In vitro studies have shown that pharmacological doses of genistein, the main composition of soy isoflavones, may stimulate IGF-1R signaling human breast cancer cells [51].Although we did not find associations between soy intake and serum IGF-1 as previous studies did [52], we observed that high soy intake enhanced the association between carrying CC genotype for IGF-1 rs1520220 and lower circulating IGF-1 levels among women aged <50 years. Here, IGF1 is linked to breast cancer.