Hormone replacement therapy lowers risk of breast cancer by 25% for women who have had hysterectomies - but raises risks by nearly as much for anyone who still has a uterus, study finds

• Researchers looked at postmenopausal women taking hormone replacement therapy (HRT) compared to those being given a placebo
• Women who had undergone hysterectomies and taking HRT had a 25% lower risk of breast cancer than women with no uteruses but taking a placebo
• The risk of breast cancer mortality was also lower with 53% fewer women on HRT dying than those on placebos
• But in women who had not undergone hysterectomies, HRT raised the risk of breast cancer by almost 25%

Hormone replacement therapy (HRT) could lower the risk of breast cancer for some women, but raise it for others, a new study finds. 

Researchers found that women who had had their uteruses removed and were taking HRT were about 25 percent less likely to develop cancer than those being given a placebo.

What's more, this same group of women was more than 50 percent less likely to die from breast cancer. 

But, the team, from University of California Los Angeles Medical Center, also found that women who had not had their uteruses removed raised their risk of cancer by almost one-quarter by taking HRT.

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Women who had undergone hysterectomies and taking hormone replacement therapy had a 25% lower risk of breast cancer than women with no uteruses but taking a placebo (file image)

There are two main types of HRT: combination HRT, which contains both estrogen and progesterone, and estrogen-only HRT. 

Previous research has found that combination HRT, often used by postmenopausal women to alleviate menopausal symptoms, increases the risk of breast cancer by about 75 percent. 

There is also a greater likelihood for users of combination HRT that the cancer may be found at a more advanced stage.

Scientists believe this is because cancerous cells often contain hormone receptors. 

The risk decreases when it comes to estrogen-only HRT. Only when used for more than 10 years is the prospect of a breast cancer diagnosis raised. 

For the study, published in JAMA, the team followed-up on two placebo-controlled randomized clinical trials involving more than 27,000 postmenopausal women. 

Women were enrolled at 40 centers across the country from 1993 to 1998 and were followed-up with through December 31, 2017.

In one trial, involving more than 16,600 women with a uterus, about 8,500 received two doses of HRT - estrogen-only and estrogen plus progestin, which is a synthetic progestogen - while about 8,100 received a placebo.

In the second trial, researchers look at women who hysterectomies, procedures during which the uterus and ovaries are removed.

Around 5,300 received one dose of estrogen-only HRT and approximately 5,400 were given a placebo.  

Results showed that women with a prior hysterectomy and taking HRT were much less likely to develop breast cancer.

There were 238 cases among women without uteruses and taking the medication compared to 296 cases being given a placebo - a 24.3 percent difference.

Additionally, there was lower breast cancer mortality among women on HRT with 30 deaths compared to 46 deaths, a difference of 53 percent.

By comparison, in women with uteruses, HRT was linked to statistically significantly higher breast cancer incidence.

About 23 percent more women on HRT developed breast cancer with 584 cases compared to 447 cases.

However, there was no notable difference in breast cancer mortality between these groups.

IS THERE ANY RISK USING HRT FOR WOMEN GOING THROUGH MENOPAUSE?

Menopause, which commonly strikes women in their late 40s and early 50s, can cause depression, hot flushes, headaches and night sweats. Long term, it can also cause bone disease and memory loss.

Hormone replacement therapy (HRT) tackles these symptoms by replacing the female sex hormones - oestrogen and progestogen - as the body stops producing them.

But while it can transform the lives of many women, studies have shown that there may be an increased risk of breast cancer and heart disease from HRT. As a result, many women no longer accept HRT treatment and some doctors will not prescribe it.

It was however noted by the Woman's Health Concern (WHC) that one of the American studies used women in their mid-sixties who were often overweight as subjects, and these are unrepresentative of women in the UK.

Furthermore, a controlled trial from Denmark reported in 2012 has demonstrated that healthy women taking combined HRT for 10 years immediately after the menopause had a reduced risk of heart disease and of dying from heart disease, contradicting the reports of the earlier studies.

The WHC says HRT is safe provided it is taken for the correct reasons, i.e. to alleviate the symptoms of the menopause, and at the minimum effective dose.