(USA TODAY) -- A Food and Drug Administration advisory panel will consider Tuesday whether Evista, an osteoporosis drug, should be approved to lower breast cancer risk in some women.

At least two women's health advocacy groups oppose such a move, and, in a briefing document for the panel, FDA scientists question whether Evista's benefits outweigh its risks. The FDA usually follows advisory committee recommendations.

Evista was approved to prevent osteoporosis in 1997 and to treat it in 1999. Now, Eli Lilly wants to market it for lowering invasive breast cancer risk in postmenopausal women who either have osteoporosis or a high risk for breast cancer.

"There's a large, robust body of data that has to be looked at," Lilly spokesman Gregory Clarke says, noting that Evista's ability to cut breast cancer risk has been tested in four trials totaling 37,000 women. And, he says, more than 22 million worldwide have taken it to treat or prevent osteoporosis.

The FDA scientists say their analysis of one of those trials found Evista reduced breast cancer risk only in women at normal risk, not high risk. "A careful consideration of the risk/benefit ratio is especially important" because Lilly wants to market Evista to healthy women, the scientists say.

Only tamoxifen is approved for trimming breast cancer risk in women who have never had the disease. But tamoxifen's risks -- a higher rate of uterine cancer, blood clots and stroke -- have put off many women.

Tamoxifen is "very much underutilized for breast cancer prevention," says Len Lichtenfeld, American Cancer Society deputy chief medical officer. "There are clearly women who are at high risk of getting breast cancer who would benefit from preventive therapy." Women and doctors might be more open to Evista because it seems to be safer, Lichtenfeld says.

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. There were fewer cases of uterine cancer, blood clots and cataracts among women who took raloxifene, which, unlike tamoxifen, did not protect against non-invasive breast cancers. The drugs' risks of other invasive cancers, heart disease or stroke were similar.

Breast cancer activist Barbara Brenner says she already has heard about doctors prescribing Evista off-label for reduction of breast cancer risk. "Everybody overestimates their risk (of breast cancer), which is one of the problems," says Brenner, executive director of Breast Cancer Action.

Like Brenner, Cindy Pearson, executive director of the National Women's Health Network, expressed concern that women with little to gain would end up on Evista.

"Approval allows advertising, and the advertising, almost by definition, is going to be misleading," Pearson says. "It's going to imply that there's a bigger net benefit than we know to be true."

Copyright 2007 USA TODAY, a division of Gannett Co. Inc.