These CpG sites are located in the genes SCMH1, PXDNL, and GNAS. We validated the majority of the BC risk associated CpG sites (198/212) within MZ pairs, and with significantly higher effect sizes than within DZ pairs, suggesting that these 198 CpG sites associate with BC independent of genetic factors and are likely attributed to environmental BC risk. Here, GNAS is linked to breast cancer.