Breast Neoplasms/genetics; Breast Neoplasms/metabolism; Chromosomal Proteins, Non-Histone/metabolism; Estrogen Receptor alpha/metabolism; Oncogene Proteins/metabolism; Base Sequence; Breast Neoplasms/drug therapy; Breast Neoplasms/pathology; Cell Death/drug effects; Cell Death/genetics; Cell Line, Tumor; Cell Proliferation/drug effects; Chromatin Immunoprecipitation; Chromosomal Proteins, Non-Histone/genetics; Estradiol/pharmacology; Estrogen Antagonists/pharmacology; Estrogen Receptor alpha/genetics; Estrogens/pharmacology; Female; Gene Expression Regulation, Neoplastic; Humans; Molecular Sequence Data; Oncogene Proteins/genetics; Poly-ADP-Ribose Binding Proteins; Progesterone/pharmacology; Promoter Regions, Genetic; Receptors, Androgen/genetics; Receptors, Androgen/metabolism; Receptors, Steroid/genetics; Receptors, Steroid/metabolism; Signal Transduction/genetics; Tamoxifen/pharmacology