One cohort study recently published in Diabetes Care about the association between metformin use and lung cancer risk was interesting. Smiechowski et al. (1) have reported that metformin use cannot correlate with decreased risk of lung cancer in patients with type 2 diabetes (rate ratio 0.94; 95% CI 0.76–1.17). However, one well-designed meta-analysis by Noto et al. (2) has shown that metformin use can correlate with decreased risk of lung cancer in diabetic patients (risk ratio 0.67; 95% CI 0.45–0.99). Noto et al. have carefully selected the best studies, and no methodological shortcomings of these cited studies can be found. Moreover, in our cohort study (3), metformin use might correlate with decreased risk of lung cancer in diabetic patients (hazard ratio 0.55; 95% CI 0.37–0.82). We have discussed that though the real mechanism of the observed risk reduction of lung cancer is not clear, it is more plausible that unmeasured factors associated with the metformin use may partially explain the association of decreased risk (3).
In our opinion, the exact role of metformin use on lung cancer risk cannot be completely determined from existing data. Thus, more prospective clinical trials of metformin in nondiabetic individuals are needed to explicitly clarify this major public health problem.
Acknowledgments
No potential conflicts of interest relevant to this article were reported.
