Swedish researchers have cut short a study because of the dangers. They say that HRT (hormone replacement therapy) poses an unacceptably high risk of breast cancer recurring in women with a previous history (of the disease).

Originally, this was to be a five-year study (following women?s medical histories). However, after just two years the researchers found that the risk was more than three times higher for those on HRT than those who were not (risk of recurrence of breast cancer).

The research team was led by Professor Lars Holmberg of University hospital, Uppsala (Sweden).

The latest blow to the drug lauded for years as offering a new quality of life for post-menopausal women is reported in the early online publication of the medical journal the Lancet.

The risk has long been suspected, and product and information leaflets already give warnings to that effect.

There have also been strong warnings that HRT increases the risk of breast cancer in previously healthy women, as well as raising the risk of coronary heart disease, stroke and dementia.

Drug watchdogs have been so concerned that they have said HRT must not be used as a frontline preventative for osteoporosis, after years in which it was regarded as extremely useful in preventing bone disease as well as treating menopause symptoms.

Doctors here were told in December that the 'minimum effective dose' of HRT should be used only for the 'shortest duration' to combat menopausal symptoms.

These decisions have been criticised for exaggerating the dangers of HRT and for leaving women with little official guidance on effective alternatives to combating menopause or preventing osteoporosis. Companies selling herbal and vitamin supplements are seeking to fill that gap.

The Uppsala study suggested that 26 of 174 women on HRT reported a recurrence or new case of breast cancer, compared with seven of 171 in the non-HRT group.

Another Swedish study, known as the Stockholm study, indicated that the differences might not be so significant. Nevertheless that trial too has ended, because the pooled analysis of the two studies showed an increased overall risk.

Women on active HRT treatment in the Uppsala trial have been advised not to take the medication any longer.

Improving survival from breast cancer has made management of menopause, which can be brought on early by anti-cancer treatments, an increasingly important issue for breast cancer patients.

Richard Sullivan, head of the clinical programme for Cancer Research UK, said the Swedish trials provided different evidence, so it would have been a difficult decision to call a halt.

'The downside is that women who develop breast cancer early in their lives will be left wondering whether or not it is safe to take HRT, a question which is now unlikely ever to be answered,' he said.

Delyth Morgan, the chief executive of Breakthrough Breast Cancer, another charity, suggested that the results of other trials needed to be seen before conclusions about HRT use in breast cancer survivors could be established.