Type 2 diabetes mellitus and the risk of colorectal cancer.

BACKGROUND & AIMS: Type 2 diabetes mellitus might increase the risk of colorectal cancer on the basis of chronic hyperinsulinemia and hyperglycemia. However, epidemiologic evidence for this association is inconclusive. We conducted a population-based study to clarify this association. METHODS: We conducted a case-control study in the United Kingdom General Practice Research Database. Cases included all patients with incident colorectal cancer diagnoses (n = 10,447). Up to 10 control subjects were selected for each case, matching on year of birth, enrollment date, and duration of database follow-up. The exposure of interest was type 2 diabetes mellitus. Odds ratios (ORs) were calculated by using conditional logistic regression. RESULTS: A prior diagnosis of type 2 diabetes mellitus was associated with a modestly increased risk of colorectal cancer (OR, 1.42; 95% confidence interval CI], 1.25-1.62). The association between type 2 diabetes mellitus and colorectal cancer was observed in both men (OR, 1.36; 95% CI, 1.16-1.61) and women (OR, 1.38; 95% CI, 1.14-1.67). The risk increase was observed in both colon (OR, 1.45; 95% CI, 1.25-1.70) and rectal (OR, 1.34; 95% CI, 1.08-1.68) cancers. CONCLUSIONS: Type 2 diabetes mellitus is associated with an increased risk of colorectal cancer. The risk increase is present in both sexes, as well as in both colonic and rectal cancers.