Evaluation of morphological patterns and immunohistochemical characteristics of well-differentiated and dedifferentiated liposarcomas

Background: Liposarcomas (LPSs) represent a morphologically diverse group among mesenchymal malignancies. During the diagnostic process of soft tissue tumors, the possibility of well-differentiated (WDLPS) and dedifferentiated LPS (DDLPS) should always emerge. So far, the most robust immunohistochemical (IHC) marker for these neoplasms is MDM2, however, LPSs can show a large variety of positivity with other markers. Methods In our study, all cases of WDLPS and DDLPS from 2017 to 2022 at the University of Szeged were examined, and if necessary, additional IHC was performed, including MDM2, CDK4, p16, and STAT6. Results Our cohort included 7 cases of WDLPS, and 11 of DDLPS. All morphological patterns were registered and photographed. In more than half of the cases, the tumor was localized to the retroperitoneum (n = 10), and 8 patients presented with T4 stage disease. All cases were focally or diffusely positive with MDM2 IHC (n = 18), while CDK4 and p16 proved to be diffuse in almost every case (n = 17). Despite morphological diversity, all DDLPSs (n = 11) were positive for MDM2, CDK4, and p16, as well. STAT6 showed multifocal nuclear positivity in 3 DDLPS cases. Conclusions According to our results, MDM2, CDK4, and p16 IHC reactions, and MDM2 fluorescence in situ hybridization should be performed to establish the proper diagnosis of LPS. A small, but significant minority of our DDLPS cases showed multifocal positivity for STAT6, hence performing MDM2 IHC for small samples of solitary fibrous tumours is highly recommended to exclude the possibility of LPS. Our study is the first to include all well-known morphological patterns of LPS.