[Estrogen receptors and breast cancer]

Activation of oestrogen receptor has a promoting effect in early steps of mammary carcinogenesis. Loss of oestrogen receptor, or of its functionality is associated to more aggressive and hormone unresponsive breast cancers. Anti-oestrogens are antiproliferative agents inhibiting oestrogens and growth factors action by binding to the oestrogen receptor. Assay of oestrogen and progesterone receptors, in the cytosol of primary breast cancer provides information on the differentiation and prognosis of the tumour and on the efficacy of endocrine treatment. Several oestrogen receptor variants have been detected in breast cancer, but their significance remains hypothetical. They could act in a positive constitutive fashion (e.g. anomaly of the hormone binding site with conservation of the DNA binding site) or be nonfunctional (e.g. anomaly of the DNA binding domain and or transactivation). They are often associated in the tumor with normal wild type receptors and could decrease their activity by forming nonfunctional heterodimers.