Diagnosis of osteosarcoma in a patient previously treated for Ewing sarcoma.

Primary malignant bone tumors, whether Ewing sarcoma or osteosarcoma, are a rare type of tumor. The sequential occurrence of two bone sarcomas, Ewing sarcoma and high-grade osteosarcoma, in the same patient at two different locations is an exceptionally rare phenomenon. We present the case of a 13-year-old girl who presented with a high-grade osteoblastic osteosarcoma of the distal femur, 7 years after treatment for Ewing sarcoma of the left pelvis. She did not receive radiation therapy. Following the recent developing multidisciplinary therapy, long-term follow-up for monitoring latent treatment-related adverse effects may be necessary for survivors of primary malignant bone tumors.