In the present study, although the initial histological diagnosis was an undifferentiated pleomorphic sarcoma, the histological diagnosis of the recurrent mass was MPNST with positive immunohistochemistry for vimentin and bcl-2, focally positive for EMA, but negative for AE1/AE3, desmin, S-100, CD99 and CD34. This evidence concerns the gene CD99 and malignant peripheral nerve sheath tumor.