The reassuring news comes from nearly 29,000 women enrolled in the Nurses' Health Study. It reinforces a recent report from the Women's Health Initiative finding no increased risk of breast cancer after more than seven years of estrogen-only hormone therapy.
The finding applies just to estrogen-only HRT prescribed for women who have had a hysterectomy (removal of the uterus). For women with a uterus, estrogen alone greatly increases the risk of uterine cancer. To avoid this risk, HRT for women with a uterus balances estrogen with progesterone. But adding progesterone to estrogen increases the risk of breast cancer.
15 Years of Treatment
Women who keep taking estrogen-only HRT for 15 years or longer do up their risk of breast cancer.
Study leader Wendy Y. Chen, MD, MPH, is an oncologist at Brigham and Women's Hospital and Dana Farber Cancer Institute, Boston. "In long-term users of estrogen, after 15 years there was a statistically significant increased risk in hormone-receptor-positive breast cancers," Chen tells WebMD. "After 20 years, there was a significantly increased risk for all types of breast cancer."
Chen and colleagues report the findings in the May 8 issue of Archives of Internal Medicine.
How Much Breast Cancer Risk?
Some breast cancers grow faster in the presence of the sex hormones estrogen and progesterone. Only these hormone-sensitive breast cancers were seen 48% more often in women taking estrogen HRT for 15-20 years. Women who took estrogen-only HRT for 20 years or more had a 73% higher risk of hormone-sensitive breast cancer than women who never used HRT.
That's still not a huge increase in risk, says Hugh Taylor, MD, director of the menopause program at Yale University. Taylor has received speakers' fees from -- but has no financial interest in -- Wyeth Pharmaceuticals, the maker of Premarin and Prempro HRT products. Wyeth is a WebMD sponsor.
"This is a very small risk," Taylor tells WebMD. "An increase of about 50% after 15 years is still a relatively small number of breast cancers."
The risk tended to concentrate in thinner women -- those with a body mass index under 25. That finding was what researchers call a "trend." It could have been chance, but there's good reason to think it is real.
"Heavier women are well known to have higher levels of estrogen, because fat tissue converts other things in your body into estrogens," Chen says. "It's the same reason why birth control pills, which contain much more estrogen than HRT, aren't linked to breast cancer. That is because before menopause, a woman has a lot of estrogen, and adding a lot of estrogen doesn't affect her hormone balance as much as adding a little estrogen affects a postmenopausal woman who doesn't have as much in her body."
Making Treatment Decisions
The findings are good news to James Pickar, MD, assistant vice president of clinical research and development for Wyeth."For the majority of women taking estrogen in the 10-year window after hysterectomy, this finding of no increased risk in that time frame should be reassuring," Pickar tells WebMD. "We have not changed our recommendations or our labeling. Women should discuss with their doctors using the lowest dose that works for them for a time consistent with their treatment goals."
Taylor says it's good news for women, too.
"With estrogen alone, the biggest fear women have isn't there," Taylor tells WebMD. "For a woman with a hysterectomy, the decision about whether to take estrogen is an easy decision today. The heart protection is there. The bone protection is there. The breast cancer risk isn't there. For women with no hysterectomy, the decision remains more difficult."
Chen, Taylor, and Pickar agree that a woman taking HRT should see her doctor at least once a year. At each visit, she should discuss whether the benefits of HRT are worth the risks of continuing treatment.
Even though short-term estrogen-only HRT doesn't carry a breast cancer risk, it's not risk free. The treatment does increase a woman's chances of blood clots and stroke.