According to a study published in the journal Cancer, use of tamoxifen to reduce the risk of developing breast cancer appears to produce a survival benefit only among women at very high risk of developing the disease.

Breast cancer causes roughly 40,000 deaths annually in the U.S. alone. The majority of women with breast cancer have cancer that is estrogen receptor-positive (ER-positive). This type of breast cancer is stimulated to grow by the female hormones estrogen and/or progesterone.

Among postmenopausal women at high risk of developing breast cancer (women whose five-year risk of breast cancer is 1.67% or higher), preventive use of the antiestrogen agent tamoxifen has been found to cut the risk of developing breast cancer by almost half. This reduced risk of breast cancer, however, is accompanied by an increased risk of conditions such as endometrial (uterine) cancer and blood clots.

To explore the costs and survival effects of preventive use of tamoxifen, researchers at the University of California–Davis and other institutions created statistical models that took into consideration a woman’s risk of breast cancer; whether or not the woman had had a hysterectomy; and the likelihood of estrogen receptor-negative breast cancer.

Estimates of a woman’s probability of developing breast cancer are based on factors such as age, race, family history of breast cancer, number of births and age at first live birth, age at first menstrual period, number of benign breast biopsies, and diagnosis of atypical hyperplasia. Women with the highest risk of breast cancer may have the most to gain from preventive treatment with tamoxifen.

History of hysterectomy is also an important consideration. Tamoxifen increases the risk of uterine cancer, but this risk does not apply to women who have had a hysterectomy.

Consideration of the frequency of estrogen receptor-negative breast cancer is important because tamoxifen does not reduce the likelihood of this type of breast cancer. Failure to consider the probability of estrogen receptor-negative breast cancer could lead to an overestimation of tamoxifen’s benefits.

The results of the study suggest that use of tamoxifen for breast cancer risk reduction will produce a survival benefit in only a small subset of women:

  • Among women with a 1.67% risk of breast cancer (the low end of what is commonly considered “high risk”), use of tamoxifen had very little effect on survival, and may even increase mortality. Use of tamoxifen was also extremely expensive among women with this level of risk, costing more than $1.3 million per year of life saved.
  • A benefit of tamoxifen on survival did not become apparent until women reached a very high level of breast cancer risk (five-year risk of 3% or higher).

This study suggests that only the subset of women at very high risk of breast cancer is likely to experience improved survival as a result of using tamoxifen for breast cancer risk reduction.

Women who are taking tamoxifen for breast cancer risk reduction or who are considering taking tamoxifen for breast cancer risk reduction may wish to discuss these results with their physician.

Reference: Melnikow J, Kuenneth C, Helms LJ et al. Chemoprevention: Drug Pricing and Mortality. The Case of Tamoxifen. Cancer. Early Online Publication July 24, 2006.

Related News:Updated Results Confirm Tamoxifen Risks and Benefits (11/21/2005)

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