RESUMEN
Sarcomatous transformation [dedifferentiated chordoma] in chordoma is a very rare condition and has been emphasized as a distinct entity because of its more aggressive clinical course. Here we describe a case of dedifferentiated chordoma arising from the sacrococcygeal region of a 60-year-old man, in third tumor recurrence. This tumor showed features of sarcoma with areas more typical of chordoma The chordoma-like areas expressed cytokeratin, epithelial membrane antigen and S-100 protein in all tumor cells and the spindle-cell component exhibited vimentin positivity in all of them but negative for other markers. The results showed that the sarcomatous areas as seen in the recurrent chordoma lack epithelial cell features of chordoma and suggest the possibility of altered differentiation pathway of the tumor stem cell or emergence of a new malignant cell population within the recurrent tumor