ESR1 and breast cancer: Overall, most patients in the cohort were white (95.5%; 842/882), stage I–II at diagnosis (90.6%; 799/882), and the majority of patients had ER+/HER2−negative breast cancer, followed by ER±/HER2+ and TNBC (60.2%, 27.4%, and 12.4%, respectively) (Additional file 1: Table S1).