Dedifferentiated Liposarcoma with Heterologous and Homologous Elements-A Report of Three Cases

Abstract

Background: Osteosarcoma (OS) heterologous component in dedifferentiated liposarcoma (DDL) is rare, but should be considered and MDM2/ CDK-4 testing employed. Myxoid liposarcoma-like (ML) homologous differentiation with simultaneous MDM2 and DDDIT3 amplification is also unusual, and needs to be recognized as it has implications for diagnosis. Case series: We report three special cases of DDL, two in the retroperitoneum and one in the abdomen: a DDL with OS differentiation, confirmed by MDM2 and CDK4 positive testing, as well as two DDL with homologous ML differentiation confirmed by simultaneous positive MDM2 and DDIT3 testing. In case of a DDL with heterologous osseous differentiation, it is important to sample extensively and identify WDL areas, in order to exclude the diagnosis of extraosseous OS. Without the rare foci of WDL, the extensive high grade spindled DDL may have been misinterpreted as extraosseous OS. MDM2 and CDK4 were useful for the final diagnosis. FISH testing for MDM2 and DDIT3 amplification is also necessary in DDL with ML foci. WDL and DDL can contain ML component, a diagnostic challenge when confronted with a small biopsy. Such tumors have been shown to contain co-amplifications of MDM2 and DDIT3, further adding to a diagnostic dilemma. Conclusion: The presence of pleomorphic cells or lipoblasts in WDL or DDL, as seen in our two cases, should prompt considering MDM2 FISH testing in conjunction with DDIT3, rather than DDIT3 alone. Furthermore, the first case illustrates the utility of MDM2 and CDK4 testing in ruling out other high-grade sarcomas when a DDL diagnosis is uncertain due to absent WDL or presence of heterologous component, particularly high-grade OS.