Recent studies showed that AR is widely distributed in primary and metastatic breast cancers, with 60–80% of all, 90% estrogen receptor (ER)-positive, 50% human epidermal growth factor receptor 2 (HER2)-positive, and 75% triple negative (TNBC) breast cancers being AR-positive (Garay and Park, 2012). Here, ESR1 is linked to breast cancer.