Based on the expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth receptor 2 (HER2), breast cancer is clinically divided into four major molecular subtypes: luminal A, Luminal B, HER2-positive, and triple-negative breast cancer (TNBC) 2, 4. The gene discussed is ESR1; the disease is triple-negative breast carcinoma.