ESR1 and breast cancer: According to the different combinations of ER, PR, HER-2 and Ki67 expression, breast cancer is divided for Luminal A type (ER+, PR+ ≥20%, HER-2- and Ki67 ≤ 14%); Luminal B type (ER+ and/or PR+, HER-2- and Ki67 > 14% or HER-2+); HER-2 over expression type (ER-, PR-, HER-2 over-expressed) and triple negative type (ER-, PR-, HER-2-) [27].