A breast cancer drug that is more effective than tamoxifen with fewer side effects has been found to reduce the risk of breast cancer by over 50%, researchers have said.
Published in the Lancet, the scientists' found that anastrozole reduced the chances of high-risk women from developing breast cancer by 53%.
The study, led by Queen Mary University of London and funded by Cancer Research UK, said that the drug could offer a new option for preventing breast cancer in high risk post-menopausal women.
Lead researcher Jack Cuzick said: "This research is an exciting development in breast cancer prevention. We now know anastrozole should be the drug of choice when it comes to reducing the risk of breast cancer in postmenopausal women with a family history or other risk factors for the disease.
"This class of drugs is more effective than previous drugs such as tamoxifen and crucially, it has fewer side effects.
"Unpleasant side effects such as acute aches and pains have often been associated with oestrogen-depriving drugs. However, in this study, the reported side effects were only slightly higher than in the placebo arm.
"This means most symptoms were not drug related, and the concern about side effects for this type of drug may have been overstated in the past."
Researchers looked at nearly 4,000 postmenopausal women at high risk of breast cancer. Half were given a daily dose of anastrozole and half were given a placebo.
Women were judged to be high risk if they either had two or more blood relatives with breast cancer, if they had a mother or sister with breast cancer in both breasts or if they had certain types of benign breast disease.
After five years, just 40 women taking anastrozole developed breast cancer, compared with 85 women in the group that took a placebo.
A high proportion of breast cancers are fuelled by oestrogen and anastrozole works by preventing the body from making the hormone. The drug has been used for many years for treating women with oestrogen receptor positive breast cancer.
Cuzick said: "Our priority now is ensuring that as many women as possible can benefit from these new findings. Prevention is an important tool in the fight against breast cancer and we strongly urge the National Institute for Health and Care Excellence to consider adding anastrozole to their recommended drugs for women who are predisposed to developing breast cancer. By including this drug in their clinical guidelines, more women will benefit from this important advancement in preventive medicine."
Kate Law, director of clinical research at Cancer Research UK, said it was a landmark study and that tests were needed to establish which women would benefit most from the findings.
Dr Harpal Kumar, Cancer Research UK's chief executive, added: " We're delighted that the results will now offer women at high risk of breast cancer a new option to significantly reduce their chance of developing the disease. By supporting large trials such as this, which take a long time to complete, we can make discoveries that will help us to save many more lives in the future."