CD99 and sarcoma: Morphologically, the most interesting change was the transition of most of the primary tumours to a more undifferentiated tumour in the xenograft similar to the features described by other authors in sarcoma xenograft study [13,16], although the IHC profile revealed strong expression of CD99 and FLI-1 antibodies in all the OT, cell lines and most of the xenotransplanted tumour.