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Basic Information On Tamoxifen | Return to Previous | |
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Tamoxifen is a drug taken orally in pill form. For over a quarter of a century, physicians have prescribed tamoxifen to help treat patients with advanced breast cancer. In the 1990s, physicians began using tamoxifen to treat early stage breast cancer after breast surgery (lumpectomy or mastectomy). Tamoxifen has been shown to help prevent the original breast cancer from returning after breast surgery while also hindering the development of new cancers in the opposite breast. In late 1998, tamoxifen became the first drug to be approved by the U.S. Food and Drug Administration (FDA) to prevent breast cancer after research showed it reduced the chances of developing breast cancer by 50% in women at high risk. To grow and reproduce, breast cancer cells require the female hormone estrogen. Tamoxifen is an "anti-estrogen" and works by competing with estrogen to bind to estrogen receptors in breast cancer cells. Tamoxifen is formally known as a selective estrogen receptor modulator (SERM). By blocking estrogen in the breast, tamoxifen helps slow the growth and reproduction of breast cancer cells. While tamoxifen fights estrogen in breast cancer cells, 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). Who is a Candidate for Tamoxifen Therapy? A woman’s physician will determine whether she is a candidate for treatment with tamoxifen. Patients who have been treated with tamoxifen include:
Tamoxifen has been shown to be more beneficial for women whose breast cancer cells contain estrogen receptors (ER). An "ER-positive cell" (one that has estrogen receptors) may contain hundreds or thousands of estrogen receptors near the cell nucleus where the genetic information is stored. Because tamoxifen works by binding to estrogen receptors in cells thus blocking the body's own supply of estrogen from reaching the receptors, women with ER-positive receptors typically respond better to tamoxifen therapy than women with ER-negative receptors. A tissue sample obtained from breast biopsy may be analyzed to determine whether cancer cells are ER-positive or ER-negative. Note: the absence of estrogen receptors in breast cancer cells does not necessarily mean that tamoxifen will be ineffective. Researchers are still investigating how tamoxifen acts on ER-negative cells. Several studies have also shown the benefit of tamoxifen in preventing breast cancer is age-related. Women under 40 years of age typically show the least response to tamoxifen, women between the ages of 40 and 50 years of age show some response, and women over 50 typically benefit most from tamoxifen. In fact, early-stage breast cancer patients over 50 years of age who are treated with tamoxifen may be able to significantly reduce (or sometimes completely eliminate) the size of their breast tumors so that surgeons may perform lumpectomy instead of mastectomy. Researchers are not certain why young women do not respond as well to tamoxifen but believe it may be related to the amount of estrogen produced in their body. When a woman reaches menopause (typically around 50 years of age), her body stops producing estrogen. Typical profiles of women who take tamoxifen to help prevent breast cancer: Age 35 or older and any of the following combination of factors:
Age 40 or older and any of the following combination of factors:
Age 45 or older and any of the following combination of factors:
Age 50 older and any of the following combination of factors:
Age 55 or older and any of the following combination of factors:
Age 60 or older and:
Source: AstraZeneca, manufacturer of Nolvadex (brand name of tamoxifen) Who is not a Candidate for Tamoxifen Therapy? Tamoxifen is not for everyone. Health care providers will determine which women may benefit from taking tamoxifen. While on the drug, women should be closely monitored by their physicians for any potentially dangerous side effects or developments. Women should not take tamoxifen if:
What are the Side Effects of Tamoxifen?
As with all drug treatments, the side effects of tamoxifen vary from individual to individual. The most common side effect of tamoxifen is a higher occurrence of hot flashes. Other side effects include irregular menstrual cycles, unusual vaginal discharge or bleeding, and irritation of skin around the vagina. Tamoxifen does not cause menopause in pre-menopausal women, though its side effects may mimic menopausal symptoms. For most young women who take tamoxifen, the ovaries continue to act normally and produce estrogen in the same or slightly increased amounts. In fact, some studies have suggested that tamoxifen may make pre-menopausal women more fertile. Tamoxifen also increases a woman's chances of developing serious health problems including:
Women taking tamoxifen are two to three times more likely to develop uterine cancer (the risk is the same for women taking estrogen replacement therapy). If a woman experiences abnormal bleeding or uterine pain while on tamoxifen, she should consult her doctor immediately. Women considering tamoxifen therapy are encouraged to have an endometrial sampling (removal of cells in the lining of the uterus for microscopic examination) to make sure there are no pre-existing uterine problems. Other less common side effects of tamoxifen include:
When patients begin tamoxifen or any other chemotherapy regimen, they may experience a "flare" reaction in which bone or tumor pain increases. This may be a sign that the tumor is responsive to the treatment. Supportive measures and pain control are generally offered until the acute "flare" phase subsides. However, patients should discuss any bone pain with their physicians, especially if pain persists.
What is the Typically Prescribed Dose and Regimen of Tamoxifen? The typical daily dose of tamoxifen for women with breast cancer is 20 to 40 mg per day. Dosages greater than 20 mg per day are usually divided into two daily doses (morning and evening). The typical daily dose of tamoxifen for women at high risk for breast cancer is 20 mg daily for up to 5 years. How Long Should a Woman Take Tamoxifen? The prescribed length of time women should taken tamoxifen varies depending on the specific medical situation. Women with early stage breast cancer are typically prescribed tamoxifen for two to five years. Recent studies, including a study by the University of Pennsylvania's National Adjuvant Breast and Bowel Project (NSABP), show that women do not receive any additional benefit from taking tamoxifen for more than five years. When taken immediately after breast cancer surgery (lumpectomy or mastectomy) for a period up to five years, tamoxifen has been shown to increase patient survival and reduce the risk of a cancer recurrence. Since tamoxifen does slightly increase the risk of endometrial cancer and other conditions, researchers of these studies suggest limiting tamoxifen use to five years unless further research shows a clear benefit to taking tamoxifen for a longer period of time. Research conducted at Duke University Medical Center and the Novalon Pharmaceutical Corporation also suggests that taking tamoxifen for over five years may reverse its beneficial effect. Because tamoxifen may begin to mimic estrogen in breast cells after five years, it may actually stimulate the growth of cancers after five years of use. Recent studies, including a study by the University of Pennsylvania's National Adjuvant Breast and Bowel Project (NSABP), show that women do not receive any additional benefit from taking tamoxifen for more than five years. When taken immediately after breast cancer surgery (lumpectomy or mastectomy) for five years, tamoxifen has been shown to increase patient survival and reduce the risk of a cancer recurrence. A study of the Early Breast Cancer Trialists' Collaborative Group found that five years of tamoxifen use has been shown to reduce the risk of a breast cancer recurrence by 46% and the relative risk of death of 26%. Since tamoxifen does slightly increase the risk of endometrial cancer and other conditions, researchers of these studies suggest limiting tamoxifen use to five years unless further research shows a clear benefit to taking tamoxifen for a longer period of time. What is the NSABP? The STAR Clinical Trial? The National Surgical Adjuvant Breast and Bowel Project (NSABP) is a cooperative group that was formed in 1971 to conduct clinical trials on breast cancer and colorectal cancer. From April 1992 to 1998, the NSABP conducted a study with 13,388 women that revealed that women at high risk of breast cancer may significantly decrease their chances of developing the disease by taking tamoxifen. The NSABP is currently running its second major breast cancer prevention trial: the STAR trial. STAR, Study of Tamoxifen and Raloxifene, will compare the long-term safety of the raloxifene (a drug similar to tamoxifen) and tamoxifen in women at increased risk of breast cancer. 22,000 post-menopausal women are being recruited to participate in the STAR trial. Additional Resources and References
Updated: March 18, 2008 |
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