[Superficial extraskeletal osteosarcoma. Case report].

Background: Osteosarcoma is the most common primary malignant bone neoplasm in young people. Presentation in non-bone tissues comprises 2 to 5% of all osteosarcomas and less than 1% of all soft tissue sarcomas. On rare occasions it presents as a superficial tumor, making it necessary to make a differential diagnosis with benign entities, such as pyogenic granuloma ossificans, and malignant neoplasms, with sarcomatoid differentiation such as carcinosarcoma and dedifferentiated melanoma.