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The drug tamoxifen may be just as effective at treating breast cancer when taken in lower doses, according to the results of a recent study. Furthermore, the lower dose may reduce the chances of uncommon but potentially life-threatening side effects of the drug, such as blood clots and endometrial cancer. According to researchers, because tamoxifen works by blocking estrogen receptors on breast cancer cells, patients need only take the minimal amount of tamoxifen necessary to block these receptors. To grow and reproduce, breast cancer cells require the female hormone estrogen. Tamoxifen (brand name, Nolvadex) is an "anti-estrogen" and works by competing with estrogen to bind to estrogen receptors in breast cancer cells. By blocking estrogen in the breast, tamoxifen helps slow the growth and reproduction of breast cancer cells. Approximately 80% of breast cancer cases are estrogen-sensitive (i.e., cancer cells are dependent on estrogen). Tamoxifen has the potential to be effective in these cases. The other 20% of cases are not estrogen sensitive, and therefore, tamoxifen does not provide any benefit. While the benefits of tamoxifen usually outweigh the risks of the drug for most breast cancer patients, tamoxifen is associated with some uncommon but potentially severe side effects:
"Tamoxifen is the most widely prescribed agent in the world for the prevention and treatment of breast cancer," said Andrea Decensi, MD, Director of the Division of Cancer Prevention, European Institute of Oncology, Milan, Italy, in an American Association for Cancer Research news release. "Although tamoxifen has been studied since the 1970s, we have yet to determine the optimal biologic dose." To test whether lower doses of tamoxifen might still be effective at treating breast cancer while decreasing the risk of negative side effects, Dr. Decensi and colleagues enrolled 120 women with estrogen-sensitive breast cancers and gave them either five or 20 milligrams of tamoxifen for a period of four weeks prior to breast cancer surgery. The women were then compared to other groups of patients, with both estrogen sensitive and non-estrogen sensitive breast cancers. The results showed that lower doses of tamoxifen can still fight breast cancer. "This study demonstrates that tamoxifen doses as low as one milligram per day maintain clinical effect against the treatment of breast cancer," said Dr. Decensi. "Since lower tamoxifen doses may also reduce the risks of potential serious side effects such as endometrial cancer, this study concludes that more drug may not be necessarily better." The findings, which were scheduled to be presented at the annual meeting of the American Association for Cancer Research, showed that because tamoxifen works to block estrogen receptors in breast cancer cells, a higher dose is not always necessary. Once the receptors are blocked, no further amount of the drug is needed. This is unlike other treatments such as chemotherapy, which can sometimes provide additional benefits with different regimens or doses. While tamoxifen fights estrogen in breast cancer cells, another feature of the drug is that it also mimics the positive effects of estrogen in other body systems. Post-menopausal women who take tamoxifen may decrease their risk of heart disease or osteoporosis (a degenerative bone disease) without having to use hormone replacement therapy (HRT). In the study, lower doses of tamoxifen decreased the occurrence of beneficial side effects, such as cholesterol reduction, in addition to reducing negative effects.
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