Long‐Term Outcomes After Endoscopic Resection for Strictly Defined Ulcerative Colitis‐Associated Neoplasia: An Exploratory Retrospective Cohort Study

OBJECTIVES: Ulcerative colitis (UC)-associated neoplasia (UCAN) carries a risk of metachronous development; however, risk stratification based on inflammatory origin remains unclear. This exploratory study aimed to classify UCAN arising in colitis-affected areas and to evaluate long-term outcomes after endoscopic resection (ER). METHODS: We retrospectively analyzed the data of 102 patients with UC who underwent ER for colorectal neoplasia between 2004 and 2024. Lesions in colitis-affected areas were operationally classified as confirmed UCAN, based on non-polypoid morphology and characteristic p53 and Ki-67 immunostaining patterns, or as probable UCAN. Lesions in colitis-unaffected areas were classified as sporadic neoplasia (SN). Cumulative incidences of metachronous neoplasia and overall survival were estimated using the Kaplan-Meier method, and associations with metachronous confirmed UCAN were assessed using univariate Cox proportional hazards models. RESULTS: The median follow-up period was 4.3 years. Among 102 lesions, 13 were classified as confirmed UCAN, 68 as probable UCAN, and 21 as SN. The 5-year cumulative incidence of metachronous confirmed UCAN was significantly higher in the confirmed UCAN group (52%) than in the probable UCAN (4%) and SN (0%) groups (p < 0.01). Confirmed UCAN remained independently associated with metachronous confirmed UCAN (hazard ratio, 11.05; 95% confidence interval, 2.01-60.7; p < 0.01). Overall survival did not differ significantly among groups. CONCLUSIONS: Using an exploratory classification, confirmed UCAN was associated with an increased incidence of metachronous neoplasia after ER. These findings suggest that this subgroup may warrant closer surveillance; however, further validation is required.