Co-amplification of MDM2 and CDK4 is a common feature in well-differentiated liposarcoma and is thought to be the initiating “driving” factor in fat tumorigenesis, resulting in proliferation through combined effects upon p53 (by inactivating TP53) and the cell cycle (by RB1 phosphorylation), respectively. The gene discussed is CDK4; the disease is liposarcoma.