A study from researchers at the Universities of Nottingham and Oxford provides new estimates of the increased risks of breast cancer associated with use of different hormone replacement therapy (HRT) preparations in the UK. HRT is used to relieve menopausal symptoms such as hot flushes and night sweats. Treatments include tablets containing oestrogen only, or a combination of oestrogen and progestogen, as well as patches, gels and creams. Previous research has shown that long term use of HRT tablets is associated with increased risks of breast cancer, mostly due to progestogens. Last year, a large meta-analysis reported higher than expected breast cancer risks associated with HRT, but there is still uncertainty around the risks associated with different types and durations of HRT.
Published in the British Medical Journal, the latest study used two UK primary care databases (QResearch and CPRD) linked to hospital records to compare HRT prescriptions for 98,611 women aged 50-79 who were diagnosed with breast cancer with those of 457,498 women of the same age and from the same general practice who didn’t develop breast cancer. The analysis confirms that HRT use is associated with increased risks of breast cancer, particularly for older women. Risk increases were mostly associated with combined oestrogen-progestogen treatments, but small increases were also associated with oestrogen only treatments. However, it suggests that, for longer term HRT use, the increased risks are lower than those reported in last year’s meta-analysis that combined the results of 24 studies. Today’s study also shows a more noticeable decline in risks once HRT has stopped, compared with the same meta-analysis.
This is an observational study so it cannot establish cause, and the researchers point to some limitations that may have affected the accuracy of their results. Nevertheless, they say this was a large study, using consistent sources of “real world” primary care data, and the results were similar after further analyses, suggesting that the findings withstand scrutiny.
This research is important as it strengthens the evidence base to help patients and their doctors make better decisions on the risks associated with HRT. We thank all of the GP practices who contribute anonymised data to QResearch without whom this research would not be possible. - Co-author, Professor Julia Hippisley-Cox, Nuffield Department of Primary Care Health Sciences and Director of the QResearch database which was utilised for this research
The study was funded by the National Institute for Health Research School for Primary Care Research and Cancer Research UK.