TNFSF13B and synovial sarcoma: Overexpression of BAFF system molecules has been detected in patients with various types of autoimmune diseases, including systemic lupus erythematosus (SLE), Sjögren’s syndrome (SS), systemic sclerosis (SSc), bullous pemphigoid, pemphigus vulgaris, and alopecia areata, and may be involved in the pathogenesis of these diseases (11–20).