The interest in understanding the role of metformin in cancer prevention was first sparked by an observational study conducted in 2005 that showed its ability to suppress the incidence and progression of various cancers through several mechanisms, including the inhibition of insulin-like growth factor-1 (IGF-1) [56], activation of the adenosine 5′-monophosphate-activated protein kinase (AMPK) [57], inhibition of the mammalian target of rapamycin complex I (mTORC1) [58], inhibition of nuclear factor-kB (NF-kB) [59], and inhibition of oxidation phosphorylation in cancer cells [60,61]. This evidence concerns the gene IGF1 and cancer.