ESR1 and breast cancer: When ER-β is expressed in parallel with ER-α, which is the case of our patients with a ratio of ER-α/ER-β Allred scores between 1 and 1.5, the activation of AP-1 elements is inhibited by ER-β [40,54], and this could play an important role in the behavior of BC cells in response to tamoxifen.