The two drugs were chosen because earlier trials have offered hints that each might help prevent breast cancer. Tamoxifen, manufactured by AstraZeneca and sold under the name Nolvadex, has been in use for about 20 years, primarily to treat existing cases of breast cancer. Other studies have shown that tamoxifen can reduce the occurrence of a second breast cancer after a woman suffers a first case, and that five years of taking the drug can have a beneficial effect for five more years after a woman stops taking the drug. But tamoxifen also has side effects. It can increase the risk of uterine cancer, although Raich said it prevents the onset of the more-deadly breast cancer in far more cases than the number of uterine cancer cases it triggers.
Tamoxifen also can cause problems such as blood clots and hot flashes.
Raloxifene, manufactured by Eli Lilly and sold under the name Evista, was found in one trial to prevent breast cancer without triggering uterine cancer. Raich said, and the numbers that came out of the study were too small to be statistically significant. Raloxifene, which is structurally similar to tamoxifen, also can cause blood clots, hot flashes, leg cramps and vaginal discharges, he added. The National Cancer Institute is sponsoring this latest trial, run by the National Surgical AdjuvantBreast and Bowel Project, to see which drug does the most good with the least harm in preventing breast cancer. The evaluation has been dubbed the Study of Tamoxifen and Raloxifene, or STAR, trial.