ER is a nuclear hormone receptor that activates transcription of various genes, especially in reproductive tissues, regulated by its ligand estrogen. The antibody stains nuclei of cells with high levels of ER, e.g. epithelial cells and carcinoma of breast, uterus, ovary, and prostate. ER is expressed in approximately 75 % of all breast cancer cases. It is reported that patients with ERpositive tumors have better prognosis than patients with ERnegative tumors. The stated antibody may be helpful in detection of breast carcinoma. ^1-3