Several studies have also shown that metformin could inhibit the cellular proliferation and tumor growth of various cancer cells both in vitro and in vivo, such as breast, lymphoma, endometrial, HCC, and thyroid cancer, and metformin exerts its anticancer effects through the human epidermal growth factor receptor-2 (HER-2), AMP-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), insulin-like growth factor-1 (IGF-1), c-Jun N-terminal kinase/mitogen-activated protein kinase (JNK/p38 MAPK), and nuclear factor kappaB (NF-κB) pathways [12,13,14,15,16,17]. Here, IGF1 is linked to thyroid cancer.