Dedifferentiated liposarcoma presenting with ascites as the initial clinical manifestation: a case report and literature review.

Dedifferentiated liposarcoma (DDLPS) is a high-grade soft tissue sarcoma predominantly arising in the retroperitoneum, characterized by an insidious clinical course. This study reports a 63-year-old female patient who presented with abdominal distension and decreased appetite, without other systemic complaints. Malignant tumor cells were identified in both ascitic smears and cell blocks. Combined with immunohistochemical (IHC) staining, the findings were consistent with sarcoma cells. Fluorescence in situ hybridization (FISH) analysis of the tissue biopsy revealed clustered amplification of mouse double minute 2 homolog (MDM2) gene. Based on the combined results of IHC and FISH testing, the final pathological diagnosis of the tissue biopsy was DDLPS. To the best of existing knowledge, this is one of the few reported cases of DDLPS initially manifesting with malignant cells detected in peritoneal fluid. This case highlights the diagnostic challenge of rare sarcomas presenting with serosal effusions and emphasizes the importance of integrating cytopathological, radiological, and molecular testing for accurate diagnosis and optimal management. Preventing misdiagnosis of this tumor as other histological subtypes is of great clinical significance, while IHC features and FISH can provide important clues for its accurate diagnosis.