Immune checkpoint inhibitor-induced inflammatory arthritis: a novel clinical entity with striking similarities to seronegative rheumatoid arthritis.

IA-irAE is a new subset of IA that resembles seronegative RA immunologically. Our findings suggest that further study of IA-irAE might provide a window into underlying pathogenic mechanisms of early-stage seronegative RA. Key Points • Comprehensive comparison of clinical features between inflammatory arthritis irAE (IA-irAE) and regular rheumatoid arthritis indicates IA-irAE as a new subset of inflammatory arthritis. • IA-irAE resembles seronegative RA immunologically, suggesting that study of IA-irAE may provide a window into underlying pathogenic mechanisms of early-stage seronegative RA.