• Philip Mease, Laura C Coates, Philip S Helliwell, Mykola Stanislavchuk, Anna Rychlewska-Hanczewska, Anna Dudek, Walid Abi-Saab, Chantal Tasset, Luc Meuleners, Pille Harrison, Robin Besuyen, Annegret Van der Aa, Neelufar Mozaffarian, Joy M Greer, Rebecca Kunder, Filip Van den Bosch, and Dafna D Gladman.
• Swedish-Providence-St Joseph Health Systems, Seattle WA, USA; University of Washington, Seattle, WA, USA. Electronic address: pmease@philipmease.com.
• Lancet. 2018 Dec 1; 392 (10162): 2367-2377.

BackgroundThe Janus kinase 1 (JAK1) pathway has been implicated in the pathogenesis of psoriatic arthritis. We aimed to investigate the efficacy and safety of filgotinib, a selective JAK1 inhibitor, for the treatment of psoriatic arthritis.MethodsThe EQUATOR trial was a randomised, double-blind, placebo-controlled phase 2 trial that enrolled adults from 25 sites in seven countries (Belgium, Bulgaria, Czech Republic, Estonia, Poland, Spain, and Ukraine). Patients (aged ≥18 years) had active moderate-to-severe psoriatic arthritis (defined as at least five swollen joints and at least five tender joints) fulfilling Classification for psoriatic arthritis (CASPAR) criteria, active or a documented history of plaque psoriasis, and an insufficient response or intolerance to at least one conventional synthetic disease-modifying anti-rheumatic drug (csDMARD). Patients continued to take csDMARDs during the study if they had received this treatment for at least 12 weeks before screening and were on a stable dose for at least 4 weeks before baseline. Using an interactive web-based system, we randomly allocated patients (1:1) to filgotinib 200 mg or placebo orally once daily for 16 weeks (stratified by current use of csDMARDs and previous use of anti-tumour necrosis factor). Patients, study team, and sponsor were masked to treatment assignment. The primary endpoint was proportion of patients achieving 20% improvement in American College of Rheumatology response criteria (ACR20) at week 16 in the full analysis set (patients who received at least one dose of study drug), which was compared between groups with the Cochran-Mantel-Haenszel test and non-responder imputation method. This trial is registered with ClincalTrials.gov, number NCT03101670.FindingsBetween March 9, and Sept 27, 2017, 191 patients were screened and 131 were randomly allocated to treatment (65 to filgotinib and 66 to placebo). 60 (92%) patients in the filgotinib group and 64 (97%) patients in the placebo group completed the study; five patients (8%) in the filgotinib group and two patients (3%) in the placebo group discontinued treatment. 52 (80%) of 65 patients in the filgotinib group and 22 (33%) of 66 in the placebo group achieved ACR20 at week 16 (treatment difference 47% [95% CI 30·2-59·6], p<0·0001). 37 (57%) patients who received filgotinib and 39 (59%) patients who received placebo had at least one treatment-emergent adverse event. Six participants had an event that was grade 3 or worse. The most common events were nasopharyngitis and headache, occurring at similar proportions in each group. One serious treatment-emergent adverse event was reported in each group (pneumonia and hip fracture after a fall), one of which (pneumonia) was fatal in the filgotinib group.InterpretationFilgotinib is efficacious for the treatment of active psoriatic arthritis, and no new safety signals were identified.FundingGalapagos and Gilead Sciences.Copyright © 2018 Elsevier Ltd. All rights reserved.

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