Our laboratory identified oxidative stress (SOD1, Ape1/Ref-1, Trx, TrxR and PDI) and DNA repair (NM23-H1, MPG and Ape1/Ref-1) proteins associated with the DNA-bound ERα [15-18,25,26] and showed that each of these proteins influences estrogen-responsive gene expression in MCF-7 human breast cancer cells. The gene discussed is APEX1; the disease is breast cancer.