MTOR and cancer: Circulating IGF-1 is positively related to several cancer types (Knuppel et al. 2020), and is known to stimulate healthy and malignant cell proliferation through ligand binding to the IGF-1 receptor and activation of downstream intracellular pathways, including the PI3K-Akt-mTOR and mitogen-activated protein kinase (MAPK) pathways (Iams and Lovly 2015).