Borderline Sign of A Rare Dedifferentiated Liposarcoma: Report of A Case

Abstract Background: Dedifferentiated liposarcoma (DDLPS) is a unique subtype of liposarcoma, which has obvious histological heterogeneity. Most of them manifested as the dedifferentiation of high-grade histological morphology, but a few could be the dedifferentiation of low-grade histological morphology, or present as some special types of histological or immunophenotypic characteristics. We describe, herein, a case of rare type of dedifferentiated liposarcoma, in which the dedifferentiated components are high-grade and low-grade coexisting with a relatively sharp transition.Case presentation: A 69-year-old woman with severe abdominal pain lasting for 1 hour presented to our hospital. Physical examination revealed a mobile large left abdominal mass, which was shown on abdominal CT and MRI as a huge retroperitoneal tumor with lipogenic component and solid nonlipogenic components. Tumor resection was performed. Gross examination of the resected specimen showed the gray yellow fatty mass and a round like solid nodule adjacent to the fatty mass, the cut surface of the nodule was gray-white or fish flesh color, and gray yellow in the nodular center. Microscopic examination demonstrated the tumor contains the well-differentiated liposarcoma (WDLPS) component and the DDLPS component. The latter was composed of coexisting high-grade and low-grade components in which multiple focal regions of a sudden transition between the high-grade and the low-grade dedifferentiated component were identified. Immunohistochemistry showed that P16, CDK4, and MDM2 were diffusely positive. The FISH analysis revealed the presence of MDM2 gene amplification in the nuclei of the atypical cells. A final diagnosis of DDLPS was rendered.Conclusion: In our case, the borderline sign between the high-grade and low-grade dedifferentiated components in the histology may indicate that there can be obvious differentiation lines in tumor dedifferentiation, which is classically and typically abrupt. Low-grade dedifferentiation may be a precursor lesion of high-grade dedifferentiation. MRI images cannot distinguish the two components.