CD99 was the former marker for Ewings' sarcoma; however, it is also expressed in other tumors such as synovial sarcoma, Wilms' tumor, vascular malignancy, neuroendocrine tumors, and lymphoblastic lymphoma, and therefore nowadays is not considered a reliable marker of tumor origin [1, 7, 8]. This evidence concerns the gene CD99 and Ewing sarcoma.