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[A CASE OF EXTRASKELETAL EWING'S SARCOMA IN THE RETROPERITONEUM].

A 23-year-old man was admitted to our hospital with a huge pelvic tumor. MRI showed a tumor mixed with a solid component and polycystic cyst with maximum diameter of about 20 cm. Percutaneous tumor needle biopsy was performed and diagnosis was Ewing sarcoma. At that time, operation is extremely difficult, so the neoadjuvant chemotherapy with ifosfamide, etoposide, Adriamycin, and vincristine were administered. After 6 courses, MRI showed tumor reduction to maximum diameter of 10 cm. We planned tumor resection with total cystectomy for radical resection, but we also tried to preserve bladder considering the young age and quality of life. Although the bladder was partially resected, tumor resection was succeeded without removing surrounding organs. Histopathological examination revealed viable cells remained, but more than 95% was disappeared and the surgical margins were negative. Here we report a case of extra skeletal Ewing sarcoma in the retroperitoneum that was treated with chemotherapy and surgery without scarifying surrounding organs.