Triple-negative breast cancer refers to breast cancers negative for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), accounting for about 15% of breast cancers of all types.1–4 Triple-negative breast cancer progresses rapidly and is susceptible to distant metastasis due to the lack of the effective targeted endocrine therapy and anti-HER-2 therapy, resulting in a high mortality. This evidence concerns the gene ESR1 and breast cancer.