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Pink balloons hang on a stage during an event to raise awareness on breast cancer in Kosovo in 2013 Getty

A major study has revealed that a group of hormonal drugs known as 'aromatase inhibitors' can substantially reduce the number of deaths caused by breast cancer.

Aromatase inhibitors are taken by some post-menopausal women in the treatment of breast cancer and can also be used to halt the production of oestrogen.

Data garnered from more than 30,000 women was used to highlight the benefits of the oestrogen suppressant in the fight against breast cancer. It found that taking aromatase inhibitors for five years reduced the chance of death in post-menopausal women with ER-positive breast cancer – which accounts for 80% of breast cancer cases – by 40% if they begin taking them within 10 years of the commencement of treatment, according to the report published in The Lancet.

Researchers from the Aromatase Inhibitors Overview Group – chaired by Professor Mitch Dowsett at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust – worked with colleagues at the Clinical Trials Service Unit at The University of Oxford, to combine the results from 31,920 women in nine clinical trials, after receiving funding from Cancer Research UK and the Medical Research Council.

Lead author Dowsett said: "Our global collaboration has revealed that the risk of post-menopausal women with the most common form of breast cancer dying of their disease is reduced by 40% by taking five years of an aromatase inhibitor – a significantly greater protection than that offered by tamoxifen.

"Aromatase inhibitors remove only the tiny amount of oestrogen that remains in the circulation of women after the menopause – but that's enough to have a substantial impact on a wide range of ER-positive tumours, despite their extraordinary differences at the molecular level.

"But aromatase inhibitor treatment is not free of side-effects, and it's important to ensure that women with significant side-effects are supported to try to continue to take treatment and fully benefit from it."

Professor Paul Workman, chief executive of The Institute of Cancer Research, added: "The evidence on aromatase inhibitors has been accumulating for well over a decade, but it has taken this huge and complex study to make sense of all the data, and provide a firm basis for clinical guidelines.

"It tends to be the discovery of new treatments that grabs the headlines, but it is just as important to maximise the benefit patients get from existing treatments, through major, practice-changing studies like this."