An analysis of dozens of studies found that women taking the therapy remain at a higher risk for more than a decade after stopping use
A sweeping new analysis adds to the evidence that many women who take hormone therapy during menopause are more likely to develop breast cancer—and remain at higher risk of cancer for more than a decade after they stop taking the drugs.
The study, published recently in the Lancet, looked at data from dozens of studies, including long-term data on more than 100,000 women who developed breast cancer after menopause. Half of those women had used hormone therapy, or HRT. The longer women took the medicine, the more likely they were to develop breast cancer. Experts say the findings could shape how women and their health care providers decide how to manage symptoms of menopause.
“This is a consensus of many researchers and many studies all around the world. These are important new results,” said said Valerie Beral, a cancer epidemiologist at the University of Oxford and one of the lead authors of the new study.
Women have long been prescribed synthetic versions to replace the hormones that decline during menopause. The medications—usually delivered in a pill, but sometimes in a patch, gel, or injection—provide women either estrogen or a combination of estrogen and progestogen, a synthetic form of progesterone. For some women, they may help to tamp down symptoms of menopause.
For years, research has suggested a potential link between HRT and an increased risk of breast cancer. In 2002 and 2004, the Women’s Health Initiative released reports that showed women who used combination HRT were more likely to develop breast cancer. HRT use fell after the reports received widespread coverage. That was followed by a decline in breast cancer rates.
But there wasn’t much information on whether that risk persisted, or how it differed based on the type of HRT a woman took. So an international group of researchers pulled together data from dozens of studies—published and unpublished—to examine the issue more closely. They took a woman’s age at first use of HRT, how long she used the medication, and the time elapsed since she last used it into account. The mean age of women starting menopause was 50, which was also the mean age at which women started using HRT.
The researchers found that compared with women who never used HRT, women who did had a significantly higher risk of developing invasive breast cancer. They estimated that 6.3% of women who never used HRT developed breast cancer, compared to 8.3% of women who used the combination drug continually for five years. That’s roughly one extra cancer diagnosis for every 50 users.
The longer women used HRT, the greater their risk of breast cancer. Women who were no longer using HRT had a lower relative risk than women who were currently using it—but they remained at an elevated risk for more than a decade after they stopped taking the drug. The level of risk was dependent on how long a woman took HRT. The study also found that women who took the combination drug were more likely to develop cancer than women who took the estrogen-only drug.
“The findings are significant,” said Joanne Kotsopoulos, a breast cancer researcher at Women’s College Research Institute in Toronto. “The longer you use it, the higher the risk,” added Kotsopoulos, who wasn’t involved in the research but wrote a commentary on the study, also published in the Lancet. “It’s a balance. Every woman is different, but the risk is high for breast cancer, so they need to take a very serious approach.”