The company has applied to the US Food and Drug Administration for approval to market the drug as a preventive treatment - despite European fears that it doesn't work.

An advisory committee of the FDA is to hold a hearing on the drug on 2 September and Zeneca expects approval to granted soon after this.

The move follows the halting of a large-scale US trial of the drug, marketed as Novaldex, in April.

The study of 13,000 women considered at high risk of developing breast cancer found that those taking the drug were 45% less likely to get cancer as those not taking it.

Criticism

But the decision to stop the trial before it had run its course has been criticised by European scientists.

And a study by Italian and UK scientists published in the Lancet last month suggested there was no provable evidence that tamoxifen prevented cancer, although it was effective in stopping its spread.

Zeneca, however, maintains that there is only a one in 100,000 chance that the early US results were a fluke.

Tom McKillop, chief executive officer of the firm's pharmaceutical division, said: "I have never seen such a large study with this number of patients and which was as conclusive as this."

On Thursday, Zeneca announced a drop in its profits, down from £669m in the first six months of 1997 to £654m this year.