One of such molecules is CD5, a lymphocyte surface receptor constitutively expressed by all T cells and the B1a subset of mature B cells that has been involved in the production of low-affinity polyreactive antibodies [8] and is found expanded in patients undergoing autoimmune disorders such as rheumatoid arthritis (RA) [9], SLE [10], Sjögren syndrome (SS) [11], Grave's Basedow thyroiditis [12], and type I Diabetes Mellitus [13]. Here, CD5 is linked to synovial sarcoma.