Hormone Replacement Therapy and Breast Cancer

Menopausal Hormone Replacement Therapy (HRT) is a treatment prescribed to relieve the symptoms of the menopause. It replaces oestrogen that is at a lower level as you approach the menopause. HRT alleviates symptoms such as hot flushes, night sweats, vaginal dryness and mood swings. It also protects against osteoporosis (brittle bones) and in younger women, may also reduce the risk of heart disease and stroke. 


There are 2 main types of HRT:

  • Combination HRT which contains the hormones oestrogen and progesterone. Because oestrogen given alone can cause growth of lining of the womb and subsequently an increased risk of uterine cancer, progesterone is added to protect the uterus.
  • Oestrogen only HRT which only contains oestrogen. Oestrogen only HRT is usually prescribed for women who have had a hysterectomy.


HRT and breast cancer

The relationship between hormone replacement therapy and the risk of breast cancer has been a controversial topic for many years. The individual risk of breast cancer for each woman around the menopausal age will depend on her own risk factors such as family history, and different types of HRT will also have a different effect on breast cancer risk.

HRT was discontinued by many women after the publication of the Women’s Health Initiative (WHI) study in 2002, linking HRT to an increased risk of breast cancer. This study, which followed over 160,000 post-menopausal women over a 15-year period, found an increased breast cancer risk in women who took combination HRT. However, the study also showed a reduced risk of breast cancer in women who took oestrogen-only HRT. 

A review of 58 studies involving almost 500,000 women published last year not only confirmed the increased risk of breast cancer in women using combination HRT but also suggested an increased risk associated with oestrogen-only HRT. There have been a number of other studies published in the past decade showing a link between HRT, particularly combination HRT, and an increased risk of breast cancer.

However, a follow up of the WHI study published in the Journal of the American Medical Association (JAMA), last month confirmed women who’d had a hysterectomy and had been taking oestrogen-only HRT for 20 years had a reduced risk of developing breast cancer of 25% and 40% reduced risk of death from breast cancer. Women who were taking combination HRT had a slightly increased risk of developing breast cancer but no increase in the risk of death from breast cancer. 

The increased risk of breast cancer with HRT is small and only appears to show after 4-5 years of use. To put it in perspective, in women not taking HRT we expect 3 out of 50 to develop breast cancer between the ages of 50 and 69 years.  For women taking combination HRT for 5 years, one extra woman will develop breast cancer between the ages of 50 and 69 years.

Any increase in the risk is related to treatment duration and reduces after stopping HRT. Higher dose combination HRT increases breast cancer risk more than low at dose combination HRT. Breast cancer risk goes back down to average about 2 years after you stop taking the HRT.

What should you do?

If you are going through the menopause and your symptoms are severe enough to affect your quality of life then talk to your doctor about your symptoms and health risks. Although controversy with hormone replacement therapy remains, new data and newer products suggest that the risks of HRT are small and are usually outweighed by the benefits, particularly if you are younger than 60 years old and within 10 years of the menopause. HRT is the most effective treatment available to relieve many menopausal symptoms, it can reduce your risk of developing osteoporosis (weak bones) and improve muscle strength. 

Your doctor can discuss with you the pros and cons of the different types of HRT as well as alternative treatments. If you have a history of breast cancer or you are at increased risk for breast cancer then you should not use HRT.



So in summary, while the WHI found that oestrogen-only hormone replacement therapy reduced breast cancer risk a number of other studies have found both types of HRT increase the risk of breast cancer so the issue is far from resolved.

The risks of HRT depend on the type, dose, duration of use, route of administration and age of starting treatment. The decision whether to take HRT is a personal decision based on the severity of menopausal symptoms and individual risk factors for adverse effects of HRT but in the majority of women with menopausal symptoms, the benefits of HRT far outweigh the risks.



Rossouw et al Writing Group for the Women’s Health Initiative Investigators. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women’s Health Initiative randomized controlled trial. JAMA. 2002; 288321-333

Collaborative Group on Hormonal Factors in Breast Cancer. Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the world. Lancet 2019. 394(10204): 1159-1168

Chlebowski et al Association of Menopausal Hormone Therapy With Breast Cancer Incidence and Mortality During Long-term Follow-up of the Women’s Health Initiative Randomized Clinical Trials JAMA. 2020;324(4):369-380