tamoxifen citrate

A synthetic nonsteroidal estrogen antagonist used in the prevention and treatment of breast cancer.By competing with naturally occurring estrogen for binding sites on tissue cells, tamoxifen inhibits the stimulant effect of estrogen on breast cancers. Tumors that have been shown by biochemical assay to be rich in estrogen receptors are most likely to respond to treatment. Since 1985, tamoxifen has been used in patients who have undergone surgery or irradiation for breast cancer, to delay or prevent relapse. The drug has been found effective in reducing the risk of cancer recurrence or disease progression in women with or without axillary node metastasis. In women with extensive disease, tamoxifen therapy has been as effective as oophorectomy in retarding progression. In 1992, the National Cancer Institute's Breast Cancer Prevention Trial (BCPT) enrolled more than 13,000 women in the U.S. and Canada to study the preventive value of tamoxifen. All participants were considered at high risk of breast cancer because of age (>60), strong family history, or a prior diagnosis of lobular carcinoma in situ. By March 1998 the difference in incidence of breast cancer between treated and placebo groups was so great that researchers concluded that the ethical need to inform participants of the clear benefits of active drug prophylaxis outweighed any possible benefits of further controlled study. Women in the highest risk categories showed 45% reduction in breast cancer. However, this study demonstrated no effect on mortality, and in two similar trials in Europe, tamoxifen failed to show a statistically significant protective effect. Women taking tamoxifen are at increased risk of endometrial carcinoma, deep venous thrombosis, pulmonary embolism, and cataracts. The danger of these adverse consequences is greatest in women over 50. Long-term use of the drug is associated with recurrent vaginal candidiasis. It is contraindicated during pregnancy because of the risk of fetal harm.

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ta·mox·i·fen cit·rate (tə-mokґsĭ-fən) [USP] a nonsteroidal oral antiestrogen also having weak estrogenic effects; used as an antineoplastic in the prophylaxis and treatment of breast cancer.