New research from UC Davis and three other universities suggests that most women who take tamoxifen to prevent breast cancer do not extend their life expectancy. The study was published in the Sept. 1 issue of the American Cancer Society's journal Cancer.

"We found that for women at the lower end of the high-risk range for developing breast cancer, there is a very small likelihood that taking tamoxifen will reduce mortality," said lead author Joy Melnikow, a professor of family and community medicine at UC Davis.

Groups such as the U.S. Preventive Services Task Force now recommend that physicians counsel women who have at least a 1.67-percent chance of developing breast cancer over the next five years about the benefits and risks of taking tamoxifen to prevent the disease.

Melnikow's work suggests a 3-percent risk threshold is more appropriate. The study showed that women above this risk level can expect to live longer if they take tamoxifen for breast cancer prevention.

In addition to its use in breast cancer prevention, tamoxifen is an effective breast cancer treatment. The study did not question the drug's benefits as a treatment for the disease.