Insulin-like growth factor binding proteins (IGFBPs) in breast cancer.

The IGFBP family comprises six proteins with high affinity for the IGFs and several lower affinity IGFBP-related proteins. Their production in the breast is controlled by hormones, other local regulators and in tumors relates to the estrogen receptor status. Their functional activity can also be affected by various post-translational modifications. The IGFs are generally present at levels far in excess of that required for maximal receptor stimulation, and the IGFBPs are critical regulators of cellular action. IGFBPs can affect cell function in an IGF-dependent or independent manner. IGF bioactivity locally in the breast is influenced not only by local tissue expression and regulation of IGFs, IGFBPs, and IGFBP proteases, but also by these factors delivered from the circulation. Changes in the balance of the components of the IGF system may lead to a disruption of tissue homeostasis.