POS1038 THE EFFECT OF FILGOTINIB ON ENTHESITIS: 100-WEEK DATA FROM AN OPEN-LABEL EXTENSION STUDY IN PATIENTS WITH ACTIVE PSORIATIC ARTHRITIS

Abstract

Background:Filgotinib (FIL), a novel preferential Janus kinase 1 inhibitor, was assessed in patients with active psoriatic arthritis (PsA) in the 16-week, Phase 2, EQUATOR trial (NCT03101670).1 EQUATOR2 (NCT03320876) is the open-label extension (OLE). As previously reported, an interim analysis of the OLE showed that the majority of patients had clinical resolution of enthesitis by Week 52.2Objectives:This post-hoc analysis evaluated the effect of FIL on clinical enthesitis after 100 weeks of treatment in the OLE, as assessed using the Leeds Enthesitis Index (LEI) and Spondyloarthritis Research Consortium of Canada (SPARCC) index, and evaluated the discriminatory capacity of the two indices. In addition, we assessed which of the sites included in LEI and SPARCC were most frequently involved and whether treatment effect was consistent across sites.Methods:In EQUATOR, patients with active moderate-to-severe PsA (≥5 swollen joints and ≥5 tender joints, fulfilling Classification for PsA criteria) were randomised 1:1 to receive oral FIL 200 mg or placebo (PBO) once daily (QD) for 16 weeks. At Week 16, all patients could continue into the OLE, receiving FIL 200 mg QD for up to an additional 304 weeks. We compared changes from core baseline in LEI and SPARCC measures, the effect on enthesitis at sites included in LEI and SPARCC assessments and the discriminatory capacity of both enthesitis indices.Results:Of 131 patients randomised to EQUATOR, 122 entered the OLE. There was strong agreement between LEI and SPARCC at baseline. While most patients had enthesitis at baseline according to either index (76/131 [58.0%] by LEI; 85/131 [64.9%] by SPARCC), a minority had enthesitis at a large number of sites (6.9% with 5–6 LEI sites; 12.2% with ≥9 SPARCC sites). The sites most frequently involved at baseline were the lateral epicondyle humerus and Achilles tendon, sites common to both LEI and SPARCC. There was greater variability in the change from baseline to Week 16 in SPARCC compared with LEI (Table 1). LEI showed a greater discriminatory capacity than SPARCC when change from baseline was compared for FIL vs PBO at Week 16, as shown by higher absolute standardised mean difference: −0.70 (LEI) and −0.30 (SPARCC) (observed cases; Table 1). Subgroup analyses indicated that the treatment effect of FIL vs PBO at Week 16 for all sites was consistent with the overall treatment effect seen for LEI or SPARCC, and indicative of an improvement with FIL vs PBO for nearly all sites. The proportion of patients with enthesitis decreased from baseline up to OLE Week 100 (Figure 1). There were no major differences in long-term effect on enthesitis between sites.Conclusion:FIL improved enthesitis consistently across sites compared with PBO. Rapid improvement in enthesitis was seen up to Week 16 of the core study and improvements continued up to Week 52, after which responses were generally stable up to Week 100. LEI assesses fewer locations than SPARCC, but reassuringly captured the sites most commonly affected by enthesitis; LEI also had greater discriminatory capacity.