The insulin-like growth factors (IGF), named for their structural homology to proinsulin, are potent mitogens involved in the endocrine, paracrine, and autocrine regulation of growth. IGF bioactivity may be altered by changes to any level of the IGF axis. The IGF axis is comprised of IGF-I and IGF-II, two IGF receptors, six IGF binding proteins (IGFBPs), and at least nine IGFBPrelated proteins (IGFBP-rPs).
