Myxoid liposarcoma with pleomorphic cells: Report of two cases with molecular confirmation of FUS gene rearrangements.

Myxoid liposarcoma is usually composed of uniform oval to short spindle cells in a prominent myxoid stroma. We report here two cases of myxoid liposarcoma containing unusual pleomorphic cells harboring FUS gene rearrangements. One of the lesions arose in the right loin of a 70-year-old man, while the other in the right upper arm of a 73-year-old woman. Both tumors were composed of a lobular proliferation of short spindle to oval cells, admixed with lipoblastic cells and scattered pleomorphic cells including pseudolipoblast-like or Touton-type giant cell-like cells, embedded in an abundant myxoid stroma containing a network of delicate capillary vessels. An FUS gene rearrangement was detected by fluorescence in situ hybridization in one case, and an FUS-DDIT3 fusion gene transcript by reverse transcription-polymerase chain reaction in the other. These unique cases focus our attention to a much wider histological variation of myxoid liposarcoma than expected, as well as to the value of molecular testing for final diagnosis of such myxoid sarcomas.