The use of gene expression profiles has further classified breast tumors into at least five biologically and clinically relevant molecular subtypes: the low proliferative ER‐positive/HER2‐negative luminal A, the high proliferative ER‐positive/HER2‐negative luminal B, the basal‐like (mainly triple‐negative), the HER2‐enriched, and the normal‐like subtypes (Sorlie et al, 2001; Sotiriou et al, 2006; Cleator et al, 2007; Prat & Perou, 2011; Prat et al, 2012a). Here, ESR1 is linked to breast neoplasm.