The Fecal Immunoassay Occult Blood Test Combined With Calprotectin Sequential Linkage Imaging Endoscopy Screening Strategy for Monitoring Tumor Changes Associated With Long-duration Ulcerative Colitis

Ulcerative colitis (UC) is a chronic inflammatory bowel disease associated with an increased risk of colorectal cancer, known as UC-associated neoplasia (UCAN). Current guidelines recommend regular colonoscopy surveillance for long-standing UC patients, but this strategy faces challenges including poor adherence and low neoplasia detection rates. This study aims to evaluate the diagnostic performance of a non-invasive pre-screening strategy combining fecal immunochemical test (FIT) and fecal calprotectin (FC), followed by linked color imaging (LCI) colonoscopy, for detecting UCAN in patients with long-standing UC. This is a multicenter, prospective, diagnostic cohort study. Eligible patients with long-standing UC (disease duration \>8 years for extensive colitis or \>10 years for left-sided colitis, or with PSC) will undergo FIT and FC testing, followed by LCI colonoscopy within 4 weeks regardless of stool test results. The primary outcome is the diagnostic performance (sensitivity, specificity, PPV, NPV) of combined FIT+FC testing for UCAN, using LCI colonoscopy with histopathology as the reference standard. A total of 250 participants will be enrolled from 6 centers in China. Secondary outcomes include UCAN detection rate, feasibility indicators, patient adherence and acceptability, optimal cut-off values for FIT and FC, and 12-month miss rate.

Inclusion Criteria: * Age 18-75 years, any gender. * Definite diagnosis of ulcerative colitis by clinical, endoscopic, and pathological criteria. * Meeting at least one of the following high-risk criteria (with first onset of mucopurulent bloody stool as the starting time): E1/E2 disease duration \>10 years; E3 disease duration \>8 years; with primary sclerosing cholangitis (PSC); first-degree family history of colorectal cancer; history of colorectal neoplasia resected. * Discontinued any form of glucocorticoids for at least 4 weeks prior to enrollment. * In clinical remission at enrollment (stool frequency score \