The subtypes of breast cancer are classified by the following immunohistochemical features: estrogen receptor (ER) positive (+), progesterone receptor (PR)+, and human epidermal growth factor receptor 2 (HER2) negative (−) luminal A (LA); ER+, PR+, and HER2+ luminal B (LB); ER-, PR-, and HER2+ HER2-enriched (HER2); ER-, PR-, and HER2- basal-like (BL) subtypes [10]. This evidence concerns the gene ESR1 and breast cancer.