Extraskeletal osteosarcoma of the breast in an adolescent girl.

: Extraskeletal osteosarcoma (ESOS) is a rare malignancy, usually arising in older adults. We were unable to find reports of children or adolescents affected by an ESOS of the breast. Here, we present the case of a high-grade osteosarcoma arising in the breast of a 16-year-old girl. The tumor was treated with breast-conserving resections and adjuvant multiagent chemotherapy, based on a regimen of doxorubicin, high-dose methotrexate, cisplatin, and ifosfamide. At last follow-up, the patient was in first complete remission, 29 months after initial diagnosis.