Background: Experimental studies have suggested that metformin may decrease the incidence of colorectal cancer in patients with type II diabetes. However, previous observational studies have reported contradictory results, which are likely due to important methodologic limitations. Thus, the objective of this study was to assess whether the use of metformin is associated with the incidence of colorectal cancer in patients with type II diabetes.
Methods: A cohort study of patients newly treated with non-insulin antidiabetic agents was assembled using the United Kingdom Clinical Practice Research Datalink. A nested case-control analysis was conducted, where all incident cases of colorectal cancer occurring during follow-up were identified and randomly matched with up to 10 controls. Conditional logistic regression was used to estimate adjusted rate ratios (RR) of colorectal cancer associated with ever use, and cumulative duration of use of metformin. All models accounted for latency and were adjusted for relevant potential confounding factors.
Results: Overall, ever use of metformin was not associated with the incidence of colorectal cancer [RR: 0.93; 95% confidence interval (CI), 0.73-1.18]. Similarly, no dose-response relationship was observed in terms of cumulative duration of use.
Conclusions: The use of metformin was not associated with the incidence of colorectal cancer in patients with type II diabetes.
Impact: The results of this study do not support the launch of metformin randomized controlled trials for the chemoprevention of colorectal cancer.