An international team led by Professor Jack Cuzick, of the charity Cancer Research UK, conducted an extensive review of the drug's track record in prevention trials.

It may be possible to reduce side-effects of tamoxifen by using a lower dose or adding low dose aspirin Professor Jack Cuzick

The findings show the drug reduced the incidence of breast cancer by 38% in healthy women with a high chance of developing the disease.

Researchers say the next challenge is to minimise the side-effects of tamoxifen so that it can fulfil its potential as a frontline preventative drug.

Professor Cuzick said: "In our analysis we combined all the available evidence from studies using tamoxifen for breast cancer prevention collectively involving over 40,000 women - and it is clear to us now that the drug can reduce the chance of high-risk women developing the disease."

The team, involving scientists from Australia, Italy and the UK, combined and re-analysed the results of 14 trials.

In trials using tamoxifen after an initial tumour had been removed, scientists found that the number of new cancers in the opposite breast dropped by 46%.

Limitations

However, tamoxifen was only able to prevent breast cancers that carry receptors for the hormone oestrogen.

There was no reduction in incidence for women with oestrogen receptor negative breast tumours.

Researchers also calculated that women taking tamoxifen were more than twice as likely to develop blood-clotting disorders, and endometrial (lining of the womb) cancer.

Professor Cuzick said: "The evidence to date clearly shows that tamoxifen can reduce the risk of breast cancers stimulated by the hormone oestrogen.

"However, it is crucial that we follow all the trials to their conclusions and find ways to reduce the side-effects of tamoxifen before we can recommend that high-risk women take the drug to prevent breast cancer.

"It may be possible to reduce side-effects of tamoxifen by using a lower dose or adding low dose aspirin.

"Carefully selecting women to exclude those already at risk of blood clotting disorders or endometrial cancer may also be a way of making the use of tamoxifen more viable."

Dr Michelle Barclay, of the charity Breakthrough Breast Cancer, said: "This data does look very promising. However, we are concerned about the side effects of using tamoxifen in healthy women.

"Clearly more research is needed into tamoxifen and other drugs when used for the prevention of breast cancer."

The research is published in The Lancet.