P0570A Distinct Disease Course: Clinical Predictors and Reduced Inflammatory Burden in UC Patients with Extent Regression

Abstract Background Approximately 30% of patients with ulcerative colitis (UC) experience proximal extension within 10 years of diagnosis. However, emerging evidence suggests that in a non-well-defined subset of patients, disease extension may regress over time. Our aim was to characterise patients whose disease extent regresses and to determine the time to regression. Methods We conducted a retrospective study at the University Hospital Reina Sofía. Regression was defined according to the Montreal classification in patients with initial left-sided or extensive colitis. Patients who showed regression during follow-up were compared with those who did not. Logistic regression was used to identify predictors of regression, and Cox regression to evaluate time to regression. Inflammatory burden was quantified using area-under-the-curve (AUC)/year for fecal calprotectin (FC) and C-reactive protein (CRP) from 2005 onwards using multivariable linear models. Results A total of 538 patients were included, of whom 93 (17.3%) experienced disease regression after a median follow-up of 14.5 years. Median time to regression was 8.7 years. Patients with regression were younger and more likely to have extensive colitis and extraintestinal manifestations. No differences were found in colonoscopy frequency, hospitalisations, or use of immunosuppressants or biologics. In logistic regression, younger age, extensive colitis, and extraintestinal manifestations were independently associated with higher odds of regression. In Cox analysis, extensive colitis and extraintestinal manifestations also predicted a shorter time to regression. Patients with regression showed a significantly lower long-term inflammatory burden, with reduced faecal calprotectin and CRP AUC/year. In multivariable models, regression remained an independent predictor of lower FC and CRP burden, indicating a milder inflammatory phenotype. Conclusion Regression of disease extent in UC identifies a clinically meaningful phenotype characterised by younger age at diagnosis, higher prevalence of extensive colitis and EIMs, and a consistently lower long-term inflammatory burden. These findings suggest that regression reflects a distinct, less aggressive disease trajectory with both intestinal and systemic implications. References: 1. Gros B, Kaplan GG. Ulcerative colitis in adults: a review. JAMA. 2023;330:951-965. 2. Burisch J, Katsanos KH, Christodoulou DK, Barros L, Magro F, Pedersen N, et al. Natural Disease Course of Ulcerative Colitis during the First Five Years of Follow-up in a European Population-based Inception Cohort - An Epi-IBD Study. J Crohns Colitis. 2019 Feb 1;13(2):198–208. 3. Roda G, Narula N, Pinotti R, Skamnelos A, Katsanos KH, Ungaro R, et al. Systematic review with meta-analysis: proximal disease extension in limited ulcerative colitis. Vol. 45, Alimentary Pharmacology and Therapeutics. Blackwell Publishing Ltd; 2017. p. 1481–92. Conflict of interest: Gros, Beatriz: Beatriz Gros has served as a speaker for Abbvie, Johnson and Johnson, Takeda, Roche, Gilead, Pfizer and Galapagos and has served as an advisor for Roche, Gilead, Abbvie, Galapagos and Takeda Mr. Mirabent Moreno, Carlos: No conflict of interest Valdivia Krag, Carlos: No conflict of interest Benítez Cantero, José Manuel: has served as a speaker, consultant and advisory member for or has received research funding from AbbVie, Janssen, Takeda, Gillead, Celgene, Pfizer, Lilly, Ferring, Faes Farma, Dr. Falk Pharma, Chiesi, and Adacyte, Marin Pedrosa, Sandra: NO Soto Escribano, Pilar: No conflict of interest Iglesias Flores, Eva: has served as a speaker, consultant and advisory member for or has received research funding from AbbVie, Janssen, Takeda, Gillead, Celgene, Pfizer, Lilly, Ferring, Faes Farma, Dr. Falk Pharma, Chiesi, and Adacyte,