Background mucosal inflammation affects colorectal cancer prognosis in ulcerative colitis: a nationwide, multicenter study

Background and aims Chronic background mucosal inflammation contributes to colorectal cancer (CRC) development in ulcerative colitis (UC), but its prognostic impact is unclear. We evaluated whether background mucosal inflammation documented at cancer diagnosis is associated with oncologic outcomes. Methods This retrospective study analyzed 1189 UC patients diagnosed with CRC using a nationwide, multicenter database in Japan. Patients were classified as CRC within the UC-involved area (within-area) or outside the UC-involved area (outside-area), based on tumor location relative to the UC disease extent documented endoscopically at cancer diagnosis. The primary end point was 5-year recurrence-free survival (RFS), and the secondary end point was 5-year cancer-specific survival (CSS). In within-area cases, inflammation severity was assessed using the Mayo Endoscopic Score (MES), stratified as Inactive, Mild-Moderate, and Severe. Results Of the 723 eligible patients, 683 had within-area and 40 outside-area CRC. Five-year RFS was significantly lower in within-area than outside-area CRCs (75.1% vs 87.6%, P = 0.022). Multivariable Cox regression analysis of RFS revealed this classification as an independent prognostic factor (hazard ratio = 2.99, 95% confidence interval: 1.09-8.18, P = 0.030). A significant difference was also observed in 5-year CSS (P = 0.038). Among within-area cases, higher MES was associated with stepwise declines in RFS (P = 0.150), and a similar, statistically significant gradient in CSS (P = 0.048). Conclusions Background mucosal inflammation at cancer diagnosis is associated with significantly worse prognosis of CRC in UC patients. Systematic endoscopic assessment at cancer diagnosis may aid prognostic stratification and inform management.