The impact of metformin on survival in diabetes patients with operable colorectal cancer: A nationwide retrospective cohort study

OBJECTIVE: To investigate the impact of metformin on survival of diabetic patients following surgery for colorectal cancer (CRC). METHODS: This was a retrospective cohort study. From Taiwan’s population-based National Health Insurance Research Database (NHIRD) we identified 12,512 patients with CRC and type II diabetes who underwent curative surgery between 2000 and 2012. Of these, 6222 patients were included in a matched cohort. Using Cox regression models with time-dependent covariates we examined the impact of metformin on survival. RESULTS: Average duration of follow-up was 49 and 54 months for metformin users and non-users, respectively. Cox proportional hazard model showed that metformin was associated with 5-year overall survival benefit (Hazard ratio, 0.23 [95% CI, 0.20–0.26]) and inverse association with risk of liver metastasis (Hazard ratio, 0.79 [95% CI, 0.68–0.93]). CONCLUSIONS: Metformin was associated with a survival benefit in diabetic patients with CRC following surgery, and an inverse association with risk of liver metastases suggesting a potential anti-tumorigenic effect.