In a study of the osteoporosis-preventing drug raloxifene (Evista), doctors found that the drug also lowers the rate of breast cancer. Now these doctors report that using raloxifene to help prevent breast cancer works mainly in women with high blood levels of the estrogen hormone estradiol.

The report by Steven Cummings, MD, and his colleagues was published in the Journal of the American Medical Association (Vol. 287, No. 2: 216-220). The researchers studied 7,290 postmenopausal women. The women, whose average age was 66, all had osteoporosis (bone-thinning).

All had been entered into the MORE (Multiple Outcomes of Raloxifene Evaluation) trial. The trial was designed to test whether the drug raloxifene could prevent spine fractures in women with osteoporosis.

Two-thirds of the women were given raloxifene and one-third received a placebo (inactive pill). Raloxifene was beneficial. Women on the drug had a lower rate of vertebral fractures.

But the women on the drug also had lower rates of breast cancer. This came as no surprise to the MORE doctors. Raloxifene is similar to tamoxifen, a drug widely used to treat breast cancer. It has also been shown to prevent breast cancer in high-risk women.

Both drugs act on the estrogen receptor. This is a protein found in most breast cancer cells. In the presence of estrogen, the estrogen receptor stimulates the cell’s growth. Anything that blocks this will stop the cancer cell from growing.

Many investigators have found that breast cancer more readily occurs in postmenopausal women who have higher blood levels of estradiol. In this study, women with the highest estradiol levels had a breast cancer rate around seven times that of women with no estradiol.

Raloxifene lowered the breast cancer rate only in women who had some estradiol in their blood. It was most effective in those with the highest levels. It did not prevent the few cases that occurred in women without any estradiol.

Should women measure their estradiol levels to see if need to take raloxifene? Not yet say the MORE investigators as well as experts at the American Cancer Society (ACS). Measuring estradiol accurately is both difficult and expensive.

The solution is actually simpler. Most studies have linked high estradiol levels to obesity and alcohol intake.

The ACS epidemiologists recommend eating a healthy diet, exercising more, and drinking less alcohol as a better way to reduce breast cancer risk and improve all around good health.