Studies of relative binding affinity (RBA) for the estrogen receptor (ER) and activity against breast cancer lines MCF–7 ER+ and MDA–MB–231 ER– and PC–3 prostate cancer cells showed the greatest difference in cytotoxicity of the compounds on hormone–independent MDA–MB–231 and PC–3 cells. The gene discussed is ESR1; the disease is breast carcinoma.