Interestingly, in many reported ER-selective bioassays, such as the proliferation of breast cancer cell lines, gene reporter assays in mammalian or non-mammalian cells, and ER binding assays, it was found that most phytoestrogens preferentially interact with ERβ and display high specificity toward ERβ transactivation [55,56,57]. The gene discussed is ESR1; the disease is breast cancer.