By LAURAN NEERGAARD, AP Medical Writer
Mon Apr 17, 7:24 PM ET



WASHINGTON - A newer drug prevents breast cancer in older, high-risk women just as well as today's standby tamoxifen — but with fewer side effects, the National Cancer Institute announced Monday.

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Called raloxifene, the newer drug already is sold to treat bone-thinning osteoporosis.

But the striking new results, from a government study of nearly 20,000 women, suggest that raloxifene may supplant its older cousin as the first choice for breast cancer prevention in postmenopausal women at high risk of developing the disease.

"Now women have a choice," Dr. Leslie Ford, NCI's cancer prevention chief, said in an interview Monday. "It's good news, because we're giving you a choice with fewer side effects."

Manufacturer Eli Lilly & Co., which sells raloxifene under the brand name Evista, plans to seek Food and Drug Administration approval for the new use.

Until now, tamoxifen has been the only drug approved to reduce the chances of breast cancer striking high-risk women.

Both drugs are "selective estrogen response modulators" — they act like the estrogen hormone in some tissues but like an anti-estrogen in others.

Estrogen can fuel certain breast cancers, making tamoxifen a longtime top choice both to prevent the disease's return in women with estrogen-sensitive tumors and to reduce the odds of it striking high-risk women in the first place.

However, tamoxifen causes some rare but serious side effects: It acts like an estrogen in the uterus and bloodstream, thus increasing users' risk of getting uterine cancer or a life-threatening blood clot.

Raloxifene is a close chemical relative, and earlier research suggested that it might help breast cancer, too. So the NCI launched the $88 million study to compare the two.

Taking either tamoxifen or raloxifene daily for up to five years cut in half women's chances of developing invasive breast cancer, NCI announced Monday.

Raloxifene caused the same side effects, but not as many. Raloxifene users had 36 percent fewer uterine cancers and 29 percent fewer blood clots, according to initial results of the "Study of Tamoxifen and Raloxifene," or STAR project. Raloxifene users also suffered fewer vision-blocking cataracts.

Some 2 million U.S. women every year are thought to be candidates for tamoxifen risk-reduction therapy, but many have avoided it for fear of those side effects, said STAR researcher Dr. Kathy Albain of Loyola University.

While the reduction in those side effects was significant, the study also showed how uncommon the effects are. Thirty-six tamoxifen users developed uterine cancers, compared with 23 raloxifene users. The risk of blood clots was similarly low: 54 tamoxifen users had one in the lung, compared with 35 raloxifene users.

Still, "here we have something that's a little less scary," Albain said of the raloxifene findings. "It might tip the scales for a lot of women."

The new study means no change for premenopausal women — there's no data showing whether raloxifene is safe for them, Albain stressed.

Nor does it mean that tamoxifen users should necessarily switch, she said. Women currently are prescribed tamoxifen for five years, and its breast cancer prevention benefit continues even after they stop taking the drug — as raloxifene's seems to. So a woman already in, say, year four of her tamoxifen course with no sign of side effects probably has little to gain by switching, she explained.

But that's a question researchers were girding for as they spent Monday notifying study participants of the results.

One puzzle: While raloxifene was equally effective in blocking invasive breast cancer, it didn't protect quite as well as tamoxifen against noninvasive types of breast cancer such as ductal carcinoma in situ, noted Dr. Len Lichtenfeld of the American Cancer Society.

That type of tumor isn't life-threatening and shouldn't water down the overall message of raloxifene's benefit, said Dr. Victor Vogel of the University of Pittsburgh, who oversaw the study's design.

Among postmenopausal women, who's at high risk? Most of the study participants had a 4 percent chance of getting breast cancer within five years — because of advanced age, a close relative with the disease, never having a child or having one late in life, or other well-known risk factors that women can calculate on a government Web site: http://cancer.gov/bcrisktool.

In simpler terms, for every 1,000 of those women, doctors expected 40 to develop breast cancer within five years if they did nothing, but taking one of the drugs cut that number to 20, Ford explained.

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On the Net:

NCI study information: http://www.cancer.gov/star