Extraskeletal myxoid chondrosarcoma. A 72-year-old asymptomatic man was found to have a large mass in the thigh by physical examination. This was removed surgically, and radiation therapy was administered to the area. Despite multiple bilateral, slowly enlarging pulmonary metastases, he remained in good health 4 years later. Immunoperoxidase stains of the tumor were positive for vimentin and negative for actin, desmin, myoglobin, S-100 protein, keratin, and epithelial membrane antigen. By electron microscopy, the tumor was composed of interconnected chains of plump polygonal and elongate spindle cells in an abundant edematous matrix. Tumor cells were focally invested in basal lamina, displayed large, electron-lucent, cytoplasmic glycogen pools (G) and extensive enlarged cisterns of rough endoplasmic reticulum packed full with tubules (arrowheads). This tubular array is seen at higher magnification and in both longitudinal and cross-sectional views in the inset. Original magnification ×8,000 (inset, ×59,000). (Courtesy of Ann M. Dvorak, MD, Department of Pathology, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215.) {/ANNT;80256n;;center;0n}