n.
Synthetic hormone , marketed as Nolvadex, that prevents the binding of estrogen to estrogen-sensitive breast cancer cells.
Initially used to prevent recurrences of breast cancer after successful treatment, it was later found to prevent first occurrences in women at high risk. The most serious side effect is an increased risk of thrombosis , which may require patients to take an anticoagulant as well. Studies on its effectiveness against breast and other cancers continue.