That came as a surprise because estrogen is known to fuel the growth of many breast cancers. In fact, a separate portion of the WHI showed that combination HRT with estrogen and progestin (which is given to women who still have their uterus) did raise the risk of breast cancer, as well as other problems like heart attack, stroke, and blood clots. The researchers performed this new analysis to better understand how estrogen-only HRT affects the disease.
"The clinical trial results for estrogen-alone and for estrogen-progestin are very different," said lead study author Marcia Stefanick, PhD, in a statement. She's a professor of medicine at the Stanford University School of Medicine. "The use of estrogen-progestin clearly showed an increased risk for breast cancer; estrogen-only therapy shows no evidence of an increased risk."
More Abnormal Mammograms
After about 7 years of follow-up, the women on estrogen-only had slightly lower rates of breast cancer than women on placebo. But the difference was not large enough to be statistically meaningful, and researchers say it could have occurred by chance.
Some women did see a significant benefit, though. Estrogen appeared to lower the risk of breast cancer substantially in those who already had a low risk because they had no family history of the disease and had never had benign breast disease. There were also fewer cases of ductal carcinoma in situ (DCIS) in the estrogen group.
However, women on the HRT had more abnormal mammograms that required follow-up with another mammogram within 6 months. They also needed more biopsies to investigate suspicious findings.
That fact is important and something women who are considering estrogen-only HRT should keep in mind, Stefanick said. Having to have repeated mammograms can cause emotional distress, she and her colleagues note.
Separate Study Hints at Higher Risk for Black Women
The new WHI findings were published a day after a separate report came to a slightly different conclusion about the effects of hormone replacement therapy in African-American women. That study, which appears in the Archives of Internal Medicine, found an increased risk of breast cancer with both types of hormone therapy.
That raises the question of whether hormone therapy may have different effects in women of different races. About 90% of the women in the WHI trials were white.
Researchers from Boston University and Howard University looked at data on hormone use and breast cancer from more than 32,000 African-American women age 40 or older who were enrolled in the Black Women's Health Study. Both women who took combination estrogen-progestin HRT and those who took estrogen-only had higher rates of breast cancer than women who had never used hormone therapy. The effects of hormones were greater in lean women than heavy women.
However, those increases were not statistically significant -- meaning they may have been due to chance. So it's really not clear yet whether hormone therapy actually does increase the risk of breast cancer among African-American women, said Len Lichtenfeld, MD, deputy chief medical officer for the American Cancer Society.
"That does not mean that it is safe to conclude the alternative, namely that all hormone therapy is safe for black women," he added. "It is simply that this particular study at this particular time doesn't allow me to draw the conclusion that there are differences in risks of hormone therapies between black and white women."
Lichtenfeld said longer study of this group of women may provide more answers.
"The vast majority of women in this study were in their 40s, which is not the primary age when women develop breast cancer," he said. "Follow these women for another 20 years and the data may indeed become more informative."
Individualized Decisions Important
Both new studies underscore the need for women to talk with their doctors about their individual medical history if they are considering using hormone therapy.
"The practical problem has been that for many women, hormonal replacement therapy is critical for their general sense of well-being," Lichtenfeld explained.
He and other experts say if women are going to use hormone therapy to relieve symptoms of menopause, they should do so at the lowest effective dose and for the shortest possible time.
And they should always keep in mind the potential side effects. In addition to the higher risk of strokes, the WHI study found that estrogen-only also raises the risk of blood clots in the legs and memory problems. However, it may also lower the risk of hip fractures.
Citations: "Effects of Conjugated Equine Estrogens on Breast Cancer and Mammography Screening in Postmenopausal Women with Hysterectomy." Published in the April 12, 2006, Journal of the American Medical Association (Vol. 295, No. 14: 1647-1657). First author: Marcia L. Stefanick, PhD, Stanford Prevention Research Center.
"A Prospective Study of Female Hormone Use and breast Cancer Among Black Women." Published in the April 10, 2006, Archives of Internal Medicine (Vol. 166, No. 7: 760-765). First author: Lynn Rosenberg, ScD, Boston University. |
