The insulin-like growth factors (IGFs) are proteins with high sequence similarity to insulin. IGFs are part of a complex system that cells use to communicate with their physiologic environment. This complex system consists of two cell-surface receptors (IGF1R and IGF2R), two ligands (IGF-1 and IGF-2)  and family of six high-affinity IGF binding proteins (IGFBP 1-6).