Today results from the Breast Cancer Now Generations Study have revealed that the risk of developing breast cancer from taking combined hormone replacement therapy (HRT) is likely to have been underestimated by previous studies. Here we lay out the facts on this topic and what today’s results mean.

Tuesday 23 August 2016      Research blog
Today’s hormone replacement therapy results explained

Results from the Breast Cancer Now Generations Study have revealed new information about HRT and breast cancer risk

Will using HRT increase my risk of breast cancer?

So far studies have shown that the use of HRT does increase the risk of breast cancer. The risk that is linked to the type of HRT called ‘combined HRT’ is greater than the risk associated with oestrogen-only HRT.

The longer you use HRT, the higher your risk of developing breast cancer will be but the increased risk of breast cancer begins to fall as soon as you stop using HRT.

This consensus is broadly supported by the results published today.

How much does combined HRT increase my breast cancer risk and what does the study published today add?

The size of the increase in risk has been debated by scientists. Today’s results focus on combined HRT, for which previous studies have suggested that for every 1,000 women taking combined HRT for five years between the ages of 50 and 54, about 22 will probably develop breast cancer during that time.

In contrast, of 1,000 women who don’t use HRT, about 14 will probably develop breast cancer between the age of 50 and 54. So, evidence to date suggests that using combined HRT causes 8 more women out of 1,000 to develop breast cancer in their early fifties.

The results from today’s research suggest that previous studies may have underestimated this increase in risk by around 60%.

Although the results published today are not given in terms of cases per 1,000 women over five years, to help put the results in simpler terms we have calculated that a 60% underestimation would mean that 34 women per 1,000 taking combined HRT might develop breast cancer. This is an increase of 20 cases rather than 8.

Using combined HRT for 5 years between the ages of 50 and 54

What did the Generations Study do differently?

Because today’s research comes from our landmark Breast Cancer Now Generations Study, the researchers had collected detailed information from the women signed up to the study, including their age at menopause and the type of HRT they used and how long they used it for.

Some studies in the past haven’t taken into account women’s age at menopause and haven’t updated-information on their HRT use over time when calculating the impact of HRT on women’s breast cancer risk. To demonstrate why it’s so important to collect this kind of information, the Generations Study scientists ran an analysis with and without these factors accounted for and the difference between the increase in risk in the two types of analysis was around 60%.

The study authors believe their findings provide a more accurate estimate of the increased risk of breast cancer for combined HRT users.

What is “combined HRT”?

HRT relieves the symptoms of menopause by increasing oestrogen levels. You can take it through patches for the skin, tablets, a cream or a gel. There are two main types of HRT, one containing just oestrogen (‘oestrogen-only HRT’) or a combination of oestrogen and a progestogen (‘combined HRT’) and it can be taken in four ways: through tablets, skin patches, a cream or a gel. A third less commonly used type of HRT known as ‘tibolone’ contains a steroid that acts like oestrogen and progestogen.

The type of HRT you are recommended to use will depend on whether you have had a hysterectomy.

Why does combined HRT increase risk?

Taking HRT increases levels of the hormones oestrogen and progestogen (the drug version of natural progesterone) in the body. It is thought both hormones may affect the growth of some breast cancers, so this overall higher hormone level might explain why HRT increases the risk of breast cancer, although we don’t yet know for sure.

I have had breast cancer – is it safe to take HRT?

It is not clear whether any type of HRT is safe for women who have had breast cancer. Talk to your oncologist before beginning any treatments or taking any supplements to relieve menopausal symptoms to check whether they are safe and suitable for you.

What else should I consider when making a decision about HRT?

HRT relieves many women’s menopausal symptoms and so can improve their lives. It can also reduce a woman’s risk of developing osteoporosis (weak bones) and cancer of the colon and rectum. However, as well as increasing the risk of breast cancer, HRT slightly increases the risk of ovarian cancer, womb (endometrial) cancer and stroke.

Breast Cancer Now thinks that you should decide whether to start or stop using HRT with your doctor, who can provide information and advice. Consider the impact of menopausal symptoms on your life, your medical history, the pros and cons of HRT, and your personal preferences.

It is usually not possible to swap between oestrogen-only and combined HRT, because for most women only one or the other will be suitable.

Experts recommend that, to minimise the risk of breast cancer, the lowest effective dose of HRT necessary to relieve menopausal symptoms should be used for the shortest possible time.

I’m taking / have taken HRT, what can I do to reduce my risk?

Many things affect our risk of developing breast cancer. Some of these things we can’t change, like the genes we inherit or getting older, but our lifestyles can play a part too.

Leading a healthy lifestyle isn’t a guarantee against breast cancer, but it can help lower the chances of the disease developing.

A significant proportion of breast cancers can be linked to lifestyle and women can help to reduce their risk of breast cancer by limiting how much alcohol they drink, maintaining a healthy weight and being regularly physically active.

Click here for more information on reducing your risk.