Based on the status of estrogen receptor (ER), progesterone receptor (PR) and receptor tyrosine-protein kinase erbB-2 (HER2), breast cancer is classified as Luminal A, Luminal B, HER2-positive (HER2-E) and triple-negative breast cancer (TNBC) subtypes (3). Here, ESR1 is linked to triple-negative breast carcinoma.