Abstract
Extraosseous osteosarcoma is a rare malignancy, but simple lipomas are common. This article is the first report of a case of radiation-induced extraosseous osteosarcoma that developed within a simple lipoma in a 72-year-old woman. We correlate the magnetic resonance imaging, computed tomography, positron emission tomography, and plain radiographic findings. The patient, treated with systemic therapy and wide surgical resection of the neoplasm, remained clinically free of disease during the first 22 months of follow-up.