One of these subtypes, triple-negative breast cancer (TNBC), which is characterized by a lack of ER, PR and HER2 expression, accounts for 10% to 20% of all breast cancers, and has a high probability of early tumor relapse after diagnosis, increased propensity to develop brain metastases, and rapid risk of death after tumor relapse [1,7-9]; adjuvant therapy is thus necessary for patients with TNBC [10]. Here, ESR1 is linked to breast cancer.