A rare, fast-growing type of cancer that begins in fat cells. It usually forms in the deep soft tissues of the arms or legs, but it may also form in the abdomen or chest. Pleomorphic liposarcoma often recurs (comes back) after treatment and spreads to other parts of the body, including the lungs. It usually occurs in older adults, and is rare in children and adolescents. Pleomorphic liposarcoma is a type of soft tissue sarcoma.