Insulin-like growth factor 1 (IGF1) is a peptide which stimulates mitosis and inhibits apoptosis.1, 2 Interest in the role of IGF1 in the development of breast cancer began in the 1980s.3, 4 An early case-control study reported higher plasma concentrations of IGF1 in women with breast cancer than in controls,5 and in the first prospective study plasma concentrations of IGF1 were positively associated with breast-cancer risk for premenopausal women, but not for postmenopausal women.6 This evidence concerns the gene IGF1 and breast cancer.