CD99 and neoplasm: Further immune-histochemical markers were performed to confirm the cell origin, revealing diffuse cytoplasmic positivity for vimentin in tumor cells (Figure 14), membranous positivity for CD99 and CD31 in tumor cells, and weak positivity for FLI-1 (Figure 15), while testing negative for CD34, CD45, SMA, S100, NKX2.2, ERG, and MYOD1.