ESR1 and endometrial cancer: Tamoxifen stimulated Hec1A proliferation as an ER-α–36 agonist13; it clinically induced human endometrial cancer and mice EEC mitosis as estrogenic agent11; and that tamoxifen as well as E2 induced EEC mitosis in a manner that was dependent on ER-α but independent of the classic ER-α nuclear pathway11.