Metformin users with diabetes and individuals without diabetes were at lower risk of overall cancer incidence than metformin non-users with diabetes based on the Korean NHIS-HEALS cohort

Abstract Background Several studies have reported the preventive effect of metformin on cancer development. This study aimed to investigate the relationship between use of metformin and risk of cancer in Koreans. Methods This study was designed retrospectively using the National Health Insurance Service-National Health Screening Cohort conducted between 2002 and 2015. Forty to 69-year-old subjects who received a health screening examination from 2002 to 2003 were enrolled. Hazard ratios (HRs) and 95% confidence intervals (CIs) for cancer were estimated in a multivariate Cox proportional regression analysis. Results A total of 323,430 subjects was enrolled (301,905 individuals without diabetes [No DM], 8,643 diabetic patients with metformin treatment [metformin users], and 12,882 diabetic patients without metformin treatment [metformin non-users]). The median follow-up period was 12.7 years. Cumulative incidence of overall cancer was 7.9% (7.7, 10.3, and 11.1 % in No DM, metformin users and non-users, respectively). Compared to metformin non-users, the fully adjusted HRs (95% CIs) of metformin users and No DM for overall cancer incidence were 0.73 (0.66-0.81) and 0.75 (0.64-0.88), respectively, in men and 0.83 (0.78-0.89) and 0.81 (0.72-0.92) in women. Conclusions Diabetic patients receiving metformin treatment, and individuals without diabetes were at lower risk for cancer incidence than diabetic patients without metformin treatment.