[Evaluation of morphological patterns and immunohistochemical characteristics of well-differentiated and...

Introduction: Liposarcomas represent a morphologically diverse group among mesenchymal malignancies. During the diagnostic process of soft tissue tumors, the possibility of well-differentiated and dedifferentiated liposarcoma should always emerge. So far, the most robust immunohistochemical (IHC) marker for these neoplasms is MDM2, however, liposarcomas can show a large variety of positivity with other markers. Methods: In our study, all cases of well-differentiated and dedifferentiated liposarcomas from 2017 to 2022 at the University of Szeged were re-examined, and if necessary, additional IHC was performed, including MDM2, CDK4, p16, and STAT6. Results: Our cohort included 7 cases of well-differentiated, and 11 of dedifferentiated liposarcomas. All morphological patterns were registered and photographed. In more than half of the cases, the tumor was localized to the retroperitoneum (n = 11), 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 dedifferentiated liposarcomas (n = 11) were positive for MDM2, CDK4, and p16 as well. STAT6 showed multifocal nuclear positivity in 3 dedifferentiated liposarcoma cases. Conclusions: Based on our results, MDM2, CDK4, and p16 IHC reactions, and MDM2 fluorescence in situ hybridization should be performed to establish the proper diagnosis of liposarcoma. A small, but significant minority of our dedifferentiated liposarcoma 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 liposarcoma. Our study is the first to include all well-known morphological patterns of liposarcomas. Orv Hetil. 2024; 165(43): 1700–1706.