ESR1 and breast cancer: For instance, it has been shown that heparin treatment in MDA-MB-231, a triple-negative breast cancer cell line, and MCF-7, an estrogen receptor-positive human breast cancer cell line, downregulates pathways such as the RAF/MEK/ERK, PI3K/Akt, and TGFβ/SMAD (in MCF-7) pathways [47].