Objective: To determine cancer risk in a cohort of 459 rheumatoid arthritis (RA) patients treated with methotrexate in community practice.
Methods: All RA patients who started methotrexate prior to June 1986 and were attending 1 of 6 rheumatologists were studied. Demographic data were matched to the State Cancer Registry to identify all malignancies (except nonmelanoma skin cancer) for 1983-1998, and to the National Death Index to identify all deaths to the end of 1999. Followup started on the date when methotrexate was started and ended either on the last confirmed date on which the patient was seen by the rheumatologist or at death. Standardized incidence ratios (SIRs) were calculated using state population cancer rates stratified by sex, age (in 5-year groups), and calendar year.
Results: There were 4,145 person-years of followup (average 9.3 years). Eighty-seven malignancies were identified (14 before, 64 during, and 9 after the followup period). There was an estimated 50% excess risk of malignancy among methotrexate-exposed RA patients relative to the general population (SIR 1.5, 95% confidence interval [95% CI] 1.2-1.9), with a 3-fold increase in melanoma (SIR 3.0, 95% CI 1.2-6.2), a 5-fold increase in non-Hodgkin's lymphoma (SIR 5.1, 95% CI 2.2-10.0), and an almost 3-fold increase in lung cancer (SIR 2.9, 95% CI 1.6-4.8).
Conclusion: Compared with the general population, methotrexate-treated RA patients have an increased incidence of melanoma, non-Hodgkin's lymphoma, and lung cancer. There may be a role for regular skin cancer screening for all RA patients, particularly those receiving immunosuppressive therapy.