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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:

• they are pregnant
• have a history of uterine problems
• have a history of blood clots
• have a history of cataracts

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:

• endometrial cancer (cancer of the lining of the uterus)
• deep vein thrombosis (blood clots in large veins, particularly in the legs)
• pulmonary embolism (blood clot in the lung)
• possibly stroke

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:

• Nausea
• Weight loss
• Irregular menstrual periods
• Headache
• Mood changes
• Skin rashes
• Cataracts or other eye problems

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.

Click here to learn more about the side effects and complications of tamoxifen, including statistics on incidence and methods of coping with these side effects.

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

• For an in-depth discussion on the possible side effects of tamoxifen, please visit http://www.imaginis.com/breasthealth/side_effects.asp.
• The Imaginis article, "Studies Find Uterine Cancer Screening and Biopsy Unnecessary for Women on Tamoxifen" is available at http://www.imaginis.com/breasthealth/news/news10.20.00.asp.
• The Imaginis article, "Treating Breast Cancer with Tamoxifen May Also Protect the Heart," is available at http://www.imaginis.com/breasthealth/news/news2.25.05.asp
• The Imaginis article, "No Need for Women to Take Tamoxifen Longer Than Five Years, Study Finds," is available at http://www.imaginis.com/breasthealth/news/news3.27.01.asp
• The Imaginis articles, "Study Finds Lower Doses of Tamoxifen May Work for Breast Cancer Patients," is available at http://www.imaginis.com/breasthealth/news/news8.19.03.asp
• http://www.nolvadex.com/pr3.cfm The Nolvadex Tamoxifen Citrate website managed by AztraZeneca Pharmaceuticals is a good source of information on tamoxifen and the NSABP tamoxifen trials.
• Tamoxifen and Breast Cancer (1999) by Michael W. DeGregorio and Valerie J. Wiebe discusses the benefits, risks, and limitations of breast cancer treatment with the drug tamoxifen. Click here for pricing and ordering information
• For more information on the tamoxifen and raloxifene STAR trial, please visit http://www.imaginis.com/breasthealth/star/
• For more information on the National Surgical Adjuvant Breast and Bowel Project (NSABP), please visit http://www.imaginis.com/breasthealth/star/nsabp_info.asp.
• The American Cancer Society provides in-depth information on tamoxifen at http://www.cancer.org/
• For additional books on tamoxifen, please visit http://www.imaginis.com/bookstore/breasthealth/diagnosis.asp

Updated: March 18, 2008

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