Retroperitoneal Dedifferentiated Liposarcoma With Penetrating Abscess Formation Secondary to Ileal Invasion: A Case Report.

Liposarcoma is a relatively common malignant soft tissue tumor in adults. Dedifferentiated liposarcoma (DLS) is a particularly invasive subtype characterized by high recurrence rates and a poor prognosis. We describe a case of a retroperitoneal liposarcoma with poor differentiation that presented with peritonitis accompanied by ileal infiltration and perforating abscess formation. A 77-year-old male presented to our hospital with abdominal pain and fever. Computed tomography revealed a 13 cm tumor in the right lower abdomen with internal air density. An ileocecal resection was performed. Histopathological examination revealed a solid proliferation of spindle-shaped atypical cells. Immunohistochemical results were positive for MDM2 and negative for CD34 and c-kit. Fluorescence in situ hybridization confirmed MDM2 amplification, leading to a diagnosis of dedifferentiated liposarcoma. The postoperative course was initially favorable; however, 6 months later, a penetrating abscess recurred and progressed to an enterocutaneous fistula. Intestinal penetration by dedifferentiated liposarcomas is extremely rare. This case highlights the challenges of preoperative diagnosis, the importance of surgical strategies that balance infection control with curative resection, and the need for multidisciplinary management of recurrence.