ESR1 and breast cancer: BC is classified into four subtypes based on the expression of human epidermal growth factor receptor 2 (HER2/neu), progesterone receptor and estrogen receptor triple-negative breast cancer (TNBC), namely as HER2-positive, Luminal A and Luminal B. The treatment options for BC primarily involve surgical interventions, chemotherapy, radiation therapy, hormonal therapy and immunotherapy (3).