CD99 and Ewing sarcoma: A complementary set of observations was made by Burns et al., who reported that late passage human mesenchymal cells that spontaneously transformed after introduction of telomerase (hMSC-TERT20) took on an immunohistochemical profile that was reminiscent of Ewing's sarcoma, namely, CD99+, vimentin+, CD45−, cytokeratin−, and desmin− [72].