An ultrastructural study of extraskeletal mesenchymal chondrosarcoma.

A rare case of extraskeletal mesenchymal chondrosarcoma in a 47-year-old woman is reported. The tumor was located in the soft tissue of left upper arm without any involvement of the humerus. The outer portion of the tumor was histologically composed of primitive mesenchymal cells, and the inner portion showed zones of cartilaginous differentiation. Ultrastructurally, the tumor cells in the primitive areas had a relatively small number of mitochondria, rough endoplasmic reticulum, and free polysomes, and the matrix of the tumor consisted of dense bundles of collagen fibrils. The cartilaginous cells seen in the central portion of tumor were embedded in the matrix of abundant collagen fibrils and matrix granules. They had polysomes, well-developed Golgi complexes, and ample rough endoplasmic reticulum frequently with dilatation. Clear zones adjacent to the cells were seen in the extracellular matrix. With a review of the literature, the histogenesis of this particular tumor is discussed.