Molecular Mechanism of Action at Estrogen Receptor α of a New Clinically Relevant Antiestrogen (GW7604) Related to Tamoxifen**This work was supported by NIH CA-56143 (to V.C.J.); Fundaçao Coordenaçao de Aperfeiçoamento de Pessoal de Nível Superior, (CAPES) Scholarship, Brazil (to R.D.); the U.S. Army Medical Research and Material Command Breast Cancer Research Program, DAMD17–96-16169 (to H.L.); the generosity of the Lynn Sage Breast Cancer Research Foundation of Northwestern Memorial Hospital; and the Avon Products Foundation.