Well-differentiated extraskeletal osteosarcoma. A soft-tissue homologue of parosteal osteosarcoma.

We describe a unique case of a low-grade extraskeletal osteosarcoma revealing both histologic and radiologic features reminiscent of parosteal osteosarcoma. The tumor, which had been present for 10 years, occurred in the left axilla of a 74-year-old black woman. To date, all the published cases of extraskeletal osteosarcoma have been high-grade neoplasms; to our knowledge, this is the first reported case of a low-grade extraskeletal osteosarcoma.