Cancer drug shown to have long-term protective effect

High-risk women who take the drug tamoxifen to prevent breast cancer stand a good chance of keeping the disease at bay for 20 years, research has shown.

The protective effect of tamoxifen lasts at least two decades, during which time it reduces breast cancer rates by around 30%, scientists found.

After 20 years, the estimated risk of developing breast cancer was 8% in women treated with tamoxifen for five years compared with 12% for women given an inactive placebo pill.

Professor Jack Cuzick, from Queen Mary, University of London, who led the Ibis-I (International Breast Cancer Intervention Study) trial, said: “

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.”

A total of 7,154 pre- and post-menopausal women aged 35 to 70 took part in the trial, all of whom were considered at high risk of breast cancer. Most had a family history of the disease.

The women were randomly allocated either 20mg daily doses of tamoxifen or a placebo for a total of five years. After completing the treatment course, their health was monitored for up to 22 years.

The findings, published in The Lancet Oncology journal, showed that women on hormone replacement therapy while taking tamoxifen benefited significantly less than those who did not boost their oestrogen levels.

Tamoxifen works by blocking molecular receptors on cancer cells that are stimulated by oestrogen. It is only effective against hormone-sensitive breast cancer.

Rates of endometrial, or womb, cancer — a known but uncommon side effect of taking the drug — were 3.8 times greater among women in the tamoxifen group during the five years of treatment.

Despite helping to prevent breast cancer, there was no evidence that tamoxifen reduced deaths caused by the disease.

In total, 31 women given tamoxifen died from breast cancer compared with 26 of those assigned to the placebo treatment.

In addition, five women receiving tamoxifen died from womb cancer compared with none in the placebo group.