BC is molecularly classified based on the expression of common biomarkers: estrogen/progesterone receptors (ERα/PR) and human epidermal growth factor receptor-2 (HER2) [4], and is further subclassified into: Luminal A, Luminal B, HER2-enriched, and triple-negative breast cancer (TNBC) (including Basal-like and Claudin-low). Here, ESR1 is linked to breast cancer.