A new breast cancer drug, tipped to replace tamoxifen as the gold standard hormone treatment, also has the potential to prevent or delay up to 80 per cent of breast tumours in most high risk post-menopausal women.
The results of the biggest ever international study on breast cancer, led by Professor Michael Baum for Cancer Research UK, mean that the new drug called Arimidex could be as effective in preventing breast cancer as it is in treating it.
The fast track study, published in The Lancet1, involved more than 9,000 post-menopausal women in 21 countries including 3,000 from Britain.
Women with cancer in one breast have an increased risk of contracting the disease in the other breast which is known as contralateral cancer. Earlier studies have shown that tamoxifen reduces the risk of this happening by 50 per cent; now this new trial, known as ATAC, has shown that Arimidex has the potential to reduce the risk by up to 80 per cent.
Arimidex – also known as anastrozole – inhibits the production of oestrogen and the study has found it works more effectively than tamoxifen in breast cancer patients who respond to hormone treatment.
A major advantage of Arimidex is that it has fewer of the side effects associated with tamoxifen such as increased risk of endometrial cancer, vaginal bleeding, hot flushes and blood-clotting disorders.
The ATAC trial randomly assigned one third of the women Arimidex, one third tamoxifen and the final third were given a combination of the drugs. Patients were followed up for just under three years.
“The ATAC trial treated women with existing breast cancer but we found a reduction in contralateral breast cancer,” says senior lecturer Joan Houghton who worked as a researcher on the project. “Therefore there is the suggestion that anastrozole would also be a good drug to use as a preventative agent – especially as side effects are reduced.”
But Houghton emphasises that the ATAC trial only compared tamoxifen and Arimidex when treating newly diagnosed breast cancer.
“Arimidex is currently only licensed to treat advanced cancer in the UK,” she says. “As a result of the ATAC trial it is now going through the licensing process to treat early breast cancer and may be available by the end of the year. But there has been no research to suggest that women already on tamoxifen would benefit by switching to Arimidex. It is still early days and more clinical trials are being done.”
Professor Gordon McVie, Director General of Cancer Research UK, says: “Trials have already shown that tamoxifen can cut down the risk of breast cancer but there were some concerns about the side effects. Prevention is better than cure and Arimidex is a drug that promises to do better on both prevention and side effects.”
Professor Michael Baum, based at Cancer Research UK and UCL Cancer Trials Centre in London, says: “Evidence from this first analysis of the ATAC trial is encouraging. An important consideration at this time is how to treat newly diagnosed patients.
“An overall assessment of the benefits versus harm, based on current data, supports the use of anastrozole for the adjuvant treatment of early breast cancer in postmenopausal women, meaning there is now a choice of adjuvant endocrine therapy for postmenopausal women with hormone-responsive tumours.”
Epidemiologist Dr Jack Cuzick, who analysed the results of the ATAC study, is now leading a new trial, run and partly funded by Cancer Research UK, into cancer prevention. He said: “The results of this study provide great encouragement for evaluating this new drug in post-menopausal women at high risk of developing breast cancer.”
Around 38,000 women are diagnosed with breast cancer in the UK each year and 13,000 die from it. But the mortality rate has fallen by 22 per cent in the last 10 years largely due to better treatment and a national breast screening programme. The lifetime risk of getting breast cancer is 1 in 9 for women.
- The Lancet359 pp.2131-2139
ATAC (Arimidex, Tamoxifen Alone or in Combination)