Giant primary retroperitoneal myxofibrosarcoma mimicking myxoid liposarcoma: a diagnostic and surgical challenge.

Myxofibrosarcoma (MFS) is a fibroblastic sarcoma that typically arises in the extremities of elderly patients; primary retroperitoneal involvement is exceptionally rare and often mimics myxoid liposarcoma. We report a 53-year-old man with a three-month history of progressive abdominal distension caused by a giant retroperitoneal mass measuring 26 cm. Core needle biopsy suggested a low-grade myxoid sarcoma, with myxoid liposarcoma not excluded. Multidisciplinary discussion led to en bloc left compartmental resection, including left colectomy, nephrectomy, adrenalectomy, and splenopancreatectomy. Histopathology confirmed a FNCLCC grade II myxoid sarcoma; fluorescence in situ hybridization showed no MDM2 amplification, confirming MFS and excluding dedifferentiated liposarcoma. The patient remained disease-free at 22 months. This case underscores the diagnostic overlap between retroperitoneal MFS and liposarcoma, the pivotal role of molecular pathology, and the importance of complete compartmental resection for local control.