Beyond the bones: Extraskeletal osteosarcoma of the thigh.

Extraskeletal osteosarcoma (ESOS) is a rare malignant mesenchymal soft tissue tumor that usually arises in the lower extremities. It is typically a high-grade malignancy that represents only around 1%-2% of all soft tissue sarcomas and 2%-4% of all osteosarcomas. In this report, we describe a case of a 67-year-old female who presented with a 4-day history of a painless lump in her posterior right thigh.