CD248 and synovial sarcoma: Endosialin (also known as tumor endothelial marker-1 or TEM-1) is a cell surface glycoprotein that is found on mural cells, myofibroblasts, as well as a variety of pediatric tumors including ES, rhabdomyosarcoma, osteosarcoma, synovial sarcoma, and neuroblastoma (150–153).