ESR1 and breast cancer: The down regulation of IGF-1 in the parous breast, in association with the significant down-regulation of SOX6, EBF1 (early B-cell factor 1), ABHD5, RASD1, a potential miR-375 target that negatively regulates ER alpha expression in breast cancer[51], and RALGAPA2, could represent a significant driving force in the reduction of breast cancer risk conferred by pregnancy.