TRIM21 and synovial sarcoma: Compared to the control group, the SS group had significantly greater anti-SS-A/Ro antibody, antinuclear antibody, and rheumatoid factor positivity and significantly higher serum IgG levels and LSG biopsy focus scores (p < 0.001, p < 0.01, p < 0.01, p = 0.014, and p = 0.002, respectively).