OBJECTIVE: Patients with rheumatoid arthritis (RA), in particular those with the most severe disease, are at increased risk of malignant lymphoma. Whether this increase is entirely consequential to the RA disease and/or its treatment or reflective of shared susceptibility to the two diseases remains unclear. To resolve this, we assessed whether patients with RA are at increased risk of lymphoma or of other cancers, already before diagnosis of RA, and if the relative risk increases with time since RA diagnosis.
METHODS: 6,745 patients with incident RA (ACR criteria, symptom duration < 1 year) registered in the Swedish Early RA register from 1997 through 2006 were identified. For each patient, five general population controls were randomly matched by gender, age, marital status and residence (n=33,657). All individuals were linked to the nationwide Swedish Cancer Register 1958-2006. Relative risks (RR) of lymphoma and cancer overall before and after the diagnosis of RA were estimated using conditional logistic and Cox regression, respectively.
RESULTS: Before diagnosis of RA, no increased risk of lymphoma (RR= 0.67, 95% CI 0.37-1.23) or other cancers (RR= 0.78, 95% CI 0.70-0.88) was observed. During the first ten years following diagnosis of RA, the overall RR of lymphoma was 1.75 (95 % CI 1.04-2.96).
CONCLUSION: Overall, a history of cancer, lymphoma included, does not increase the risk of subsequent RA development. Shared susceptibility for RA and lymphoma may thus be of limited importance. By contrast increased lymphoma risks were observed already within the first decade following RA diagnosis.
2010. Vol. 62, no 5, 1252-1258 p.