American drug regulators look like opening the floodgates on the use of the breast cancer drug tamoxifen. It is about to be licensed in the US as a preventative and there's a good chance the UK may follow suit, even though some here are much more circumspect about the drug's powers.

A scientific advisory panel of the US's Food and Drug Administration (FDA) has overwhelmingly voted to recommend the approval of tamoxifen as a prophylactic.

Their approval is based on a major study in the US which showed that women at higher risk of developing cancer possibly because of family patterns or lifestyle went on to develop fewer cases if they were taking the drug, compared with women who were given a placebo. Controversially, the findings were not repeated by a UK study. English scientists have also criticised the US study as poor science, and have cast doubts on the findings.

The likely problem with the US decision to extend the use of tamoxifen for women at risk from developing breast cancer is that nobody is properly defining what those dangers are. As a result, doctors may start prescribing the drug to women at very minimal risk, and so expose them to the considerable risks that accompany tamoxifen. These include an increased incidence of endometrial cancer, pulmonary embolism and cataracts. Studies have also shown that women with a family history of cancer may benefit least from tamoxifen's protective powers (BMJ, 1998; 317: 697).