Hormone therapy seeks to prevent breast cancer cells from receiving stimulation from estrogen. Such stimulation occurs primarily in tumors that contain hormone receptor protein, so tumors that contain this protein may respond to hormone therapy. The most commonly used hormone therapy is tamoxifen, which may be used alone or in combination therapy. Trials indicate that five years of tamoxifen therapy are superior to one to two years of such treatment. Tamoxifen has been associated with an increased risk of endometrial cancer and venous thromboembolism, but in most women, the benefit of tamoxifen treatment far outweighs its risks.
Ovarian ablation appears to produce a similar benefit to some chemotherapy regimens.
However, ovarian ablation is associated with the development of premature menopause and symptoms associated with menopause, including osteoporosis. On the basis of available data, the NIH consensus panel indicates that adjuvant chemotherapy regimens that include an anthracycline result in improvement in survival compared with programs that do not contain anthracycline. Trials have demonstrated threshold dose effects for two of the most active chemotherapeutic agents, doxorubicin and cyclophosphamide. These two drugs, which are frequently administered together, appear to result in a comparable survival outcome. They may be administered preoperatively or postoperatively.