17 December 2019

Research presented at the San Antonio Breast Cancer Symposium suggests that oestrogen only hormone replacement therapy, otherwise known as HRT, may decrease breast cancer risk in postmenopausal women, while combined HRT (oestrogen plus progestin) may increase it.

The study presents findings from two large trials following 27,347 postmenopausal women. It found that after 16 years of follow-up, women taking oestrogen only HRT were 27% less likely to have been diagnosed with breast cancer and 44% less likely to have died from the disease compared to women who had not taken HRT. However, this type of HRT can only be given to women after they have undergone an operation to remove the womb (hysterectomy), as oestrogen only HRT is linked to an increased risk of womb (endometrial) cancer.

After an average of 18 years of follow-up, they found that women who were taking the combined HRT (oestrogen plus progestin) were 29% more likely to have been diagnosed with breast cancer in comparison to women who had not taken HRT.

The findings regarding oestrogen-only HRT differ from other studies that have previously suggested most oestrogen only and oestrogen plus progestin HRT can increase a woman’s risk of breast cancer. Further research is needed to clarify the effect of oestrogen-only HRT.

Baroness Delyth Morgan, Chief Executive at Breast Cancer Now, the research and care charity, said:

We’ve long known that certain forms of hormone replacement therapy (HRT) can increase breast cancer risk, and this important study offers new insight on how different types of HRT may influence this risk in different ways.

It’s really interesting that this research suggests oestrogen-only HRT may actually reduce the risk of breast cancer in women who have undergone a hysterectomy. While this may seem reassuring, this finding does contradict what has been suggested in other studies and so further research is now needed to clarify its effect and help provide clear information to this group of women.

Taking HRT is a really personal decision, and it’s vital that everyone has the information they need on the benefits and risks, discusses them with their GP and is supported to make the choice that’s right for them. We’d encourage anyone concerned about HRT and their breast cancer risk to speak to their GP or call our free Helpline on 0808 800 6000.