The antiestrogenic agent tamoxifen, touted by some as a miracle drug, is currently the most widely prescribed hormonal agent used for the treatment of breast cancer. Although it cannot take the place of systemic chemotherapy, tamoxifen does provide a less toxic alternative in patients unable to tolerate the side effects of systemic chemotherapy. Effective alone and in combination with systemic chemotherapy, tamoxifen is primarily used in postmenopausal patients with hormone-dependent (estrogen-receptor-positive) breast cancers. But in recent years its role has expanded to include all ages and hormone receptor statuses. Its exact role in the treatment of breast cancer continues to be controversial. As a result, patients are often uncertain whether they should be receiving the drug. The following chapters discuss the information currently available on tamoxifen and its role in the treatment and prevention of breast cancer.
Tamoxifen, commercially available since the mid-1970s, is a synthetic nonsteroidal compound. It has hormone-like effects, however, and can act to block estrogen receptors. Tamoxifen was first made in 1966 by scientists at the Imperial Chemical Industries in Great Britain. They were attempting to synthesize agents that could be used for birth control. Although tamoxifen was successful for this purpose in some animals, in mammals it was found to be less effective than many other agents. Because it was also observed to block the effects of estrogens (or to have antiestrogenic effects), it was then studied as a potential breast cancer therapeutic agent.