ESR1 and breast cancer: In the another experiment, as shown in Figure 3C, we demonstrated that EGCG at 50 μg/ml significantly inhibited the proliferation of human estrogen receptor positive breast cancer cells (MCF-7) and triple negative breast cancer cells (MDA-MB-231) by 91% and 52%, respectively, compared to the control group (n = 6; P < 0.01), but not at 10 μg/ml.