Friday, October 1, 1999 Published at 10:42 GMT 11:42 UK
Tamoxifen works in smaller doses
Tamoxifen is associated with side effects
Women may be able to cut the dose of a cancer-preventing drug by three quarters and still gain the same protection, scientists have discovered.
The findings could mean that patients taking the drug - found to reduce the incidence of breast cancer in women at high risk by more than 40% - avoid some of its side effects.
Dr Andrea Decensi, of the European Institute of Oncology in Milan and colleagues in Norway, gave a group of 105 women varying doses of tamoxifen.
They found that a much smaller dose - one that reduced the amount of tamoxifen in the blood by 80 percent - still seemed to be working.
Tamoxifen, sold under the name Nolvadex, has been used for years to treat breast cancer. But last year it was also found to prevent breast cancer in some women when they took it for five years.
The drug works by blocking the action of the female sex hormone oestrogen on cells.
Oestrogen is believed to stimulate breast cancer in some women.
However, the side effects of the drug include:
The drug has also been associated with weight gain and depression.
Dr Decensi, writing in the Journal of Clinical Oncology, said: "Despite the universal use of this drug for more than 20 years, its minimal active dose has never been established."
More tests will be needed. One thing doctors will want to see is if the lower dose reduces the risk of uterine cancer.
In a second report in the journal, a team at the University of Pittsburgh and the University of California at Los Angeles said women taking tamoxifen to prevent breast cancer only suffer some of the bad side effects.
The 11,000 women taking the drug had vaginal discharge, hot flushes and some of the sexual dysfunction that has been reported but not weight gain and depression.
But he said research had suggested that doses of 40mg of the drug could be effective administered weekly, rather than daily.
"Lower doses are worthy of evaluation," he said.
"Tamoxifen does hang around in the blood for a long time compared to average drugs, so it might be that you do not need so much of it."
Professor McVie said that standard doses of the drug were set during clinical research 30 years ago when measurement techniques were not very sensitive.
He said tests were already under way on second generation tamoxifen drugs, raloxifene and toremifene, which appeared not to increase the risk of uterine cancer.