[Giant lipomas or retroperitoneal liposarcomas? Controversies in their diagnosis and treatment].

Background: Retroperitoneal lipomas are extremely rare tumors that must be differentiated from well-differentiated liposarcomas (WD-LPS).

Objectives: To summarize the evidence about giant retroperitoneal lipomas or liposarcomas; and to elaborate recommendations for their management.

Data Sources: A systematic literature search from January 1985 to December 2019 and a review of our own cases was performed.

Results: Our series comprises four patients, two females and two males. The diagnosis was incidental in two cases. The medium size was 26 cm, being two cases located exclusively in the retroperitoneum, one in the inguinal region and one in the buttock via pelvic space. All cases were surgically removed being confirmed the initial diagnosis of retroperitoneal lipomas in two cases, as the rest two cases were classified as WD_LPS after MDM2/CDK4 genetic analysis. The review of the available literature plus our own cases revealed 30 cases, of which 58% were woman. Only two cases were asymptomatic. The main symptom was abdominal mass (53%) followed by abdominal pain (40,6%). The median size of the lesions was 24,9 cm with a median weight of 4.576,3 g. All cases were surgically removed, being necessary to remove contiguous organs in only four cases (12,5%).

Conclusions: Retroperitoneal lipoma is a rare tumor which must be differentiated from WD-LPS. This is a very difficult task, being necessary to determinate MDM2 status (by FISH or MLPA), present in liposarcoma but not in lipomas, for its correct diagnosis. The treatment must be based on a complete surgical resection with negative margins.