Large Retroperitoneal Extraosseous Osteosarcoma Invading into the Spine: a Case Report.

Extraosseous osteogenic sarcoma is a very rare malignant neoplasm. The most common sites are the extremities, thorax, and the abdomen. Retroperitoneal osteosarcomas are rare and very few cases have been reported. They are similar in their biology to high-grade soft tissue sarcomas. R0 resection appears to be the best possible treatment for these tumors but there are no published cases on how to manage them when it involves posterior and intra-spinal regions. We report a 62-year-old male who presented with a backache, and investigations revealed a large retroperitoneal fibrosarcoma invading into the lumbar spine, but was found to be an extra osseous osteosarcoma on final histopathological examination. It is important to emphasize that due to the rarity of soft tissue sarcomas as well as the uniqueness of the multimodal treatment plan for each subtype, soft tissue sarcomas involving the spine are best managed by a multi disciplinary team. Overall, patients with soft tissue sarcomas involving the spine usually present a poor long-term prognosis. Therefore, whenever feasible, "en bloc" resection of such lesions has been shown to play a crucial role in improving the overall and recurrence-free survival rates.