The expanded histologic spectrum of myxoid liposarcoma with an emphasis on newly described patterns: implications for diagnosis on small biopsy specimens.

The variety of histologic patterns in myxoid liposarcoma is underappreciated. The diversity of these patterns can lead to diagnostic difficulty. We examined the morphologic spectrum of myxoid liposarcoma by cataloguing and describing different patterns identified in biopsy and resection specimens of 46 primary, recurrent, and metastatic myxoid liposarcomas. The patterns identified in the 46 cases included traditional myxoid (43 [93%]), traditional round cell (17 [37%]), pseudoacinar (24 [52%]), lipoblast-rich (13 [28%]), island (11 [24%]), lipomatous (10 [22%]), stromal hyalinization (7 [15%]), cord-like (5 [11%]), nested (3 [7%]), chondroid metaplasia (2 [4%]), and hemangiopericytoma (HPC)-like (1 [2%]). Island and nested patterns had not previously been described. The diagnosis of myxoid liposarcoma was confirmed by fluorescence in situ hybridization studies for DDIT3 (also known as CHOP) rearrangement. The morphologic spectrum of myxoid liposarcoma spans well beyond its typical appearance of spindle cells in a myxoid stroma with a prominent vascular pattern. Awareness of the variety of histologic patterns is critical to avoid misdiagnosis, especially in small biopsy specimens.