Molecular profiling distinguishes five subtypes of breast cancer: luminal A (ER+/PR+, HER2−), luminal B (ER+/PR+, HER2− or HER2+), triple-negative BC, HER2-enriched (ER-/PR-HER2+), and normal-like (ER+/PR+, HER2−) breast cancer [3]. Here, ESR1 is linked to breast cancer.