C3 and synovial sarcoma: The mean time since diagnosis in the SS group was 3.92 ± 1.93 years, mean ESSDAI was 5.75 (range: 1–18), IgG was 16.11 ± 6.74 g/L, complement C3 was 0.85 ± 0.14 g/L, complement C4 was 0.21 ± 0.08 g/L.