To evaluate the efficacy, radiographic changes, and safety of abatacept and methotrexate therapy through 2 years in a long‐term extension of a previously published 1‐year study.

Patients who received placebo during year 1 were switched to abatacept. Patients taking abatacept continued to take it. Efficacy and safety were assessed through 2 years.

Of 539 patients enrolled in the initial 1‐year study, 488 completed 1 year of the long‐term extension (2% discontinued for lack of efficacy). At 2 years, patients taking abatacept had maintained their responses on the American College of Rheumatology (ACR) improvement criteria and the Disease Activity Score in 28 joints (DAS28; using the C‐reactive protein [CRP] level), as well as their physical function (according to the Health Assessment Questionnaire [HAQ] disability index [DI]) and health‐related quality of life (HRQOL; assessed with the Short Form 36 [SF‐36] health survey), that were observed at the end of the double‐blind period (year 1 versus year 2 values were 81.9% versus 80.3% for ACR 20% improvement, 25.4% versus 30.9% for a DAS28 [CRP] of <2.6, 71.8% versus 66.8% for the HAQ DI, and 9.7 versus 10.6 and 7.3 versus 7.2, respectively, for the mean change in the physical and mental components summary scores of the SF‐36). In the abatacept group, post hoc analysis demonstrated further inhibition of radiographic progression during year 2 (57% reduction in mean change of total score in year 2 versus year 1; P < 0.0001), and minimal radiographic progression was observed (mean change in total score from baseline was 1.1 and 1.6 at year 1 and 2, respectively). Rates of adverse events (AEs) and severe AEs were consistent throughout the cumulative period.

The improvements in signs and symptoms, physical function, and HRQOL observed after 1 year of abatacept treatment were maintained through 2 years of treatment. This durability was accompanied by a safety profile consistent with that in the double‐blind portion of the study. Radiographic progression was further inhibited in year 2 compared with year 1, suggesting an increasing effect of abatacept on the inhibition of structural damage in year 2.