WASHINGTON — The hormone estrogen that millions of American women take to offset menopause symptoms may cause nearly 5,000 new cases of breast cancer each year, government researchers reported Tuesday.
An analysis of 16 studies of the relationship between estrogen replacement therapy and breast cancer found that women who took the hormone for at least 15 years had about a 30% greater risk of breast cancer.
Based on estimates of at least 3 million U.S. women taking estrogen, about 4,708 new breast cancer cases and 1,468 deaths from the disease may be caused annually by estrogen use, the researchers at the Centers for Disease Control in Atlanta reported.
"Although the overall benefit of estrogen replacement after menopause may outweigh the risks for most women, our analysis supports a small but statistically significant increase in breast cancer risk due to longterm estrogen use," the researchers said in the Journal of the American Medical Assn.
The study indicates that more research is needed to examine the link between estrogen and breast cancer, especially which women may be at increased risk due to estrogen use, said Karen Steinberg, who led the study.
The increased risk detected in the study may be due to pre-menopausal women and women with a family history of breast cancer taking estrogen, she said.
"I think the bottom line is if you're talking about public health many women will benefit from estrogen therapy," she said. "We need to find out who really is at higher risk for breast cancer."
Doctors prescribe estrogen to many women to alleviate symptoms of menopause.