The aromatase inhibitor Exemestane can prevent the breast cancer risk by 65 percent in moderate to high-risk postmenopausal women.
This conclusion has been drawn by a three-year study in 4560 women in the US and Europe.
Importantly, there were no reports of lethal side effects like those caused by breast cancer drugs tamoxifen and raloxifene.
The team reporting the new results say that the lack of side effects with exemestane could make it far more attractive as a preventative treatment, reports New Scientist.
"Our hope is that our trial results turn up the volume on the debate around breast cancer prevention," says Paul Goss of the Massachusetts General Hospital Cancer Center in Boston, head of the research team.
He said that women might do well to take the drug for five years or so when they reach menopause, an age when the risk of breast cancer rises because of increases in the hormone oestrogen.
The trial results suggest that over three years, for every 94 women taking exemestane, a single case of breast cancer would be prevented.