The MDM2 (murine double minute-2) gene is an oncogene whose expression plays important roles in controlling the cell cycle and tumorigenesis. gated the amplification status of MDM2 in MPNSTs. The p53 and MDM2 proteins function in the same cell proliferation pathway and have directly antagonistic functions. The MDM2 gene is located on chromosome 12, and has been reported to be amplified in a subset of malignant tumors. MDM2 is known to be abnormally upregulated in a variety of human neoplasms, secondary to gene amplification. Assessment of MDM2 amplification is most useful clinically for separating lipomas (nonamplified) from atypical lipomatous neoplasms or well-differentiated liposarcomas (amplified). Dedifferentiated liposarcoma (DDLPS) has been defined as a tumor composed of well-differentiated liposarcoma associated with a nonlipogenic undifferentiated sarcoma and is genetically characterized by a 12q13-15 amplicon with MDM2 amplification. Some peripheral (extremities, trunk wall, head/neck) undifferentiated pleomorphic sarcomas (UPS) without areas of well-differentiated liposarcoma present an MDM2 amplification.