The association between diabetes, insulin use, and colorectal cancer among Whites and African Americans

Abstract

Colorectal cancer and diabetes are common diseases that share many risk factors. It has been hypothesized that diabetes is a risk factor for colorectal cancer. We usedtwo large population-based case-control studies from North Carolina to determine whether diabetes and/or insulin therapy was associated with colon cancer and/or rectal cancer (defined as cancer of the sigmoidcolon, rectosigmoid, or rectum) and whether this association differed by race. Cases and matched controls from the North Carolina Colon Cancer Studies I and II were interviewed about demographics, dietary factors, diagnosis of diabetes, and use of medications to treat diabetes. Odds ratios (OR) and 95% confidence intervals (95% CI) were estimated using unconditional logistic regression. Colon and rectal cancer cases reporteda higher prevalence of diabetes than their respective control groups. Compared with Whites without diabetes, Whites with diabetes had adjusted ORs of 1.40 (95% CI, 0.93-2.12) for colon cancer and1.38 (95% CI, 1.00-1.90) for rectal cancer. Diabetes was not associated with colon or rectal cancer among African Americans [OR, 1.17 (95% CI, 0.81-1.70) and0.75 (95% CI, 0.44-1.28), respectively]. Among Whites with diabetes, insulin use was positively associatedwith rectal cancer. The same association was not seen for African American diabetics using insulin; however, the number of African Americans using insulin was small. In sum, diabetes was positively associated with rectal cancer and approacheda positive association with colon cancer among Whites. No association was present among African Americans. Insulin use was also positively associated with rectal cancer among Whites. Copyright © 2009 American Association for Cancer Research.