Purpose: Existing studies suggest that metformin lowers the risk and mortality of colorectal cancer. However, the effect of metformin on the suppression and prevention of colorectal adenomas is not clear. The aim of this study was to evaluate the effect of metformin on the recurrence of colorectal adenoma in diabetic patients with previous colorectal adenoma. Methods: Among 423 diabetic patients who underwent surveillance colonoscopy after resection of colorectal adenoma between 2005 and 2011, 257 patients were retrospectively reviewed. The patients were divided into two groups: one group comprising 106 patients who took metformin and another group comprising 151 patients who did not take metformin. The clinical characteristics, colorectal adenoma recurrence, and valuable factors for adenoma recurrence were analyzed. Results: At surveillance colonoscopy after colonoscopic polypectomy for adenoma, 38 patients (35.8%) exhibited colorectal adenoma among 106 patients who took metformin, compared with 85 patients (56.3%) with colorectal adenoma among 151 patients who did not take metformin (odds ratio 0.434, 95% confidence interval 0.260–0.723, P = 0.001). Multivariate Cox analysis showed that metformin was associated with decreased recurrence of colorectal adenoma (hazard ratio 0.572, 95% confidence interval 0.385–0.852, P = 0.006) in diabetic patients with previous colorectal adenoma. The cumulative probability of colorectal adenoma recurrence was significantly lower in the metformin group than in the non-metformin group (P = 0.001). Conclusion: Metformin use in diabetic patients with previous colorectal adenoma is associated with a lower risk of colorectal adenoma recurrence.
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