TNFSF13B and synovial sarcoma: The efficacy of belimumab, a human monoclonal antibody targeting soluble BAFF, approved for the treatment of SLE, in a phase II clinical trial of primary SS strongly supported the pathogenic role of BAFF in this autoimmune disease (75, 76), and a phase III trials of belimumab in co-administration with rituximab in primary SS is ongoing (NCT02631538).