A potential mechanism linking the environment with cancer risk

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.2-4

The risk of cancer is higher among people with raised concentrations of insulin-like growth factor-I, and it is lower among those with high concentrations of insulin-like growth factor binding protein-3 (the main binding protein). The associations are similar when people whose blood samples were taken soon before diagnosis are excluded from analyses, suggesting that the observed relations are not due to the release of the growth factor by preclinical cancers.2-4 The effects are sizeable and stronger than the effects seen in relation to most previously reported risk factors.1 Weaker evidence from case-control studies suggests that the ratio of insulin-like growth factor-I to insulin-like growth factor binding protein-3 may …