Mechanisms Controlling Steroid Receptor Binding to Specific DNA Sequences

The biological actions of steroid hormones are mediated by specific nuclear receptors to regulate an increase or decrease in transcription of specific genes and thereby exert their influence on development and growth of normal and malignant tissues of the reproductive tract. In hormone-dependent breast cancer, the primary hormone responsible for stimulating cellular proliferation is estrogen. A number of gene products under estrogen control have been identified and characterized,1–4 and several of these estrogen regulated proteins are under investigation for their value as clinical prognostic markers.5,6 The physiological effects of progesterone in breast cancer and the gene products under progesterone control have been studied less extensively.7 In general, progestins have been observed to be antiproliferative in experimental studies with human breast cancer cells8–10 and progestin therapy is receiving renewed attention in treatment of hormone dependent breast cancer.11,12