Current status of endocrine therapy for metastatic breast cancer

Hormonal manipulation is currently the mainstay of palliative care for metastatic breast cancer because it is well tolerated and produces significant responses in approximately one-third of unselected patients. Tamoxifen, a nonsteroidal antiestrogen, is currently considered first-line therapy. Second-line agents include progestins and aromatase inhibitors. New agents, such as the "pure" antiestrogens and the gonadotropin-releasing hormone (GnRH) agonists, are being tested. Other approaches for affecting the hormonal milieu are also under investigation, including combinations of hormonal agents, hormonal agents plus biologics, and hormonal agents plus antiproliferative agents. This review will address the basis for endocrine therapy and possible mechanisms of hormonal resistance, currently available agents and newer ones on the horizon, and areas of future interest.