Survival benefit of metformin use according to cancer diagnosis in diabetic patients with metabolic syndrome

Background: Metabolic syndrome (MetSyn) is a disease cluster causing cardiovascular disease, cancer, and high mortality. Metformin is the most common antidiabetic agent inhibiting the tumorigenesis and insulin resistance of MetSyn. We describe the association between metformin intake and survival of patients with type 2 diabetes mellitus (T2DM) and MetSyn, according to the presence of cancer.

Methods: We analyzed the clinical characteristics and all-cause mortality of patients with T2DM and MetSyn using a 5-year dataset between January 1, 2009 and December 31, 2013 derived from the Korean National Health Insurance Service-National Health Screening Cohort (NHIS-HEALS). Cox proportional hazards regression models were used to investigate metformin effects adjusted for other potential confounding variables.

Results: Among a total of 43,043 patients with both MetSyn and T2DM, 24,725 patients (57.4 %) received metformin regularly. Female sex, high income, regular exercise, and metformin use were good prognostic factors, whereas hypertension, current smoking, cancer, and diabetes medication (except metformin) were poor prognostic factors. After adjustment for possible confounding variables, metformin showed a significant effect on patient survival (hazard ratio [HR], 0.68; 95 % confidence interval [CI], 0.63-0.75; p < 0.001). The effect of metformin was pronounced on the group of patients with liver, lung, colorectal, or prostate cancers (HR, 0.57; CI, 0.46-0.70).

Conclusions: Metformin intake may be related to favorable survival among patients with T2DM and MetSyn. The efficacy might be more remarkable in those with liver, lung, colorectal, and prostate cancers. The potential benefit of metformin in patients with these risk factors should be further investigated.