PDCD1 and synovitis: Considering the involvement of activated T cells and the development of arthralgia, synovitis, tenosynovitis and IA in some of the cancer patients receiving anti-PD-1 antibody therapeutics, we hypothesized that dysregulated PD1-PD-L1/PD-L2 pathway may be involved in the progression of arthralgia and IA/UA to early and established RA.