Well-Differentiated Extraskeletal Osteosarcoma Arising from the Retroperitoneum That Recurred as Anaplastic Spindle Cell Sarcoma

<table>Abdominal CT revealed a large mass with diffuse calcification in the right retroperitoneal space.</table>

Case Reports in Medicine

Figure 1: Well-Differentiated Extraskeletal Osteosarcoma Arising from the Retroperitoneum That Recurred as Anaplastic Spindle Cell Sarcoma 