HRT and cancer
High levels of our own natural hormones can increase our risk of cancer. But some medical treatments can also increase our hormone levels, including hormone replacement therapy (HRT) and the contraceptive Pill.
This page will talk about HRT, how it affects cancer risk, and how you can weigh up the risks.
What is hormone replacement therapy (HRT)?
After menopause, a woman’s ovaries stop producing the hormone oestrogen. As a result, she may experience menopausal symptoms including hot flashes and mood swings.
HRT treats these symptoms by boosting the body with more female sex hormones. There are three types of HRT:
- Oestrogen-only HRT, which consists only of oestrogen.
- Cyclical HRT, where oestrogen is taken continuously but progestogen, another female sex hormone, is given in monthly or three-monthly doses.
- Continuous combined HRT, which contains oestrogen and progestogen, taken at the same time.
HRT and cancer
The evidence that HRT can cause some types of cancer (breast, womb and ovarian) is strong. It includes a study of one million women, run by Cancer Research UK scientists, which has shown that different types of HRT can increase the risk of different cancers.
The risk of developing breast cancer is increased for women who are using combined HRT, and may also be increased for users of oestrogen-only HRT. The Million Women Study results suggested that women who are using combined HRT have double the risk of breast cancer compared to non-users. And if they use HRT for over 10 years, their risks are even higher.
Once a woman stops using HRT, her risk of breast cancer will start to drop back down again. It takes about 5 years to go back to the same risk as if she hadn't used HRT.
Breast cancer is much more common than either ovarian or womb cancer. This means that, if you look at the total effect of HRT on these types of cancer, combined HRT is linked to more cases than oestrogen-only HRT, because of its effect on the risk of breast cancer.
Womb (endometrial) cancer
HRT which uses oestrogen-only increases the risk of womb cancer. But the picture for combined HRT is a bit more complicated. There is evidence that the progestogen part of combined HRT can counteract the cancer-causing effects of the oestrogen part. Studies have shown that the more days per month a woman uses progestogen, as part of combined HRT, the less the increase in risk of womb cancer. At the moment there isn't enough research to say whether, above a certain dose, the progestogen can outweigh the oestrogen and actually reduce the risk of womb cancer overall.
Using either oestrogen-only or combined (oestrogen and progestogen) HRT increases a woman's risk of ovarian cancer. In 2015 new research found that there is an increased risk of ovarian cancer even for women who are taking HRT for under 5 years.
When a woman stops taking HRT the risk starts to go back down over time.
In the UK, for every 1000 women using any type of HRT for 5 years from age 50 there is thought to be 1 extra case of ovarian cancer.
HRT may reduce the risk of bowel cancer, but the evidence is mixed. Some scientists have concluded the evidence is stronger for oestrogen-only HRT, but others think combined HRT shows a more convincing link. It's also unclear whether any reduction in the risk of bowel cancer would only last for as long as a woman is using HRT. More research needs to be carried out in this area before this link is confirmed.
Should I take HRT?
Your doctor will be able to help you weigh up the pros and cons of different types of HRT and make the right choice based on your own circumstances. HRT is still an effective short-term treatment for menopausal symptoms, but there are other risks and benefits to take into consideration too.
If you are considering starting or stopping HRT, or using it for a long time, you should consider the risks involved and discuss them with your doctor. The issues are different for every woman.
Read more about HRT, including risks and benefits not related to cancer, on NHS Choices.