Computed tomography (CT) scan of the abdomen of a patient with a dedifferentiated liposarcoma (spherical, left) in the retroperitoneum. 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. Treatment is with surgical removal of the tumour.