Insulin-like growth factor-I acts as an important mediator between growth hormone and growth throughout fetal and childhood development. Its effects and those of the other insulin-like growth factors are modulated by at least six different binding proteins. The role of insulin-like growth factor-I in promoting cancer has been investigated for many years, but recently the quality and quantity of evidence has increased.1 In particular, a number of prospective studies using stored blood collected up to 14 years before the onset of disease have shown associations between insulin-like growth factor-I and prostate cancer, premenopausal breast cancer, and colon cancer