cancer cells attackingA new report into the effect of combined hormone replacement therapy (HRT) should allow women to make an informed choice regarding the benefits and drawbacks of HRT, its authors have said.

Speaking following the publication of the new report in the British Journal of Cancer, study leader Anthony Swerdlow, Professor of Epidemiology at the Institute of Cancer Research, said: “Our research shows that some previous studies are likely to have underestimated the risk of breast cancer with combined oestrogen-progestogen HRT. We found that current use of combined HRT increases the risk of breast cancer by up to three-fold, depending on how long HRT has been used. 

“Our findings provide further information to allow women to make informed decisions about the potential risks and benefits of HRT use. This research was only possible because of the detailed information provided over many years by the dedicated participants in the Generations Study.”

The new research was part of the Breast Cancer Now Generations Study — a major prospective study led by scientists at The Institute of Cancer Research, London, following more than 100,000 women for 40 years to investigate the causes of breast cancer. 

Some 39,000 women with a known age at menopause were identified and monitored for 6 years, with follow-up questionnaires gathering comprehensive data on any HRT use (type and duration) as well as their general health and lifestyle. 

During this time, 775 of these women developed breast cancer, with the researchers finding that women using combined HRT (for a median duration of 5.4 years) were 2.7 times more likely to develop breast cancer during the period of HRT use than women who had never used HRT. 

This risk increased with duration of use, with women who had used combined HRT for more than 15 years being 3.3 times more likely to develop breast cancer than non-users. However in women using oestrogen-only HRT there was no overall increase seen in breast cancer risk compared with women who had never used HRT. 

Importantly, this increased risk level has been found to return to about normal once HRT use ends: after a year or two had gone by since women stopped taking combined HRT, the scientists did not find a significantly increased risk of breast cancer, confirming the findings of previous studies.

Baroness Delyth Morgan, Chief Executive of Breast Cancer Now, said: “Whether to use HRT is an entirely personal choice, which is why it’s so important that women fully understand the risks and benefits and discuss them with their GP. We hope these findings will help anyone considering the treatment to make an even more informed decision. 

“On balance, some women will feel HRT to be a necessity. But in order to minimise the risk of breast cancer during treatment, it is recommended that the lowest effective dose is used for the shortest possible time.

“The good news is that the increased risk of breast cancer begins to fall once you stop using HRT.

“If anyone is at all worried about either HRT or breast cancer, we’d highly encourage you to speak to your GP.”

The Breast Cancer Now Generations Study participants will continue to complete further questionnaires as the study progresses, enabling the researchers to investigate — with even more detail and precision — the risk of breast cancer in relation to duration of HRT use and to the types of HRT used.