CT-Guided Iodine-125 Seed Implantation Combined with Anlotinib for Recurrent Retroperitoneal Undifferentiated Pleomorphic Sarcoma: A Case Report

Introduction: Undifferentiated sarcoma is a rare and highly aggressive malignancy with a high risk of postoperative recurrence and limited treatment options. The management of recurrent retroperitoneal sarcoma remains challenging. CT-guided iodine-125 (I-125) seed implantation provides localized brachytherapy, while anlotinib, a multi-target tyrosine kinase inhibitor, has demonstrated efficacy in soft-tissue sarcomas. However, evidence regarding their combined use is limited. Case Presentation: We report a patient with recurrent retroperitoneal undifferentiated sarcoma following prior surgical resection. The recurrence was identified on follow-up imaging as a retroperitoneal mass with irregular margins and heterogeneous enhancement, and was deemed unresectable due to its proximity to critical structures. After multidisciplinary evaluation, the patient underwent CT-guided I-125 radioactive seed implantation for local tumor control. The procedure was successfully completed without complications. Subsequently, the patient received oral anlotinib therapy. The combined treatment was well tolerated, with no severe adverse events observed. Serial follow-up imaging demonstrated a reduction in tumor size and sustained local disease control, indicating a favorable therapeutic response. Conclusion: This case suggests that CT-guided I-125 seed implantation combined with anlotinib may be a safe and effective therapeutic option for patients with recurrent retroperitoneal undifferentiated sarcoma who are not candidates for surgery. Further studies are warranted to confirm these findings.