AMEERA-4 (NCT04191382) was a phase II preoperative window of opportunity that compared the safety and efficacy of two dose levels of amcenestrant and a standard dose of letrozole with paired biopsies assessed for biomarkers in a 1:1:1 randomization design among early stage ER+ HER2− breast cancer patients [62]. The gene discussed is ESR1; the disease is breast cancer.