A number of epidemiologic studies have shown a direct association between circulating IGF-I levels and breast cancer risk, especially in young women (Peyrat et al, 1993; Bruning et al, 1995; Bohlke et al, 1998; Hankinson et al, 1998; Toniolo et al, 2000; Muti et al, 2002; Yu et al, 2002). Here, IGF1 is linked to breast cancer.