The drug, formestane, can be used when other hormonal drugs stop working for women with post-menopausal breast cancer. It starves tumours of the hormones they need to grow.
Professor Charles Coombes, head of the Department of Medical Oncology at Charing Cross and Westminster Medical Schools, London, said the drug was 'a real advance'.
'For women with advanced breast cancer, the choices of treatments are limited. In the past, chemotherapy with its distressing side efects such as nausea and hair loss, was often the next option once tamoxifen (another hormonal drug) stopped working.'
In a trial of 240 women with post-menopausal breast cancer, a quarter responded to injections of formestane, and in another quarter their condition stabilised.