POS1299 RANDOMIZED PLACEBO-CONTROLLED TRIAL TO EVALUATE EFFICACY AND SAFETY OF SUBCUTANEOUS ABATACEPT IN ADULTS WITH ACTIVE IDIOPATHIC INFLAMMATORY MYOPATHY: OUTCOMES FOR JAPANESE STUDY PARTICIPANTS
Authors: M. A. Maldonado, R. Aggarwal, T. Gono, I. E. Lundberg, Y. W. Song, A. Shaibani, V. P. Werth
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> A randomized, placebo-controlled phase 3 trial of subcutaneous abatacept and standard of care (SOC) was conducted in patients with idiopathic inflammatory myopathy (IIM; NCT02971683). 52-week results for the global population were reported (primary endpoint not met).<sup>1</sup> Patients who enrolled at Japanese study sites were required to complete an additional 24 weeks of treatment and observation. <h3>Objectives:</h3> To evaluate the efficacy and safety of abatacept in patients enrolled at Japanese sites through the full 76 weeks of treatment. <h3>Methods:</h3> Adults with active, treatment-refractory IIM received 125 mg weekly subcutaneous abatacept+SOC or placebo+SOC in the double-blind period (weeks 0–24). In the 28-week open-label period (weeks 24–52, data not shown), patients receiving placebo were switched to abatacept+SOC. In the 24-week open-label extension (weeks 52–76), all patients randomized in Japan continued abatacept+SOC. The primary endpoint was the proportion meeting International Myositis Assessment and Clinical Studies definition of improvement (IMACS DOI). Secondary endpoints and safety/tolerability were assessed. Here we report results from the full 76-week observation period for the subset of patients at Japanese sites. <h3>Results:</h3> Of 148 patients randomized, 21 were from Japanese sites (abatacept, n=11; placebo, n=10) and 19 out of 21 completed the open-label extension. Baseline demographics and disease characteristics were similar to those of the full study population. Distribution of IIM disease subtypes was similar in both treatment groups (abatacept vs placebo: dermatomyositis 7 vs 7, polymyositis 3 vs 3, autoimmune necrotizing myopathy 1 vs 0). Proportions of abatacept vs placebo patients achieving IMACS DOI at week 24 were 72.7% vs 50%, and, at week 76, 90% vs 87.5% (<b>Table 1</b>), demonstrating a sustained benefit of continuing abatacept (abatacept group) and an improvement after switching to abatacept (placebo/abatacept group). Adjusted mean Myositis Response Criteria Total Improvement Scores were no different between groups at week 24; at week 76, values were 46.8 and 55.3 in the abatacept and placebo/abatacept groups, respectively (<b>Table 1</b>). The proportions of patients with Myositis Response Criteria moderate/major responses at week 76 were 70% and 100% in the abatacept and placebo/abatacept groups, respectively. Improvements were seen in most secondary endpoints when continuing abatacept and switching to abatacept (<b>Table 1</b>). The safety and tolerability of abatacept in this subset of patients from Japan were consistent with the full study population. <h3>Conclusion:</h3> Throughout the 76-week study, patients in Japan tolerated abatacept well and showed continued clinical responses with abatacept treatment, consistent with findings from the full study population. <h3>REFERENCES:</h3> [1] Aggarwal R, et al. <i>Arthritis Rheumatol</i> 2022;74 (suppl 9): abstract 2237. <h3>Acknowledgements:</h3> Study funded by Bristol Myers Squibb, executed by Sandra Overfield and Robin Scully. Medical writing: Joanna Wright (Caudex, a division of IPG Health Medical Communications), funded by Bristol Myers Squibb. <h3>Disclosure of Interests:</h3> Michael A. Maldonado Bristol Myers Squibb, Bristol Myers Squibb, Rohit Aggarwal Actigraph, Alexion, ANI Pharmaceuticals, Argenx, AstraZeneca, Boehringer-Ingelheim, Bristol Myers Squibb, CabalettaBio, Capella Bioscience, Corbus, CSL Behring, EMD Serono, Galapagos, Horizon Therapeutics, I-Cell, Immunovant, Janssen, Kezar, Kyverna, Merck, Novartis, Nuvig Therapeutics, Octapharma, Pfizer, Regeneron, Roivant, Sanofi, Teva, Boehringer Ingelheim (BI), Bristol Myers Squibb, EMD Serono, Janssen, Mallinckrodt, Pfizer, Q32, Takahisa Gono Asahi Kasei Pharma, Astellas, Boehringer-Ingelheim, Bristol Myers Squibb, Chugai, Eli Lily, Ono Pharmaceuticals, and Tanabe-Mitsubishi, Ingrid E. Lundberg Boehringer Ingelheim, Roche, Novartis, Pfizer, Chugai, Janssen, Serono, Yeong Wook Song: None declared, Aziz Shaibani: None declared, Victoria P Werth Janssen, Lilly, Pfizer, Biogen, BMS, Gilead, Amgen, Nektar, Incyte, EMD Sorona, CSL Behring, Crisalis, Viela Bio, Argenx, Kwoya Kirin, Regeneron, AstraZeneca, Abbvie, Octapharma, GSK, Astra-Zeneca, Cugene, UCB, Corcept, Beacon Bioscience, Rome Pharmaceuticals, Horizon, Merck, Kezar, Sanofi, Bayer, Akari, Calyx, Cabaletta Bio, Nuvig Pharmaceuticals, Pfizer, Biogen, Gilead, Corbus Pharmaceuticals, Genentech, Viela, Amgen, Regeneron, Argenx, CSL Behring, Ventus, q32 Bio, BMS, Horizon, Rome Pharmaceuticals, Priovant