They include luminal A (resembling the histological phenotype: ER+, PR+, HER2−, Ki67Low), luminal B (ER+, PR+, HER+/−, Ki67High), HER2-enriched (ER−, PR−, HER2+), and basal-like subtype (ER−, PR−, HER2−) which largely resembles triple-negative BC (TNBC) and comprises approximately 15% of all BC cases [2]. Here, ESR1 is linked to breast cancer.