MDM4 and soft tissue neoplasm: Mutation of the TP53 gene occurs in approximately 50% of common adult sporadic cancers, resulting in inactive protein.2,3 Alternatively, p53 may be silenced by the overexpression of the regulatory proteins MDM2 or MDMX (MDM4).4–6 MDM2 amplification has been reported to occur in approximately 11% of all tumors and the paralogue MDMX has been reported to be amplified in brain (11%), breast (5–40%), and soft tissue tumors (17%).