Metformin and the risk of cancer in Type 2 diabetes: methodological challenges and perspectives

Metformin is a classical oral antidiabetes drug (OAD) that has been used for more than half a century for management of Type 2 diabetes (T2D). Recently, there is growing interest in this drug because of its potential anticancer properties (1). A large number of clinical studies have studied the association of use of metformin and the risk of cancer for possible prevention and treatment; while many animal and cell-based studies have been conducted to explore the underlying mechanisms of the anticancer properties of metformin. On the other hand, clinical studies have been criticized to have a mysterious bias, immortal time bias, and the association between metformin use and the cancer risk was weak, just because these studies did not use methods proposed by some authors to control for immortal time bias (2).