ESR1 and cancer: The percentage of Ki67‐positive cancer nuclei was categorized with 14% immunostained cells as the cutoff.19 The molecular subtypes of breast cancer, including luminal A (ER + and/or PR+, HER2–, and Ki67 < 14%), luminal B (ER+ and/or PR+, HER2−, and Ki67 ≥ 14% or ER+ and/or PR+, HER2+), HER2‐overexpressing (ER−, PR−, and HER2+), and triple‐negative (ER−, PR−, and HER2−) subtypes, were defined.12, 19