IGF2 and breast cancer: Second, the IGF-binding proteins (IGFBPs) are widely expressed in breast cancer and linked to outcome.5 The IGFBPs regulate6 interactions between ligand and receptor and also serve to transport IGF-1 and IGF-2 in extracellular fluids.7 Third, sources of IGF-1 and IGF-2 are abundant and available to tumor cells by endocrine sources as well as through autocrine/paracrine production from tumor tissue.8, 9