Ulcerative colitis (UC) is a chronic inflammatory bowel disease that causes symptoms such as bloody diarrhea, abdominal pain, and frequent bowel movements. It can significantly affect patients' quality of life. Etrasimod is an oral medication taken once daily that has been shown in clinical trials to be effective for treating active UC. However, clinical trial results may not fully reflect how the drug works in real-world clinical practice, where patients have more diverse backgrounds and medical conditions.

This is a prospective, multicenter, observational registry study conducted at approximately 80 hospitals across China. The study will enroll about 500 Chinese adults with active UC who are receiving or about to start treatment with etrasimod. Participants will be followed for at least 52 weeks. The study does not assign any treatment-all participants receive etrasimod as part of their routine clinical care, and treatment decisions are made by their doctors.

The main goal of this study is to describe the characteristics of Chinese adults with active UC who are treated with etrasimod in real-world settings, including their age, sex, disease duration, disease activity, and prior treatments. The study will also track how UC symptoms change over time, how often disease flares occur, and how treatment is adjusted during follow-up. Additional goals include describing medication use patterns, changes in physician-assessed and patient-reported outcomes, treatment-related economic burden, and safety information including adverse events.

Data will be collected at baseline and at Weeks 2, 12, 24, and 52 through routine clinic visits, medical records, and patient questionnaires. The study will help provide a more complete understanding of how etrasimod performs in everyday clinical practice in China.

Ulcerative colitis (UC) is a chronic inflammatory condition of the large intestine that causes symptoms such as bloody stools, frequent diarrhea, abdominal cramps, and an urgent need to move the bowels. These symptoms often come and go over time, and the unpredictable nature of the disease can severely disrupt daily activities, work, and emotional well-being. While several treatments are available, many patients do not achieve lasting remission or may experience side effects. Etrasimod is a once-daily oral medication that works by modulating immune cell activity in the gut to reduce inflammation. Although clinical trials have shown that etrasimod is effective and generally safe for treating active UC, data from routine clinical practice-where patients have a wider range of health conditions, treatment histories, and lifestyle factors-are still limited, especially in the Chinese population.

To address this gap, this study is designed as a prospective, multicenter, observational registry. It is not a clinical trial, meaning that no study medication is assigned or provided by the research team. All enrolled participants are already prescribed etrasimod by their own doctors as part of their standard medical care. The study will be conducted at approximately 80 hospitals across China and aims to enroll about 500 adults aged 18 years or older who have active UC and have been receiving etrasimod for no more than 6 months at the time of enrollment. Participants will be followed for at least 52 weeks (12 months). Those who have previously used three or more biological therapies, or two biological therapies plus one JAK inhibitor, are not eligible to join.

The study includes two participant groups. The first group consists of patients who are starting etrasimod for the first time at enrollment. The second group includes patients who have already been taking etrasimod for up to 6 months before joining, for whom past medical data will be collected retrospectively. All participants will attend routine clinic visits at baseline (enrollment), Week 2, Week 12, Week 24, and Week 52. These visits align with normal clinical care, and the study does not require any additional tests beyond what doctors would typically order for managing UC.

At each study visit, data will be collected from medical records and patient-completed questionnaires. Information collected includes participants' age, sex, disease duration, disease extent and severity, previous treatments, and any other health conditions. The study will track changes in UC symptoms-such as stool frequency and rectal bleeding-as well as disease flare-ups, adjustments in treatment, and the development of new health issues. Participants will be asked to complete validated questionnaires, including the Inflammatory Bowel Disease Questionnaire (IBDQ), which measures quality of life, and the 8-item Morisky Medication Adherence Scale (MMAS-8), which assesses how well participants follow their prescribed treatment plan. The study will also collect information on healthcare costs, including medication expenses, hospitalization fees, and indirect costs such as transportation and lost work time.

In terms of clinical outcomes, the study will describe disease activity using the partial Mayo score, which evaluates stool frequency and bleeding. For those who undergo routine endoscopy as part of their care, the study will record endoscopic findings and, when available, tissue biopsy results to assess mucosal healing. Blood and stool tests, including C-reactive protein (CRP) and fecal calprotectin (FCP), will also be collected if performed in routine practice. Safety is an important focus; the study will systematically document any adverse events or serious adverse events that occur during follow-up.

A planned interim analysis will be performed when approximately 40% of the target enrollment (about 200 participants) is reached, to assess data quality and recruitment progress. No efficacy comparisons or hypothesis testing will be conducted in this interim review. All final analyses will be descriptive in nature, summarizing participant characteristics, treatment patterns, clinical outcomes, patient-reported outcomes, and safety data over the 52-week period.

The findings from this registry are expected to provide valuable real-world evidence on the use of etrasimod in Chinese adults with active UC. This information will help clinicians better understand how the medication performs in everyday practice, support informed treatment decisions, and ultimately improve the management and quality of life for patients living with UC in China.

Inclusion Criteria:

1. Age ≥ 18 years at baseline, of any sex.
2. Have a documented diagnosis of active ulcerative colitis (UC) and be judged by the treating physician as likely to benefit from etrasimod therapy. Active UC is defined as an endoscopic subscore ≥ 2, OR a stool frequency subscore (SFS) ≥ 1, OR a rectal bleeding subscore (RBS) ≥ 1. Any disease extent (Montreal classification E1, E2, or E3) is eligible. Participants must provide an endoscopy (including sigmoidoscopy) report obtained within 12 months prior to enrollment.
3. Have been receiving etrasimod for no more than 6 months at the time of enrollment.
4. Voluntarily sign a written informed consent form and have the ability to understand and complete study-related questionnaires and visit procedures.

Exclusion Criteria:

1. Have any contraindication to etrasimod use as per the approved prescribing information.
2. Have received prior treatment with ≥ 3 biologic therapies (including infliximab, adalimumab, vedolizumab, guselkumab, risankizumab, and mirikizumab), OR ≥ 2 biologic therapies plus 1 JAK inhibitor (including upadacitinib and tofacitinib).
3. Have any condition that, in the investigator's judgment, may compromise data quality or threaten participant safety. The reason for exclusion must be documented.

This study will enroll approximately 500 Chinese adults (aged ≥ 18 years) with a documented diagnosis of active ulcerative colitis (UC) who are receiving or about to start etrasimod as part of their routine clinical care. Participants will be recruited from approximately 80 hospitals across China, including tertiary referral centers and regional hospitals. Eligible participants must have active UC defined as an endoscopic subscore ≥ 2, OR a stool frequency subscore ≥ 1, OR a rectal bleeding subscore ≥ 1, with any disease extent (Montreal classification E1, E2, or E3). Participants may be either etrasimod-naïve (starting treatment at enrollment) or etrasimod-experienced (receiving etrasimod for up to 6 months at enrollment). Individuals with contraindications to etrasimod, or those who have previously received ≥ 3 biologics or ≥ 2 biologics plus 1 JAK inhibitor, will be excluded. The study population reflects the real-world UC patient population seeking care at participating gastroenter