Women who take estrogen-only pills for at least 15 years run a markedly higher risk of developing breast cancer, according to a study of nearly 29,000 nurses. But no increased danger was found among those who took the hormone for less than 10 years.
Researchers said the findings should be reassuring for women who want to use estrogen for a short time to relieve menopausal symptoms such as hot flashes and vaginal dryness.
Hormone supplements were once thought to help postmenopausal women postpone age-related ills. But the government’s Women’s Health Initiative study in 2002 contradicted those beliefs for estrogen-progestin supplements, finding an increased risk of breast cancer, strokes and heart attacks. That led millions of American women to stop taking supplements.
Later, a WHI study of estrogen alone — an option only for women who have had a hysterectomy — linked the supplements to strokes and memory problems. But it found that using estrogen alone for seven years does not raise the risk of breast cancer.
The new findings came from the less-rigorous but longer-running Nurses’ Health Study, overseen by Harvard-affiliated researchers.
It found no increased risk of breast cancer in women who had taken estrogen for less than 10 years. But for women who had been on estrogen for at least 15 years, the risk of hormonally driven breast cancer (the most common type in the United States) climbed 48 percent. At the 20-year mark, the risk of any type of breast cancer rose 42 percent.
'You don't need to panic'
“This says at least for the shorter-term users, you don’t need to panic” about breast cancer, said lead author Dr. Wendy Chen, an oncologist and epidemiologist at Brigham and Women’s Hospital and the Dana-Farber Cancer Institute in Boston. “But for the longer-term users, you need to think about why am I still taking estrogen for this long of time, and are there are alternatives I could take instead?”
The risk of breast cancer also appeared to rise between 10 and 15 years of use, but the increase was not statistically significant, the researchers said.
The study, published in Monday’s Archives of Internal Medicine, involved 28,835 women who were postmenopausal, had had a hysterectomy and reported their estrogen use every two years. Just 3.2 percent of the women, or 934, developed breast cancer during the study.
The researchers said it is unclear how many American women are taking estrogen for 15 or 20 years, especially in light of the WHI findings and doctors’ recommendation since then that women who want to use the pills take them for the shortest possible duration.
Dr. Carolyn D. Runowicz, president of the American Cancer Society, said a few women in her practice have chosen to remain on estrogen for a long time because they feel the improvement in their quality of life outweighs the risks.
Runowicz called the study reassuring for short-term estrogen use but also said it underscores the need for patients to regularly “justify every medication” they take with their doctors.
“Is it estrogen forever? That’s what we thought in the 1970s,” said Runowicz, director of the Cancer Center at the University of Connecticut Health Center, “but we’ve completely reversed our thinking on that.”
Estrogen-alone supplements are given only to women who have had their uteruses removed, because the hormone can spur uterine cancer. Other women get estrogen plus progestin, to counteract the risk of uterine cancer.
The Women’s Health Initiative was a clinical trial in which women were randomly assigned estrogen pills or placebos. Scientists consider that approach the gold standard. The new study relied on nurses who reported on their own health every two years.
Runowicz said nurses could differ somewhat from women in the general population — perhaps they are healthier, for instance — but she said she had no reason to doubt the validity of the data, especially because its conclusions regarding short-term estrogen use are backed up the WHI findings.
Wyeth, which produces the estrogen pill Premarin, considers the Nurse’s Health Study a well-respected study and the most recent research a “fairly reasonable trial,” said Dr. James Pickar, assistant vice president for clinical research and development.
Pickar said he sees the results as good news for women because they back up the WHI findings that found no increased breast cancer risk for short-term estrogen users.
“I think it’s very important for women to talk to their physician and review on a regular basis whether they need to continue therapy,” Pickar said. “Each patient has an individual risk profile that only they and their physician can evaluate.”