ESR1 and breast cancer: To investigate the effect of hMSC-derived soluble factors on the proliferation of breast cancer cells, 10% (v/v) -75% (v/v) conditioned media derived from PL-hMSCs and CH-hMSCs were used to culture two human breast cancer cell lines, the estrogen receptor-expressing MCF-7 cells and the estrogen receptor-negative MDA-MB231 cells, for five days.