Higher Checkpoint Inhibitor Arthritis Disease Activity may be Associated With Cancer Progression: Results From an Observational Registry.

Forty-two patients with ICI-arthritis were followed for a median (interquartile range [IQR]) of 7.4 (1.7, 14.7) months. Fifty-seven percent were female, 33% had melanoma, and 69% received anti-programmed death ligand 1 monotherapy. Median time from ICI initiation to arthritis onset was 2.8 (0.8, 11.2) months. Sixty-two percent had a rheumatoid arthritis (RA)-like small-joint presentation; 27% of all patients were rheumatoid factor and/or cyclic citrullinated peptide positive. Median (IQR) Clinical Disease Activity Index (CDAI) on presentation was 15 (8, 24); 62% required systemic glucocorticoids, 55% required disease-modifying antirheumatic drugs (DMARDs), and 69% had ongoing arthritis at 6 months. Arthritis led to ICI discontinuation in five patients. In univariate analysis, baseline CDAI, DMARD use, earlier arthritis onset, and longer duration of follow-up were associated with shorter PFS. In multivariable Cox regression analysis controlling for DMARD use and time to arthritis onset, CDAI was a significant predictor of cancer progression (hazard ratio 1.09, 95% confidence interval [CI] 1.00-1.19, P = 0.05) CONCLUSION: ICI-arthritis most commonly presents with an RA-like phenotype. High disease activity, as measured by CDAI, may portend cancer progression.