Triple-negative breast cancer (TNBC) is pathologically defined as a subgroup of breast cancers that lacks estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) expression;1,2 this precludes the use of targeted therapies, and the most available systemic treatment option is chemotherapy. The gene discussed is ESR1; the disease is triple-negative breast carcinoma.