The samples were divided into three molecular subtypes of breast cancer: luminal A (positive expression of ER and/or PR, negative HER-2 status, Ki-67 expression < 20%), luminal B (positive expression of ER and/or PR, negative HER-2 status, Ki-67 expression ≥ 20% or positive expression of ER and/or PR, positive HER-2 status at any Ki-67 level) and triple negative molecular subtype of breast cancer (negative expression of ER and PR, negative HER-2 status) (Figure 4a). This evidence concerns the gene ESR1 and breast cancer.