Extraskeletal osteosarcoma of the diaphragm presenting as a chest mass

Extraskeletal osteosarcoma is a rare malignancy that has not been previously reported to arise from the diaphragm. We describe the case of a 47-year-old woman who had a large thoracic mass found at operation to be an extraskeletal osteosarcoma arising from the diaphragm. The tumor was completely resected en bloc with a margin of surrounding diaphragm, which necessitated a diaphragmatic reconstruction. The literature concerning this rare tumor is reviewed.