They say combined HRT is responsible for 15,000 of those cases.
The study is also the first to report that HRT increases the risk of dying from breast cancer, by 22%.
About 20 women in every 1,000 will usually develop breast cancer.
But the study found for every 1,000 women who use HRT for 10 years from the age of 50, there will be an additional 19 cases of cancer in those using the combined oestrogen and progestogen version and an extra five in those using oestrogen-only HRT.
Using tibolone, a steroid treatment, also increased a woman’s cancer risk.
Women also have to bear in mind that oestrogen-only HRT carries an increased risk of uterine cancer.
Women’s risk of developing breast cancer decreases when she stops and is back to normal levels after five years, claims the research.
The data, published in The Lancet, covered a million women who went for mammograms between 1996 and 2001.
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