Hormone replacement therapy (HRT) could reduce a woman’s risk of food pipe, stomach and bowel cancers, although the breast cancer risk still outweighs the positive effects, Cancer Research UK-funded scientists have discovered.

The research*, presented this week at the National Cancer Research Institute (NCRI) Cancer Conference in Liverpool, showed that the risk for all three cancers – which make up the majority of gut cancers – was reduced by 20 to 30 per cent in women taking HRT compared with those who were not.**

But scientists warned that on balance the protective role of HRT for gastrointestinal cancers was far outweighed by the drug increasing the risk of breast cancer – the most common cancer in women in the UK.

The study showed that there was one less case of gastrointestinal cancer for every 2000 women aged 50-64 using HRT for five years compared to those who did not use the drug during the same period. Over the same time, in the same number of women, there would be an estimated 20 extra cases of breast cancer with HRT use.

Our results are interesting in showing what effect HRT can have on cancers along the length of the gut. However, the reduced risk of gastrointestinal cancers needs to be seen in the wider context of other risks and benefits. Overall, cancer risk is increased in women who take HRT.

Lead researcher Dr Jane Green, based at Cancer Research UK’s epidemiology unit at the University of Oxford

The reduction in risk of gastrointestinal cancers was the same for both oestrogen-only and combined forms of HRT.

The risk was also reduced in both existing and past users of the drug, and regardless of how long HRT was taken.

Studies like this are valuable in adding to existing information about how HRT affects a woman’s risk of cancer. While this study finds that HRT may protect against some cancers, there is stronger evidence to show that taking the drug can do more harm than good for most women. There are a variety of reasons why women take HRT; those thinking of taking the drug should talk to their doctor and be aware of all the information about HRT so they can make a decision appropriate to their condition. Cancer Research UK’s advice is that women should only take HRT for medical reasons and for as short a time as possible.

Dr Lesley Walker, director of cancer information at Cancer Research UK