time from recognition of fibrous dysplasia to malignant changes was 17.7 years. In 14 cases local radiotherapy preceded the development of sarcoma. Femur and jaws were the most common sites. There were 30 osteosarcomas, 11 fibrosarcomas and 7 chondrosarcomas. The prognosis is bad: only 14 patients survived for 5 years. But malignant change is rare in fibrous dysplasia. It occurs in less than 1% of cases. Severe forms of poly-ostotic fibrous dysplasia which still progress in adults with a raised alkali phosphatase appear to show an increased tendency towards malignant degeneration.