IGF1 and breast cancer: An association between levels of endogenous sex hormones with breast cancer risk have been shown in post-menopausal women [6,7], whereas other hormones and circulating biomarkers such as serum IGF-1, IGFBP-3 and also testosterone have been demonstrated to be associated with risk, especially in pre-menopausal women, although more recent data have also demonstrated relevance in post-menopause [8–12].