According to the expression of progesterone receptor (PR), estrogen receptor (ER), ERBB2 receptor (HER2), and Ki-67, breast cancer can be divided into five groups: triple negative, HER2-enriched (non-luminal), Luminal B-like HER2+, Luminal A type, Luminal B type [3, 4]. This evidence concerns the gene ESR1 and breast cancer.