A woman’s exact risk is dependent on the type of HRT being taken, how long it is taken, and how high the dose is.
HRT is taken by women going through menopause to help reduce symptoms such as hot flashes, night sweats, and mood changes. It works by increasing the amount of estrogen, which naturally drops during menopause, in the body.
HRT does have benefits for women. It can improve quality of life by relieving many of the symptoms of menopause. There is also evidence that it can reduce a woman’s risk of developing colorectal cancer and osteoporosis (thin or weak bones).
A woman should discuss whether to start or stop using HRT with her doctor, who will be able to tell her what options are available. For some women, the benefits may outweigh the risks. However, to minimize the risk of breast cancer, it is preferable to use the lowest dose of HRT necessary to relieve symptoms for the shortest possible time.
Not smoking, followed by maintaining a healthy weight, keeping active, and eating a healthy diet, are the most effective ways to reduce cancer risk.
HRT does affect different cancers in different ways, though the overall increased risk is small.
- Breast Cancer. Studies have shown that taking combined HRT (which contains the hormones estrogen and progesterone) increases the risk of breast cancer. The evidence about estrogen-only HRT is less clear: It may also increase risk, but to a lesser extent than with combined HRT.
With combined HRT, the risk of developing breast cancer increases slightly the longer a woman takes HRT, but the risk decreases gradually once she stops. Five years after stopping HRT, a woman’s risk of developing breast cancer will be the same as if she had never taken HRT. The evidence is less clear for estrogen-only HRT.
Naturally occurring estrogen and progesterone are thought to affect the growth of some breast cancers. Having higher levels of these hormones from taking HRT might explain why it increases the risk of breast cancer, but we don’t yet know for sure.
- Endometrial Cancer. There is strong evidence that estrogen-only HRT increases the risk of endometrial cancer. The evidence relating to combined HRT is less clear. The increase in endometrial cancer risk seems to be smaller in women using combined HRT than estrogen-only HRT. It is also possible that, with the correct dose of progesterone within combined HRT, there is no effect on risk, but research has not yet demonstrated this.
- Ovarian Cancer. Evidence has shown an increase in the risk of ovarian cancer from taking both combined and estrogen-only HRT. The size of the increase in risk is small, but it is seen soon after a woman begins taking HRT (appearing in women who have been taking HRT for less than five years). However, when a woman stops taking HRT, her risk does start to reduce.
- Colorectal Cancer. There is some evidence that HRT may reduce the risk of colorectal cancer, but as yet there is insufficient evidence to confirm which type of HRT is most beneficial, the size of the reduction in risk, or how long the benefit lasts. More research is needed to answer these questions.
Visit the National Cancer Institute for more information on hormones.