Approximately 20% of breast cancers are classified as triple-negative breast cancer (TNBC) as they do not express estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2), encompassing the molecular subtypes of basal-like and the more recently defined claudin-low group2. The gene discussed is ESR1; the disease is triple-negative breast carcinoma.