Association Between Metformin Use and Risk of Lung Cancer in Patients With Type 2 Diabetes: A Systematic Review and Meta-Analysis.

Lung cancer remains one of the leading causes of cancer-related mortality worldwide. Type 2 diabetes mellitus (T2DM), the most prevalent endocrine disorder, is commonly managed with Metformin, an antidiabetic medication that has demonstrated potential anticancer properties. This meta-analysis aimed to discover the association between Metformin use and the risk of lung cancer in patients with T2DM. A comprehensive search of online databases was conducted up to January 1, 2026, to identify relevant observational studies. After screening, appropriate data were extracted. Meta-analyses utilized the most fully adjusted hazard ratio (HR) with corresponding 95% confidence intervals (CI) as the effect measures. All statistical analyses were performed using R Statistical Software. The pooled analysis of 29 observational studies showed a significant reduction in lung cancer risk among Metformin users compared with nonusers (HR: 0.85, 95% CI: [0.77-0.94], p = 0.002). Subgroup analyses revealed significant associations in cohort studies (HR: 0.79, 95% CI: [0.70-0.89], p < 0.01) and in studies conducted in Asia (HR: 0.82, 95% CI: [0.68-0.99], p = 0.04). Extended Metformin use (> 3 years) was associated with a significant reduction in lung cancer risk (HR: 0.87, 95% CI: [0.79-0.95]; p < 0.01), whereas no significant effect was observed for shorter durations. This meta-analysis indicated a potential protective effect of Metformin use in individuals with T2DM against lung cancer, with a significant risk reduction observed, particularly among long-term users and in Asian populations. The significant associations identified in cohort studies and in extended-duration use underscore metformin's promise in lung cancer prevention.