Soft tissue osteosarcoma: a case report.

Osteosarcomas arising from extraskeletal locations are extremely rare and their true prevalence is unknown. We describe a case of soft tissue-origin-osteosarcoma arising from the vastus medialis muscle in a 58-year old woman. The possibility of a malignant tumour was not suspected initially and she was referred to a specialist unit only one year after the onset of the swelling. She was successfully treated with a surgical resection, chemotherapy and radiotherapy. Because of the rarity of the tumour, a high degree of suspicion is required to make an early diagnosis. The differential diagnosis of a soft tissue mass located in the thigh in a patient over the age of 40 years, should include extraskeletal osteosarcoma.