Women who take tamoxifen to prevent breast cancer may have cut their risk of disease by almost a third, according to the findings of a major study reported yesterday.
But taking the drug failed to cut death rates, researchers found.
Latest findings from a 22-year study of the benefits of the drug were reported to the San Antonio Breast Cancer Symposium in the USA yesterday.
Women in the research had taken tamoxifen or a placebo for five years. More than 7,000 women of all ages took part.
Researchers say tamoxifen was linked to a 29% reduction in rates of breast cancer among women taking the real drug – some 251 cases compared with 350 among those taking the placebo.
Two thirds of cases were oestrogen receptor positive invasive cancer – and tamoxifen was linked to a 35% reduction in these cases, they reported.
Over 20 years women taking tamoxifen had an 8% rate of breast cancer – compared with 12% among those who took placebos.
But women taking tamoxifen faced an increased risk of developing endometrial cancer – and five died from this disease compared with none of those on placebo.
Researcher Professor Jack Cuzick, of Queen Mary University of London, said: "Tamoxifen is a well-established and effective treatment for certain breast cancers, but we now have evidence of its very long-term preventive benefits. The preventive effect of tamoxifen is highly significant with a reduction in breast cancer rates of around a third, and this impact has remained strong and unabated for 20 years.
“We hope these results will stimulate more women, particularly younger women, to consider treatment options for breast cancer prevention if they have a family history of the disease or other major risk factors."
He added: "Despite a clear and continuing reduction in breast cancer rates, this has not yet resulted in a reduction in breast cancer deaths. However, the number of deaths is still small compared with the number of breast cancer cases – which is 10 times higher.
“We will need to continue monitoring these women for a further decade to get a clearer picture of the impact of tamoxifen on death rates.”
* The conference also heard evidence of how breast-feeding may prevent breast cancer.
The UK Royal College of Midwives said the finding would make the case for supporting breast-feeding “even stronger.”
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