AMEERA-4 (NCT04191382) was a WOO study undertaken to compare the pharmacodynamic effects of amcenestrant, a selective estrogen receptor degrader, with those of letrozole in postmenopausal women with newly diagnosed, operable estrogen receptor–positive, human epidermal growth factor receptor 2−negative (ER+/HER2−) breast cancer. The gene discussed is ESR1; the disease is breast cancer.