Study: Tamoxifen Appears to Reduce Risk of Breast Cancer by a Third

Women taking tamoxifen to prevent breast cancer appear to reduce their risk of the disease by about a third, according to U.K. researchers.

Three clinical trials on the use of tamoxifen to prevent breast cancer have reported mixed results. Most of the evidence shows a reduction in the risk of breast cancer, but whether the benefits outweigh the risks and side effects of tamoxifen has been unclear.

In the latest study, researchers performed a double-blind, placebo-controlled randomized study of tamoxifen in 7,152 women ages 35 to 70, all at an increased risk of breast cancer. The women were given 20 mg of tamoxifen over a five-year period.

After an average follow-up period of 50 months, 69 breast cancers had been diagnosed in 3,578 women in the tamoxifen group and 101 in 3,566 in the placebo group, the researchers reported in The Lancet.

The women's age, degree of risk, and use of hormone replacement therapy did not affect the results. The incidence of endometrial cancer was not significantly increased. However, the incidences of blood clots were significantly increased, especially after surgery.

"This study has confirmed that tamoxifen can reduce the risk of breast cancer in healthy women during the active treatment phase," concluded the researchers. "The increased frequency of gynecological problems, particularly the increased requirement for hysterectomy and oophorectomy (removal of ovaries), is of some concern."

The researchers warn that blood clotting is the most important complication of tamoxifen use and every effort should be taken to reduce this risk.

The researchers advised that treatment with tamoxifen be discontinued temporarily during and after major surgery. Use of tamoxifen is also ill advised in women at a high risk of blood clots, they said.

The researchers stated, "Long-term follow-up to study breast cancer incidence and mortality, other causes of death, and side effects in the current trials remains essential."

Other sources: The Lancet