The controversial research trial has been approved by the Department of Health even though the Medical Research Council refused to fund the study because of worries that the drug, tamoxifen, may increase the risk of liver cancer and because little is known about its long-term effect on well women. Other studies pointed to an increased risk of cancer of the womb.
But, if successful, the use of tamoxifen should reduce the number of breast cancers by 150 among the women in the trial. In the population it could reduce the number of new cancers by 1,500 a year. Breast cancer is the biggest single cancer killer of women in Britain, which has the highest death rate from the disease in the world. Every year 15,300 British women die from the disease and 27,000 new cases are diagnosed.
Over the coming months 15,000 women with no disease will be recruited and given tamoxifen or a placebo for five years. They will be monitored for 10 years. Ten to 15 per cent of the women will be aged 35 to 44 and have a high risk of the disease, with a mother or sister having had cancer in both breasts by the time they were 40. But the majority in the trial will be older, aged 45 to 65, and have a smaller increased risk because of family history of breast cancer or other factors.
Tamoxifen has a proven record in reducing the recurrence of breast cancer in women previously treated for breast cancer who are more at risk. It has been used by thousands of women amounting to 'millions of women years' of experience worldwide, say the researchers.
It is a complex drug which inhibits the action of the female hormone oestrogen. A pilot study in preventing breast cancer has revealed some unexpected benefits including lower blood cholesterol levels and improved bone strength in older women.
The study costing pounds 5m, is funded by the Imperial Cancer Research Fund and the Cancer Research Campaign and organised by the United Kingdom Co- ordinating Committee on Cancer Research.
Announcing the approval of the Department of Health, Dame Margaret Turner-Warwick, chairman of the UKCCCR, said it was a major initiative in which women would be given the fullest information about the possible benefits and risks.
Dr Trevor Powles, of the Royal Marsden Hospital, has led the pilot study for the trial. To date, 2,000 well women who have been followed for a maximum of 7.5 years. 'At first I was worried about recruiting women. But when we started to see the cholesterol levels coming down and the women not losing bone I felt a lot more comfortable.'
The Medical Research Council is conducting its own studies of the effects of tamoxifen, particularly in relation to cancer of the liver. Dr Lewis Smith, director of the MRC Toxicology Unit in Leicester, which is conducting the tests, said: 'We do not know what will happen to a normal population of women, with no breast cancer, over long periods of time,' he said.