Extraskeletal myxoid chondrosarcoma: a case report.

Extraskeletal myxoid chondrosarcoma is a rare mesenchymal neoplasm of uncertain differentiation, characterized morphologically by abundant myxoid stroma, a multinodular growth pattern, and uniform cells arranged in strands, clusters, and reticular networks. It usually occurs in adults in the fifth decade, most often in the deep soft tissues of the proximal extremities. The molecular hallmark of this tumor, present in over 90% of cases, is the fusion of NR4A3 with EWSR1 at 22q12.2 or TAF15 at 17q12. Many other tumors with uniform tumor cells embedded in a myxoid matrix can mimic Extraskeletal myxoid chondrosarcoma, and the distinction can be difficult, often requiring immunohistochemistry and/or molecular testing. We herein report the case of an Extraskeletal myxoid chondrosarcoma that occurred in a 74-year-old woman who consulted for a slowly enlarging thigh mass, while highlighting the key morphologic, immunohistochemical, and molecular features of this rare type of soft tissue sarcoma, as well as a summary table gathering diagnostic features of relevance to the differential diagnosis.