ESR1 and breast cancer: Although breast cancer patients with estrogen receptor positive (ER+) have a better outcome after endocrine therapy, one-third of them are not sensitive to Tamoxifen, and the rest of them have a risk of relapse [4, 5]; The subtype, “Triple Negative Breast Cancer” (TNBC), is more aggressive and resistance to available treatments, there has no available therapeutics for it [6, 7].