Comment on: Suissa and Azoulay. Metformin and the Risk of Cancer: Time-Related Biases in Observational Studies. Diabetes Care 2012;35:2665-2673

We agree with Suissa and Azoulay (1) that observational studies, particularly those of drug effects, can be subject to biases and that “time-related” biases must be carefully controlled in these types of studies. In their recently published article (1), Suissa and Azoulay have attempted to “show that several of the observational studies investigating the association between metformin and cancer incidence and mortality are affected by these time-related biases.” Since several of our studies have been so charged, we have carefully considered their concerns in relation to our own research (2–5).In their article, Suissa and Azoulay criticized four of …