PGR and breast cancer: Interestingly, studies on the dynamic changes of CTCs in the epithelial and mesenchymal composition showed that tumor cells with epithelial features, which were highly representative of the CTC population in ER-positive/PgR-positive breast cancer cases and persistent in patients with initial response to therapy, overexpressed TFF1 and TFF3 compared to tumor cells with mesenchymal or intermediate features [42].