Colorectal Cancer Risk in Korean Patients with Inflammatory Bowel Disease: A Nationwide Big Data Study of Subtype and Socioeconomic Disparities.

: The two major subtypes of inflammatory bowel disease (IBD)-Crohn's disease (CD) and ulcerative colitis (UC)-are known to increase the likelihood of developing colorectal cancer (CRC). While this relationship has been well studied in Western populations, evidence from East Asia remains limited and inconsistent. Using nationwide cohort data, this study explored the potential connection between IBD and CRC in a large Korean population. : We conducted a retrospective cohort study using data from the Korean National Health Insurance Service-National Sample Cohort from 2005 to 2019. A total of 9920 CRC patients were matched 1:4 with 39,680 controls using propensity scores based on age, sex, income, and region. Overlap weighting and multivariable logistic regression were used to evaluate the association between IBD and CRC. Subgroup analyses were conducted to assess effect modification by demographic and clinical factors. : IBD markedly increased the likelihood of developing CRC (adjusted odds ratio (aOR) = 1.38; 95% confidence interval (CI): 1.20-1.58; < 0.001), with the association primarily driven by UC (aOR = 1.52; 95% CI: 1.27-1.83). CD appeared unrelated to heightened CRC risk overall, though a significant association was observed among low-income CD patients (aOR = 1.58; 95% CI: 1.15-2.16). The UC-CRC association persisted across all subgroups, including patients without comorbidities. : Our findings support an independent association between IBD-particularly UC-and increased CRC risk in Korea. These results underscore the need for personalized CRC surveillance strategies that account for disease subtype, comorbidity burden, and socioeconomic status, especially in vulnerable subpopulations.