A reassessment of "chordoid sarcoma". Ultrastructural and immunohistochemical comparison with chordoma and skeletal myxoid chondrosarcoma.

The relationship of "chordoid sarcoma" (CS) to chordoma and myxoid chondrosarcoma has been debated for several years. In order to reassess this issue, we studied 5 CS, 5 chordomas, and 3 skeletal myxoid chondrosarcomas ultrastructurally and immunohistochemically. By electron microscopy, CS demonstrated smooth cellular outlines, macular intercellular junctions, and cytoplasmic inclusions of matrix-like material. Chordomas displayed a closely similar fine structural appearance, but in addition contained small, membrane-bound, glycogen-containing inclusions. Skeletal myxoid chondrosarcomas resembled CS, except that the former lesions had spiculated cell membranes and lacked intercellular junctions. Immunohistochemically, all CS cases expressed vimentin and lacked cytokeratin (CK). Leu 7 and S100 protein were seen in four cases each of CS, and three of these tumors demonstrated diffuse or focal reactivity for epithelial membrane antigen (EMA). Similar phenotypic features were seen in chordomas, except that all of them stained diffusely for CK, as well as EMA. Skeletal myxoid chondrosarcomas expressed vimentin, S100, and Leu 7 uniformly, but were devoid of epithelial markers. In aggregate, these data support the classification of "chordoid sarcoma" as a form of chondrosarcoma, but reveal that it may exhibit an "epithelial" antigen in some cases.