ESR1 and breast cancer: The relation between the concentration of TFF3 mRNA and estrogen status is explained by the results of May and Westley who stated that TFF3 is an estrogen-responsive gene, and its expression level is positively correlated with ER status in breast cancer. Pandey et al. [28] found that the coexpression of TFF3 and ER positivity in breast cancer increased tumor invasion and metastatic seeding.