Insulin-like growth factor-1 (IGF-1) has become recognized as a growth factor with pro-mitogenic and antiapoptotic effects on a variety of human cells. This article reviews the potential role of IGF-1 ligand in the clinical management of breast cancer patients. Many studies have shown that IGF-1 acts synergistically with oestrogen to stimulate breast cancer cells. Case-control studies have also demonstrated that premenopausal women with high levels of serum IGF-1 have an increased risk of developing breast cancer later in life. Serum IGF-1 levels can therefore be used as a potential biomarker for predicting breast cancer risk. Furthermore, there is evidence that serum IGF-1 levels can serve as a response biomarker in chemoprevention drug trials. The role of IGF-1 expression in breast cancer tissue as a prognostic marker is not clearly established. Identifying the IGF-1 gene polymorphism can potentially be used in predicting breast cancer risk.