p53 is the most frequently mutated tumor suppressor genein human cancer. It prevents cell cycle progression andpromotes cell cycle arrest following DNA damage. TheMDM2 (murine double minute-2) protein was firstidentified as an oncogene and is now known to function asa negative regulator of p53 by binding and blocking itstranscriptional activity.Overexpression or amplification of MDM2 is common inhuman sarcomas, particularly well-differentiated anddedifferentiated liposarcomas, as well as someosteosarcomas, where it can serve as a useful marker.Research applications of MDM2 include studyingtumorigenesis, p53 regulation, and differential diagnosis oflipomatous tumors.