Malignant transformation in a patient with fibrous dysplasia and aneurysmal bone cyst

A 38-year old woman, with a history of monostotic fibrous dysplasia (MFD) of the right femur, developed secondary transformationto both an osteosarcoma and an aneurysmal bone cyst. The patient was initially treated with wide resection and insertion of a hipprosthesis and postoperative chemotherapy. After 3 months she had a recurrence and a hemipelvectomy was performed, followedby a new series of chemotherapy. Seven years after treatment the patient is still alive with no signs of metastasis. It is unknownwhether the osteosarcoma developed from the MFD or from the aneurysmal bone cyst. Secondary transformation of fibrous dysplasia into osteosarcoma is a rare event, especially in MFD without concomitant McCune-Albright syndrome or in patients with MFD without prior radiation therapy. Transformation of an aneurysmal bone cyst is aneven more rare event. This case is reported due to the rare event of malignant transformation of MFD with a concomitant aneurysmal bone cyst and dueto the favorable outcome, in spite of the poor prognosis associated with the condition.