"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 Joy Melnikow, professor of family and community medicine at UC Davis School of Medicine and Medical Center. "This would support revising the current recommended risk threshold for physicians to counsel women about tamoxifen."
Tamoxifen was approved by the U.S. Food and Drug Administration in 1998 for breast cancer prevention in women who have at least a 1.67-percent chance of developing the disease over the next five years. Such women are considered at high risk for breast cancer. Groups such as the U.S. Preventive Services Task Force and the Canadian Task Force on Preventive Health Care recommend that physicians counsel women above this threshold about the benefits and risks of tamoxifen as a means of preventing the disease.
Tamoxifen is a selective estrogen receptor-modulating drug used to treat estrogen receptor-positive breast cancers. In addition, it has been shown to reduce the incidence of invasive breast cancer among high-risk women by up to 49 percent.
However, tamoxifen is associated with significant adverse effects, including cataracts requiring surgery, deep vein thromboses, endometrial cancer and stroke. Women taking tamoxifen, if they do develop breast cancer, are also more likely to develop an estrogen receptor-negative tumor, which has a worse prognosis.
In the new study, Melnikow and her colleagues calculate that tamoxifen can be expected to extend life expectancy only when a woman's five-year risk of developing breast cancer reaches 3 percent or more. This is especially true for women who have not had a hysterectomy, and therefore face the risk of endometrial cancer related to tamoxifen use.
To arrive at their findings, Melnikow and her colleagues used a complex mathematical model based on a hypothetical group of 50-year-old women.
MEDICA.de; Source: University of California - Davis