Mesenchymal Chondrosarcoma : Immunohistochemistry
Immunohistochemistry: The cartilaginous areas in mesenchymal chondrosarcomas (MC) show strong S-100 immunoreactivity. Small, undifferentiated cells are CD99 positive (membranous); negative for broad-spectrum keratins and focally EMA positive (35% of cases). SOX9 - a marker of chondroid lineage - is positive (nuclear staining) in both small mesenchymal cells as well as cartilaginous component. Focal positivity for desmin, actin, MyoD1, myogenin, and NSE is often present. Positivity for myogenic markers can create confusion with spindle cell/sclerosing rhabdomyosarcoma. NKX2-2 - a nuclear marker expressed by 100% of Ewing sarcomas is also seen in 75% of mesenchymal chondrosarcomas. FLI1 is negative in MC. This image shows cartilaginous focus undergoing calcification and merging into mesenchymal component consisting of undifferentiated round, oval, or spindle cells.