Epithelioid variant of pleomorphic liposarcoma as potential mimic of metastatic carcinoma

We report a case of epithelioid variant of pleomorphic liposarcoma (EPL) found in the the infrapatellar fat pad of Hoffa of a 31-year old male. Histologically, the predominant population was formed by epithelioid cells with eosinophilic or clear cytoplasm admixed with rare pleomorphic lipoblasts. The immunohistochemical panel was not helpful in the diagnosis. FISH analysis using the locus-specific indicator CHOP (12q13) dual color break apart was applied to representative formalin-fixed, paraffin-embedded tissue sections. The result of FISH indicated a rearranged CHOP (DDIT3) gene and confirmed the diagnosis of EPL. The EPL should be differentiated from a metastatic carcinoma or other type of sarcoma. In these cases a clinicopathological correlation and an exhaustive sampling of the specimen for demonstration of lipogenic areas or pleomorphic lipoblasts is always necessary. FISH with demonstration of CHOP gene rearrangement is useful in providing specific ancillary information for the difficult differential diagnosis of this case.