A drug that lowers oestrogen levels in women with hormone-sensitive breast cancer could save more than 1,000 lives a year if it was adopted throughout the UK, new research has shown.
Switching from the gold-standard breast cancer treatment tamoxifen to the new drug exemestane after two or three years resulted in death rates falling by 17 per cent.
The findings emerged from a study of 4,742 women who were treated for a total of five years and monitored for a further three.
Women were randomly assigned either to a full five years of tamoxifen, or treatment with tamoxifen followed by exemestane.
Giving women tamoxifen after surgery already reduced the risk of dying by 33 per cent compared with no treatment. After another two to three years of exemestane, plus a further three years of post-treatment follow-up, survival was found to be significantly improved.
The chances of dying were now 50 per cent lower than they would have been with no chemotherapy, and 17 per cent lower than they were without the switch from tamoxifen.
The charity Cancer Research UK, whose scientists were involved in the study, said the treatment protocol would prevent an estimated 1,300 deaths each year if it was rolled out across the UK.
Professor Charles Coombes, director of The Cancer Research UK Laboratories and head of cancer medicine at Imperial College, London, said: "Tamoxifen has already saved the lives of many breast cancer patients. Our latest research shows that we can build on that success by treating women first with tamoxifen then switching to the new drug, exemestane.
"This is the first time any hormone treatment has been shown to reduce the death rate more than tamoxifen alone. Switching drugs also seems to avoid the side-effects of long-term tamoxifen therapy, such as cancer of the womb and deep vein thrombosis."
Cancer Research UK's medical director Professor John Toy said: "These results are really very encouraging because they suggest that a sequence of tamoxifen and exemestane could help reduce breast cancer deaths.
"We will continue to follow the results of this study to see how well the women fare in the long-term."
An estimated 31,000 post-menopausal women are diagnosed with breast cancer in the UK each year.
In 80 per cent-85 per cent of these cases, the disease is fuelled by oestrogen. Whereas tamoxifen interferes with the activity of the hormone, exemestane reduces the levels produced in a woman's body.
The drug, sold under the brand name Aromasin, is recommended by the National Institute for Health and Clinical Excellence (Nice) as an alternative to tamoxifen after two to three years of initial therapy. However, it is not available everywhere.
Findings from the Intergroup Exemestane Study (IES) were published in the on-line version of The Lancet medical journal today.
The results also showed that patients treated with exemestane were 25 per cent less likely to see their cancer return than those who remained on tamoxifen.
Dr Mary McCormack, consultant clinical oncologist at University College London Hospital, said: "Exemestane is now available in the UK to the thousands of post-menopausal women who have been and will be diagnosed with hormone sensitive breast cancer.
"It is important that women with the disease who are suitable to be treated with exemestane are fully informed of the benefits of switch therapy."
Dr Alexis Willett, senior policy and information officer at the charity Breakthrough Breast Cancer, said: "This will be very welcome news for many post-menopausal women with oestrogen-sensitive early breast cancer.
"Previous studies had already shown that after switching from tamoxifen, exemestane could reduce the risk of breast cancer returning. This new evidence shows that it could also improve overall chance of survival.
"Aromatase inhibitors, like exemestane, now increase the treatment options available for breast cancer patients.
"However, it is important to remember that they are not suitable for everyone. Anyone concerned about their treatment should speak to their doctor."