Estrogen receptor alpha (ER alpha) is a nuclear protein and member of the steroid hormone receptor family. ER alpha possesses both DNA binding and ligand binding domains, and exerts a significant role in activating the transcription of certain genes (1). Ligand-dependent dimerization and phosphorylation on serines, 104, 106, and 118 function to regulate the transcriptional activation of ER alpha (2). The phosphorylation of the human estrogen receptor (ER) serine residue at position 118 is required for full activity of the ER activation function 1 (AF-1) (3).