Evaluation of MDM2 and CDK4 gene amplification and expression as potential tools for the diagnosis of atypical lipomatous tumors/well-differentiated liposarcomas in paraffin-embedded material
Authors: Els Meulemans, Ernst-Jan Speel, Andrea Rüland, Maria Debiec-Rychter, Raf Sciot, Patrick Pauwels
Journal: Clinical Cancer Research (2006)

A38   Evaluation of  MDM2  and  CDK4  gene amplification and expression as potential tools for the diagnosis of atypical lipomatous tumors/well-differentiated liposarcomas in paraffin-embedded materialMeulemans EV 1 , Speel EJM 1,2 , Ruland AM 1 , Debiec-Rychter M 3 , Sciot R 4 , Pauwels P 1  Department of Pathology 1 , University Hospital Maastricht, and  2 Department of Molecular Cell Biology, Research Institute Growth and Development (GROW), University of Maastricht, the Netherlands, and Departments of  3 Cytogenetics and  4 Pathology, Leuven University Hospital, Belgium The distinction between lipomas and atypical lipomatous tumours/well differentiated lipo-sarcomas (WDLs) is difficult to make based on histology. Lipomas are cytogenetically characterized by a variety of balanced rearrangements often including the chromosome 12q13-15 region, whereas in WDLs supernumerary ring and giant marker chromosomes have been reported containing amplified 12q sequences. The  MDM2  and  CDK4  genes, located within the 12q13-15 region, are important candidates for amplification, which may result in protein over expression.The goal of this study was to determine if over expression of  MDM2  and/or  CDK4  as well as gene amplification can be used as (a) diagnostic marker(s) to solve differential diagnostic problems between a lipoma and WDL.We analyzed paraffin-embedded material of a series of 31 lipomas, 19 WDLs, and 3 unclassified lesions for  MDM2  and  CDK4  protein accumulation by routine immunohistochemistry and for  MDM2  and  CDK4  gene amplification by multicolor FISH using gene-specific and centromere 12-specific probes.Six of the 31 lipomas showed  MDM2  protein accumulation, particularly in areas with fat necrosis, whereas  CDK4  immunostaining was negative. All lipomas harbored two copies of the chromosome 12 loci per cell nucleus. The 19 WDLs were also disomic for centromere 12, but in 11 cases both  MDM2  and  CDK4  amplification was detected. Of these tumors, 10 exhibited  MDM2  and 9  CDK4  over expression. Accumulation of these proteins was also observed in 5 and 2 of the remaining 8 WDLs, respectively, and again fat necrosis correlated with MDM2 immunostaining. In the 3 unclassified lesions, 2 harbored amplification of both genes associated with protein over expression, implicating that these cases most probably are WDLs. The third case only showed MDM2 protein accumulation and no amplified loci.In conclusion, strong immunostaining of both  MDM2  and  CDK4  proteins is compatible with amplification of both gene loci in WDLs. In contrast, lipomas show no gene amplification and predominantly no protein expression. Because  MDM2  protein expression, however, is often up regulated in case of inflammatory infiltrates present in the tumor, gene amplification detection by FISH or CDK4 immunostaining is indicated in the differential diagnosis of lipoma and WDL. In addition, a subset of WDLs shows no  MDM2  and  CDK4  amplification, suggesting other chromosome loci to be involved in tumor genesis.