ESR1 and breast carcinoma: Specifically, we investigated clinical datasets of ER+ breast cancer patients treated with tamoxifen and observed that ESR1 (gene for ERα) levels were significantly negatively correlated with ZEB1 and SNAI2 (SLUG) levels, as well as with single-sample GSEA (ssGSEA) scores for MSigDB hallmark EMT signature (GSE6532; Figure 2A).