IGF1R and type 2 diabetes mellitus: Metformin, one of the most broadly used agents for the treatment of type 2 diabetes patients, has been shown to have anti-cancer effects because of its suppression of IGF-I/IGF-IR signaling activities by multiple mechanisms, such as the activation of AMP-activated protein kinase (AMPK) and the associated inhibition of mTOR (mechanistic target of rapamycin) signaling [59].