Metformin is associated with a lower risk of colorectal cancer in Taiwanese patients with type 2 diabetes: A retrospective cohort analysis - 14/11/17

Doi : 10.1016/j.diabet.2017.03.004

C.-H. Tseng ^a,^b,^c,^⁎
^a Department of Internal Medicine, National Taiwan University College of Medicine, Taipei, Taiwan
^b Division of Endocrinology and Metabolism, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan
^c Division of Environmental Health and Occupational Medicine of the National Health Research Institutes, Zhunan, Taiwan

^⁎Correspondence to: Department of Internal Medicine, National Taiwan University Hospital, No. 7 Chung-Shan South Road, 100 Taipei, Taiwan. Fax: +886 2 2388 3578.

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Abstract

Background

The association between metformin and colorectal cancer (CRC) has rarely been investigated in Asian populations.

Methods

This retrospective cohort study included patients with newly diagnosed type 2 diabetes during 1999–2005, recruited from Taiwan's National Health Insurance database. A total of 169,601 patients (original cohort: 153,270 ever-users and 16,331 never-users of metformin) and a subgroup of 1:1 propensity-score-matched pairs of 16,331 ever-users and 16,331 never-users (matched cohort) were followed up to 31 December 2011. Cox regression was constructed with the inverse probability of treatment-weighting, using propensity scores, and was used to estimate hazard ratios (HRs).

Results

In the original cohort, the incidence of CRC was 242.9 and 480.9 per 100,000 person-years, respectively, in ever- and never-users. The overall HR [0.50, 95% confidence interval (CI): 0.45–0.56] suggested a significantly lower risk in metformin users, while compared with never-users, the HR (95% CI) for the first (<27.1 months), second (27.1–58.1 months) and third (>58.1 months) tertiles of cumulative duration of metformin therapy was 0.86 (0.76–0.98), 0.51 (0.45–0.59) and 0.26 (0.23–0.30), respectively. Analyses in the matched cohort showed similar findings with an overall HR of 0.62 (0.53–0.74), and a tertile analysis HR of 1.02 (0.81–1.28), 0.70 (0.56–0.89) and 0.32 (0.23–0.43), respectively. Re-analyses using more stringent diagnoses of CRC and cumulative duration as a continuous variable have consistently supported a protective effect with metformin use.