Risk of Skin Cancer Associated with Metformin Use: A Meta-Analysis of Randomized Controlled Trials and Observational Studies

Previous studies demonstrate mixed evidence regarding the association between metformin and skin cancer risk. To synthesize prior evidence and evaluate the association between metformin and skin cancer risk in patients with diabetes/prediabetes, we conducted a meta-analysis. A systematic literature search was performed up to March 23, 2020 to identify randomized controlled trials (RCT) and observational studies of metformin that reported any event of squamous cell carcinoma (SCC), basal cell carcinoma (BCC), and melanoma. In a meta-analysis of 6 trials involving 8,541 patients (Peto method), compared with controls, metformin was not significantly associated with decreased risk of melanoma [OR, 0.82; 95% confidence interval (CI), 0.27–2.43], BCC (OR, 0.75; 95% CI, 0.36–1.57), SCC (OR, 0.98; 95% CI, 0.06–15.60), total nonmelanoma skin cancer (NMSC; OR, 0.69; 95% CI, 0.38–1.24), or total skin cancer (OR, 0.71; 95% CI, 0.42–1.20). This nonsignificant association pattern was consistent with the random-effects meta-analysis of 4 cohort studies with 354,746 patients (melanoma: RR, 0.91; 95% CI, 0.62–1.33; NMSC: RR, 0.65; 95% CI, 0.35–1.18; total skin cancer: RR, 0.83; 95% CI, 0.59–1.16). In conclusion, meta-analyses of both RCT and cohort studies showed no statistically significant association between metformin and skin cancer risks, although suggestive evidence of modestly reduced risks of skin cancer among metformin users was observed. Further studies are needed.

Prevention Relevance: Meta-analyses of RCT and cohort studies showed no significant association between metformin and skin cancer, although suggestive evidence of modestly reduced skin cancer risks among metformin users was observed. These findings suggest metformin use should not influence current medical decision making for diabetes patients at risk of developing skin cancer.