Purpose: The colorectal cancer (CRC) is the third leading cause of death in Korea. Ulcerative colitis (UC) is regarded as a risk factor of CRC. The aim of study is to confirm the incidence of CRC among subjects with and without a diagnosis of UC based on a sample of the Korean population. This study identified the effect of UC on incidence of CRC in Korea. Method: The data were from the population-based cohort containing National Health Insurance (NHI) claims from 2002 to 2013. We washed out first year (2002) for newly detected cases. Subjects who were under 20 years of age, diagnosed UC and CRC in 2002 development of CRC before diagnosis of UC since 2003, were excluded from analyses. Among 745,641 subjects during 11 years of follow-up (2003-2013), 7,448 patients with CRC were newly detected. Cox proportional hazard regression model was used to estimate the hazard ratio (HR) of UC for CRC incidence. Confounding variables including gender, baseline age, type of social security, income level, residence, Charlson Comorbidity Index, hypertension and diabetes mellitus were incorporated into the model. Results: Overall annual incidence of UC and CRC were 6.7 and 95.4 per 100,000 during 11 years (2003~2013), respectively. Among 522 of newly detected UC cases, CRC incident cases were 12 cases during 11 years. The effects were stronger for male. Advancing age and Charlson Comorbidity Index, hypertension and diabetes mellitus increased the risk of CRC. This study showed that the adjusted hazard ratio of UC in incidence of CRC is 1.92 (95% confidence interval: 1.09-3.38). Also, male patients with UC have more HR than female patients with UC. Conclusion: The results of this study showed that patients with UC are the high risk group in incidence of CRC. Furthermore, the effects of UC in male patients are higher than those in female. The future study is needed to identify the effect of UC on mortality of CRC.
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