Most but not all prospective studies have reported a positive association between IGF-1 and breast cancer risk particularly in ER positive breast cancer however the influence of age and menopausal status remains ambivalent as highlighted in results of studies summarised in Table 1 (risk highlighted in bold) (Rinaldi et al., 2006; Schernhammer et al., 2006; Endogenous Hormones and Breast Cancer Collaborative Group et al., 2010; Kaaks et al., 2014; Murphy et al., 2020). Here, IGF1 is linked to breast cancer.