ESR2 and breast cancer: The ESR1 is highly polymorphic, and Single nucleotide polymorphisms (SNP) in four ESR1 gene variants (rs2234693, rs9340799, rs3020314, rs3798577) and six ESR2 gene variants (rs928554, rs944459, rs4986938, rs1256049, rs1256030, rs1271572) were reported to be linked with altered risk of TNBC in 488 BC patients comprising 130 TNBC and 358 non-TNBC patients in a study performed by real time qPCR [80].