Estrogen receptor and breast cancer

Breast cancer, the most common malignancy in women, was already known to be associated with the steroid hormone estrogen more than a century ago. The discovery of the estrogen receptor (ER) provided us not only with a powerfu l predictive and prognostic marker, but also an efficient target for the tr eatment of hormone-dependent breast cancer with antiestrogens. In this pape r we will sketch the important role of ER in the development, progression, and treatment of the disease, which is complicated by the receptor's intera ction with coregulatory proteins, its cross-talk with other signal transduc tion pathways, and its involvement in the development of antiestrogen resis tance.