HRT and cancer

Happy, older woman

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. Menopausal symptoms like these can be particularly troubling for some women. In these women, HRT can be helpful.

HRT treats these symptoms by boosting the body with more female sex hormones.

There are two main types of HRT:

  • Oestrogen-only HRT, which consists only of oestrogen
  • Combined HRT, which consists of oestrogen, plus progestogen, another female sex hormone

Combined HRT can be given in two ways:

  • Cyclical (or sequential) combined HRT, where oestrogen is taken every day but progestogen is given in monthly or three-monthly doses
  • Continuous combined HRT, where both oestrogen and progestogen are taken together every day

HRT can be taken in several different ways, including as tablets, patches or gels.

There are other forms of HRT which are less commonly prescribed. These can include a medication called tibolone. Tibolone is a synthetic (man-made) hormone that has effects similar to oestrogen, progestogen and also testosterone, a male sex hormone. 

HRT and cancer

The evidence that HRT can cause some types of cancer (breastwomb 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.

But it’s important to remember that the increased cancer risk with HRT is small compared to many other risk factors, like smoking or being overweight, as shown below. HRT is only responsible for a very small proportion of cancer cases.

An infographic looking at the benefits and harms of HRT

Breast cancer

The risk of developing breast cancer is increased for women using any type of HRT, but the risk is greatest for women using the combined type. 

These increased risks were similar between the types of oestrogen and progestogen used, and between continuous vs cyclical combined HRT.

The Million Women Study found that women who are current users of 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.  

For women currently using oestrogen-only HRT, the risk of breast cancer is also higher compared to women who have never used HRT. But this risk is not as high as for women using combined HRT.

Once a woman stops using HRT, her risk of breast cancer will start to drop back down again. It takes about 4 years to go back to the same risk as if she hadn’t used HRT.

Users of tibolone may also be at increased risk of breast cancer.

Womb (endometrial) cancer

Oestrogen-only HRT increases the risk of womb cancer.  Because of this, oestrogen-only HRT is generally only offered to women who have had their womb removed (hysterectomy). So they have no risk of womb cancer to begin with.

The picture for women using 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, when it comes to womb cancer. But it depends on the type of combined HRT used.

But it’s important to remember that combined HRT causes the greatest increase in risk for breast cancer.

The Million Women Study also found that the risk of womb cancer in women using tibolone was increased by around 80% compared with never users of HRT.

Ovarian cancer

Using oestrogen-only or combined HRT increases a woman’s risk of ovarian cancer.  It’s not yet clear if there’s any link between ovarian cancer and tibolone.   

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.

Other cancers

HRT may reduce the risk of other cancers like bowel and stomach cancer, but more research is needed to investigate this.

And it’s important to note that these reductions in risk are small compared to the increased risk of breast and other cancers associated with HRT.

Should I take HRT?

Your doctor will be able help you weigh up the pros and cons of different types of HRT and make the right choice based on your own circumstances. HRT can improve quality of life for women with troublesome menopausal symptoms, and is still an effective short-term treatment. 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.

You can read more about HRT, including risks and benefits not related to cancer, on the NHS Choices website.

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