INS and type 2 diabetes mellitus: Metformin (MTF), which improves peripheral insulin sensitivity and is commonly used to treat type 2 diabetes, has been studied with respect to decreasing thyroid volume and nodule size in subjects with IR (6–10) and might be a potential antitumor drug (11) The mechanism of its action can be attributed to its growth-inhibitory effect via insulin/insulin-like growth factor (IGF) signaling and AMP-activated protein kinase/mammalian target of rapamycin (AMPK/mTOR) pathway (11).