Retroperitoneal extraskeletal osteosarcoma (ESOS) is a rare and highly invasive tumor that is usually diagnosed at an advanced stage due to the insidious onset. The present study analyses a case of retroperitoneal ESOS and its clinical, radiological and therapeutic conditions, and also provides a review of the literature. A 52-year-old male was diagnosed with retroperitoneal ESOS. The patient succumbed to the condition one year after the initial surgery. During treatment, the patient underwent two additional surgeries and two courses of chemotherapy. In the present case, a peritoneal metastatic lesion of ESOS was shed from the peritoneum and implanted into the outer membrane of the stomach and metastasis was identified, this has rarely been reported in the literature. Retroperitoneal ESOS should be considered in the differential diagnosis of a retroperitoneal mass in order to facilitate the management of surgery and help determine the appropriate treatment of the disease.
Keywords: implantation metastasis; retroperitoneal extraskeletal osteosarcoma; therapy.