[Retroperitoneal Dedifferentiated Liposarcoma with No Recurrence after 5 Years of Postoperative Radiation Therapy --A Case Report-].

A 49-year-old woman presented to our hospital with right lower back pain and epigastric pressure. A computed tomographic scan showed a 12×7×20 cm retroperitoneal mass comprising fatty components and contrast areas around the right kidney. Based on the results, a right retroperitoneal liposarcoma was suspected. Thus, right retroperitoneal tumor resection combined with right kidney resection was performed. Instances of tumor adhesion were found in the ascending colon, duodenum, and the iliopsoas muscle, which could be dissected ; therefore, combined resection of the intestinal tract was not performed. The resected tumor was found to be mixed with dedifferentiated and well-differentiated components and was diagnosed as dedifferentiated liposarcoma. Due to the presence of positive margins, the patient received 50 Gy in 25 fractions of radiation therapy to the right side of the retroperitoneum as postoperative adjuvant therapy. During the irradiation period, vomiting and anorexia were observed as adverse events. Five years have passed since the surgery, and no local recurrence or late complications due to radiation have been observed. Although dedifferentiated liposarcoma is a highly malignant histological type with a very high local recurrence rate, no adjuvant therapy has been established. Some reports have suggested that postoperative radiation therapy for retroperitoneal sarcoma is effective in terms of survival and local control. However, there are no reports of prospective clinical trials, and the evidence is expected to widen in the near future.