RESUMEN
<p><b>OBJECTIVE</b>To study the clinicopathologic and immunohistochemical features of mesenchymal chondrosarcoma.</p><p><b>METHODS</b>The clinical and histologic features of 23 cases of mesenchymal chondrosarcoma were analyzed. Immunohistochemical study was also performed in 14 of the cases.</p><p><b>RESULTS</b>The age of patients ranged from 12 to 47 years. Fourteen of them occurred in males. Thirteen cases involved the bony skeleton and 5 cases affected the soft tissue. The patients presented with pain and/or swelling. Histologically, the tumor consisted of a mixture of undifferentiated small round cells and hyaline cartilage. Transition between the two components was demonstrated and growth plate-like cartilage was observed. Immunohistochemical study showed that the small round cells were positive for Sox9 (14/14), CD99 (12/14), vimentin (6/14), CD56 (4/14), CD57 (4/14), neuron-specific enolase (3/14) and desmin(1/14). They were negative for Coll-II, S-100 protein, epithelial membrane antigen, pan-cytokeratin, synaptophysin, chromogranin A, CD34 and c-erbB2.</p><p><b>CONCLUSIONS</b>Mesenchymal chondrosarcoma is a rare malignant tumor. Thorough histologic examination, when coupled with immunohistochemical findings, is helpful in arriving at a correct diagnosis.</p>