Extraskeletal myxoid chondrosarcoma: a study using a quick-freezing and deep-etching method

A case of extraskeletal myxoid chondrosarcoma (ESMC), which developed in the right thigh of a middle-aged Japanese woman, was studied using immunohistochemistry, conventional electron microscopy, and the quick-freezing and deep-etching (QF-DE) method. In addition to typical light microscopic findings of ESMC, conventional electron microscopy indicated that the tumor cells had features of chondrocytes. Immunohistochemically, the tumor cells showed a positive immunoreaction for S100 protein. A diagnosis of ESMC was made. An interesting observation was the ultrastructural features of collagen fibrils in the myxoid matrix highlighted by the QF-DE method. These collagen fibrils consisted of relatively thin collagen (20-35 nm) with pleated surface structures. The surface striation at 65 nm was obscure. We consider that such a finding of collagen fibrils identified by the QF-DE method is one of the characteristics of the myxoid matrix of ESMC, and this is useful for the differential diagnosis of myxoid soft tissue tumors.