Triple-negative breast cancer (TNBC) (tumors that do not express estrogen receptor (ER) and progesterone receptor (PR) genes and with nonoverexpressed/nonamplified HER-2 gene) accounts for 10%–24% of invasive breast cancers, and it is typically high-grade tumor with different histological types. The gene discussed is ESR1; the disease is triple-negative breast carcinoma.