A new study has found that women on certain hormone replacement therapies, are 2.7 times more likely to develop breast cancer, than those who are not.
The findings in the British Journal of Cancer relate only to women taking combined HRT, to deal with the effects of menopause.
For women taking oestrogen and progestogen HRT, for 15 years or more, the risk was 3.2 times greater.
No increased risk was found for women on oestrogen-only HRT.
The study involved nearly 40,000 women over six years.
After HRT use finished, the increased risk returned to normal levels.
Speaking on RTÉ's Today with Keelin Shanley, a consultant oncologist at St Vincent’s University Hospital, said that studies linking HRT to breast cancer had been reported before and there had been conflicting studies also.
Dr Janice Walshe said the risks need to be assessed for each individual woman and not the population as a whole.
She said that even at the risk levels reported, these were still very low.
Dr Walshe said there were significant benefits for women on HRT and ideal use was at low dose, over a short duration.
The advice is that no woman should stop taking their medication without discussing the issue with their GP.