Women taking hormone replacement therapy (HRT) have a lower risk of developing breast cancer than previously feared, a new study suggests.
A large meta-analysis by Oxford University last year showed that long term use of HRT tablets are linked with increased risks of breast cancer, mostly due to progestogens.
However, although the new research did find a link, it was not as high as the previous study.
Around one million women take HRT treatments in the UK, which include tablets containing oestrogen only, or a combination of oestrogen and progestogen, as well as patches, gels and creams.
Most women take a combined form of progestogen alongside oestrogen.
But there is still uncertainty around the risks associated with different types and durations of the therapy.
This latest study, by the University of Nottingham, compared HRT prescriptions for around 98,000 women aged 50 to 79 who were diagnosed with breast cancer between 1998 and 2018, with those of around 457,000 women of the same age, and from the same general practice, who did not develop breast cancer.
Researchers analysed risks by HRT type, by recent and past use, and by short term and long term use. Other relevant factors, such as smoking, alcohol consumption and pre-existing conditions were taken into account.
Overall, a third of women with a breast cancer diagnosis and just under a third of women without had used HRT recently or in the past.
For recent long-term users, compared with those who had never used the treatment, there was a 15 per cent associated increased risk of developing breast cancer for oestrogen only therapy.
This rose to a 79 per cent associated increased risk for combined oestrogen and progestogen therapy, compared to those who had never used HRT. An analysis by Oxford found the risk was higher.
Per 10,000 women aged 60 to 69 who are taking combined oestrogen progestogen therapy, there would be, on average, 15 extra cases of breast cancer in those who have been taking it for less than five years, and 26 extra cases for those who have been taking it for more than five years, study author Dr Yana Vinogradova, of the University of Nottingham, explained.
Being an observational study, a cause between HRT and breast cancer cannot be established, Dr Vinogradova, said.
Past long term use of oestrogen only therapy and past short term use of oestrogen-progestogen were not associated with increased risk of breast cancer.
The risk associated with past long term oestrogen-progestogen use, however, remained increased at 16 per cent versus never use.
“Our results add more evidence to the existing knowledge base and should help doctors and women to identify the most appropriate HRT formulation and treatment regimen, and provide more consistently derived information for women’s health experts, healthcare researchers, and treatment policy professionals,” the researchers said.
The research was published in the BMJ.
CORRECTION: An earlier version of this article stated that women taking hormone replacement therapy were more likely to develop breast cancer than previously feared. This was based on a comparison with an earlier Oxford University study. In fact, the research conducted by University of Nottingham suggested the risk was not as high as the Oxford study. The article has been amended to reflect this.