Prevalence, incidence, and risk factors of malignancy in patients with rheumatoid arthritis: a nationwide cohort study from Korea

Background/Aims: This study aims to evaluate the incidence of malignancy in patients with rheumatoid arthritis (RA) and to investigate risk factors for such in a nationwide, population-based cohort.Methods: In a large, prospective, observational cohort study, 5,077 patients with RA were enrolled from July 2009 to December 2011 and followed until February 2017. Standardized incidence ratios (SIRs) for malignancy were calculated using age- and sex-specific cancer rates in the Korean general population. Poisson regression was used to identify the risk of incident malignancy.Results: The cohort included 5,023 participants with RA contributing 16,689 person-years of follow-up. A total of 148 malignancies were recorded. The risks of stomach cancer (SIR, 0.41; 95% confidence interval [CI], 0.21 to 0.74), colon cancer (SIR, 0.13; 95% CI, 0.03 to 0.37), and lung cancer (SIR, 0.35; 95% CI, 0.14 to 0.72) were lower in RA patients than in the general population. Poisson regression modeling demonstrated that the malignancy risk was more than two-fold greater in patients with thyroid disease than in those without thyroid disease. Hydroxychloroquine therapy was associated with a reduced risk (relative risk, 0.39; 95% CI, 0.189 to 0.801) of malignancy development.Conclusions: The overall risk of malignancy in patients with RA is decreased relative to in the general population. In particular, stomach, colon, and lung cancers in Korean RA patients are less common, while brain and central nervous system cancers in male RA patients are more frequent. The patients with thyroid disease and longer RA disease duration were at increased risk for developing malignancy, while hydroxychloroquine users were at lower risk.