Metformin, a drug with a very safe toxicity profile, is an attractive molecule to be tested in patients with newly diagnosed GBM in a phase I clinical trial. This is based on its potential to inhibit the proliferation of GBM CSCs through its mechanism of action which is similar to IR and TMZ. Metformin, IR, and TMZ stimulate AMPK leading to the subsequent inhibition of cellular proliferation. Therefore, it is hypothesized that the addition of Metformin to concomitant IR and TMZ may increase the efficiency of IR and TMZ, which are currently considered as the standard of care for patients with GBM. In addition, Metformin lowers blood glucose levels, and subsequently reduces the insulin and Insulin-Growth-factors which are growth-promoting factors with a direct impact on GBM cellular proliferation and invasion.