CD34 and synovial sarcoma: Further supporting these findings, increased levels of endothelial microparticles (EMPs) and an altered early-to-mature EPC ratio (CD34+CD309+CD133+ vs. CD34+CD309+CD133−) have been observed in SS, indicating endothelial apoptosis and a reactive mobilization of progenitor cells from the bone marrow aimed at vascular repair [87].