[A Case of Retroperitoneal Primary Undifferentiated Pleomorphic Sarcoma with a Rapid Course].

A 50-year-old woman presented to our hospital in May2021 with a fever of approximately39 °C and abdominal pain. A contrast-enhanced computed tomography (CT) scan revealed an 88 mm right renal tumor. Two weeks later, a follow-up CT scan demonstrated rapid tumor growth, with the major axis measuring 100 mm. During this interval, her abdominal pain worsened, and she developed lower leg edema. A contrast-enhanced CT scan conducted 5 days before the scheduled surgery, four weeks after initial presentation, showed further tumor progression, with a diameter of 155 mm. The tumor, which had infiltrated the ascending colon, duodenum, liver, gallbladder, and inferior vena cava (IVC), was surgically removed along with the right kidney. Due to its complexity, the planned wide excision was deemed infeasible. Therefore, a tumor resection was performed macroscopically. Histopathological examination confirmed the diagnosis of undifferentiated pleomorphic sarcoma (UPS). Subsequently, the patient experienced a postoperative tumor recurrence. Although the patient received doxorubicin chemotherapy, she passed away5 weeks after the operation. This case highlights the critical importance of prompt surgical excision with adequate tumor margins in the management of UPS.