Insulin-like growth factor I receptor (IGF-1R): IGF-1R is a tyrosine kinase cell-surface receptor containing two α and two β subunits joined by disulfide bridges forming a heterotetrameric receptor complex. When ligand binds to IGF-1R, a conformational change occurs, leading to trans-autophosphorylation of the cytoplasmic tyrosine kinase domain, resulting in activation of the PI3K and Raf/MAPK pathways. [PI3K, phosphatidylinositol 3-kinase; TOR, target of rapamycin; MEK, mitogen-activated protein kinase kinase; ERK, extracellular signal-regulated kinase; Raf/MAPK, RAF-mitogen-activated protein kinase]