The association of diabetes with colorectal cancer risk: the Multiethnic Cohort

BACKGROUND: Diabetics have been found to have a greater risk of colorectal cancer than non-diabetics. METHODS: We examined whether this relationship differed by ethnic group, cancer site or tumour stage in a population-based prospective cohort, including 3549 incident colorectal cancer cases identified over a 13-year period (1993-2006) among 199 143 European American, African American, Native Hawaiian, Japanese American and Latino men and women in the Multiethnic Cohort. RESULTS: Diabetics overall had a significantly greater risk of colorectal cancer than did non-diabetics (relative risk (RR) 1.19, 95% confidence interval (CI) 1.09-1.29, P-value (P)<0.001). Positive associations were observed for colon cancer, cancers of both the right and left colon, and cancers diagnosed at a localised and regional/distant stage. The association with colorectal cancer risk was significantly modified by smoking status (P(Interaction) -0.0044), with the RR being higher in never smokers (RR 1.32, 95% CI-1.15-1.53, P<0.001) than past (RR=1.19, 95% CI=1.05-1.34, P=0.007) and current smokers (RR=0.90, 95% CI=0.70-1.15, P=0.40). CONCLUSION: These findings provide strong support for the hypothesis that diabetes is a risk factor for colorectal cancer. British Journal of Cancer (2010) 103, 120-126. doi:10.1038/sj.bjc.6605721 www.bjcancer.com Published online 8 June 2010 (C) 2010 Cancer Research UK