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

OBJECTIVE: To describe clinical features associated with cancer outcomes of patients with immune checkpoint inhibitor (ICI)‐associated arthritis. METHODS: Observational study of patients with ICI‐arthritis enrolled in a single‐center registry. Arthritis phenotype and activity, medications, and cancer status were recorded at every visit. We used descriptive statistic, and Kaplan‐Meier curves using two‐sided log‐rank test and Cox regression analysis were used to identify factors associated with cancer progression‐free survival (PFS). RESULTS: 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.