ESR1 and breast cancer: Practically, the receptors of breast cancer cells such as Her2, estrogen receptor (ER) and progesterone receptor (PR) have been clinically used as markers reflecting the prognosis of breast cancer [4,5], i.e. The patients with lymph node-positive tumors, ER/PR-negative and HER-2 over-expressing (LN+ER/PR-Her2+) are at high risk for cancer recurrence, and patients with lymph node negative, ER/PR-positive and HER-2 negative tumors (LN-ER/PR+Her2-) are at low risk for cancer recurrence [6].