Insulin-like growth factor I (IGF1) belongs to the family of insulin-like growth factors that are structurally homologous to proinsulin. Mature IGFs are generated by proteolytic processing of inactive precursor protein containing N-terminal and C-terminal propeptide regions. Mature human IGF-I consisting of 70 amino acids with 94% identity with mouse IGF1 and exhibits cross-species activity. IGF1 binds IGF-1R, IGF-2R, and the insulin receptor and plays a key role in cell cycle progression, cell proliferation and tumor progression. IGF1 expression is regulated by growth hormone.