The use of biomarkers, such as estrogen receptor, progesterone receptor, and HER-2, for predicting breast cancer outcome or targeting endocrine therapy is widespread.[3] The diagnosis and treatment of breast cancer has progressed over the past few decades, however, recurrence and metastasis is still incurable and has become the biggest challenge in clinical treatment.[4] Therefore, finding new biomarkers and discovering their mechanisms in breast cancer is crucial for the diagnosis, treatment, and prognosis of patients with breast cancer. This evidence concerns the gene ESR1 and breast cancer.