Mouse double minute protein 2 (MDM2) is a gene encoded on the 12q13-14 chromosomal sequence.^1-5 It encodes for a 483 amino acid residue protein which binds to the amino-terminal transcription region of p53.^2,5  MDM2 has been shown to negatively regulate the tumor-suppressor activity of p53 by three mechanisms:  Blocking p53 transcription, binding to p53 causing it to be exported from the nucleus, and accelerating the destruction of p53.¹ MDM2 up-regulation has been shown in liposarcoma while being absent in lipoma.^2,4 Therefore, anti-MDM2 has been demonstrated to be a potentially useful tool in distinguishing well-differentiated liposarcoma (atypical lipomatous tumor) from lipoma, with the neoplastic cells positive in the former lesion and negative in lipoma.^2,4