Previous epidemiological studies have associated circulating sex hormones (oestrogens and androgens) and the growth factor insulin-like growth factor-1 (IGF-1) with an increased risk of breast cancer.5–8 The results for sex hormones have been less conclusive in pre-menopausal women due to fewer data being available in this group, and it is not clear if the associations differ by menopausal status. This evidence concerns the gene IGF1 and breast carcinoma.