To increase the efficiency of controlled ovarian stimulation (COS) outcomes, several markers related to prognosis associated with breast cancer, such as hormone receptor profiles [estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2)], and BRCA mutations, have been studied, in addition to conventional ovarian reserve markers, such as anti-Müllerian hormone (AMH), for their correlation with COS outcomes. This evidence concerns the gene ESR1 and breast cancer.