ESR1 and breast cancer: In the present study, we employed MCF-7, a differentiated breast cancer cell line that express estrogen receptor, and MDA-MB-231, a poorly differentiated triple- negative breast cancer cell line, as models and found that the scorpion analgesic peptide BmK AGAP, could effectively inhibit breast cancer cell stemness and epithelial-mesenchymal transition both in vitro and in vivo.