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Introduction Mirikizumab, a p19-directed interleukin-23 monoclonal antibody, is efficacious in inducing clinical response at Week(W) 12 and maintaining clinical remission through W52 in patients with moderately-to-severely active Crohn’s disease (CD). We present maintenance outcomes analysis through W52 for Patient-Reported Outcome (PRO) clinical responders and nonresponders at W12.Methods The analysis set includes patients randomized to mirikizumab at baseline, who did or did not achieve PRO clinical response at W12 after intravenous (IV) induction treatment (900 mg mirikizumab IV every 4 weeks [Q4W]) before entering subcutaneous (SC) maintenance treatment (300 mg mirikizumab SC Q4W). Descriptive statistics are used to summarize data, applying nonresponder imputation for missing binary endpoints. As a treat-through study, no rerandomization was applied.Results Of 551 patients who entered SC maintenance treatment, baseline characteristics of age, duration of CD, and baseline Crohn’s Disease Activity Index (CDAI) were similar between W12 PRO responders (n=402, 73.0%) and W12 PRO nonresponders (n=149, 27.0%). PRO responders at W12 had a higher objective inflammatory burden at baseline (faecal calprotectin, C-reactive protein, and Simple Endoscopic Score-CD), whereas concomitant or prior medication usage was similar between groups. For W12 PRO responders, SC mirikizumab treatment from W12 to W52 resulted in an increase in CDAI clinical remission from 52.2% to 65.4%, PRO clinical remission from 53.2% to 65.4%, and endoscopic response from 35.1% to 54.7%, respectively. Among W12 PRO nonresponders, PRO response was achieved by 39.6% at W16, 45.6% at W20, 44.3% at W24, and 56.4% at W52 with continued mirikizumab SC treatment, while CDAI clinical remission and PRO clinical remission were achieved by 33.6% and 31.5% at W52, respectively. Endoscopic response increased from 30.2% at W12 to 40.3% at W52 among W12 PRO nonresponders ( table 1).Conclusions Subcutaneous mirikizumab maintenance treatment over 40 weeks leads to incremental and sustained improvements in rates of clinical and endoscopic response regardless of PRO clinical response status after induction. A substantial proportion of clinical nonresponders at W12 improved early during maintenance treatment suggesting continued treatment with mirikizumab can be beneficial and lead to long-term response.Abstract P208 Table 1PRO Nonresponders at W12(N=149)PRO Responders at W12(N=402)CDAI clinical remission, n (%)aW128 (5.4%)210 (52.2%)W1616 (10.7%)208 (51.7%)W2028 (18.8%)243 (60.4%)W2435 (23.5%)242 (60.2%)W5250 (33.6%)263 (65.4%)Endoscopic response, n (%)aW1245 (30.2%)141 (35.1%)W5260 (40.3%)220 (54.7%)aPercentage of response is calculated by n/Nx*100%.CDAI: Clinical Disease Activity Index; PRO: patient-reported outcome; W: week.