Breast cancer, the most common type of cancer after lung cancer, originates from cells in the tissues producing or carrying human breast milk, 80% of which are the epithelial layers of the lactiferous ducts [6] which contain estrogen receptors, and approximately 50 to 85% of breast tumors contain estrogen receptors and are seen in the cytosol [7]. The gene discussed is ESR1; the disease is breast cancer.