ESR1 and breast cancer: However, associations observed between genetic variants in sex-hormone related genes and breast cancer risk have generally been inconsistent [10], [11], except for two single nucleotide polymorphisms (SNP) near the ESR1 gene (rs2046210 and rs12662670) that were significantly associated with risk in several genome wide association studies [12], [13], [14], [15], [16], [17].