CD99 and Ewing sarcoma: In Ewing sarcoma (ES), cell surface markers such as CD99, Fli-1, and caveolin-1 are used in diagnostics, while glycosphingolipid ganglioside antigen G (D2) (GD2) can serve as a possible target for anti-GD2 monoclonal antibody therapy [3, 10, 11].