Computed tomography (CT) scans of the abdomen of a 63 year old female patient with a cystic dedifferentiated liposarcoma (at lower right in scan at left) in the retroperitoneum before (left) and after (right) surgery to remove it. Liposarcomas are malignant (cancerous) tumours that develop from fat tissue. A dedifferentiated liposarcoma is an aggressive cancer that arises from a pre-existing well-differentiated liposarcoma, which is a slow-growing cancer. A dedifferentiated liposarcoma is more likely to spread (metastasise) and more likely to reoccur than a well-differentiated liposarcoma. The formation of cysts (fluid-filled sacs) is rare in liposarcomas. Treatment is with surgical removal of the tumour.