ESR1 and breast cancer: Furthermore, we discovered that BC stages exhibited overexpression of ESPL1, E2F8, and MKI67, as well as downregulation of ESR1 and PGR. Our study also found a strong negative association between the expression of ESPL1, E2F8, and MKI67 and the genes for estrogen and progesterone receptors (ER/PR) (Supplementary Figures S4G–J).