Dedifferentiated liposarcoma (DDLPS) is a subtype of sarcoma that originates from atypical lipomatous tumor/well-differentiated liposarcoma and undergoes varying degrees of dedifferentiation. DDLPS can occur either concurrently with or after atypical lipomatous tumor/well-differentiated liposarcoma, with the dedifferentiated component predominantly consisting of high-grade sarcomas. Notably, only approximately 10% of DDLPS cases present as purely low-grade sarcomas. Cases exhibiting characteristics of both low-grade fibromyxoid sarcoma (LGFMS) and inflammatory myofibroblastic tumor (IMT)-like features have not been reported. Moreover, histopathologic overlap with other mesenchymal neoplasms, particularly IMT and LGFMS, poses significant diagnostic challenges. This morphologic similarity frequently causes diagnostic confusion with critical therapeutic implications, given the markedly divergent management strategies for these entities. This study aims to clarify the pathologic features and differential diagnosis of DDLPS to improve diagnostic recognition among pathologists. A 60-year-old man presented with a 1-month history of progressive enlargement of a painless left abdominal mass. Associated constitutional symptoms, including fever and unintentional weight loss, were absent. Dedifferentiated liposarcoma (FNCLCC grade 2) featuring well-differentiated, IMT-like, and LGFMS-like components. This conclusion was confirmed by the demonstration of MDM2 amplification via fluorescence in situ hybridization. The patient underwent complete resection. Postoperatively, no adjuvant therapy was administered. Surveillance comprised quarterly abdominothoracic computed tomography scans for the first 2 postoperative years, per institutional protocol. At the 1-year follow-up, surveillance imaging showed no evidence of local recurrence or distant metastasis. The patient remained asymptomatic with preserved renal and gastrointestinal function. This case underscores critical clinical lessons: diagnostic vigilance is paramount when assessing sarcomas with mixed morphological patterns, given that DDLPS may closely mimic IMT or LGFMS. To prevent misdiagnosis, a systematic diagnostic approach radiological, immunohistochemistry, and confirmatory molecular testing is essential. Therapeutic management relies on complete surgical resection, with adjuvant therapy decisions guided by multidisciplinary evaluation. Long-term surveillance remains necessary due to recognized risks of late recurrence in retroperitoneal DDLPS, mandating sustained follow-up.
Huang et al. (Fri,) studied this question.