Clinical Utility of New Antiestrogens

Tamoxifen (Fig. 1) is the endocrine treatment of choice for all stages of hormone-responsive breast cancer. Additionally tamoxifen has been shown to reduce the incidence of cancer of the opposite breast (1) and has recently been demonstrated to prevent breast cancer (2). Although most women with hormone-responsive advanced breast cancer respond to tamoxifen, their disease eventually becomes refractory to tamoxifen. These patients are known to respond to second-line hormonal therapies. In this chapter, we will focus on new antiestrogens that are currently available or are being developed for use following tamoxifen failure. We have divided these new agents into three groups according to their target-site specificity and molecular properties (3); tamoxifen-like agents, raloxifene-like agents, and pure antiestrogens.