ESR2 and cancer: Although our study used murine and human in vitro BBB models to test the efficacy of ERβ-targeted therapy in TN and Her2+ BCBM, further investigation is needed to determine whether treatment with ER antagonists, such as tamoxifen, can inhibit the stimulatory effects of physiologically present estrogens in the human body, allowing for a reduction in cancer cell migration by ERβ-targeted treatment of the brain endothelial cell barrier.