Unusual subcutaneous dedifferentiated liposarcoma exhibiting coexistence of meningothelial‐like whorls and inflammatory myofibroblastic tumor‐like structures

Abstract To explore the clinicopathological features of a rare dedifferentiated liposarcoma (DDLPS) with meningothelial‐like whorls, we retrospectively analyzed 46 reported cases and 1 case that we encountered. Fluorescence in situ hybridization (FISH) analysis of the MDM2 amplification status of our case was also performed. Our case involved a 73‐year‐old male patient who had a mass in the upper part of his left arm for 10 years and was treated by surgical ablation of the tumor because of the mass' recent rapid enlargement. Microscopically, the tumor tissues showed coexistence of well‐differentiated and dedifferentiated components, the latter of which included meningothelial‐like whorls and inflammatory myofibroblastic tumor‐like structures. The dedifferentiated components diffusely expressed vimentin, MDM2, CDK4, p16, and smooth muscle actin. They were also focally positive for desmin but negative for S‐100, CD117, CD34, ALK, EMA, SOX‐10, p53, and β‐catenin. FISH detection showed MDM2 amplification. In conclusion, subcutaneous DDLPS with meningothelial‐like whorls and inflammatory myofibroblastic tumor‐like features is rare. This case broadens the histopathological lineage of DDLPS, and confirms DDLPS with myogenic differentiation. The use of the combination of MDM2, CDK4, p16, and FISH to detect MDM2 amplification is a reliable basis for the diagnosis of DDLPS with meningothelial‐like whorls.