The effect of combined hormone replacement therapy on breast cancer risk has been underestimated, according to a new analysis by British researchers.
The study suggests that women taking combined HRT faced a 2.7 times increased risk of developing the disease.
Women who had taken the treatment for longer than 15 years faced a 3.3 times increased risk, the researchers found.
The analysis at the Institute of Cancer Research, London, UK, has been reported in the British Journal of Cancer.
The findings come from an analysis of some 39,000 women during the years of menopause. Some 775 women developed breast cancer.
The increased risk was only found when women took combined oestrogen and progestogen therapy but not when they took oestrogen on its own.
The researchers say their findings are more accurate than previous studies because they took pains to ensure establish that women in the study were post-menopausal. Researchers also updated details of women’s use of HRT at regular intervals.
Researcher Professor Anthony Swerdlow 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.”
British Journal of Cancer 22 August 2016
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