Background: The effect of metformin on colon cancer is rarely investigated in Asian populations.

Methods: This is a retrospective cohort study. Patients with newly diagnosed type 2 diabetes during 1999-2005 were recruited from Taiwan’s National Health Insurance. A 1:1 propensity score matched-pair sample of 16314 ever users and 16314 never users of metformin were followed until December 31, 2011. Cox regression incorporated with the inverse probability of treatment weighting using propensity score was used to estimate hazard ratios.

Results: The incidence of colon cancer was 272.04 and 392.44 per 100,000 person-years, respectively, in ever and never users. The overall hazard ratio (0.691, 95% confidence interval: 0.578-0.826) suggested a significantly lower risk in metformin users. While compared to never users, the hazard ratio (95% confidence interval) for the first (<20.00 months), second (20.00-45.20 months) and third (>45.20 months) tertile of cumulative duration of metformin therapy was 1.455 (1.165-1.816), 0.683 (0.526-0.885) and 0.224 (0.152-0.331), respectively. The protective effect of metformin on colon cancer was not affected by the use of aspirin and statin or the infection of Helicobacter pylori in additional analyses.

Conclusions: Metformin reduces colon cancer risk in patients with type 2 diabetes. The protective effect is more remarkable when the cumulative duration is more than 20 months.

Citation Format: Chin-Hsiao Tseng. Metformin reduces colon cancer risk in patients with type 2 diabetes: a retrospective cohort analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2296. doi:10.1158/1538-7445.AM2017-2296