Before the osteoporosis drug Evista is approved for breast cancer in the U.S. the Food and Drug Administration (FDA) will take the advice of an advisory panel.
The panel will look at whether the benefits of the drug outweigh the risks of serious side effects in some patients.
The FDA say although Evista reduces the risk of invasive breast cancer in certain patients there are for some, serious risks, such as deep vein thrombosis, pulmonary embolism and possibly stroke death.
Evista was given FDA approval in 1997 for use in women past menopause for the treatment of osteoporosis.
The drug company Eli Lilly now wants approval to promote the drug for the reduction in risk of invasive breast cancer in postmenopausal women with osteoporosis and postmenopausal women at high risk for breast cancer.
Lilly says Evista's ability to cut breast cancer risk has been tested in four trials totaling 37,000 women and more than 22 million worldwide have taken it to treat or prevent osteoporosis.
But FDA scientists say their analysis of one of those trials found Evista reduced breast cancer risk only in women at normal risk, but not at high risk.
The FDA says careful consideration of the risk/benefit ratio is especially important because Lilly aims to market Evista to healthy women.
Research has shown Evista reduced the risk of breast cancer in postmenopausal women whose cancer needs the hormone estrogen to grow.
But researchers say there appeared to be no reduction in risk in patients whose cancers do not need estrogen to grow.
At present only tamoxifen is approved for reducing the breast cancer risk in women who have never had the disease; but tamoxifen too carries risks such as a higher rate of uterine cancer, blood clots and stroke and many women have been discouraged from taking it.
A study released in 2006 that compared tamoxifen and raloxifene, the generic name for Evista, found the drugs were equally effective in cutting the risk of invasive breast cancers.