ESR1 and breast cancer: Gallen Consensus 2011, molecular subtypes of breast cancer can be classified into Luminal Type A which is characterized by being progesterone receptor (PR) positive, estrogen receptor (ER) positive, human epidermal growth factor receptor 2 (HER2) negative, and lowKi-67; Luminal B is PR positive, ER positive, may be either HER2 positive or negative, and high Ki-67.