NCI: An intermediate malignant mesenchymal neoplasm composed entirely or in part of mature adipocytes that vary in cell size and show at least focal nuclear atypia in adipocytes and stromal cells. Recurrent cytogenetic aberrations are specifically associated with this entity: supernumerary ring and giant marker chromosomes with amplification of MDM2 and, often, CDK4.,NCI: A locally aggressive malignant neoplasm composed of mature adipocytes showing cell size variation and nuclear atypia. It is often associated with the presence of hyperchromatic multinucleated stromal cells, and varying numbers of lipoblasts. There are three histologic subtypes, sclerosing, inflammatory, and spindle cell liposarcoma. These tumors do not usually metastasize unless they undergo dedifferentiation.