Other proposed mechanisms include (i) a joint effect of insulin-like growth factor 1(IGF-1) and estrogens on breast cancer risk (Schernhammer, 2002; Vatten et al., 2002); (ii) a potential link between loss of genetic imprinting of IGF-2, which could play a role in fetal growth (Constancia et al., 2002) and breast cancer risk (McCann et al., 1996; Wu et al., 1997; van Roozendaal et al., 1998). This evidence concerns the gene IGF2 and breast cancer.