Research suggests previous assessments of treatment may have underestimated risk levels
Women undergoing some forms of hormone replacement therapy (HRT) are more 2.7 times more likely to develop breast cancer than those who are not, according to new research.
Combined HRT, a combination of oestrogen and a progestogen, is used to combat menopause symptoms such as hot flushes, migraines, disrupted sleep and mood changes.
A study published in the British Journal of Cancer found that previous assessments of the treatment may have understated the risk posed by the treatment by around 60%.
It also concluded that women taking combined HRT for more than 15 years were 3.3 times more likely to develop breast cancer than non-users.
Those using oestrogen-only types of HRT, however, faced no additional risk.
Dr Miriam Daly of the Irish College of General Practitioners advised women with concerns not to stop their course of therapy.
"This study suggests a slightly higher risk with combined HRT than previously reported but that risk is still very small," she told the Irish Times.
The research was carried out as part of the Breast Cancer Now Generations Study led by scientists at the Institute of Cancer Research in London.
Some 39,000 women of menopausal age were monitored for six years, with 775 developing breast cancer during this period.
Significantly, the risk level was found to return to about normal within a year or two of participants stopping the treatment.
Professor Anthony Swerdlow of the ICR, who led the research, said: "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."