A chemosensitive pediatric extraosseous osteosarcoma: case report and review of the literature.

Osteosarcoma arising in soft tissues is exceedingly rare in children. The tumor most often affects older adults, involves the lower extremity, responds poorly to chemotherapy, and carries a grave prognosis. The authors describe a 12-year-old girl with an extraosseous osteosarcoma of the left sternocleidomastoid muscle with pulmonary metastases. The patient responded well to neoadjuvant chemotherapy and remains disease-free nearly 3 years after her initial diagnosis. The authors review available information about this disease in children and adults. Children with extraosseous osteosarcoma may have a more favorable response to treatment than adults; thus, a curative approach using combined modality therapy appears warranted.