Atypical Lipomatous Tumor/Well-Diff Liposarcoma : MDM2 Amplification
MDM2 and CDK4 are amplified in atypical lipomatous tumor/well-differentiated liposarcomas (ALT/WDLs). Immunoreactivity for MDM2 and CDK4 is useful in separating benign lipomatous tumors (neg for CDK4 & MDM2) from ALT/WDL and separating pleomorphic soft tissue sarcomas from de-differentiated liposarcomas. The vast majority of ALT/WDLs are positive for these markers but the percentage of positive cells is variable. The staining is limited to the hyperchromatic nuclei of atypical stromal cells. CDK4 and MDM2 immunohistochemistry has significant limitations. False positive staining may be detected in a small percentage of spindle cell/pleomorphic lipomas, foamy macrophages in areas of fat necrosis, and occasional non-lipomatous sarcomas like malignant peripheral nerve sheath tumors.