Treating Menopause Symptoms
There are two main types of hormone replacement therapy. One uses only estrogen. The other, called combined HRT, replaces estrogen that the body no longer makes and adds progestin to lower the chance of getting uterine cancer.
It can be taken as a pill or by an implant, skin patches, a cream, or a gel.
The latest research is part of the Breast Cancer Now Generations Study led by scientists at The Institute of Cancer Research in London. It is following more than 100,000 women for 40 years to investigate the causes of breast cancer.
The researchers identified 39,183 women whose age at the start of menopause was known. They were monitored for 6 years, with questionnaires gathering data on their use of HRT and how long they were on the treatment.
During this time, 775 of these women got breast cancer. The researchers found that women who used combined HRT for an average of 5.4 years were 2.74 times more likely to get breast cancer while taking HRT than women who had never used it.
They also found that the chance of getting breast cancer rose with length of use. So, women who had used combined HRT for over 15 years were 3.3 times more likely to have breast cancer than nonusers.
Women using estrogen-only HRT were at no extra risk of breast cancer than those who had never used HRT.
Crucially, the higher chance of getting breast cancer fell to around normal levels once HRT use ended. So, a year or two after women stopped HRT, the scientists could not find any extra risk of the disease.
Exposure to Hormones
The researchers say that the higher risk of breast cancer from combined HRT could be explained by an increased exposure to hormones affecting the development and growth of some breast cancers.
They calculate that previous research may have underestimated the higher chance of getting breast cancer from HRT use by up to 59%, depending on the type of HRT used and the age of menopausal onset.
"Our research shows that some previous studies are likely to have underestimated the risk of breast cancer with combined estrogen-progestin HRT,” study leader Anthony Swerdlow, professor of epidemiology at The Institute of Cancer Research in London, says in a statement. “We found that current use of combined HRT increases the risk of breast cancer by up to three fold, depending on how long HRT has been used.
"Our findings provide further information to allow women to make informed decisions about the potential risks and benefits of HRT use."
Whether to use HRT is a personal choice, and it’s important that women understand the risks and benefits and discuss them with their doctors, says Baroness Delyth Morgan, chief executive of the breast cancer research charity Breast Cancer Now. “We hope these findings will help anyone considering the treatment to make an even more informed decision,” she says.
"On balance, some women will feel HRT to be a necessity. But in order to minimize the risk of breast cancer during treatment, it is recommended that the lowest effective dose is used for the shortest possible time."