She underwent subtotal resection and the histopathology report showed sheets of round blue cell tumor cells with scant cytoplasm and hyperchromatic nuclei, positive immunohistochemical (IHC) stains of CD99, NKX2.2, BCL2, a high Ki67, and negative IHC stains of Cytokeratin AE1/AE3, LCA, SALL-4, Desmin, CD20, CD10, suggestive of Ewing Sarcoma. This evidence concerns the gene CD99 and Ewing sarcoma.