In the present study, murine and human breast cancer cells, including ER+ breast cancer cells (MCF-7, ERα+) and TNBC cells (MDA-MB-231 and 4 T1) were treated with morusin, the cell proliferation of cancer cells were suppressed in dose and time-dependent manner (Fig. 1), the colony growth potential of cancer cells was inhibited in a dose-dependent manner (Fig. 1d, p < 0.01), and little cytotoxicity to normal mammary epithelial cells was noted (Fig. 1a). Here, ESR1 is linked to breast cancer.