Undifferentiated sarcoma arising from fibrous dysplasia in a young adult.

Fibrous dysplasia (FD) is a skeletal disorder characterized by the replacement of normal bone by fibrous tissue. Malignant transformation of FD is extremely rare and has been reported in both monostotic and polyostotic forms of FD. The most frequently reported malignant transformation is osteosarcoma. Among malignant bone tumors, spindle cell sarcomas are uncommon and difficult to diagnose. This report presents the case of a 30-year-old woman with an unusual presentation of a malignant undifferentiated spindle cell neoplasm secondary to fibrous dysplasia. The clinical features, radiological findings and management are discussed.