Oestrogen receptor. Molecular model of an oestrogen receptor (green, purple) bound to a glucocorticoid receptor-interacting protein (light blue, orange). Oestrogen receptors are cytoplasmic proteins that bind oestrogens and then migrate to the nucleus where they can regulate DNA transcription. Evaluation of the state of oestrogen receptors in breast cancer patients has become clinically important and determines the likelihood of response to anti-oestrogen therapy with the drug tamoxifen.