ESR1 and breast carcinoma: In our study, a co-culture model was established using hormone receptor-negative MDA-MB-231 breast cancer cells (ER−/PR−/HER2−) and estrogen receptor-positive MCF-7 breast cancer cells (ER+), along with THP-1 acute monocytic leukemia cells and/or Jurkat acute T lymphocyte leukemia cells.