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Tamoxifen, an anti-estrogen, plays an important role in both the treatment and prevention of breast cancer among women at high risk of the disease. Because treatment with tamoxifen involves some risks, however, researchers continue to evaluate long-term health effects. An important goal of this research is to identify women who are most likely to benefit from treatment.

Studies Address Treatment and Prevention

Three recently published studies contribute to this effort. One study evaluated the use of tamoxifen for the prevention of breast cancer in high-risk women. Two studies evaluated the use of tamoxifen for the treatment of breast cancer.

  1. Prevention: Updated results from the National Surgical Adjuvant Breast and Bowel Project (NSABP) Breast Cancer Prevention Trial confirmed that five years of tamoxifen reduces the risk of breast cancer among women at high-risk of the disease.[1] Tamoxifen reduced the risk of invasive breast cancer by 43%. Tamoxifen also reduced the risk of noninvasive breast cancer and osteoporotic fractures. In contrast, tamoxifen increased the risk of endometrial (uterine) cancer and pulmonary embolism. The risks and benefits of tamoxifen will need to be weighed on an individual basis, but the researchers note that for certain subgroups of women (such as women under the age of 50 who have a high five-year risk of breast cancer), the benefits are likely to substantially outweigh the risks. They also note that for the time being, “…tamoxifen remains the only proven chemopreventive treatment for breast cancer risk reduction.”
  2. Treatment: A second study addressed the use of tamoxifen for the treatment of early, hormone-receptor negative breast cancer.[2] Although previous studies have suggested that tamoxifen is not effective at treating hormone-receptor negative breast cancer, few studies have focused specifically on this population of women. In response, researchers in Germany conducted a clinical trial among 802 postmenopausal women with early, hormone-receptor negative breast cancer. Following surgery and radiation, with or without chemotherapy, women were assigned to receive either five-years of tamoxifen or no further therapy. After a median of five years of follow-up, there was no evidence of a benefit of tamoxifen. Survival and risk of recurrence were similar in the two study groups.
  3. Treatment: A third study compared two different durations (two years vs. five years) of tamoxifen for the treatment of breast cancer.[3] The study was conducted in Sweden and enrolled 4610 postmenopausal women with early-stage breast cancer. Compared to women treated with two years of tamoxifen, women treated with five years of tamoxifen had a lower risk of death from breast cancer, coronary heart disease, or all causes combined. Five years of tamoxifen, however, increased the risk of endometrial (uterine) cancer. The researchers concluded that their results “strongly support the use of tamoxifen in the adjuvant treatment of breast cancer patients.”
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These studies contribute to an increasing body of knowledge that will help women and their physicians make informed decisions about breast cancer treatment and prevention.

1) Fisher B, Costantino JP, Wickerham DL et al. Tamoxifen for the Prevention of Breast Cancer: Current Status of the National Surgical Adjuvant Breast and Bowel Project P-1 Study. Journal of the National Cancer Institute. 2005;97:1652-62.

2) Kaufmann M, Graf E, Jonat W, et al. Tamoxifen versus control after adjuvant, risk-adapted chemotherapy in postmenopausal, receptor-negative patients with breast cancer: A randomized trial (GABG-IV) – The German Adjuvant Breast Cancer Group. Journal of Clinical Oncology. 2005;31:7842-7848.

3) Nordenskjöld B, Rosell J, Rutqvist L-E et al. Coronary Heart Disease Mortality After 5 Years of Adjuvant Tamoxifen Therapy: Results from a Randomized Trial. *Journal of the National Cancer Institute.*2005;97:1609-1610.