ER receptors are present in normal endometrial myometrium cells of the uterus in normal epithelial cells of the breast and in some breast cancer cells (about 50-60% of breast cancer patients).Researches have shown that ER positive breast cancer patients respond effectively to hormone therapy and have a better prognosis than the ER negative group.Therefore, ER, PR, and C-erbB-2 are used together to guide patient treatment.