- What is Tamoxifen?
- How Does Tamoxifen Work?
- Who is a Candidate for Tamoxifen Therapy?
- Typical profiles of women who take tamoxifen to help prevent breast cancer:
- Who is not a Candidate for Tamoxifen Therapy?
- What are the Side Effects of Tamoxifen?
- What is the Typically Prescribed Dose and Regimen of Tamoxifen?
- How Long Should a Woman Take Tamoxifen?
- What is the NSABP? The STAR Clinical Trial?
- Additional Resources and References
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
Side effects of tamoxifen include:
- Hot flashes
- Irregular menstrual cycles
- Unusual vaginal discharge or bleeding
- Irritation of skin around vagina
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.
Learn more about the side effects and complications of tamoxifen, including statistics on incidence and methods of coping with these side effects.
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.
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.
A March 2011 British study published in the Journal of Clinical Oncology found that taking tamoxifen for five years may provide the best protection against a recurrence of breast cancer. In that study, for every hundred women who completed the full five year course of tamoxifen, the cancer came back in around six fewer women.
However, 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.
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.
- In-depth discussion on the possible side effects of tamoxifen.
- More information on the National Surgical Adjuvant Breast and Bowel Project (NSABP).
- The American Cancer Society provides in-depth information on tamoxifen.
