and the Incidence of Lung Cancer in PatientsWith Type 2 Diabetes. Diabetes

We thank Lai et al. (1) for the atten-tion given to our article on theeffect of metformin on lung cancer incidence (2). We take this opportunity to address an important methodological concern with many of the observational studies published on this topic to date, namely time-related bias. The authors ’ own study used the Taiwanese National Health Insurance databases to identify a cohort of 19,624 patients treated with antidiabetic drugs (3). It found that the use of metformin was associated with a significant 45% (hazard ratio 0.55; 95 % CI 0.37–0.82) reduction in the incidence of lung cancer and an identical reduction with the use o