Five proteins (C-X-C motif chemokine 13 (CXCL13), tumor necrosis factor receptor 2 (TNF-R2), CD48, B-cell activating factor (BAFF), and programmed cell death protein 1 ligand 2 (PD-L2)) related to the disease activity of SS, including the B-cell activating factor (BAFF) [23], which was recently identified by the European League Against Rheumatism (EULAR) as a biomarker that is correlated with the European League Against Rheumatism Sjögren Syndrome Disease Activity Index (ESSDAI) score, have been identified in serum. This evidence concerns the gene PDCD1LG2 and synovial sarcoma.