The normal and malignant mammary gland: A fresh look with ER beta onboard

Estrogens are important for the development and function of the normal mamm ary gland as well as for development of mammary cancer. The frontline thera py for treatment of estrogen receptor (ER alpha)(4) positive breast cancer is antiestrogens. A second estrogen receptor (ER beta) is also expressed in the breast but it has not been measured because it is not detected by the immunoassays used to detect ER alpha. In many cell systems ER beta has acti ons which are opposite to those of ER alpha and this finding has raised que stions about the role of ER beta in the development and treatment of breast cancer.