Patients with rheumatoid arthritis (RA) are at increased risk of malignant lymphomas with a strong correlation with RA disease severity. Given the changes in RA therapy over recent decades, this study was undertaken to assess whether lymphoma risk remains increased, and if so, to explore risk predictors and lymphoma subtypes.
We identified 12,656 cases of incident RA in the Swedish Rheumatology Quality Register 1997-2012 and obtained information on therapy and inflammatory activity during the first year after diagnosis. Each patient was matched to 10 population comparator subjects. Through linkage to the Swedish Cancer Register, lymphomas, including subtypes, were identified. We assessed hazard ratios (HRs) using Cox regression.
Overall, the HR for lymphoma was increased in RA, to 1.6 (95% confidence interval [95% CI] 1.2-2.1). Taking RA duration into account, risks did not appear to have declined over successive calendar years of RA diagnosis. Neither use of methotrexate the first year after RA diagnosis nor ever use of tumor necrosis factor inhibitors (TNFi) increased lymphoma risk (HR 0.9 [95% CI 0.4-1.9]). Use of oral corticosteroids the first year after RA diagnosis was associated with a reduced risk (HR 0.5 [95% CI 0.3-0.9]). Inflammatory activity during the first year after RA diagnosis did not predict future lymphoma risk. Chronic lymphocytic leukemia occurred less frequently, and Hodgkin's lymphoma occurred more frequently, in RA patients than in the general population.
The average lymphoma risk in recently diagnosed RA is similar in magnitude to that reported in historical cohorts. Standard antirheumatic treatment including TNFi did not predict future lymphoma risk. Distribution of lymphoma subtypes warrants further investigation.