Risks and benefits of tamoxifen therapy.

Tamoxifen is the most widely prescribed endocrine therapy for breast cancer, with more than 7.5 million woman-years of clinical experience. Tamoxifen has both antiestrogenic and estrogenic activity. The antiestrogenic activity accounts for its efficacy against breast cancer, while the estrogenic activity is considered to be associated with positive effects on bone mineral density and lipid profiles and a proliferative effect on the endometrium in some women. Tamoxifen has a good tolerability profile and has demonstrated benefits for breast cancer patients in prolonging overall and disease-free survival and reducing the incidence of contralateral breast cancer. These known benefits of tamoxifen far outweigh the risk of endometrial cancer in tamoxifen-treated patients with breast cancer.