A clinical trial on raloxifene was organized because studies testing its effectiveness against osteoporosis surprisingly revealed that it appeared to have a favorable effect on breast cancer. Both it and tamoxifen interfere with estrogen, which can promote the growth of breast cancer cells.

But patients taking raloxifene had fewer of the serious illnesses linked to tamoxifen, including cancer of the uterus and blood clots.

"This gives women a real choice to treat two real threats of morbidity as they age: breast cancer and bone fractures," said Dr. Leslie Ford, an associate research director for the National Cancer Institute, which sponsored the study.

Stroke, Heart Attack Risk Remains

University of North Carolina-Chapel Hill and Duke University participated in the nationwide research, which involved more than 19,000 women who had experienced menopause.

The Food and Drug Administration approved tamoxifen, a drug widely prescribed to treat breast cancer, as a prevention treatment in 1998. It was good at preventing cancer -- logging a 50 percent reduction in breast cancers for older women -- but its side effects scared women and doctors alike, said UNC oncologist Dr. Stephen Bernard.

Raloxifene appears safer, but it is by no means a perfect drug, Bernard said. Women who took Eli Lilly and Co.'s osteoporosis drug had the same rates of stroke and heart attacks as those who took AstraZeneca's tamoxifen in an earlier, large-scale study.

But it is cheaper. A month's supply of raloxifene costs about $75, versus $100 for tamoxifen.

Doctors and their patients must decide whether the improvements are enough to put the drug in a woman's medicine cabinet, Bernard said.

"I don't know where the threshold is," he said, referring to when people will be comfortable with the risks.

Breast Cancer Actually Several Diseases

More than 212,000 women are expected to be diagnosed with breast cancer in the United States this year. Close to 40,000 will die of the disease.

Medicine has improved its aim when identifying which women are more likely to develop breast cancer than others.

Not only those with mutations of BRC -- the so-called breast cancer gene -- carry greater risk. As women age, their vulnerability increases. Those with mothers, sisters or daughters with the disease are more likely to develop it. So are those whose breast biopsy results display certain types of cellular changes.

Identifying such women and protecting them are different matters, said Dr. Kelly Marcom, clinical director of Duke's breast medical oncology program.

Increasingly, doctors recognize that breast cancer on the molecular level is actually several types of disease. Profound progress will be made when scientists recognize all of them, classify them and figure out how to treat them. But that will take time.

"Everyone is focused on what drug we need. What we really need is to know what kind of cancer a given individual is getting," Marcom said.

'Sneaky Kind of Thing'

A clinical trial on raloxifene was organized because studies testing its effectiveness against osteoporosis surprisingly revealed that it appeared to have a favorable effect on breast cancer. Both it and tamoxifen interfere with estrogen, which can promote the growth of breast cancer cells.

Jeanne Hagen, 77, participated in the raloxifene trial at UNC-Chapel Hill because she wants to do everything she can to help medicine better attack breast cancer.

The Fearrington Village resident in Chatham County lost her mother to the disease when her mother was in her 50s. Her sister developed it, and so did her niece. Both have survived, but cancer takes a huge toll on patients and their families, Hagen said.

"It's so sad. It's such a sneaky kind of thing," she said.

Hagen doesn't assume that raloxifene is a silver bullet. But she said she hopes every study and every step taken by individual women, including getting recommended mammograms, beats back cancer.

"We're getting close to it," she said. "We're getting very close."