TNFSF13B and synovial sarcoma: As B-cell hyperactivity is associated with the pathogenesis of SS and may contribute to the development of systemic manifestations, several B-cell associated biomarkers have been investigated in different body fluids, as follows: B-cell activating factor (BAFF), β2-microglobulin (β2M), soluble interleukin-2 receptor (sIL-2R), and free light chains (FLC) [11,12,13,14,15,16,17,18].