Insulin-like growth factor-binding protein 4 (IGFBP-4) is also known as IGF-binding protein 4, which contains an IGFBP domain and a thyroglobulin type-I domain. IGFBP-4 binds both insulin-like growth factors (IGFs) I and II and circulates in the plasma in both glycosylated and non-glycosylated forms. Binding of this protein prolongs the half-life of the IGFs and alters their interaction with cell surface receptors. IGFBP-4 is a unique protein and it consistently inhibits several cancer cells in vivo and in vitro. Its inhibitory action has been shown in vivo in prostate and colon. IGFBP-4 is secreted by all colon cancer cells.