Researchers have discovered that a drug used to combat osteoporosis can also prevent invasive breast cancer.
The scientists stumbled on the discovery while carrying out trials into the preventative effects of the drug, raloxifene, on heart disease.
The study of more than 10,000 women found that, while there was no impact on heart disease, it did reduce the risk of aggressive, invasive breast cancers by as much as 55%.
Raloxifene, sold under the brand name Evista, is used to prevent and treat brittle bone disease in postmenopausal women and works by activating receptors in bone tissue that normally respond to oestrogen.
The team of researchers, writing in the Journal of the National Cancer Institute, say that by blocking the receptors, raloxifene may prevent some of the effects of oestrogen that spur cancer growth. They did, however, note an unwanted side-effect of the treatment which meant that women taking the drug could be at increased risk of blood clots and fatal strokes.
Study leader Dr Deborah Grady, from San Francisco's University of California, said: "Assuming that the relative risks from the trial apply to women in the general population, the best benefit-to-risk ratio would occur in women at high risk of breast cancer and osteoporosis and low risk of venous thrombosis and stroke."