TNFRSF13C and synovial sarcoma: Since data on the presence of the BAFF-R His159Tyr mutation were available in the present cohort from our previous study [31], we calculated the frequency of either mutation in the younger-onset SS (≤40 years old) complicated by lymphoma, which was found to be 38.1% vs. 7.2% in the older SS-lymphoma group increasing the risk by 7.9-fold in this population (95% CI: 2.2–28).