Objectives: To evaluate efficacy and safety of abatacept+methotrexate (MTX) in biologic-naive, anticitrullinated protein antibody (ACPA)-positive Japanese patients with active rheumatoid arthritis (RA) and early erosion versus placebo+MTX. Methods: In this phase IV, multicentre, double-blind study (NCT01758198), patients were randomised (1:1) to receive intravenous abatacept (~10 mg/kg) or placebo, plus MTX (≥6 mg/week). Primary efficacy objectives were to compare American College of Rheumatology 20 (ACR20) response rates at week 16 and mean change from baseline in van der Heijde-modified total Sharp score (vdH-mTSS) at week 24 between abatacept+MTX and placebo+MTX groups. Results: Overall, 203 and 202 patients received abatacept+MTX and placebo+MTX, respectively. At week 16, ACR20 response rates were higher in the abatacept (75.4%) versus placebo group (27.7%; p<0.001). Mean change from baseline in vdH-mTSS at week 24 was 0.84 in the abatacept and 1.26 in the placebo group (p=0.017). Radiographic nonprogression rates (change in vdH-mTSS≤smallest detectable change (2.4)) were 88.1% and 75.4% in abatacept and placebo groups, respectively. Adjusted mean change from baseline in Disease Activity Score 28 (C-reactive protein) (DAS28 (CRP)) at week 16 demonstrated a numerically greater reduction in the abatacept versus placebo group. Proportions of patients with DAS28 (CRP), Simplified Disease Activity Index and Clinical Disease Activity Index remission up to week 52 were higher in the abatacept versus placebo group. The abatacept safety profile was consistent with previous observations. Conclusions: C ompared with MTX alone, abatacept+MTX improved clinical symptoms and inhibited structural damage progression in ACPA-positive, Japanese patients with RA, early erosion and inadequate response to MTX.
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