The mRNA expression of core EMT transcription factors ZEB1, ZEB2, SNAI1, SNAI2, and TWIST1 displayed a reverse correlation with claudin expression, and was up-regulated in claudin-low breast cancers, while basal ER-negative/HER2-negative and ER-positive/HER2-negative cancers with no claudin suppression displayed lower levels of expression of these core EMT transcription regulators (Figure 2). This evidence concerns the gene ESR1 and breast cancer.