[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. Accurate diagnosis requires correlation of the histological, macroscopic and imaging characteristics of the neoplasm, which is of great relevance since the biological behavior and treatment differ from that of bone osteosarcoma and dedifferentiated neoplasms. Clinical case: We present the case of a 52-year-old man with superficial extraskeletal osteosarcoma, with radiological and pathological characteristics characteristic of this neoplasm. Conclusions: Superficial extraskeletal osteosarcoma is extremely rare, representing less than 10% of extraskeletal osteosarcomas, histological evaluation and imaging studies are mandatory for diagnosis, and clinical history is useful both to rule out differential diagnoses and to contribute to the diagnosis. definitive. Superficial extraskeletal osteosarcoma was diagnosed in this patient based on histological criteria. However, the few findings reported prevent us from knowing the prognostic factors.