The detection of estrogen (ER) and progesterone (PR) receptors using immunohistochemical staining of formalin fixed, paraffin embedded (FFPE) tissue, has gradually replaced ligand binding assays, to become the most common method for the determination of the ER/PR status of breast tumors (Yaziji et al. 2008). ~75% to 80% of breast tumors have estrogen and/or progesterone receptors, and the presence of these receptors helps determine both the patient’s prognosis and the effectiveness of hormonal therapy (Bhargava et al. 2012).