Tamoxifen can reduce the chance of breast cancer by one third in healthy women with a high risk of developing the disease.
The International Breast Cancer Intervention Study (IBIS-I), led by Professor Jack Cuzick from Cancer Research UK, undertook a study of the drug involving around 7,000 women from the UK, Australia, New Zealand and Europe.
The women were aged between 35 and 70 years and were at an increased risk of breast cancer; for example, they had a family history of the disease or had a benign lesion associated with an increased risk.
The frequency of breast cancer was reduced by more than 30 per cent among women given the drug. This finding clearly establishes that breast cancer can be prevented, and clarifies conflicting results seen in previous studies.
However, tamoxifen was associated with more than a doubling in the risk of blood-clotting complications, especially after surgery or long periods of immobility.
The findings were initially presented, in advance of publication, at the 3rd European Breast Cancer Conference in Barcelona in March 2002. This decision was taken in agreement with the Independent Data Monitoring Committee after the study confirmed the potential side effect.
Professor Cuzick, from Cancer Research UK’s London Research Institute, says: “All along the line, we have kept the volunteers in the trial fully informed of developments. That is why we felt it was right to report the preliminary findings ahead of publication.
“This possible side effect, along with other known conditions, was explained to all women before they joined the trial and it was recommended to them that they should take a break from the study medication prior to certain operations and not to restart until they were mobile again. Our current findings reinforce the importance of this advice.
“It is also important to emphasise that women with breast cancer who are taking tamoxifen as a treatment should continue to do so. The benefits of tamoxifen as a treatment are well documented and far outweigh any potential side effects.”
Cancer Research UK wrote to all the women involved in IBIS in March, informing them of these results and advising them to contact their doctor or local center if they were concerned. Since then, virtually all the women have continued to participate.
The study co-ordinator, Clare O’Neill from Cancer Research UK, says: “Most of the women on the trial have a family history of breast cancer and are participating because they want to make a difference, not only for themselves, but for their daughters, grand-daughters and all women at high-risk of the disease.
“From the very beginning, we have always made it clear to all women who wanted to join the trial of the potential risks, however remote, of taking part. I think it is a testament to the ethical and open approach that Cancer Research UK has adopted that virtually all the women are continuing with the trial.”
Sir Paul Nurse, Chief Executive of Cancer Research UK, says: “Cancer Research UK will continue to fund the IBIS trial to its conclusion. It is vital for women at high risk of breast cancer that we establish firmly the benefits of taking tamoxifen for preventing the disease versus the potential risks. Further long-term follow-up to study breast-cancer incidence and mortality, other causes of death, and side-effects in the current trial remains essential.”
Note to editors:
The trial was a double blind, placebo controlled, randomised study.